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Risultati sfruttabili
Physical gelation and interaction in polymer solutions were investigated via high-accuracy experiments (small-angle scattering of X-rays and neutrons both in the laboratory and at the Large European Installations; static and dynamic light scattering; acoustic spectroscopy; rheology; Langmuir-Blodgett technique) and subsequent advanced methods of data analysis developed.
Extensive data on the morphological characteristics of the gels formed with aqueous and aliphatic hydrocarbon extender were accumulated in static and dynamic regimes. A transition to another type of polycrystalline (BCC) morphology has been observed for the triblock copolymer gels (with aliphatic extender) at elevated temperature. This phase persists only in a well-defined temperature window and disappears beyond it. Further ordering to a twinned BCC quazi-monocrystal was detected under the influence of oscillating shear. This treatment seems to stabilize the BCC morphology. An approach to understand this transition was made via real-time small-angle X-ray scattering (SAXS) experiments using synchrotron radiation. A correlation was found between the spontaneous appearance of the BCC morphology and the specific (close to statistical coil) conformational state of the middle blocks of the copolymer (links of the network). In addition to the phase-separation of the end- and midblocks, solvent penetration to the (phase-separated) end-block domains seems to be a key point for the transition. In the case of polyelectrolytic polysaccharide carrageenan, gelation occurs via the mechanism of conformational transition and subsequent separation of the fragments with ordered and disordered conformation. At gelation-favourable conditions the formation of a particle type scattering was observed by small-angle neutron scattering (SANS) in D2O solution, which corresponds to the formation of the network junctions. This process was followed by a slow (hours) increase of the (negative) scattering contrast of the junctions. The phenomenon was only observed above a certain concentration of the polymer and interpreted as squeezing of solvent out of the junction zones.
Conformational state of potential modifiers of the order in the network, globular protein HSA (human serum albumin) and phospholipid clusters in monolayers, has been investigated in solution and found sensitive to changing pH and presence of physiologically active compounds (PAC).
Based on the previously developed algorithms, a program for an ab initio low-resolution shape determination from solution scattering data was written. The program works directly with the experimental curves on a relative scale and takes into account a finite width of the particle-solvent interface. The program was tested on solution scattering data from several proteins with known atomic resolution crystal structures. The program CRYSOL developed at an earlier stage of this project was extended and used to experimentally analyze the structure of the macromolecule-solvent interface.
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