Quantitative measurements of polymer chain-end edge dislocation strain fields by high resolution electron microscopy

The strain fields around chain-end edge dislocations in poly(diacetylene) crystals were analyzed by high resolution electron microscopy (HREM). Experimental measurements of the tilt of the polymer chain axis as a function of azimuthal angle phi at a constant radius r from the dislocation core were compared to theoretical predictions. The shear deformation was localized in parabolic regions parallel to the Burger's vector b near the chain end. For an edge dislocation in the poly(diacetylene) 1,6-di(-N-carbazolyl)-2,4-hexadiyne (DCHD) with a Burger's vector of b = 3a/2 [100] (2.4 nm), we found a tilt distortion of +/-6 degrees at 12 nm from the core. A parameter W was introduced to describe the anisotropy of the compliance matrix with respect to the chain direction. A parameter of W = 3.5 was needed to fit the measured tilt deformation with anisotropic linear elastic dislocation theory. We also found that the theory of distortions near dislocations in columnar liquid crystals could closely predict our experimental observations. A value of 0.8 nm (the interchain spacing) for the characteristic length, lambda(3), was the best fit for the columnar liquid crystal solution. This analysis reveals similarities between the elasticity of anisotropic crystals and liquid crystals.