Surface‐ and interfacial tensions of liquid crystalline polymers

Abstract

Surface tensions (γA) of two side group liquid‐crystalline (lc) polymethacrylates and the interfacial tensions (γAB) between the lc‐polymers (LCP) and branched polyethylen respectively polymethylmethacrylat were measured in the isotropic and nematic phase with the pendant‐drop method. The surface tensions vs. temperature characteristics show anomalous behavior. The slope is initially negative but changes its sign near the isotropic‐nematic transition. This behavior is in agreement with surface‐tension measurements on low‐molar‐mass liquid crystals from other authors. The interfacial tension mainly depends on the density difference Δρ between the two phases, at the phase‐transition so we observed a jump of the interface‐tension values and a change of the slope. The pendant‐drop apparatus contains a video image processing system, that allows to acquire the pendant‐drop profile with a personal computer. The program used to analyse the experimental data is based on the “robust‐shape method”. This algorithm allows to calculate both the surface‐tensions and the interface‐tensions respectively with a personal computer.

Use of the pendant drop method to measure interfacial tension between molten polymers

“…In general, the equilibrium static methods are most commonly used. They involve the evaluation of a profile of either a sessile drop [3][4][5][6][7][8][9][10][11] , or a spinning drop [12][13][14][15][16] or a pendant drop [17][18][19][20][21][22][23][24][25][26][27] . Dynamic methods, based on the breaking thread and imbedded fiber were also used [28][29][30][31][32][33][34][35] to determine interfacial tension.…”

Gas-influenced surface and bulk properties of a liquid crystalline side-group polymer

“…The densities of the polymers were measured by an automated capillary mercury dilatometer. [1][2] The measurement setup reaches a sensitivity of l 0.001 g/cm 3 with approximately 200 mg of sample.…”

“…In contrast to the most common polymers, only few reports have been published regarding the surface-energetic investigations on LCPs [1][2][3] until now. In our previous papers, [1][2][3] it was pointed out that such measurements are seriously limited by the generally high viscosity of LCPs, and for this reason the pendant drop method has been demonstrated to be the only suitable method.…”

“…In our previous papers, [1][2][3] it was pointed out that such measurements are seriously limited by the generally high viscosity of LCPs, and for this reason the pendant drop method has been demonstrated to be the only suitable method. By using this method, Uzman et al [1] studied the surface tension-temperature characteristics of LC side-group polyacrylates.…”

“…These results were confirmed by Song. [3] Runke et al [2] have investigated the surface tension of two LC side-group polymethacrylates and the interfacial tension between the LCPs and branched polyethylene as well as polymethylmethacrylat. The experiments confirmed the above conclusion as well.…”