Apparatus for the measurement of light reflection of cholesteric mesophases at high pressures

Abstract

An apparatus for determining the wavelength of maximum reflection of light lambda _R of cholesteric mesophases at high static pressures is described. The arrangement of the whole high pressure equipment is briefly outlined. The pressure chamber allows optical measurements up to 5000 bar and can be thermostated by oil on the outside. Details of the sample cell are illustrated. The generated oil pressure is transmitted to the sample layer of 25 mu m by means of a thin Teflon membrane. By way of example the effect of pressure on the reflection of a cholesteric mixture of cholesteryloleylcarbonate and cholesterylchloride is shown. In a definite pressure range the sensitivity of lambda _R to pressure is so large that it can provide a new accurate means of pressure measurement. This behaviour is probably caused by a pretransition effect of the mesophase.