In the past, we have reported the crystallization of poly(caprolactone) (PCL) from metastable monolayer at the air/water interface. When PCL/poly(t-butyl acrylate) (PtBA) mixed monolayers were dynamically compressed past the collapse transition of liquid-expansion phase, compositional PCL dendrites were observed. To grow PCL crystals at well-controlled surface pressure values, a series of isobaric area-relaxation experiments were performed for PCL/PtBA monolayers at the A/W interface. PCL crystals obtained from isobaric area relaxation experiments at different P values demonstrate a striking morphological transition from highly branched symmetric dendrites to six-arm dendrites, four-arm dendrites, seaweedlike crystals, and distorted rectangular crystals, indicating that the degree of undercooling (i.e., the surface pressure values) plays a key role for controlling crystal morphologies through the interplay of the diffusion coefficient, surface tension, and surface tension anisotropy. The overall growth rate of these quasi-2D dendrites was also found to increase with increasing surface pressure. The gross morphology of PCL dendrites was primarily controlled by the number, the location, and the growth rates of dendritic fingers developed on the {100} face. Increasing P results in a smaller diffusion length in the LE phase and therefore a decreased stability length, which favours the propagation of interfacial instability, leading to highly branched PCL dendrites. In addition, the noise level (compositional fluctuations) varies with crystallization P and the blend composition, which can be considered as another effective parameter for morphological selection in the diffusion-limited growth regime.

Surface pressure-induced crystallization behaviour of poly(caprolactone)-based mixed monolayers at the air/water interface

2019 Fall National Meeting

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