This thesis is devoted to the study of the response of functional polymer materials to the external stimuli. The magneto-sensitive elastomers filled with carbonyl iron particles, photo-responsive liquid crystalline polymer brush with azobenzene chromophores, and thermo-responsive polymer brush with the properties of poly(N-isopropylacrylamide) were considered.
Study of the properties of magneto-sensitive elastomer (MSE) consist of several parts. Different models with their magnetic energies of interaction between pairs of particles were compared. It was found that mutual magnetisation of dipoles is enough to describe column-like structures. More detailed model, derived from the solution of the Laplace equation for two magnetizable spheres, was used in order to describe density of the magnetic energy of spheroidal MSE in pairwise approximation. It was shown, using micro-sphere formalism, that demagnetization factor is the same in such approach as in the theory of continuous media.
Dependency of MSE's magnetostriction on the spatial distribution of magnetic particles was considered. The spatial distributions of the magnetic particles considered were SC, FCC, BCC and HCP lattices. It was found that magnetostriction factor depends on the volume fraction of the particles, which was not observed for dipoles. The magnetostriction factor is dependent on orientation of the lattices with respect to the magnetic field, which is exemplified by the differences between HCP and FCC lattices. This model predicts very large but finite negative values of magnetostriction factor in the case of FCC, HCP and SC lattices and distances between nearest neighbors close to the diameter of the particle, which is likely a result of used approximations.
The next functional polymer material considered was liquid crystalline brush (LCPB), consisting of polymers of comb-like architecture with azobenzene chromophores in their side-chain groups. Uniaxial planar (UPL) arrangement for chromophores in such a brush with photo-controlled director of nematic order is possible. The exposure to UV light, with all chromophores in cis polar non-mesogeneic state, does not lead to UPL formation. Similarly, during the Vis. light exposure, with all chromophores in trans mesogenic non-polar state, self-assembly results in local ordering only. Contrary to that, the short exposure to the aligning field, mimicking the polarized light, allowed to obtain UPL phase in the appropriate range of grafting densities and temperatures.
The modeling of the similar LCPB as adsorbing surface for nanoparticles (NP), decorated with polymer chromophore ligands was also considered. The adsorption was taking place under Vis. light irradiation. It was found to depend on grafting density non-monotonically with the presence of some optimal grafting density. At first, the efficiency increased with the density due to mere increase in the number of chromophores in the brush, later the brush becomes dense and steric effects did not allow NP to penetrate inside the brush. These findings were supplemented with the study of mean square displacement of NP inside brush, which show them to be frozen, contrary to the NP in the bulk.
Also, using dissipative particle dynamics, the model of polymer brush with properties of poly(N-isopropylacrylamide) (PNIPAM) was considered. Change of hydrophilic character of polymer below T<LCST to hydrophobic above T>LCST lower critical solution temperature was mapped to the interactions between polymer and solvent particles according to Soto-Figueroa et al. The single polymer chain scaling laws were checked for radius of gyration and other characteristics, it was shown to be in good agreement with good solvent behavior for T<LCST and slightly smaller compared with the poor solvent behavior when T>LCST. For the polymer brush, the existence of optimal grafting density ρg≈0.3 was found, for which changes of the shape characteristics of individual polymers was maximal at transition of LCST. This phenomena can be explained, within the formalism of Alexander and de Gennes, by the different overlap grafting densities at two temperature regimes and by expulsion of the solvent from the dense brush.
