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    Phase behavior of poly(epsilon-caprolactone)-b-poly(tert-butyl acrylate) block copolymer at the air/water interface

    Year: 2020

    Journal: Colloid Surf. A-Physicochem. Eng. Asp., Volume 587, FEB 20

    Authors: Xie, Qiongdan; Li, Bingbing; Esker, Alan R.

    Organizations: National Science FoundationNational Science Foundation (NSF) [CHE-0239633]; Institute for Critical Technologies and Applied Sciences at Virginia Tech

    Keywords: Langmuir monolayer; Isotherms; Polymer crystallization; Poly(epsilon-caprolactone)

    Thermodynamic phase behavior of poly(epsilon-caprolactone)-b-poly(tert-butyl acrylate) (PCL-b-NBA) block copolymers at the Air/Water (A/W) interface was studied by analyzing surface pressure-area isotherms. Optical microscopy and atomic force microscopy were utilized to reveal the morphological features of three-dimensional domains grown in the Langmuir films. A series of PCL-b-NBA block copolymers synthesized for this study share the same PCL block with molecular weight of M-n = 7.5 kg.mol(-1), while the length of NBA blocks varies. Homogeneous Langmuir monolayers were formed at the A/W interface before reaching the dynamic collapse pressure of PCL blocks. The growth of PCL flat-on crystalline domains predominately took place during the plateau regime after the collapse transition, though nucleation process occurred prior to the collapse transition. The tethered NBA blocks remain as a monolayer at the A/W interface prior to the second collapse pressure at similar to 24 mN.m(-1), which is comparable to the collapse pressure of NBA homopolymer monolayer. Depending on the length of NBA blocks, the block copolymer crystals exhibit morphological features from distorted hexagonal shape, truncated parallelogram, dendrites with defects, stripes, and nano-scale domains, suggesting that the tethered amorphous NBA block significantly reduced the mobility and packing efficiency of PCL blocks during the crystallization of PCL-b-NBA copolymers at the A/W interface.
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