Experimental and theoretical estimations of surface tensions for commercial liquid crystalline polymers, Vectra™ A-950, B-950 and Xydar™ SRT-900

By using the Lifshitz-Van der Waals-Acid-Base theory, we have determined the surface tensions (γ_s) of three commercially available liquid crystalline polymers (LCPs) from the measurement of contact angles on thin films. The values obtained are 43.1, 41.1 and 41.5 mJ/m² (dyn/cm) for Vectra™ A-950, Vectra™ B-950 and Xydar™ SRT-900, respectively. Experimental data suggest that all the three LCPs are monopolar. The strength of Lewis base (tendency to donate a pair of electrons for the formation of a covalent bond) for these three LCPs is as follows: Vectra™ B-950 > Xydar™ SRT-900 > Vectra™ A-950. We also theoretically estimated γ_s from both parachor (P_s) and cohesive energy (E_coh) utilizing the concept of molecular group contribution. It was found that γ_s's calculated from Hoftyzer & Van Krevelen and Hayes' E_coh values are close to our experimental results obtained from contact angle measurements. This is especially true for Xydar™ SRT-900 LCP, where γ_s obtained from contact angle measurements is 41.5 mJ/m₂, while from Hoftyzer and Van Krevelen, and Hayes it is 42.4 and 41.8 mJ/m², respectively. However, more adequate group contributions for naphthalene and amide groups are urgently needed.