Entropically-Driven Formation of Smectic A1, A2, and A3 phases in Binary Mixtures of Rigid-Rod Helical Polysilanes with Different Molecular Weights

Abstract

The smectic liquid crystal arrangements of binary mixtures of rod-like polymers, i.e., poly[ndecyl-(S)-2-methylbutylsilane]s, with narrow molecular weight distributions, were investigated by synchrotron radiation small-angle X-ray scattering (SR-SAXS) and atomic force microscopy (AFM) analyses. Depending on the molecular weight ratio, r (higher molecular weight/lower molecular weight), and the mixing ratio, three types of smectic phases are formed with different accommodations by two polymers. In the binary mixture of the shorter and longer polymers with the lower r values of 1.0-1.7, the two polymers are randomly mixed within a layer, forming the conventional smectic A1 phase with a layer thickness corresponding to an average length of the two polymers. In contrast, when two kinds of polymers with the higher r values of 1.7-2.8 are mixed, different types of smectic A structures are formed. Upon the addition of the shorter polymer to the abundant longer polymer, a smectic A2 phase in which a pair of smectic layers of shorter polymers nested in a smectic layer of the longer polymers was first formed, and then converted into the smectic A3 phase in which the longer polymers randomly straddled a pair of smectic layers of the shorter polymers. These experimental results are discussed along with a comparison of the theoretical predictions.

Stability of the columnar and smectic phases of length-bidisperse parallel hard cylinders

“…In accordance with our results the system of short and long polysilanes shows only S 1 ordering both in short and long rod rich phases in the range of 0.59<l<1 [38]. At l=0.5 the smectic phase is microsegregated on the short rod side in accordance with Eq.…”

“…5c), because it has not been predicted theoretically before. The first experimental evidence for the existence of a S 3 smectic structure is reported in the very recent study of Okashi et al [38]. It is found that the two-layer accommodation is possible in the length ratio interval of 0.34<l<0.59.…”

“…As a natural continuation of our previous work, the present work is devoted to mixtures of parallel cylinders having equal diameters but different lengths. The experimental motivation of our work is the very recent study of the smectic phase in binary mixtures of short and long helical polysilanes [38]. The main feature of the…”

Nano-Segregation of Squalane between Smectic Layers of Rigid-Rod Polysilane

“…During the initial stage of these studies, the numerical experiments and computer simulations revealed that the most common LC sequence of the nematic-smecticcolumnar phases could be reproduced in the hard-rod particle model systems [1,2]. These theoretical predictions agreed well with the thermotropic LC behavior of rigidrod helical polysilanes with narrow molecular weight distributions [3][4][5][6][7][8][9].…”

Chirality responsive helical poly(phenylacetylene) bearing L‐proline pendants

“…The spacing of the fringes corresponding to the half‐pitch of the cholesteric helical structure was 3.8 μm, suggesting that poly‐1 is a stiff rodlike helical polymer due to its main‐chain rigidity (For other examples of LC helical polymers solely due to the main‐chain stiffness, see Refs. 35–46). On the other hand, poly‐2 did not form an LC phase in the concentrated THF solutions.…”