Anisotropic nucleation and Janus-faced crystals of poly(l -lactic acid) interacting with an amorphous diluent

Atomic-force microscopic and X-ray techniques were applied to reveal and analyze uniquely three types of distinctly different crystals, including a Janus-face composite type of spherulites in LM_w-PLLA induced by mixing with aPMMA (20 wt %). One type (Type-1) is completely packed by fibrous lamellae, while the second type (Type-2) is completely packed by flat-on platelet crystals; and the third type, a dual-faced (i.e., Janus-faced - Type-3) spherulite with two distinguished patterns filling the composite spherulite's perpendicular quadrants that is originated from sheaf-like directional growth from nuclei to pack into fibrous lamellae, while the perpendicular growth was diffusion-drained leading to thinner flat-on platelets. The Janus-face spherulite type (half-and-half fibrous lamellae and flat-on platelets) became more significant only when the 80/20 mixtures were melt-crystallized at T _c = 110-115 °C. That is, existence of Type-3 Janus-faced spherulite is composition- and temperature-selective for favorable nucleation and growth. Mechanisms leading to such diversified patterns and Janus-face spherulites in the LM_w-PLLA/aPMMA blend were probed.