Comments on: ‘A critical assessment of unbalanced surface stresses: Some complementary considerations’, by DC Bassett

The complementary considerations developed by Bassett are welcome additions to our paper that surveyed the origin of twist in polymer lamellae. They point to alternate mechanisms than those suggested by Keith and Padden. Polyethylene is not, however, an archetypical system, and the mechanisms uncovered may not have general value. Development of non-planar lamellar geometries associated with unbalanced surface stresses can have different origins. They all rest on structural asymmetries (with chains normal or not to the fold surface), either produced directly on crystallization, or after reorganization. This is best illustrated by the analysis of the structural origin of scrolled lamellae, for which different origins of unbalanced surface stresses have been uncovered for the three systems analyzed so far. In ultimate analysis, the unbalanced stresses are linked with the unbalanced fold structure and its orientation relative to the growth direction of the lamella.