First evidence of anisotropic quenched disorder effects on a smectic liquid crystal confined in porous silicon

TL;DR

This study uses neutron scattering to reveal how anisotropic quenched disorder in porous silicon suppresses the smectic transition in liquid crystals, leading to a unique short-range ordered phase aligned along nanopores.

Contribution

It provides the first evidence of anisotropic quenched disorder effects on smectic liquid crystals confined in one-dimensional nanopores, highlighting the role of surface disorder.

Findings

Smectic transition is suppressed in porous silicon confinement.

A short-range ordered smectic phase persists along pore axis.

Quenched disorder acts as random fields affecting smectic order.

Abstract

We present a neutron scattering analysis of the structure of the smectic liquid crystal octylcyanobiphenyl (8CB) confined in one-dimensional nanopores of porous silicon films (PS). The smectic transition is completely suppressed, leading to the extension of a short-range ordered smectic phase aligned along the pore axis. It evolves reversibly over an extended temperature range, down to 50 K below the \textit{N-SmA} transition in pure 8CB. This behavior strongly differs from previous observations of smectics in different one-dimensional porous materials. A coherent picture of this striking behavior requires that quenched disorder effects are invoked. The strongly disordered nature of the inner surface of PS acts as random fields coupling to the smectic order. The one-dimensionality of PS nano-channels offers new perspectives on quenched disorder effects, which observation has been restricted to homogeneous random porous materials so far.