ANNUAL REPORT 2011 - Instituto de Estructura de la Materia

morphological model for Natural Rubber indicating that during strain-induced crystallization shorter chains areprogressively incorporated into the crystals while a significant amount of longer chains remains rather coiled.Self-assembly of primary alcohols. The transformation of supercooled liquids into rotational disordered crystals isa well-known example of entropy-driven transitions which, together with standard phase transitions, are present inplenty of natural and daily situations. In this respect, hydrogen bonding alcohols are of special interest. Ascontinuation of previous studies of crystallization of hydrogen bonding systems carried out in SOFTMATPOL wehave investigated the complex phase diagram of deuterated ethanol by means of a particular technique that allowsobtaining simultaneous structural and dynamic information. Precisely, we have investigated the transformation ofethanol from supercooled liquid into a plastic crystal or rotator phase by means of a particular experimental setup,developed by us, which combines simultaneously dielectric spectroscopy with neutron diffraction techniques. Wehave demonstrated that, previous to the growth of the body centered cubic (bcc) lattice characteristic of the plasticcrystalline phase, the formation of a precursor or intermediate phase through a liquid-liquid phase separation takesplace. Once this precursor phase is formed, subsequent (plastic) crystalline nucleation and growth is expected todevelop. Our results may be relevant to further understand the well known hydrogen bond network of waterresponsible of most of its unique properties.Dynamics of self-assembled block copolymers. The dynamics of di-block copolymers in the phase separatedlamellar structure and in the mixed state has been studied by dielectric spectroscopy. By choosing a system in whichthe glass transition temperatures of the two constituent polymers are not very different, we were able to investigatethe differences between hard and soft confinement imposed by the more rigid chains. The results indicate that underhard confinement, the segmental dynamics of the softer component experiences a slowing down due to interactionwith the more rigid chains in both separated and mixed phase cases. For the separated phase case no difference inthe dynamics of the softer block is observed upon going from the hard to the soft confinement regime. However forthe mixed system under soft confinement, i.e. at temperatures higher than the Tg of the more rigid polymer block, aslowing down of the dynamics of the softer block polymer towards the dynamics of the more rigid block is clearlyevidenced.Self assembly of block copolymers. As a continuation with previous years work, we have studied the impact ofself-assembling at the nanoscale on the dynamics of block copolymers, by means of different spectroscopies, likedielectric spectroscopy and X-Photon Correlation Spectroscopy. Besides, and in collaboration with the group ofProf. Enrique Vallés from the Universidad Nacional del Sur, Argentina, we are working on the study of the phasediagram of diblock copolymers of polystyrene (PS) and poly(-caprolactone) (PCl) by simultaneous small and wideangle X-ray scattering (SAXS and WAXS). For rich PS concentrations a certain inhibition of the crystallization ofPCl is observed due to the confinement imposed by the phase segregation and by rigidity of PS domains. For all theother concentrations, and due to the high crystallizability of PCl, the phase segregation is partial.NANOFABRICATION OF POLYMER STRUCTURESPolymer nanogratings.We have started to exploit the possibilities of using laser beams in order to nanostructuratethe surface of thin polymer films. In cooperation with the group of Dr. M. Castillejo (IQFR-CSIC) we havesucceeded in nanofabricating laser induced periodic surface structures (LIPSS) in a series of strongly absorbingmodel spin-coated polymer films such as poly(ethylene terephthalate), poly(trimethylene terephthalate), andpoly(carbonate bisphenol A), and in a weaker absorbing polymer, such as semicrystalline poly(vinylidene fluoride).We have evaluated the potential of using grazing incidence X-ray scattering techniques in the investigation of thistype of systems. Irradiation of the polymer films by laser pulses of 6 ns at a wave length of 266 nm producescharacteristics nanogrooves (polymer nanogratings) with period lengths similar to the laser wavelength. Weproposed that the nanostructures are formed by devitrification of the film surface at temperatures above thecharacteristic glass transition temperature of the polymers. The structural information obtained by both atomic forcemicroscopy (AFM) and grazing incidence small-angle X-ray scattering (GISAXS) correlates satisfactorily.Comparison of experimental and simulated GISAXS patterns suggests that LIPSSs can be well describedconsidering a quasi-onedimensional paracrystalline lattice and that irradiation parameters have an influence on theorder of such a lattice.74