Lu Hongwei, Wang Danling, Huang Daye, Feng Luyao, Zhang Huapeng, Zhu Peng
College of Textile Science and Engineering (International Institute of Silk), Zhejiang Sci-Tech University, Hangzhou, Zhejiang 310018, China.
Zhongce Rubber Group Co., Ltd, Hangzhou, Zhejiang 310018, China.
J Colloid Interface Sci. 2023 Mar 15;634:769-781. doi: 10.1016/j.jcis.2022.12.097. Epub 2022 Dec 20.
PNIPAM as a stimuli-responsive polymer has generated extreme interests due to its versatile applications. However, there is no research report on whether PNIPAM micro/nano-particles can be extracted from its suspension after phase separation. In the present work, LCST-type phase separation in self-synthesized PNIPAM/water system was investigated in depth by dividing the DLS testing process into four stages. In addition to quenching duration, temperature rise process, quenching temperature and PNIPAM concentration all have a great influence on particle size of the suspension. Meanwhile, the steady-state rheology and dynamic viscoelasticity results show that PNIPAM micro/nano-particles in the suspension are "soft" that can deform. Finally, FE-SEM was used to observe the morphology of dehydrated PNIPAM extracted by sessile droplet evaporation under different conditions. The results indicate that these "soft" particles are easier to fuse together, do not have sufficient mechanical strength to maintain their spherical morphology after dehydration. But the above fusion can be suppressed by adjusting evaporation conditions to acquire smaller PNIPAM particles which have sufficient mechanical properties to keep their basic particle morphology. Further, by changing evaporation pressure to positive or negative pressure, dehydrated PNIPAM micro/nano-particles with excellent uniformity and separation can be obtained. This work will provide guidance for extracting micro/nano-particles from polymer/diluent systems with LCST.
聚N-异丙基丙烯酰胺（PNIPAM）作为一种刺激响应性聚合物，因其广泛的应用而引起了极大的关注。然而，关于PNIPAM微/纳米颗粒在相分离后能否从其悬浮液中提取出来，尚无研究报道。在本工作中，通过将动态光散射（DLS）测试过程分为四个阶段，对自合成的PNIPAM/水体系中的最低临界溶液温度（LCST）型相分离进行了深入研究。除了猝灭持续时间外，升温过程、猝灭温度和PNIPAM浓度对悬浮液的粒径也有很大影响。同时，稳态流变学和动态粘弹性结果表明，悬浮液中的PNIPAM微/纳米颗粒是“软”的，可以变形。最后，利用场发射扫描电子显微镜（FE-SEM）观察了不同条件下通过静滴蒸发提取的脱水PNIPAM的形态。结果表明，这些“软”颗粒更容易融合在一起，脱水后没有足够的机械强度来保持其球形形态。但是，通过调整蒸发条件可以抑制上述融合，从而获得具有足够机械性能以保持其基本颗粒形态的较小PNIPAM颗粒。此外，通过将蒸发压力改变为正压或负压，可以获得具有优异均匀性和分离性的脱水PNIPAM微/纳米颗粒。这项工作将为从具有最低临界溶液温度的聚合物/稀释剂体系中提取微/纳米颗粒提供指导。
