The interest in using semicrystalline polymers in nanotechnology applications has been growing over the last few decades. In this presentation, I will introduce the recent progress on understanding the features of confined crystallization of polymers using anodic alumina oxide templates (AAO) as a model system. The crystallization of polymers under nanoconfinement generally shows a large degree of supercooling, indicating a transition of the nucleation mechanism. We have shown that the frequently reported “multiple nucleation events” is most probably resulted from the surface residue due to insufficient sample preparation. The size dependence of nucleation rate can be a criterion to discriminate surface nucleation and homogeneous nucleation. We measured the nucleation rate of poly(ethylene oxide) and found it proportional to the volume of the microdomains. Different from previous viewpoints on the orientation of crystallines, we have shown that there are one or two dominant growing directions, which can be explained by the scenario that the “fast-growing direction align parallel to the pore axis”. A new orientation diagram has been proposed to explain the diverse observations reported in the literature. By in-situ X-ray diffraction and simulation, fractional Avrami index is observed which is explained by the blocking of the growing lamellae by the preexisting crystallines. The interaction between polymer and AAO wall may influence crystallization in several ways. For example, surface nucleation has been observed in poly(lactic acid) (PLLA). The reason for the accelerated crystallization is shown to be attributed to the segmental mobility of PLLA chains near the AAO wall. The surface effect manifests itself in poly(butene-1) by the retarded solid-solid phase transition (Form II to Form I) under confinement. A stable Form II interfacial layer with a thickness of ∼12 nm was postulated to explain the experimental observation.

Confined crystallization of polymers within nanopores: Nucleation, orientation, and kinetics

ACS Spring Meeting 2021

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