Khazimullin Maxim, Müller Thomas, Messlinger Stephan, Rehberg Ingo, Schöpf Wolfgang, Krekhov Alexei, Pettau Robin, Kreger Klaus, Schmidt Hans-Werner
Experimentalphysik V, Universität Bayreuth, DE-95440 Bayreuth, Germany.
Phys Rev E Stat Nonlin Soft Matter Phys. 2011 Aug;84(2 Pt 1):021710. doi: 10.1103/PhysRevE.84.021710. Epub 2011 Aug 29.
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.
研究了介晶侧链嵌段共聚物与低分子量向列型液晶二元混合物在从稀释状态到约3%的液晶凝胶态的质量浓度范围内的粘弹性。在凝胶态下，该体系不流动，在微观层面呈现多畴结构，且强烈散射光。在凝胶化点以下，体系是均匀的，表现得像普通向列相，因此液晶连续体理论可用于解释实验数据。利用动态弗雷德里克斯转变技术，得到了展曲弹性常数和旋转粘度对聚合物浓度的依赖性。将嵌段共聚物溶液与相应的均聚物溶液的动态行为进行比较表明，在质量浓度高于1%时，嵌段共聚物链段会自组装成簇，在更高浓度下形成凝胶态。有效簇尺寸作为浓度的函数进行了估算，并证实了在溶胶-凝胶转变附近的标度律行为。该技术可作为确定凝胶化点的一种替代方法。
