"LARGE AREA FABRICATION OF PERIODIC POLYMERS STRUCTURES BY DIRECT LASER INTERFERENCE PATTERNING"

O.1.A.01-NA "LARGE AREA FABRICATION OF PERIODIC POLYMERS STRUCTURES BY DIRECT LASER INTERFERENCE PATTERNING" D.A. ACEVEDO, C. A. BARBERO, M. F. BROGLIA, M. POLITANO and A. F. LASAGNI. Departamento de Química, Universidad Nacional de Río Cuarto, Ruta Nacional 36 Km 601, X5804ZAB, Río Cuarto. Córdoba. Argentina Department of materials science. Saarland University, Institute of Functional Materials, Building C6.3, 7. Stock, P.O. Box 15 11 50, D-66041, Saarbrücken, (Alemania) dacevedo@ing.unrc.edu.ar ; cbarbero@exa.unrc,edy,ar ; mbroglia@exa.urnc.edu.ar ; mpolitano@ing.unrc.edu.ar ; lasagni@iws.fraunhofer.de INTRODUCTION The process of patterning is commonly referred as lithography, which involves a flow of information that typically begins with the design of a pattern in the form of a dataset and ends as a patterned array of features on the surface of a substrate [1]. Various techniques have been utilized in the past to produce such modulated surfaces with controlled dimensions. These methods normally require multiple steps in order to produce the final microstructure. Obviously, such procedures are quite slow and the necessary writing time increases as a larger area must be processed. In this communication, we report a novel method for the advanced design of architectures in different kind of polymers in a single step process, and technological applications of these surfaces [3-6]. METHODS Interference Experiments: A high-power pulsed Nd:YAG laser (Quanta-Ray PRO 290, Spectra Physics) was employed for the laser interference experiments. For the laser induced patterning experiments, we used a wavelength (k) of 266 nm and 355 nm. The frequency of the laser was 10 Hz and the pulse duration was 10 ns. The primary laser beam was split into two or three coherent beams to interfere with each other on the sample surface as shown in Fig. 1a. One pulse was chosen for each experiment. The laser beam was focused onto the targets by a fused silica lens with focal distance of 2000 mm. In the case of two-beam interference experiments, the period (P) of the periodic line-like pattern can be controlled by changing the angle between the laser beams (a) and the wavelength of the laser light as indicated in Eq 1. (1) P 2sin If three-beams laser interference experiments are conducted, a dot-type interference pattern with a hexagonal intensity distribution is obtained, and the period is given by Eq 2. (2) P 3 sin Fig. 1. (a) Interference experimental setup showing the optical elements and (b) calculated intensity distribution of the two-beam interference pattern. The period of the pattern can be changed by varying the angle (a) between the incident beams. Sample Characterization: All samples were imaged with a high-resolution SEM equipped with a field emission gun (FEI Strata DB 235) at 5 kv acceleration voltage. Cross-sectional analyzes were performed with the aid of a dual beam workstation (FEI Strata DB 235) using the electron beam for imaging and the focused ion beam (Ga) for milling of the sample and Pt deposition. Surface topography was measured using a white light interferometer (Zygo New View 3D Imaging Surface Structure Analyzer) with a vertical and lateral resolution of 0.3 nm and 0.73 m, respectively. Different structures have been produced using DLIP. Applying interference patterns on PMMA PS copolymers is possible to fabricate complex surface architectures which result from the mixed properties of the individual components, Figure 2. Additionally, due to the contribution of the polymer with high absorption coefficient (PS), lower laser fluences comparable to that of pure PS are necessary for the local and periodic ablation process. The following topographies were observed according to the used laser intensity: (a y b) at low fluences, the irradiated surface swells up due to the formation of microbubbles that are the results of the degradation of PMMA; (c y d) for high laser intensities (1 J cm -2 ), the bubbles release from the surface forming a periodic micropored structure with a long-range order. The same behavior is observed for three-laser beam interference setup (Figure 3). 18

O.1.A.01-NA 194 mj cm 2 ). Note that for PI the substrate is also ablated (c), while for PC only the PANI film is removed at the interference maxima positions (a, b). Figure 5 shows a robust method for the fabrication of highly ordered electrode arrays composed of strips of platinum nanoparticles deposited onto gold substrates. It is suggested that the patterned gold-platinum electrode acts as an array of ultramicroelectrodes. Fig. 2. Irradiated (60:40) PMMA/PS copolymer surfaces using two-laser beam interference setup. (a) A quite well-homogeneous structure is obtained in a large area (laser fluence = 0.36 J cm -2 ); (b) inflated linelike structures at low laser fluences (laser fluence = 0.36 J cm -2 ), the period of the pattern was 4.85 m; (c, d) crater-like structures obtained at relative large laser fluences (0.91 and 1.81 J cm -2 for (c) and (d), respectively). The insert in (d) shows the cross-section of the structure. Fig. 3. Irradiated (60:40) PMMA/PS copolymer surfaces using three-laser beam interference setup. (a) Microbumps ordered in a hexagonal arrange fabricated a low laser intensities (laser fluence= 0.28 J cm -2 ); (b) crater-like structure observed at higher laser fluences (0.75 J cm -2 ). It has been demonstrated that micro/nanometer-sized PANI arrays could be easily fabricated (as thin as ca. 600 nm) by using DLIP using PANI thin films deposited on dielectric polymers (Polycarbonate PC or Polyimide PI), Figure 4. The width of the PANI lines could be controlled by changing the intensity of the laser beams. After the structuring process, the conductive PANI arrays retain their chemical and electronic properties. The underlying polymer could also be ablated depending on its optical properties at the working wavelength. Since macroscopic areas can be structured in each laser pulse (mm 2 cm 2 ) this process can be easily adapted to produce micro- or nanoscopic patterns on large areas. These investigations may be relevant for the development of high-performance materials for polymeric sensors. Fig. 4. SEM images of PANI nanostructures supported onto PC (a: laser fluence = 325 mj cm 2 ; b: laser fluence = 174 mj cm 2 ) and PI (c: laser fluence = Fig. 5. SEMs of the electrodes: (a) PANI patterned by DLIP on gold; (b) platinum nanoparticle array produced after platinum deposition on part a and removal of the PANI lines. CONCLUSIONS It is shown that DLIP technique is a versatile method to modify several kind of surfaces. Using DLIP it is possible obtain regular structures over several mm2 in a few seconds. DLIP shows many advantages such as: 1- PERIDICITY: allows the creation of periodic structures with a very well order in the range of nanomicrometers in only one laser pulse. 2- QUICKNESS: it is possible structured areas ranging mm 2 to cm 2 in a few seconds 3- SIMPLICITY: to produce substrtes it is no necessary the use of special instalation, such as ultra clean rooms, the technique works at room temperatura without vacum. 4- ECONOMY: the subtrates manufacturated in a quick and simple maner does that the commercialization of these may be viable to very low costs. REFERENCES [1] Lasagni A., Holzapfel C., and Mücklich F. Periodic pattern formation of intermetallic phases with long range order by laser interference metallurgy. Adv. Eng. Mater, 7, 487-492 (2005). [2] Xia Y., and Whitesides G. M.,, Angew. Chem., 37, 550-575 (1998). [3] Acevedo, D.F., Lasagni, A.F., Barbero, C.A., and Mucklich, F. Simple fabrication method of conductive polymeric arrays by using direct laser interference micro-nanopatterning. Advanced Materials 19 (9), 1272-1275, (2007) [4] Lasagni, A.F., Acevedo, D.F., Barbero, C.A.,and Mucklich, F. One-step production of organized surface architectures on polymeric materials by direct laser interference patterning. Advanced Engineering Material, 9, 99-104, (2007). 19

ARCHIPOL 09 O.1.A.02-NA SPHERE FORMING BLOCK COPOLYMER THIN FILMS ON CORRUGATED SUBSTRATES L.R. GÓMEZ, E.M. VALLES, and D.A. VEGA Physics Department, Univ. Nacional del SUR - Conicet, Av. Alem 1253 - (8000) Bahía Blanca Argentina. Plapiqui (Univ. Nacional del SUR - Conicet) Camino la Carrindanga KM 7 - (8000) Bahía Blanca Argentina lgomez@uns.edu.ar ; valles@plapiqui.edu.ar ; dvega@criba.edu.ar INTRODUCTION In the last years, the studies of self-assembled block copolymers have been driven by the possible applications to nanotechnology (Segalman, 2005). For example, thin-film patterns of block copolymers have been used as nanolithographic masks for pattern transfer (Harrison et al., 2000). One of the main difficulties associated to these systems is the lack of long-range order due to the presence of unavoidable topological defects (Gómez et al., 2006). At present different strategies have been employed to reduce the density of defects (Segalman, 2005). More recently, there has been an increasing interest in the study of 2D modulated phases on nonflat substrates (Nelson, 2002). One of the main differences between planar and curved 2D modulated phases is the nature of topological defects. The curvature of the substrate can impose a topological requirement involving defects in the equilibrium state. This topological requirement is given by the Gauss-Bonnet theorem which relates the integral of the Gaussian curvature with the total defects (disclination) charge (Vittelli and Turner, 2004). In this work we investigate on the possibility of using curved substrates to control the density and location of topological defects in thin films of sphere forming block copolymers. corresponds to a lamellae phase while f 1/2 corresponds to spheres packed with hexagonal order. The other parameters a, v, u, D and b are usually considered as phenomenological constants. In Eq. 1 2 is the Laplace-Beltrami operator, which reduces to the classical Laplacian for the case of flat substrates. This operator has all the geometric information (through the metric) of the corrugated substrate. To study the influence of the substrate s curvature on sphere forming systems, we solved Eq. 1 for different sinusoidal substrates. The initial homogeneous state is modeled with a random noise distribution. Eq. 1 is numerically solved through a finite difference scheme in a 512 x 512 lattice, with periodic boundary conditions. Figure 1 shows a typical configuration of a sphere forming diblock copolymer deposited on a hexagonally sinusoidal substrate, as obtained through the model Eq. 1. METHODS We use the Cahn-Hilliard model, which has been extensively used in non-equilibrium studies of diblock copolymers (Otha and Kawasaki, 1986): 2 2 M f ( ) D Mb (1) t where f ( ) is the map function: 2 2 3 f ( ) a(1 2 f ) v(1 2 f ) u (2) The order parameter is related with the fluctuations in the density, M is the mobility coefficient, is related with the deep of quench, and f is the average value of the density. This last parameter can be used to set the symmetry of the phase; in two-dimensions, f=1/2 Fig. 1. Block Copolymer configuration on a sinusoidal substrate. In Block Copolymers and related systems the detailed analysis of defect configurations can be done by means of the Delaunay Triangulation. Through this method the defects are found by counting the number of near neighbors of each sphere. Although this process is 20

ARCHIPOL 09 O.1.A.02-NA standard to study flat systems, here we need to modify it to account for the corrugated substrate. Once the position of each sphere in the systems is determined, our algorithm calculates the geodesic distances between the different spheres. Through the geodesic distance is possible to determine the number of near neighbors and to identify the defects. repulsion of defects. These results are in good agreement with the current theories for crystalline systems deposited on curved substrates (Vittelli and Turner, 2004). Figure 2 also shows the presence of grain boundary scars (linear arragements of dislocations). These are large angle grain boundaries that abruptly end at a disclination. As a consequence of its enormous energetic cost, these configurations of defects are not observed in planar systems (Gómez et al., 2006). Then, contrary to flat systems here these arrays of defects are stabilized by the curvature and belong to the equilibrium ground state. CONCLUSIONS We solved the Cahn-Hilliard model to study the morphology of block copolymer thin films deposited onto curved substrates. In good agreement with current theories of condensed matte, here we found a strong coupling between defects and geometry that produces the preferential location of defects. This opens the possibility of use corrugated substrates to control block copolymer morphologies. Fig. 2. Defect configurations on sinusoidal substrates. DEFECT CONFIGURATIONS Figure 2 shows a Delaunay Triangulation of a sphere forming Block copolymer on a sinusoidal substrate. Tipically, hexagonal systems display disclinations and dislocations. Disclinations are elementary defects given by spheres with a number of near neighbors different from 6. In Fig. 2 we show positive disclinations (spheres with 5 neighboors) trough red circles, and negative disclinations (spheres with 7 neighboors) trough green circles. Dislocations are composed defects (dipoles 5-7), which are indicated with yellow lines. We observe that in general positive defects (5 s) tend to locate in regions of positive curvature (crest and valleys). On the other hand, negative defects tend to be located in the regions of negative curvature (saddle points). This preferential location evidence a coupling between defects and geometry. Here the substrate works as an external potential that produce the atraction or REFERENCES Segalman, R.A., Patterning with Block Copolymer Thin Films, Mater. Sci. Eng., R. 48, 191-296 (2005). Harrison, C.K., Adamson, D.H., Cheng, Z., Sebastian,, J.M., Sethuraman, S., Huse, D.A., Register, R.A., and Chaikin, P.M., Mechanisms of Ordering in Striped Patterns, Science 290, 1558-1560 (2000). Gómez, L.R., Vallés, E.M., and Vega, D.A., Lifshitz- Safran Coarsening Dynamics in a 2D Hexagonal System, Phys. Rev. Lett. 97, 188302 1-4 (2006). Nelson, D.R., Towards a Tetravalent Chemistry of Colloids, Nano Lett. 2, 1125-1129 (2002). Vitelli, V. and Turner, A.M., Anomalous Coupling Between Topological Defects and Curvature, Phys. Rev. Lett. 93, 215301 1-4 (2004). Ohta, T. and Kawasaki, K., Equilibrium morphology of block copolymer melts, Macromolecules 19, 2621-2632 (1986). 21

ARCHIPOL 09 O.1.A.03-NA BUCKLING IN BLOCK COPOLYMER MEMBRANES A.D. PEZZUTTI, M.A.VILLAR, AND D.A.VEGA Universidad Nacional del Sur. Dpto. de Física. CONICET. Argentina Universidad Nacional del Sur. Dpto. de Ing. Química. PLAPIQUI. CONICET. Argentina. pezzuttialdo@yahoo.com.ar; mvillars@plapiqui.edu.ar; dvega@criba.edu.ar INTRODUCTION Recent advances in material science and nanotechnology have focused on the growth, equilibrium properties and characterization of block copolymer thin films with unusual topologies. Particularly, the properties of a two dimensional membrane formed by thin films of block copolymer embedded in three dimensional space, depend strongly on the crystalline structure and topological defects. Since the presence of topological defects in crystalline structures is almost completely unavoidable, these defects have a profound effect over the mechanical, optical or transport properties, its control have an enormous technological importance. Although equilibrium properties of topological defects in different condensed matter systems has been well established during the last century, still little is known about the dynamic mechanisms leading to their formation at the onset of phase transitions (Gómez et al., 2006). Free standing thin film membranes of block copolymers may be not confined to a plane (Seung and Nelson, 1988). Thus, although the stable phase of a defect-free crystalline membrane at low temperature is flat, strains induced by topological defects can be accommodated by displacements in the normal direction, resulting in the buckling or bend of the membrane (see Fig. 1). Fig. 1. Topological defects for an hexagonal pattern in flat and curved spaces. a)- dislocation, b) positive disclination, c) negative disclination, d) buckled positive disclination, and e) buckled negative disclination. We study the kinetics of phase transition and the morphological evolution of a thin film membrane formed by a monolayer of a sphere forming block copolymer. The equilibrium structure of the block copolymer in the plane is an array of hexagonally packed spheres. The local composition and shape of the membrane are coupled through the free energy. The evolution of the compositional field is described by a Cahn-Hillard equation and the shape changes via a relaxational dynamics (Funkhouser et al., 2007). METHODS The dynamic of the compositional fluctuations of the block copolymer thin film and the shape of the membrane can be expressed as: t h t M 2 F (1) L LB F h where F[,h] is the following free energy F, h dr ( r) 2 a(1 2 f ) 2 2 b 2 ( r) 3 u 4 (1 2 f ) ( r) ( r) 3 4 c 2 dr dr G( r r ) ( r ) ( r) K C0 2 2 (3) (r) is the order parameter of the block copolymer system (density fluctuations) and h(r) is the shape of membrane (Qi and Wang, 1997). The parameters employed in eqns. 1 and 2 are phenomenological constants selected to obtain the desired symmetry of the equilibrium phase. In order to study the relaxational dynamics of an homogeneous system quenched into the unstable region of the phase diagram, we solve eqns. 1 and 2 in a square cell starting from a random initial condition. RESULTS AND DISCUSSION Fig. 2 shows a typical hexagonal pattern obtained after a quench into the unstable region of the phase diagram (spinodal region). Given the asymmetry of the block copolymer, the phase of equilibrium is hexagonal. However, the competition between the propagating domains leads to the appearance of dipoles of i i (2) 22

ARCHIPOL 09 O.1.A.03-NA disclinations (dislocations), which breaks the translational order of the system. Fig. 3 shows the shape of the membrane h(r) for the pattern of Fig. 2. We observe that defects produce a deformation of the membrane in the normal direction. Then, the free energy is strongly reduced by the distortion of the membrane. Fig. 3. Membrane s shape show important distortions around the position of the topological defects (dipoles of disclinations). Fig. 2. Pattern configuration for a free standing sphere forming block copolymer thin film. Note the presence of topological defects (dislocations). The mechanism of pattern formation in twodimensional systems undergoing phase separation has been the subject of intense investigations for more than three decades. Except in certain exceptional circumstances, it has been clearly shown through numerous studies that different systems show a coarsening process satisfying scaling at long times. In this case, the dynamics can be characterized by a simple length scale that grows in time as a power law. This feature has been observed experimentally in thin films of block copolymers with different symmetries. However, here the coupling between the geometry of the membrane and the topological defects can deeply affect the dynamics as well as the equilibrium configuration of the system. CONCLUSIONS We examined phase separation in a block copolymer membrane using a coupled composition - deformation phase field method. In the hexagonal morphology the topological defects have a strong effect in both, the shape of membrane and the equilibrium state of the pattern. Defects such as dislocations and disclinations can cause a thin film to spontaneously bend or buckle. While disclinations can cause the film to buckle into either shadle (negative disclinations) or a conical (positive disclinations) shapes, the nature of the bending of the membrane depends on the orientation of the Burgers vector. REFERENCES C. Funkhouser, F. Solis and K. Thornton. Coupled composition-deformation phase-field method for multicomponent lipid membranes Physical Review E, 76, 011912 (2007). Gómez, L.R., Vallés, E.M., and Vega, D.A., Lifshitz-Safran Coarsening Dynamics in a 2D Hexagonal System, Phys. Rev. Lett. 97, 188302 1-4 (2006). S.Qi and Z Wang. Kinetics of phase transitions in weakly segregated block copolymers: Pseudostable and transient states Physical review E, 55, 1682 (1997). S. Seung and D Nelson. Physical Review Defects in flexible membranes with crystalline order Physical Review A, 38, 1005 (1988). 23

O.1.A.04-NA EL PROBLEMA DE THOMSON EN COPOLÍMEROS BLOQUE CONFINADOS EN CASCARONES ESFÉRICOS N. A. GARCÍA, L. R. GÓMEZ, F. S. BUEZAS, E. M. VALLÉS, y D. A. VEGA Departmento de Física, Univ. Nacional del SUR - Conicet, Av. Alem 1253 - (8000) Bahía Blanca Argentina. Plapiqui (Univ. Nacional del SUR - Conicet) Camino la Carrindanga KM 7 - (8000) Bahía Blanca Argentina nicolas.garcia@uns.edu.ar; lgomez@uns.edu.ar; valles@plapiqui.edu.ar; dvega@criba.edu.ar INTRODUCCIÓN Los copolímeros bloque son materiales macromoleculares formados al unir dos o más bloques de polímeros diferentes. Si los bloques que forman el copolímero son termodinámicamente incompatibles, entonces por debajo de una temperatura característica, el material sufre una separación de fases que conduce al sistema a auto-ensamblarse en estructuras periódicas con distancias típicas del orden del radio de giro de la molécula (Bates and Fredrickson 1999). Las estructuras periódicas que se forman dependen de varios parámetros físicos, pero están topológicamente condicionadas por la geometría que contiene al copolímero. De manera particular, tanto desde el punto de vista básico como tecnológico interesa saber cómo se ensambla este sistema si se encuentra confinado a un cascarón esférico. En este trabajo se resuelve para diferentes radios del cascarón la ecuación de Ginzburg- Landau dependiente del tiempo para un parámetro de orden conservado. Planteado de esta forma es interesante notar que este problema resulta análogo al clásico problema de la física, el problema de Thomson, el cual consiste en distribuir n cargas iguales en la superficie de una esfera o, lo que es lo mismo, hallar la distribución que hace mínimo el potencial electrostático de las cargas (Bausch et al., 2003). En este trabajo se busca minimizar la energía libre del sistema que incluye interacciones competitivas de corto y largo alcance, adecuadas para modelar la dinámica de separación en fases de un copolímero bloque (Gómez et al., 2006). Se comparan las configuraciones finales con las obtenidas en la solución del problema de Thompson. MÉTODOS La ecuación de Ginzburg-Landau dependiente del tiempo para un parámetro de orden conservado viene dada por (modelo de Cahn-Hillard) (Gómez et al., 2006): t M 2 F donde el parámetro de orden mide las fluctuaciones en densidad en el material, M es el coeficiente (1) fenomenológico de movilidad, y F es el campo medio del funcional de energía libre para un copolímero dibloque. Aquí F se puede descomponer como (Leibler 1980): F F S F L (2) donde largo alcance: F S es el término de corto alcance y b 2 la energía local U D 2 F L es el de 3 FS U dr (3) 3 3 FL G r r r r dr dr (4) en (3) tiene la forma del doble 1 2 2 1 3 1 4 pozo U a 1 2f 2 3 4 y G r en (4) es solución de G r r. Los parámetros a,, b y están relacionados con funciones de correlación derivadas por Leibler (conocidas como vertex functions) aunque generalmente son considerados como fenomenológicos. El parámetro depende linealmente de (parámetro de Flory- Huggins), el cual provee una medida de la interacción y la miscibilidad entre los polímeros que forman el copolímero y es proporcional a la inversa de la temperatura, f es la asimetría del copolímero y D es una penalización por formar interfaces, originada por la incompatibilidad termodinámica entre los bloques. En este trabajo se estudiaron las morfologías de equilibrio de copolímeros levemente asimétricos (f 0.45). En el caso de sistemas planos este tipo de copolímeros evolucionan hacia un arreglo con orden hexagonal. Sin embargo, debido a efectos de confinamiento es de esperar que la red hexagonal sea perturbada en distinto grado para diferentes curvaturas. Para diferentes radios del cascarón se resolvió numéricamente la Ec. (1), utilizando un esquema de elementos finitos. En cada simulación el sistema desordenado fue colocado de manera instantánea en la zona espinodal y se lo dejó evolucionar hasta alcanzar la configuración final de mínima energía. RESULTADOS La fig. 1 muestra configuraciones de equilibrio 24

O.1.A.04-NA típicas, obtenidas por medio de la resolución numérica de la Ec. 1. Sobre la columna izquierda se muestran configuraciones de equilibrio de copolímeros sobre esferas de distinto radio (el radio crece continuamente hacia abajo). los dominios se arreglan en configuraciones formando poliedros regulares similares a los observados en el problema de Thomson. De la figura se observan distintos poliedros: a) tetraedro, b) octaedro, c) dipirámide pentagonal, d) dodecaedro. En sistemas hexagonales se definen los defectos topológicos como las esferas con un número de vecinos distinto de 6. La carga topológica asociada esta dada por q=6-v, donde v es el numero de vecinos. La carga topológica total de una configuración es la suma de cada una de las cargas. Existe una relación entre la carga topológica y la topología de la superficie. En el caso de esferas se tiene que la carga topológica total debe ser siempre 12. Todas las configuraciones mostradas en la fig. 1 respetan esta carga. Por ejemplo en a) existen 4 dominios cada uno de los cuales tiene 3 vecinos lo que da una carga de 4x(6-3)=12. De igual forma, para el dodecaedro (d) se tiene 12 dominios con cinco vecinos obteniéndose una carga 12x(6-5)=12. Es de notar que en este trabajo sólo se han considerado copolímeros sobre esferas relativamente chicas (del orden de los 30-100 nm de radio). En el caso de esferas de mayor radio, localmente el sistema comienza a adquirir una mayor simetría hexagonal y otros defectos topológicos, como bordes de grano, comienzan a aparecer como estructuras de equilibrio del sitema (Bausch et al., 2003). CONCLUSIONES Se estudiaron las configuraciones de equilibrio de films de copolímeros bloque levemente asimétricos, depositados sobre la superficie de esferas. Se encontró que a pequeños radios de la esfera, el sistema cristaliza en diferentes poliedros regulares análogos a las configuraciones predichas por la solución del problema de Thomson. Fig. 1. Configuraciones de Copolímeros Bloque sobre cascarones esféricos. Debido a que en este trabajo se mantuvieron fijos los parámetros que modelan las dimensiones del copolímero, la fig. 1 muestra que a medida que se incrementa el radio, un mayor número de esferas pueden ubicarse sobre la superficie de la esfera. Sobre la columna derecha de la fig. 1 se observan las configuraciones de equilibrio de los dominios, las cuales fueron obtenidas por medio de la triangulación de Delaunay. Mediante la triangulación es posible determinar el número de primeros vecinos asociados a cada dominio. En la figura, esferas que son primeras vecinas son unidas por una línea azul. Como se observa REFERENCES Bates and Fredrickson, Phys. Today, 32, (1999). Gómez, L.R., Vallés, E.M., and Vega, D.A., Lifshitz- Safran Coarsening Dynamics in a 2D Hexagonal System, Phys. Rev. Lett. 97, 188302 1-4 (2006). Bausch, A.R., Bowick, M.J., Cacciuto A., Dinsmore, A.D., Hsu. M.F., Nelson, D.R., Nikolaides, M.G., Travesset A., Weitz, D.A., Grain Boundary Scars and Spherical Crystallography, Science 299, 1716-1718 (2003). Leibler, L., Theory of Microphase Separation in Block Copolymers, Macromolecules 13, 1602-1617 (1980). Ohta, T. and Kawasaki, K., Equilibrium morphology of block copolymer melts, Macromolecules 19, 2621-2632 (1986) 25

O.1.A.05-NA EPOXY/AMINE-BASED AMPHIPHILIC PHYSICAL GELS. EFFECT OF AMINE CHAIN LENGTH ON THE PHYSICAL PROPERTIES. ILEANA A. ZUCCHI, JULIETA PUIG, MARÍA JOSÉ GALANTE, CARLOS RODRIGUEZ- ABREU, CRISTINA HOPPE and ROBERTO J. J. WILLIAMS Intema (Univ. Nacional de Mar del Plata - conicet) J. B. Justo 4302 - (7600) Buenos Aires Argentina Institut de Química Avançada de Catalunya, Jordi Girona, 18 26, 08034 Barcelona, Spain ileanazu@yahoo.com.ar ; julietapuig_mdp@hotmail.com ; galant@fi.mdp.edu.ar ; craqci@iiqab.csic.es hoppe@fi.mdp.edu.ar ; williams@fi.mdp.edu.ar INTRODUCTION In a previous work we showed that the reaction between diglycidyl ether of bisphenol A (DGEBA) and dodecylamine (DA) results in the formation of an amphiphilic linear polymer that undergoes a nanostructuration process by the self-assembly of dodecyl chains (Zucchi et al., 2007). This process was driven by the strong predisposition of alkyl chains towards selfassembling when immersed in a hydrophilic medium. The nanostructuration process took place above Tg (where the mobility of the alkyl chains was allowed) leading to a physical gel where the cross-links were formed by tail-to-tail associations among dodecyl chains. The resulting amphiphilic physical gel was very attractive as a matrix for hydrophobic additives (as alkyl coated nanoparticles, paraffins, etc) since the alkyl chains acted as stabilizers. Moreover, from the point of view of the processing, it was extremely versatile since it could be processed as a thermoplastic with the final properties of a network. Taking all these advantages into account, the purpose of this work is to extend the study to other alkyl amines like octylamine (OA) and hexadecylamine (HA) and analyze the effect of the amine chain length onto the final properties of the physical gel. RESULTS All the three amines employed in this study, OA, DA and HA presented amphiphilic character because they consisted of a hydrophilic head (NH 2 ) and a hydrophobic tail (alkyl pendant chain). They were respectively mixed with a diepoxy monomer, a highly polar solvent, in a stoichiometric formulation and the cloud point temperature (Tcp) of the mixtures was measured by transmission optical microscopy (TOM). DGEBA-HA exhibited a Tcp=54 C (coinciding with the melting point of pure amine), DGEBA-DA exhibited a Tcp=20ºC meanwhile for DGEBA-OA Tcp is below room temperature. From the experimental results, it is clear that the size of the hydrophobic tail controls amines solubility in the epoxy. Longer alkyl chains correspond to higher hydrophobicity, leading to an increase in Tcp. 100ºC was selected as the reaction temperature for the three epoxy-amine systems. This temperature is placed well above all Tcps. At this temperature epoxyamine reaction was complete after 3hs (NIR measurements showed that complete disappearance of the epoxy peak was observed after about 2.5 h at 100 C). Small angle X-ray scattering (SAXS) was performed on a DGEBA-DA sample at the selected reaction temperature (100 C), Fig. 1. From the beginning of the reaction (t=0) we could see a broad peak at q=0.265 Å -1 corresponding to a characteristic length d= 2 /q= 2.4 nm, that remains almost unchanged during the following 2 hours. The characteristic distance lies in the range of values reported for tail-to-tail associations of dodecyl chains (Shimojima and Kuroda, 2006). This is clear evidence that the system was assembled from the beginning and during the polymerization. 1000 800 600 400 200 20 min 40 min 60 min 80 min 100 min 120 min 0 0.01 0.1 1 q / Å -1 Fig. 1. SAXS spectra of DGEBA-DA during reaction at 100ºC. After 3h at 100 C all three reaction products could be easily dissolved in typical polymer solvents as tetrahydrofurane (THF), acetone, dimethylformamide (DMF), toluene, dichlorometane (CH 2 Cl 2 ) and chloroform (CHCl 3 ). However, they preserved their thermoplastic behavior only if they were stored at a temperature below their respective glass transition temperatures (Tg) (20ºC, 10.4ºC and 7.3 ºC for DER-OA, DER-DA and DER-HA respectively). On the contrary, they became insoluble as a result of the nanostructuring process. The nanostructuring process starting from the monomers was followed by rheometry at 100ºC. Figure 2 shows the evolution of the storage (G) and loss modulus (G) for the three systems. The time at which gelation occurs could be associated to the moment when G surpass G, indicating a liquid-solid transition. Gelation time was clearly dependent on the hydrophobicity of the amine, since it increases with the amount of carbons of the hanging alkyl chains (C 8 -C 12 - C 16 ). A characteristic property of physical gels is the reversibility of crosslinks. This reversibility is reflected on the appearance of a reversibility temperature (Trev) upon which the material recuperates its liquid behavior. After the isothermal scans, the samples were cooled to -20ºC and then subjected to a temperature scan in the rheometer at 1ºC/min. Figure 2 (images on the right side) shows the 26

O.1.A.05-NA evolution of G and G during heating. The sharp decrease of the storage modulus corresponds to the glass-rubber transition of the amphiphilic gels. Upon Tg, DGEBA-HA exhibited a Trev=85ºC, DGEBA-DA Trev=150ºC and no crossover between G and G is observed for DGEBA-OA up to 200ºC. 10000 1000 Hexadecylamine 27.2 Å Dodecylamine 23.3 Å Octylamine 16.4 Å 1000000 100000 10000 1000 t=6,1 h (a) 1E8 1E7 G' G'' 100 0.01 0.1 1 q / Å -1 100 10 1 0,1 1000000 100000 Fig 3.SAXS spectra recorded at 25 ºC for DGEBA-OA, DGEBA-DA, DGEBA-HA annealed at 100ºC for 90 h. 0,01 1E-3 t=90min G' G'' 10000 1,0 DER-OA 3000 t=21 h 1E-4 0 2 4 6 8 10 12 14 1000-40 0 40 80 120 160 200 0,8 2500 DER-HA Time (hours) Temperature (ºC) 0,6 DER-DA 2000 1000000 100000 10000 t=10,6 h (b) 1E8 1E7 G' G'' 0,4 1500 1000 DER-DA 1000 100 1000000 0,2 DER-HA 500 DER-OA 10 1 0,1 100000 156ºC 0,0 40 50 60 70 80 90 100 110 120 130 Temperature (ºC) 0 40 60 80 100 120 140 Temperature (ºC) 0,01 1E-3 1E-4 1000000 100000 10000 1000 100 10 1 0,1 0,01 1E-3 1E-4 0 2 4 6 8 10 12 14 16 18 t= 49 min Time (hours) 0 4 8 12 16 20 24 28 Time (hours) G' G'' t=26,2 h G' G'' (c) 10000 1000-40 0 40 80 120 160 200 1E10 1E9 1E8 1E7 1000000 100000 10000 1000 Temperature (ºC) 74ºC 100-40 0 40 80 120 160 200 85ºC Temperature (ºC) Fig. 2. Evolution of the storage (G) and loss modulus (G) of (a) DGEBA- OA, (b) DGEBA-DA and (c) DGEBA-HA at 100ºC (images on the left) and during the heating at 1ºC/min (images on the right). SAXS spectra of the samples annealed for 90 h at 100 C were recorded at room temperature (Fig. 3). Broad interference peaks with a maximum at q= 0.230 Å -1 ; q= 0.265 Å -1 and q= 0.383Å -1 for DGEBA-OA/-DA/-HA respectively were observed, corresponding to characteristic lengths d = 2 /q = 1.6, 2.4 and 2.7 nm. The broadness of these peaks suggests the absence of long-range order. The characteristic distance observed in the SAXS spectra agree with the range of values reported for tail-to-tail associations of the respective alkyl chains (Shimojima and Kuroda, 2006). The dependence of gel fraction and swelling percent on annealing-temperature (Fig. 4) was also explored for the three systems under study. G' G'' Fig 4. Gel fraction (a) and swelling percent (b) of DER-OA ( ), DGEBA- DA ( ) and DGEBA-HA ( ) as a function of annealing-temperature at constant annealing time (21h). CONCLUSIONS Physical gels were generated by thermal annealing of amphiphilic polymers obtained by reaction between a diepoxy monomer and an alkylamine. Reversibility temperature of the gels increased in the order HA DA OA, which could be associated to an increase in concentration of aggregates as well as their compactness as the alkyl chain becomes shorter. This effect could also explain higher Tgs values, lower swelling degrees and higher gel fractions obtained for DGEBA-OA respect to DGEBA-DA and DGEBA-HA. We showed that thermal annealing cycles strongly influenced swelling degree and extension of gelation of the physical networks. At both extremes of the explored temperature-range low gel fractions and very high swelling degrees were obtained. This behavior could be related with the existence of an optimum temperature range for the formation of alkyl aggregates. Very low temperatures would decrease the mobility of the chains, making the structuring process difficult, whereas very high temperatures would increase the probability of aggregate disruption, decreasing the stability of the physical crosslinks. In summary, by simple changing the length of the alkyl chain in the amphiphilic polymer and/or the annealing conditions, epoxy-based physical gels with very different properties and a variety of potential applications could be obtained. REFERENCES Zucchi, I.A.; Hoppe, C.E.; Galante, M.J.; Williams, R.J.J.; López-Quintela, M.A.; Matejka, L.; Slouf, M.; Plestil, J. Macromolecules, 41, 4895 (2008). Shimojima, A.; Kuroda, K. Chem. Rec 6, 53 (2006). 27

O.1.A.06-NA INORGANIC NANOPARTICLES DISPERSED IN EPOXY-BASED PHYSICAL GELS J. PUIG, C. E. HOPPE, I. A. ZUCCHI, A. LEDO-SUÁREZ, M. J. GALANTE AND R. J. J. WILLIAMS Institute of Materials Science and Technology (INTEMA), University of Mar del Plata and National Research Council (CONICET), J. B. Justo 4302, 7600 Mar del Plata, Argentina Department of Physical Chemistry, Universidade de Santiago de Compostela, E-15782, Santiago de Compostela, Spain. julietapuig_mdp@hotmail.com ; hoppe@fi.mdp.edu.ar; ileanazu@yahoo.com.ar; ana.ledo@usc.es ; galant@fi.mdp.edu.ar; williams@fi.mdp.edu.ar INTRODUCTION Polymer gels are fascinating materials with multiple and diverse applications as separator agents, solvent absorbers, ion exchangers, diapers, drug delivery devices, etc. (Osada et al. 2004, Sonmez and Wudl, 2005). They are wet and soft materials constituted by networks of flexible cross-linked chains with a fluid filling their interstitial space. Depending on the type of crosslink forming the network, polymer gels can be classified as chemical gels (cross-linked by covalent bonds) or physical gels (joined by weak forces as hydrogen bonds, van der Waals forces, or hydrophobic and ionic interactions). (Osada et al., 2004). Physical gelation is usually a reversible process that occurs through the so called sol gel transition. Large swelling capacities of gels make them attractive not only as absorbents or separators but also as hosts for the development of multifunctional materials. For example, by incorporation of liquid crystals (Kato et al., 2007), or metal ions (Feldgitscher et al. 2009) to the liquid phase, materials with especial properties have been obtained. In the case of physical gels, the ability to be reversibly transformed between the liquid and the gelled states add new advantages to the obtained materials. In this work, an epoxy-based physical gel is obtained by simple bulk polymerization of a diepoxy monomer and a long-chain alkylamine followed by thermal annealing of the system above its glass transition temperature (Zucchi et al, 2009). Capacity of these gels to act as hosts for the dispersion and synthesis of metal and magnetic NPs is demonstrated. Final properties of the dried systems, as well as the ability of the networks as chelating and reducing agents of metal ions are also discussed. METHODS A linear amphiphilic polymer was obtained by bulk polymerization of stoichiometric amounts of diglycidyl ether of bisphenol A (DGEBA) and dodecylamine at 100ºC for 3 hours. The obtained products were soluble in common solvents as THF, toluene, DMF, etc. Gelled specimens were obtained by annealing of the materials at 60ºC for 24 hs. These networks were not soluble but swelled absorbing large amounts of organic solvents. 2 nm gold NPs coated with dodecyl chains were obtained by the Brust-Schiffrin method (Brust et al, 1994) and dispersed in THF for infiltration experiments. Similar THF dispersions were prepared with 3.5 nm - Fe 2 O 3 NPs obtained by a microemulsion method (Vidal- Vidal et al, 2006). Cu(SO 4 ) 5H 2 O, Co(NO 3 ) 2 6H 2 O, HAuCl 4 3 H 2 O and AgNO 3 were used as metallic precursors for the preparation of DMF Co +2 and Cu +2 solutions and THF Ag + - and AuCl 4 solutions with a 6 mm ions concentration. Infiltration was carried out by immersion of weighted slices of the gel in 10 ml of the prepared solutions for 24 hs. After this time, samples were washed with pure solvent for three times and dried in vacuum at room temperature. Swelling degrees were determined by addition of a weighted dried polymer sample (gel fraction) in the selected solvent at room temperature. After 24 h, the supernatant was removed, and slices weighed in a stoppered vial. Swelling percentages were calculated using the formula: swelling % = [(Ws - Wd)/Wd] x 100 (1) where, Wd and Ws represent the weight of dry and swollenpolymer samples, respectively. RESULTS Physical gels obtained by thermal annealing of DGEBA/dodecylamine linear copolymers at 60ºC were soft, transparent materials with a glass transition temperature of 19.4ºC. These gels swelled to different extensions depending on the solvent selected (Fig. 1). The maximum swelling degree was observed for HCCl 3 with a solubility parameter, = 19 (MPa) 1/2 indicating that this value is near the value for the epoxy-based gel. The high value of swelling in DMF did not correlate with the expected shape of the curve. Calculation of dispersion, polar and hydrogen bonding components of by group contributions (Barton, 1983) could neither explain the different behavior found for this solvent. It seems possible that specific interactions 28

O.1.A.06-NA between DMF and hydroxyl groups present in the polymer could be favoring swelling of the gel. It has been reported that the strength of hydrogen bonding between the oxygen atom of DMF and hydroxyl groups may be further enhanced by the nitrogen atom of the DMF molecule (Raj et al. 2009). In any case, swelling degrees in toluene, chloroform, THF and DMF were competitive when compared with other cross-linked polymers in the literature (Sonmez and Wudl, 2005) which results very promising for applications of these materials as organic solvent absorbers. 1600 1400 1200 1000 800 600 400 200 0 Heptane Toluene HCl 3 THF Acetone DMF EtOH 14 16 18 20 22 24 26 28 MPa) 0,5 Fig. 1. Swelling behavior as a function of the solubility parameter, (MPa 0.5 ). Epoxy-based gels were used for the synthesis of metal and oxide nanocomposites. Synthesis was carried out by two different methods: (a) by immersion of gel slices in previously synthesized NPs dispersions and (b) by impregnation with metallic ions and subsequent thermal reduction of the ions to give NPs (Au y Ag). Photographs of materials obtained using method (a) can be observed in fig. 2. Fig. 2. Photographs of nanocomposites obtained by immersion of gels in Au (left) and -Fe 2 O 3 (right) NPs dispersions (note that magnetic nanocomposite is attracted by the magnet). Materials looked homogeneous at the macro-scale. Moreover, characteristic properties of the initial NPs (optical and magnetic) were retained in the nanocomposites which would point to a good dispersion of the NPs in the matrix. Gels were first impregnated with metallic ions in the method (b). After 1 hour of immersion, a clear decrease in the color of supernatants was observed, indicating a high level of metal infiltration in the matrix. Chelating capacity of the gels could be possibly associated with the presence of a large amount of hydroxyl and tertiary amine groups in the polymer structure. Interesting applications of the gelled matrices as toxic- metal ion removers can be envisaged. Gels infiltrated with gold and silver ions were used to generate NPs in-situ. The strong color developed after thermal heating of the systems by 1 hour at 100ºC, evidenced formation of metal NPs, characterized by typical plasmon absorption bands in the visible range of the spectrum. This effect could be related with the presence of weak reducing functional groups in the polymer (tertiary amines and hydroxyls). Interesting differences between both kind of nanocomposites (methods a and b) were found. In the case of method (a), glass transition temperatures (Tg) of nanocomposites remained unchanged after infiltration, whereas for materials obtained by method (b) Tg values increased from 19.9ºC for the neat matrix to 27.7 ºC for silver and 43.8ºC for gold nanocomposites. It could also be found that in the case of nanocomposites obtained by the in-situ method, immersion of thin slices in pure solvent did not produce visible migration of NPs, whereas NPs-impregnated gels easily released nanocrystals to the solvent. Further work, necessary to elucidate the origin of these differences, is currently in progress. CONCLUSIONS Epoxy-based physical gels were obtained and successfully used as hosts of solvents, metal ions and metal NPs. They also show a weak reducing ability that could be used to synthesize Ag and Au nanocomposites. Simplicity in the synthesis and variety of applications of the obtained gels make them promising for the development of advanced functional materials. REFERENCES Barton, A. F. M. Handbook of Solubility Parameters and Other Cohesion Parameters, CRC Press, Boca Ratón, Florida, (1983). Brust, M.; Walker, M.; Bethell, D.; Schiffrin, D. J.; Whyman, R. Chem. Commun. 801, (1994). Feldgitscher, C., Peterlik, H., Puchberger, M. and Kickelbick, G. Chem. Mater., 21, 695-705, (2009). Kato, T., Hirai, Y, Nakaso, S. and Moriyama, M., Chem. Soc. Rev., 36, 1857 1867, (2007). Osada, Y., Gong, J. P. and Tanaka, Y. J. Macromol. Sci., Polym. Rev. C44, 87 112 (2004). Raj, A. M. E., Resmia, L.B., Jothyb, V. B., Jayachandranc, M., Sanjeevirajad, C., Fluid Phase Equilib., 281, 78 86 (2009). Sonmez, H. B. and Wudl, F. Macromolecules, 38, 1623-1626 (2005). Vidal-Vidal J.; Rivas, J.; López-Quintela, M.A. Colloid Surf. A - Physicochem. Eng. Asp., 288, 44 51 (2006). Zucchi, I.A.; Hoppe, C.E.; Galante, M.J.; Williams, R.J.J.; López-Quintela, M.A.; Matejka, L.; Slouf, M.; Plestil, J. Macromolecules, 41, 4895 (2008). 29

O.1.A.07-NA DISPERSIÓN DE DODECANTIOLATO DE AU(I) EN UNA MATRIZ HÍBRIDA. GENERACIÓN DE NANOPARTÍCULAS METÁLICAS POR REDUCCIÓN TÉRMICA. MARÍA LORENA GOMEZ, CRISTINA E. HOPPE, ROBERTO J. J. WILLIAMS INTEMA (Univ. Nacional de Mar del Plata Conicet) Av. Juan B. Justo 4302 (7600) Mar del Plata Argentina mlgomez@fi.mdp.edu.ar; hoppe@fi.mdp.edu.ar; williams@fi.mdp.edu.ar INTRODUCCIÓN Las nanopartículas (NPs) metálicas presentan propiedades ópticas, magnéticas y electrónicas que las diferencian sustancialmente del material en masa y que las hacen especialmente prometedoras en el desarrollo de nuevas aplicaciones que van desde la fabricación de sensores y dispositivos optoelectrónicos (como por ejemplo llaves ópticas, filtros ultrarrápidos, diodos poliméricos emisores de luz (PLED)) hasta la utilización como catalizadores y dispositivos de diagnóstico médico. Un paso fundamental hacia el desarrollo de nuevos dispositivos basados en NPs lo constituye el control espacial de estas nanoestructuras en diversas morfologías y sustratos. La formación de arreglos altamente ordenados o morfológicamente controlados es crucial a la hora de explotar las propiedades únicas de las nanoestructuras metálicas y traducirlas en el diseño de un dispositivo final. (Vaia y Maguire, 2007) En este trabajo se pretende obtener una distribución uniforme de NPs metálicas en una matriz de silsesquioxano (Gómez y col., 2009) por descomposición de un precursor metálico previamente distribuido en la red. Como precursores para la generación de NPs se emplearán tiolatos poliméricos, generados a su vez durante la síntesis de la matriz. Dichos tiolatos serán reducidos por tratamiento térmico originando una distribución uniforme de NPs metálicas en la matriz. Es de esperar que este método de generación in situ permita un autoensamblado controlado con la matriz evitando la agregación y/o segregación de las NPs a la superficie. La afinidad de las cadenas hidrocarbonadas de la matriz con los tiolatos seleccionados permitirá dispersar y autoensamblar ambos sistemas en el material final. Entre los tiolatos empleados resultan especialmente interesantes los tiolatos de oro, dadas sus propiedades luminiscentes (Cha y col., 2007). MÉTODOS Como matriz se empleó un silsesquioxano puenteado (SSO) obtenido a partir de la reacción estequiométrica entre dodecilamina y glicidoxipropil trimetoxisilano. La hidrólisis y condensación de este precursor se llevó a cabo en THF empleando agua y ácido fórmico como catalizador. Conjuntamente con la obtención del film entrecruzado del SSO se llevó a cabo la reacción de generación de dodecantiolato de Au (DDT-Au). El tiolato de Au se obtuvo por reacción de dodecanotiol con HAuCl 4 en una relación tiol:au de 5:1 (Cha y col., 2007); la reacción correspondiente a la formación del tiolato se ilustra en la Ec. 1: HAuCl 4 + 3HSC 12 H 25 AuSC 12 H 25 + H 25 C 12 S-SC 12 H 25 + 4HCl (1) Una vez obtenidos los films con el DDT-Au disperso, éstos fueron sometidos a tratamiento térmico a 150 C (TT), variando el tiempo de exposición. Los materiales, originalmente incoloros o de un ligero color amarillo, se tornaron intensamente coloreados, incrementándose su color con el TT; este cambio en la coloración puede ser atribuido a la presencia de partículas metálicas de Au (Ec. 2), cuya absorción de resonancia de plasma característica se encuentra en la zona del espectro visible. 2AuSC 12 H 25 2Au(0) + H 25 C 12 S-SC 12 H 25 (2) Los films fueron caracterizados por Uv-Vis, fluorescencia, DSC, TOM y SEM. RESULTADOS Y DISCUSIÓN La matriz seleccionada se caracteriza por poseer propiedades luminiscentes en la zona visible del espectro electromagnético cuando la misma es excitada con luz UV; el máximo de emisión se encuentra alrededor de los 430 nm para longitudes de onda de excitación entre los 300 y 400 nm. Por su parte en las matrices modificadas con DDT-Au, la emisión de la misma prácticamente desaparece observándose la aparición de una banda intensa centrada en los 630 nm. La Fig. 1 muestra los espectros de emisión del SSO modificado con DDT-Au sin TT. Resultados similares fueron reportados por Cha y col. (2007), quienes estudiaron las propiedades luminiscentes de una serie de alquiltiolatos de Au(I) sintetizados a partir de tioles de distinto largo de cadena hidrocarbonada. Los resultados de luminiscencia para la matriz del SSO con DDT-Au indicarían que la presencia de los precursores, así como la posterior hidrólisis y condensación de los mismos para generar la red, no interfiere en la generación del tiolato ni en sus propiedades luminiscentes. 30

O.1.A.07-NA 9x10 7 8x10 7 7x10 7 6x10 7 5x10 7 4x10 7 3x10 7 2x10 7 1x10 7 : 300 nm Exc : 325 nm Exc : 350 nm Exc 0 500 550 600 650 700 750 800 Longitud de onda (nm) Fig. 1. Espectros de luminiscencia del SSO modificado con DDT-Au. Por otra parte, recientemente Cha y col. (2008) reportaron la formación de NPs de Au por descomposición térmica de sus respectivos tiolatos. El calor asociado al proceso de fusión del tiolato puede observarse claramente por DSC (pico centrado a 160ºC). Este pico, observable también en los SSO modificados, disminuye cuantitativamente con el incremento en el tiempo de TT. Por otra parte, los espectros UV-Vis de las muestras conteniendo DDT-Au después del TT presentan una banda plasmónica centrada alrededor de los 560 nm que puede asociarse a la presencia de NPs de oro dispersas en la matriz. (Liz- Marzán, 2006) Sin TT 2 hs TT 4 hs TT 15 hs TT Fig. 2. Efecto del TT sobre matrices de SSO modificadas con DDT-Au. Las imágenes de SEM, permitieron corroborar la presencia de formaciones metálicas de unos 100 nm de diámetro en las muestras a las que se aplicó TT (Fig. 2). Es posible observar también, un aumento en el número y tamaño de partículas observadas con el incremento de TT. Tal como muestra la figura, este método de generación in situ permite una distribución homogénea de partículas de Au en la matriz del SSO. CONCLUSIONES La evidencia experimental permite afirmar que el método empleado es útil para lograr una distribución homogénea de DDT-Au en matrices híbridas. El tiolato generado conserva sus propiedades luminiscentes al ser incorporado a la matriz. El tratamiento térmico posterior, aplicado a los SSO modificados con DDT-Au, permitió la generación de partículas del orden de 100 nm, uniformemente dispersas en la matriz, evitándose con este método los efectos de segregación anteriormente observados en este tipo de matrices (Gómez y col., 2009). Resta aun investigar la naturaleza de las partículas observadas a fin de corroborar si se trata de partículas individuales o agregados de partículas de menor tamaño. También se encuentra en curso la dispersión de tiolatos de Ag en esta matriz y el estudio de los efectos del TT. Estos tiolatos resultan particularmente interesantes por su capacidad de generar estructuras con características de cristal-líquido (Baena y col., 1992). REFERENCIAS Baena, M.J., Espinet, P., Lequerica, M. C., Levelut, A.M. Mesogenic behavior of silver thiolates with layered structure in the solid state: covalent soaps J. Am. Chem. Soc., 114, 4182-4185 (1992). Cha, S., Kim, J., Kim, K., Lee, J., Preparation and photoluminescent properties of gold(i)- alkanethiolate complexes having highly orderer supramolecular structures Chem. Mater., 19, 6297-6303 (2007). Cha, S., Kim, K., Kim, J., Lee, W., Lee, J., Thermal behavior of gold (I) thiolate complexes and their transformation into gold nanoparticles under heat treatment process J. Phys. Chem., 112, 13862-13868 (2008). Gómez, M.L., Hoppe, C.E., Zucchi, I.A., Williams, R.J.J., Giannotti, M.I., López-Quintela, M.A., Hierarchical assemblies of gold nanoparticles at the surface of a film formed by a bridged silsesquioxane containing pendant dodecyl chains, Langmuir, 25, 1210-1217 (2009). Liz-Marzán, L.M., Tailoring surface plasmons through the morphology and assembly of metal nanoparticles, Langmuir, 22, 32-41 (2006). Vaia, R.A., Maguire, J.F., Polymer nanocomposites with prescribed morphology: going beyond nanoparticle-filled polymers Chem. Mater., 19, 2736-2751 (2007). 31

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O.1.A.08-NA Ù ½ ¾±²»»½ ±¼» øùýû ï ï ³¹ ÓÒÐ óßðíóüòñ î õ ï ³Ô ÜÓÍÑô ³» øïë ³ ² ±ª» ² ¹ î Û ²± ô» ÓÒÐ óßðíóüóòñ ÒÐ óßðíóüòñ î ñùýû î ñùýû ͽ»³» ïò Ð ½ ³³±¾ ±² ±º ¼»²¼ ±²ó½±»¼ ³ ¹»³» ±² ± ÙÝÛò ðòðî ðòðð óðòðî óðòðì Þ º ½ ½» ß Ü óðòéë óðòëð óðòîë ðòðð ðòîë ðòëð Ý ²½» ²¹ ²«³¾» ±º ½ ² б»² ñ Ê ª ò ß¹ñß¹Ý Ú ¹òîò Ý ½ ½ ª± ³³±¹ ³ ðòï Ê º± ÓÒÐ ó ßÐÍóÜóÒÑ î ³±¼ º»¼ ÙÝÛ ² ðòïó ÐÞÍ ø Ø é ò Ú ½ ² ø¼»¼ ²» ²¼»½±²¼ ½ ² ø ± ¼ ²» ò ÝÑÒÝÔËÍ ÑÒÍ Ü»²¼ ½ ³±»½ó½±»¼ ³ ¹²» ½ ² ²± ½»»» ²»»¼ ²¼ ½ ½»»¼ò Ì»»» «± ² ±«³» ³» ±¼ ± ¼¼ ³ ¹²» ½ ³» ² ½ ¾±²»»½ ±¼» ²¼ «¹»²»» ±³ ²¹ «º ½» º±» ¼»ª» ± ³»² ±º ¾ ±»² ± ò Ì» ± ª»» º± ³ ² ½ ±² «½ ¾ ±½±³ ¾» ¼» ª»»³ ²¼»»½ ±² ½ ²¼ ± ±² ½ ¼»ª ½» ò É»» ½² ½ ª»» ± ²¹» ±º»» ½ ò ßÝÕÒÑÉÔÛÜÙÛÓÛÒÌÍ Ì» «± ¹»º«½µ²±»¼¹» º ² ²½ «± º ±³ ÝÑÒ ÝÛÌô ßÒÐÝ Ìô ²¼ ÍÛÝÇÌ ±º ˲ ª» ¼ ¼ Ò ½ ±² ¼» Ý- ¼±¾ ò Öò òðò» ± ²µ ÝÑÒ ÝÛÌ º±» º» ± ±ª ¼»¼ò ÎÛÚÛÎÛÒÝÛÍ Åïà ̱³ ô Üò ßò Ó» ̱¼ ô îððíô êô éîò Åîà Öò л ô Ðò Ú ± ³± ½ ô ßò Þ «ô Óò Í «³ ô Êò Þ «²» ô Û»½ ±½»³ò ݱ³³ò îððèô ïðô ëìïò Åíà Öò л ô Óò Í «³ ô Óò л¹¹ Ö òô Öò Ú» -²ô ßò Þ «ô Êò Þ «²» ô Û»½ ±½»³ò ß½ îððçô ëìô ìïçîò Åìà Öò л ô ßò Ý»» ô ßòÓò Þ «ô Êò Þ «²» ô Óò Í «³ ò Ð ±½ò ïé ÐÑÔÇÝØßΠɱ ¼ Ú± «³ ±² ß¼ª ²½»¼ Ó» ò îððçò α²ô Ú ²½»ò Åëà Çò Þ±¹«ª µ ô Íò Öò Ó ¹» ô ݱ ± ¼ ²» ºò ͽ ò îððèô íïéô ïðïò Åêà Íòßò Ù±³» óô±» ô ÎòÝò Ð ô ßò Êò Ü» ¹ ¼±ô Öò ݱ ± ¼ ²» ºò ͽ ò îððïô îìðô ìðò Åéà Óò ß ¾±ô Îò Ú» ²?²¼» óð ½»½±ô Óò Îò ¾ ô Öò Í ² ³ 3 ô Ò ²± ±¼ îððéô îô îîò Åèà Ýò Ýò Þ» ô Öò Ó» ò Ý»³ò îððëô ïëô ëìíò Åçà Óò Ì µ º«ô Íò ¼»ô Øò ô Æò È«ô Ý»³ò Ó» ò îððìô ïêô ïçééò Åïðà Èò Æ ²¹ô Ïò Ù«±ô Üò Ý«ô Í»² ± îððçô çô ïðííò Åïïà Óò Í ²¹» ³ ²±ô ßò Ð ± ô Ùò Õ± ¾» ô ßò Ö ³»²±ô ò Ù ½ ô ò Ó±²¼ ¹±²ô Ùò Î ô Ó ½ ±³± ò Ó» ò Û²¹ò îððéô îçîô çëêò Åïîà ÔòØòÓò Ú±²»½ ô ßòÉò Î ² ¼ ô ßòÚò Ϋ¾ ô ÔòÚò ݱ ½ ô ÍòÒò ¼» Ó»¼» ± ô ßò л ²± Ö òô òßò Í ² ± ô ÛòÓò Ù ± ±ô Ó» Ý»³ ²¼ Ð ½îððêô çéô îëîò 33

O.1.A.09-NA NANOINDENTATION OF HARD COATED POLYMERIC FILMS: EXPERIMENTAL AND NUMERICAL SIMULATION L. A. FASCE, R. SELTZER AND P.M. FRONTINI INTEMA-(Universidad Nacional de Mar del Plata-CONICET) - J B Justo 4302 (B7608FDQ) - Mar del Plata Argentina. Center for Advanced Materials Technology (CAMT), School of Aerospace, Mechanical and Mechatronic Engineering J07, University of Sydney - Sydney Australia lfasce@fi.mdp.edu.ar ; r.seltzer@usyd.edu.aur ; pmfronti@fi.mdp.edu.ar INTRODUCTION Thin coatings deposited on polymers are widely used in optical, microelectronic, packaging, biomedical and decorative applications. Nanoindentation is an advanced technique used to evaluate the mechanical properties of thin coatings due to its capability of deforming materials on a very small scale. However, distinguishing the coating properties from the substrate effects is critical. For hard coatings on soft compliant substrates, deformation of the substrate is predominantly plastic whilst the coating may deform or fracture as it is bent into the track created by plastic deformation of the substrate. Hence, the indentation load-penetration depth curve reflects the mechanical behavior of the coating-substrate system. Moreover, discontinuities in the curve can be attributed to fracture events such as cracking, delamination and chipping occurring in response to the indentation stress. In this work we combined nanoindentation experiments with finite element simulations to determine the intrinsic elastic modulus (E) of a hybrid PEO/SiO 2 coating deposited on a PVC substrate. EXPERIMENTAL A PVC film coated with a 30%PEO/70% SiO 2 hybrid with a thickness 1.42 m was evaluated. Nanoindentations were performed with a Berkovich tip at different maximum applied loads ranging from 100 to 1000 N with a loading/unloading rate of 500 N/s. In addition, nanoindentations with a spherical indenter (1 m tip radius) were conducted on PVC substrate. In all experiments a holding time of 15 seconds before unloading was applied to minimize viscoelastic effects during unloading. FINITE ELEMENT SIMULATIONS Indentation tests were simulated with a finite element (FE) commercial software ABAQUS 6.7-1 (2007). The system was modeled as a body of revolution. The indenter was assumed infinitely rigid, and the system frictionless. Axisymmetric linear quadrilateral elements were adopted, where a fine mesh was used close to the contact zone (12000 elements) and a coarse mesh (5500) away from it to economize computation time. The coating was assumed to have perfect bonding to the substrate. The maximum indentation depth was 1/10 of the coating thickness. A conical tip with apical angle of 19.7 0 was used to simulate the Berkovich pyramid. The substrate was assumed elastic-perfectly plastic and the coating, elastic. The mechanical properties used as input in the FE simulations are listed in Table 1. PVC elastic modulus (E) and yield stress ( y ) were determined from the spherical indentations by means of Oliver-Pharr (1992) and Dao (2001) approaches, respectively. Table 1. Properties used in FE simulations. Elastic Poissons modulus ratio (GPa) Yield Stress (MPa) Substrate (PVC) 2.8 0.4 40 Coating 10 / 70 0.4 - RESULTS Experimental load-penetration depth (P-h) curves are shown in Fig 1. The maximum load applied was low enough not to cause fracture events in the coating. In Fig. 2, the resulting stress field and plastic zone of FE simulated Berkovich indentations of two hard coatings onto a soft elasto-plastic substrate are shown. It is seen that at the same indentation depth (0.142 m), the stiffer the coating, the higher the equivalent stress generated in the coating and the larger the plastic zone in the substrate. The highest normal stress occurs at the bottom part of the hard coatings beneath the indenter. If the coating tends to fail in tension rather than in compression or shear, it will do so at the interface with the substrate. Furthermore, the stiffer the coating, the larger the normal stress values generated at a given indentation depth. In Fig. 3 the soft substrate/hard coating systems simulated indentation response is plotted together with the response of the hard coatings alone. In both cases the departure of one curve from another begins, practically, from zero depth. 34

O.1.A.09-NA 1200 1000 experimental 500 400 hard coating/soft substrate hard coating 1500 1250 hard coating/soft substrate hard coating 800 300 1000 750 600 200 500 400 200 0 0 50 100 150 200 250 300 350 h (nm) Fig. 1. Typical indentation P-h curves. 100 70 60 E coating =10 GPa 0 0 50 100 150 h (nm) Fig. 3. Simulated indentation P-h curves. simulated 250 E coating =70 GPa 0 0 50 100 150 8,5 8,0 h (nm) experimental E coating =10GPa E coating =70GPa 50 40 7,5 7,0 30 6,5 a 20 15 10 E coating =70GPa 6,0 5,5 5,0 5 E coating =10GPa 4,5 4,0 b 0 3,5 0 30 60 90 120 150 0 50 100 150 200 250 300 350 h max (nm) h max (nm) Fig. 4. Relationship between E and h max in: a) hard coating/soft substrate systems b) PEO-SiO 2 /PVC. CONCLUSIONS c Fig 2. Contours obtained from FE simulation of Berkovich indentation: a) equivalent stress (Mises); b) maximum normal stress; c) plastic zone. In Fig. 4, elastic modulus values calculated using the Oliver-Pharr method for simulated and experimental curves are plotted as a function of maximum indentation depth (h max ). The non-linearity between E and h max is accentuated with increasing coating/substrate stiffness ratio. To determine the elastic modulus of the coating from our experimental results, a second order polynomial extrapolation was used as shown in Fig.4, yielding a value of 8.13GPa. Finally, to verify the applicability of the extrapolation technique, the experimentally recorded loading indentation response was accurately reproduced using the modulus value just obtained. Moreover, experimental E values of a 0.42 m thick coating were extrapolated leading to the same elastic modulus for the hybrid coating. With the aid of FE analysis, it has been shown that the widely quoted 10% rule should not be used for Youngs modulus assessment in the case of indentation of hard coatings on soft substrates. It was noted that the Youngs modulus values (as determined with the Oliver-Pharr method) decrease monotonically with penetration depth. Hence, to determine the true property value of a hard coating on a soft substrate, extrapolation of the Youngs modulus to zero penetration depth should be performed. This procedure was successfully applied to PVC coated with PEO-SiO 2. As future work, the elastic modulus of coatings with different PEO-SiO 2 ratios and reticulation time deposited on a PVC substrate will be determined. REFERENCES Dao M, Chollacoop N., Van Vliet K.J., Venkatesh T.A., Suresh S., Computational Modeling of the Forward and Reverse Problems in Instrumented Sharp Indentation, Acta Mater 49 38993918(2001). Oliver WC, Pharr GM., An improved technique for determining hardness and elastic-modulus using load and displacement sensing indentation experiments, J Mater Res 7 1564-1583(1992). 35

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