New statistical approach to the description of spatial inhomogeneous states in heteropolymer solutions

It is shown that the free energy of polymer systems is a nonlocal functional of the distribution of monomer density, unlike usual low-molecular systems. A general statistical approach is proposed, which takes into account corresponding nonlocal effects for the polymers containing macromolecules of various chemical composition and chemical structure. The phase diagram is set up for solutions of linear heteropolymers, alternation of monomer units in the macromolecules of which obey Markovian statistics. it is shown that a melt of the Markovian multi-block copolymers undergoes a third-order phase transition to superstructure with symmetry of body-centered cubic lattice whose period depends essentially on the parameters of monomer units interactions

On thermodynamic stability of heteropolymer mesophases formed under weak segregation regime

Conditions of local and global thermodynamic stability of spatially-periodic mesophases formed in an incompressible melt of binary monodisperse copolymers with molecules of arbitrary chemical structure are theoretically scrutinized. For the first time a bifurcation analysis of the Landau free energy in the first harmonic approximation is carried out. Based upon this analysis, feasible scenarios of bifurcation and phase transitions between mesophases of different morphology are discussed. The description of thermodynamic behavior of some systems is presented to exemplify the implementation of the approach proposed

Collaborative Studies of Thermo-Oxidative Degradation of Styrene Isoprene Diblock Copolymer

Mechanisms and dynamics of thermo-oxidative degradation of styrene-co-isoprene (SI) diblock at a temperature above the order–disorder transition temperature, Todt, have been investigated both experimentally and theoretically. The structural development of SI during degradation was monitored by optical microscopy, and the reduction of molecular weight and molecular weight distribution during the degradation was determined by gel permeation chromatography (GPC). The degradation process was modeled in the framework of a kinetic model based on the framework of the Flory principle. The theoretical predictions were compared with the GPC results. Fourier transformed infrared spectroscopy (FTIR) experiment was conducted in situ during the thermo-oxidative degradation of the SI copolymers, to gain further insight into the chemical modification mechanisms, the reduction of unsaturated double bonds and the formation of carbonyl and hydroxyl groups

Diagram technique for finding of vertex functions in the Landau theory of heteropolymer liquids

The problem on finding the coefficients of the Landau free energy expansion into the power series of parameter of order has been considered for solutions and melts of linear heteropolymers whose molecules comprise several types monomeric units arranged stochastically. The presence of such a quenched structural disorder places this problem outside the framework of the traditional statistical physics inviting for its solution special approaches. One of them, based on the replica concept and actively engaged in theoretical physics of disordered systems, has been invoked in this paper to derive expressions for the vertex functions in the Landau theory of heteropolymer liquids. An algorithm has been formulated which permits one resorting to the simple diagram technique to write down expressions for these functions of any order in terms of the statistical characteristics of chemical quenched structure of polymer molecules. Explicit expressions for the contributions to the Landau free energy up to the fourth degree of order parameters for polymer systems with an arbitrary structural disorder have been presented to illustrate this general algorithm. Its potentialities have been also exemplified for the melt of random m-component copolymer where exact analytical formulas for these contributions up to n=6 at an arbitrary m have been derived for the first time. Copyright EDP Sciences/Società Italiana di Fisica/Springer-Verlag 2005