ANNUAL REPORT 2011 - Instituto de Estructura de la Materia

product. The clay can be used directly, without any previous chemical modification. One interesting aspect of thismethod is that some polymeric chains became directly grafted on the clay platelets, thus giving rise, for somecomposition,s to a complete clay exfoliation. The same method has been applied to the preparation of binary orternary blends of the polymers above cited, that are normally considered as incompatible. The results obtained arevery promising.Dielectric properties of nanocomposites based on thermoplastic polymers reversibly crosslinked.Wishing totake advantage of our previous experience in this field, we have extended our investigation to some other polymersof increasing interest and wide use, as, for instance, poly(ethylene terephthalate) PET, poly(ethylene naphthalenedicarboxylate) PEN, poly(methyl methacrylate) PMMA, and poly(vinylidene fluoride) PVDF. Moreover, we areespecially interested in applying the procedure to obtain nanocomposites in one step to the preparation ofnanocomposites of the preceding polymers with clay, graphite, and some other additives. We are making an especialemphasis in the study of the dielectrical properties of the resulting materials.Polymer/organometallic polymer nanocomposites.We have carried out a deep study on the advanced properties ofpolymer/organometallic polymer nanocomposites. In particular [Fe(II) (4-octadecyl-1,2,4-triazol)3(ClO4)2] inPolystyrene (PS). Our results confirm that, even in the presence of PS, the structural transition associated to achange in the magnectic susceptibility of the organometallic polymes occurs. This transition is associated to theconversión from lamellar to hexagonal structure in the organometallic polymer.The work has been carried out incollaboration with doctors Daniel López and Rebeca Hernández from Instituto de Ciencia y Tecnología dePolímeros (ICTP-CSIC) and with Doctor Ana Roig, from Instituto de Ciencia de Materiales de Barcelona (ICMAB-CSIC).ATOMIC FORCE MICROSCOPY(AFM)During the last year 2011the AFM facility has been implemented with a system to measure forces allowing not onlyvisualization by also assessment of mechanical properties at scales of nanometer. The new capabilities will enable toinvestigate mechanical properties such as elastic modulus, adhesion and deformation forces as well as to performnanoindentation experiments.BIOSAXCharacterization of biologically interesting colloids and lipoplexes. We have continued with research on thestructuration of mix liposomes formed by a cationic and a zwiterionic lipid in the presence of DNA. By Small AngleX ray scattering we have determined the effect of the lipidic composition in the structure of such lipoplexe and theresults have been compared with the theoretical phase diagram with an excellent agreement. This work has beencarried out in collaboration with the group of Prof. E. Aicart from the Química Física I department from UniversidadComplutense de Madrid.Research on new compounds and their influence on the assembly of microtubules.By means of X ray andNeutron scattering it is possible to extract information on the conformation of biologically interesting systems, like,as an example, proteins in solution. In collaboration with the group of Dr. F. Díaz from the Centro deInvestigaciones Biológicas (CIB-CSIC), we are carrying out SAXS experiments on the influence of new antitumoralcompounds based on taxanes on the tubulin assembly. The goal is to understand the mechanism, at atomic andmolecular level, of the microtubule assembly in the presence of the mentioned compounds.Group of BIOPHYSICS OF MACROMOLECULAR SYSTEMSSIMULATION OF PHYSICAL PHENOMENA IN MACROMOLECULAR SYSTEMSMelt macromolecular dynamics of polyolefins.Full Monte Carlo (MC) and molecular dynamics (MD) atomisticcomputer simulations of the molecular dimensions and dynamial processes in entangled linear and short chainbranched polyethylene chains were designed to establish the effect of the molecular architecture on the diffusion andviscoelastic properties. This strategy allows one to evaluate the density and the intermolecular local packing (chainsize) in the melt by mapping of MD simulations on the reptation model of de Gennes and Doi-Edwards. The resultsobtained illustrate the dependence of the chain dimensions, the entanglement features, and the characteristicrelaxation time of the transition from Rouse-to-reptation regimes with the molecular architecture of polyethylene forshort chain branching content between 0 and 55 per 1000 carbon atoms. The results are in very good agreement withthe experiments in the literature, and more interestingly with those obtained in our group in molecular models ofbranched polyolefins, characterized by a very homogeneous molecular architecture.76