Bistable Phase Behavior and Kinetics of Nonisothermal Mesophase Formation in a Chiral Side Chain Polymethacrylate

Abstract

Nonisothermal kinetics of smectic phase formation in a chiral liquid crystalline (LC) azodye polymer is studied. The Ozawa exponent value of n ∼ 2.5 is estimated for narrow polymer fractions with M w/M n ∼ 1.3−1.6 but a temerature-dependent value, 0.5 < n < 1.2, for the raw polymer of M w/M n ∼ 2.6. The effect of molar mass on mesomorphism is studied, and the dependence of melting temperature on subsequent heating from the rate of previous cooling, r, is theoretically explained. The narrow fractions show a “bistable” phase behavior forming conventional Sm A phase on slow cooling, r < 1 K/min, but another (probably a highly twisted TGB A*) mesophase on fast cooling, r > 1 K/min. A theoretical model for such a behavior is suggested, and the structure of the two phases is studied by SAXS. The applicability of the Kissinger approach to estimation of activation energy for TGB A* phase formation is discussed.

Supramolecular Chirality and Reversible Chiroptical Switching in New Chiral Liquid‐Crystal Azopolymers

“…An accurate analysis of the nature of this mesophase was achieved by the observation of their typical optical texture by POM in analogy with previous studies on similar azopolymers. [34] All the samples, during the heating/cooling process, show textures that indicate the presence of macrodomains with a SmA phase, as shown, for example, for poly[(S)-ML6A]-14 in Figure 4. In particular, the thin film slowly cooled from the isotropic melt at 128 8C shows small drops of birefringent mesophases separating from the melt (Figure 4a) that develop after shearing and annealing at 110 8C for 48 h into cylindrical LC domains on an homeotropic background ( Figure 4b).…”

Existence of Two Different Isotropic Phases as a Reason for Bistable Phase Behavior of an LC Side‐Chain Polymethacrylate

“…[7] In this work, the polymer fraction was used with the average molar mass, M w ¼ 9.3 Â 10 4 (that corresponds to the weight average degree of polymerization, X w ¼ 174), and the polydispersity index, M w =M n ¼ 2.0. The phase transition between the mesophase and isotropic phase can be observed within a wide temperature range, 44 8C < T sm < 59 8C, depending on the heating/cooling rate and on thermal prehistory of the sample.…”

“…The polymer can form at the same temperature two different mesophases depending on the rate of cooling from isotropic melt, r. [7] Slow cooling of the…”

Effect of Molecular Weight on Photoinduced Birefringence in a Chiral Liquid Crystalline Azodye Polymer

“…The polymer is characterized by a high efficiency of phase grating recording15 and by ‘bistable phase behavior’, i.e., the formation of two different mesomorphic states at ambient temperature depending on the previous rate of cooling 16…”

“…It has been shown16 that both the transition temperature ( T tr ) of the P8*NN fractions and the final phase state of the polymer at room temperature depend on the previous thermal history of the polymer sample. Fast cooling (faster than 1 °C · min −1 ) and slow cooling (less than 1 °C · min −1 ) of a polymer film at ambient temperature results in two different phase states characterized by different optical properties.…”