Antonín Sikora

Equilibrium and non-equilibrium copolymer micelles : polystyrene-block-poly(ethylene-co-propylene) in decane and in diisopropylether

Abstract When selective solvents are used for the dissolution of block copolymers, their solid-state structure may be partly preserved in solution. At room temperature, polystyrene- block -poly(ethylene- co -propylene) dissolves in decane, a selective solvent for the aliphatic block, to form a solution of metastable micellar structures with polystyrene core. These convert to stable micelles at elevated temperature; the molar mass of the micelles is reduced several times after the heat treatment. The change of the structure is explained by the existence of a frozen state of the micellar core at room temperature. A possible connection with the glass transition of the core is discussed. Static and dynamic light scattering, small-angle X-ray scattering, differential scanning calorimetry and viscometry have been used to characterize equilibrium and non-equilibrium micelles. A pronounced mutual interaction of micelles has been observed by light scattering even at a concentration as low as 5 × 10 −4 g cm −3 . The concept of sticky chains is introduced to explain the association of the micellar shells. The behaviour of micelles in another selective solvent, diisopropylether, is simpler, both effects observed in decane being absent.

Liquid crystalline structure of solutions of poly-γ-benzyl-L-glutamate☆

Abstract Over a wide interval of change in concentrations, temperature and MM from the texture of the “fingerprints” the authors have determined the pitch of the cholesteric helix P for LC solutions of poly- γ -benzyl- L -glutamate in DMFA. The experimentally obtained dependences of the pitch of the cholesteric helix on temperature, concentration and MM are discussed in relation to various theories. In particular, in relation to the kinetic approach an explanation is for the first time offered for the experimentally discovered maximum in the dependence of the pitch on MM according to which non-monotonic change in pitch is a consequence of change in the form of the molecule with increase in its contour length to a value equal to and beyond the persistent length.

Inversion temperature of the cholesterol helix pitch in solutions of poly-γ-benzyl-L-glutamate☆

The change in pitch of the cholesterol helix in liquid crystal solutions of poly-γ-benzyl-L-glutamate in DMFA and N-methylpyrrolidone is studied at various polymer temperatures, concentrations, and MM. In the case of N-methylpyrrolidone solutions the phenomenon of thermal inversion of the cholesterol helix pitch was demonstrated experimentally, and the inversion temperatures were determined: the inversion temperatures in DMFA were determined by extrapolation. The data are discussed on the basis of known theoretical ideas.