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The study and understanding of the structure and properties of styrene/vinylester (St/VE) and styrene/unsaturated polyester (St/UP) cross-linked thermosets has received technologic and scientific attention, because these resins are widely used as matrices in composites formulations, sharing advantages, such as low room temperature viscosity coupled with good mechanical properties and low cost, plus the added chemical resistance in the case of VE. To investigate the morphologies of these systems, scanning electron microscopy (SEM) offers an useful tool at a micron scale, while the atomic force microscopy (AFM) allows to reach the detail of the topography at a nanometric scale and also to determine the nanostructures of the surface [1]. In both systems, the cross-linked reaction occurs by free radical polymerisation where, big molecular structures are formed through connecting St and UP (or VE) unsaturated comonomers by both interand intra-molecular reactions. These branched structures tend to form a spherical type structure or ‘‘nanogel particle’’, due to the intramolecular cross-linking among the unreacted C = C bonds located in different pendant chains, with reactive radicals [2]. The microgel morphologies are strongly depending of the cure temperature and the initial composition of the reactive mixture as it has been previously reported [2, 3]. In the present work the relationship between the final morphologies and the St-resin initial ratio is analyzed, and the development of the microstructures resulting from the use of the two different unsaturated resins is compared. A natural UP resin was obtained from modified linseed oil in two basic steps: glycerolisis and posterior maleinization [4]. The linseed oil used was provided by Grainer S.A. (Entre Rios, Argentine) and was used without further purification. The glycerol used was 99.5% pure and was obtained from Cientifica Central (Bs. As., Argentine). A commercial soap without additives was used as emulsifier catalyst for this reaction. 2-methyl imidazole was used as catalyst during the maleinization reaction between the glycerol –OH groups and maleic anhydride, both from Fluka A.G Chemical Co. A low molar mass divinylester (VE) monomer was synthesized from the reaction of an epoxy resin diglycidyl ether of bisphenol-A (DGEBA, DER 332 Dow Chemical Co., epoxy equivalent weight 175 g/eq) with methacrylic acid (Norent Plast S.A., laboratory grade reagent), using triphenylphosfine (Fluka A.G., analytical reagent) as catalyst. The final conversion reached was higher than 97% [5]. Different final materials were prepared varying resin:St ratio in a wide concentration range. The high stiffness of these materials allows obtaining fragile fracture surfaces like mirror at room temperature. The general schemes of copolymerization of St/UP and St/VE systems are summarized in Fig. 1. Both synthesis M. A. Mosiewicki (&) AE W. F. Schroeder AE M. I. Aranguren AE J. Borrajo Institute of Material Science and Technology (INTEMA), University of Mar del Plata – National Research, Council. J. B. Justo 4302, 7600 Mar del Plata, Argentina e-mail: jborrajo@fi.mdp.edu.ar

In the present work, PANI (polyaniline) emeraldine salt (doped) and base (dedoped) were used as the sensitive layer of a silicon microcantilever, and the mechanical response (deflection) of the bimaterial (coated microcantilever) was investigated under the influence of humidity. PANI in the emeraldine base oxidation state was obtained by interfacial synthesis and was deposited on the microcantilever surface by spin-coating (dedoped). Next, the conducting polymer was doped with 1 M HCl (hydrochloric acid). A four-quadrant AFM head with an integrated laser and a position-sensitive detector (AFM Veeco Dimension V) was used to measure the optical deflection of the coated microcantilever. The deflection of the coated (doped and undoped PANI) and uncoated microcantilever was measured under different humidities (in triplicate) at room pressure and temperature in a closed chamber to evaluate the sensor's sensitivity. The relative humidity (RH) in the chamber was varied from 20% to 70% using dry nitrogen as a carrier gas, which was passed through a bubbler containing water to generate humidity. The results showed that microcantilevers coated with sensitive layers of doped and undoped PANI films were sensitive (12,717 ± 6% and 6,939 ± 8%, respectively) and provided good repeatability (98.6 ± 0.015% and 99 ± 0.01%, respectively) after several cycles of exposure to RH. The microcantilever sensor without a PANI coating (uncoated) was not sensitive to humidity. The strong effect of doping on the sensitivity of the sensor was attributed to an increased adsorption of water molecules dissociated at imine nitrogen centers, which improves the performance of the coated microcantilever sensor. Moreover, microcantilever sensors coated with a sensitive layer provided good results in several cycles of exposure to RH (%).

The fabrication of nanostructured layer-by-layer (LbL) films strives for molecular control of the film properties directly connected with modifications in the film architecture. In the present report, the photoinduced birefringence and formation of the surface-relief gratings in LbL films obtained with an azopolymer (PS119) are shown to be strongly affected by the generation of the dendrimer employed in the alternating layers. Stronger adsorption of PS119 occurred when polypropylenimine tetrahexacontaamine dendrimer (DAB) of higher generations is used, due to a larger number of sites available to interact with azochromophores in PS119. In contrast, the photoinduced birefringence for LbL films made with the generation 1 dendrimer (DABG1) was higher, which can be explained by weaker interactions between adjacent layers. Strong interactions in LbL films consisting of PS119 and generation 3 or 5 dendrimers restrict the chromophore mobility, leading to a smaller birefringence. The interpretation is supported by the fact that surface-relief gratings with larger amplitudes were obtained for 35-bilayer films of DABG1/PS119 (31 nm) in comparison with films from DABG5/PS119 (5 nm). These gratings were formed with mass transport arising from a light-driven mechanism, as photoinscription was successful only with p-polarized light and not with s-polarized light.

The interaction between poly(o-ethoxyaniline) (POEA) adsorbed onto solid substrates and humic substances (HS) and Cu/sup 2+/ ions has been investigated with UV-VIS spectroscopy and atomic force microscopy. Both HS and Cu/sup 2+/ cause the POEA film to be further doped, and alter the film morphology. This interaction was exploited in a sensor array made of nanostructured films of POEA, sulfonated lignin and HS, which could detect small concentrations of HS and Cu/sup 2+/ in water.