Smectic ordering in athermal systems of rod-like triblock copolymers

TL;DR

This study uses density functional theory to explore the phase behavior of athermal, rod-like triblock copolymers, revealing the formation of nematic, smectic-A, and smectic-C phases depending on particle dimensions.

Contribution

It introduces a theoretical framework for understanding smectic ordering in triblock copolymers, highlighting the influence of particle geometry on phase stability.

Findings

Smectic-A and smectic-C phases are observed, with no nematic-columnar transition.

The stability of smectic phases depends on the length of the central cylinder.

Diameter affects layer tilting and periodicity but not the transition packing fraction.

Abstract

The phase behavior of the system of parallel rigid triblock copolymers is examined using the second-virial density functional theory. The triblock particle consists of two identical infinitely thin hard rods of finite lengths on the opposite ends of one central hard cylinder with nonzero length and diameter. Stability analyses and free energy calculations show that the system of parallel particles can form not only uniform nematic and smectic A phases, but a smectic-C phase too. The stability and structure of the tilted structure is controlled by only the diameter and the length of the central cylinder segment. Interestingly, the diameter effects only the layer tilting and the periodicity, but not the packing fraction of the nematic to smectic-C transition. For all values of cylinder length the usual smectic-A and smectic-C transitions compete with each other and no nematic-columnar transition is observed. At low and high cylinder length the smectic-A phase is stabilized first, while the smectic C is the most stable for intermediate length values.