Reaching the structural intimacy of polymer crystals and spherulites.

The complex architecture of polymer crystals involves four interconnected levels of organization: chain conformation, unit-cell, lamellar crystals and spherulites. Many of the fundamental features of and connections between structural levels were established with the investigation of solution grown single crystals of structurally “simple” polymers such as polyethylene. Polymers with more complex chemical structure or conformation (e.g. helical) add further constraints or requirements on the crystal structure and/or the folds conformation/organization. These constraints lead to unusual features of their diffraction pattern (e.g. specific streaks) or morphology (e.g. lamellar branching, scrolled crystals). Their analysis helps reach some very finer details of the crystalline polymers’ buildup. Older and very recent examples include the impact and identification of helical hand in crystal structures and the origin of unbalanced surface stresses in the lamellae fold surfaces. These stresses induce twisted and scrolled lamellae. Observation of scrolled single crystals of even-even nylons helped solve the decades long issue of their negative spherulites’ architecture.