Compared Study of a Quenched Blue Phase by Direct Transmission Electron and Atomic Force Microscopy

Abstract

A side chain mesomorphic cooligomer presents a large blue phase temperature domain. The cooling down of the sample from BPI allows to quench coloured crystallites below the glass transition of this material. Observations by transmission electron microscopy on microtome cuts of these crystallites reveal the presence of mono- and bi-periodic domains corresponding to the respective quench of cholesteric and BPI phases at room temperature. The use of an atomic force microscopy technique directly on the cuts observed by electron microscopy, and the detection of the same textures by both methods reveal unambiguously that the TEM contrast originates from strong, “cut-induced”, surface relief. The nature of this corrugation is discussed using numerical simulations derived from a Ginzburg-Landau approach.