ANISOTROPIC TRANSLATIONAL DIFFUSION OF METHANE IN N-(4-NORMAL-PENTYLOXYBENZYLIDENE)-4-NORMAL-HEXYLANILINE (50.6)

The temperature dependence of the translational diffusion coefficients is reported for methane dissolved in the thermotropic liquid crystal N-(4-n-pentyloxybenzylidene)-4-n-hexylaniline (50. 6). The general features of methane diffusion behavior in the N, S//A and crystal S//B phases of 50. 6 are quite similar, with respect to the magnitude of the rates and corresponding anisotropies, to those found in the homolog 40. 6. The mutual characteristics are: that considerable smectic character (D// parallel less than D// PERPEND ) exists in the nematic phase, that D// parallel VM LS TH D// PERPEND with E// parallel VM GT TH E// PERPEND in the S//A phase because of increasing layer definition and of methane expulsion from the cores to the chains and that D// parallel /D// PERPEND approximately equals 30 (with E// parallel approximately equals E// PERPEND ) in the crystalline showing a slight decrease in D// PERPEND and large increases in D// parallel upon decreasing temperature with D// PERPEND /D// parallel values of from 10 to 5. This is possibly the result of the decrease in the close-packed core thickness coupled to increase in the disorder (loss of 3-d correlation) within the layer in the S//F phase. The diffusion behavior in the S//G phase is similar to that found in the S//B phase. The factor of three larger D// vertical values in the S//G over S//B is thought to be the result of persistance of disordered regions remaining from the S//F phase.