Gel formation in a mixture of a block copolymer and a nematic liquid crystal

Abstract

The viscoelastic properties of a binary mixture of a mesogenic side-chain block copolymer in a low molecular weight nematic liquid crystal are studied for mass concentrations ranging from the diluted regime up to a liquid crystalline gel state at about 3%. In the gel state, the system does not flow, exhibits a polydomain structure on a microscopic level, and strongly scatters light. Below the gelation point, the system is homogeneous and behaves like a usual nematic, so the continuum theory of liquid crystals can be applied for interpreting the experimental data. Using the dynamic Fréedericksz transition technique, the dependence of the splay elastic constant and the rotational viscosity on the polymer concentration have been obtained. Comparing the dynamic behavior of block copolymer solutions with the respective homopolymer solutions reveals that, above a mass concentration of 1%, self-assembling of the block copolymer chain segments in clusters occurred, resulting in a gel state at higher concentrations. The effective cluster size is estimated as a function of the concentration, and a scaling-law behavior near the sol-gel transition is confirmed. This technique may serve as an alternative method for determining the gelation point.

Structure-Property Relations of Liquid Crystalline Gels with ABA-Triblock Copolymers as Gelators

“…Functionalization with cyanobiphenyl moieties was performed in a subsequent polymer analogous reaction resulting in the block copolymer gelators 1a-5a. The synthesis was conducted according to [22]. Further details can be found in the supporting material.…”

“…In the second part the influence of the different block copolymers 1a-5a on the temperature-dependent rhelogical properties was studied in samples with a fixed block copolymer mass concentration. Previous electro-optical investigations [22] on the rotational viscosity of dilute solutions of 3a in 5CB have shown that formation of network clusters occurs above a mass concentration of 1 %. Dynamic measurements of rotational viscosity in these dilute solutions provided a determination of the critical gelator concentration that was estimated to be around 2.7 %.…”

“…Recently, we have demonstrated that the rotational viscosity of a liquid crystal in mixtures with ABA-triblock copolymers can be used to detect and characterize the aggregation of the A-block and to determine the critical gelator concentration [22]. However, less is known about the influence of the gelator on the properties of liquid crystalline gels formed by ABA-triblock copolymers.…”

The rubber band revisited: Wang–Landau simulation

“…Previous works on homopolymers which studied the denaturation of circular DNA are extensions of the Poland-Scheraga model [4]. Experimentally, the viscoelastic properties of a binary mixture of a mesogenic side-chain block copolymer in a low molecular weight nematic liquid crystal are studied for mass concentrations ranging from the diluted regime up to a liquid crystalline gel state [5].…”