Influence of temperature on surface tension of three liquid crystal polymers and polyethylene terephtalate

Abstract

In this work Pressure Volume Temperature (PVT) data for three different liquid crystal polymers (LCPs), namely Vectra A950^® and two LCPs based on 4,4′-dihydroxybiphenyl (PB-n) (where n is the number of methylene units present in the polymer) and polyethylene terephtalate (PET), were obtained for temperatures ranging from 50 to 300°C and pressures ranging from 0.1 to 200 MPa. The experimental data were fitted to the Flory–Orwoll–Vrij equation of state and used to predict the influence of temperature on the surface tension of the four materials studied.

The surface tension of PET was shown to decrease linearly with increasing temperature. The surface tension of both PB-11 (γ _PB-11) and Vectra A950^® (γ _Vectra) decreased linearly with increasing temperature for temperatures corresponding to the nematic phases of the materials. Abnormal behaviour was observed for the surface tension of PB-8 (γ _PB-8): at temperatures just above T _b (the temperature at which the material became birefringent), γ levelled off and then decreased. A clear discontinuity was observed for both γ _PB-8 and γ _PB-11 near the mesophase to isotropic transition. For both PB-8 and PB-11, γ decreased linearly with increasing temperature for temperatures corresponding to the isotropic phases of the materials.