Microfluidic solvent extraction of poly(vinyl alcohol) droplets: effect of polymer structure on particle and capsule formation.
Microfluidic solvent extraction of poly(vinyl alcohol) droplets: effect of polymer structure on particle and capsule formation.
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聚（乙烯醇）液滴的微流体溶剂萃取：聚合物结构对颗粒和胶囊形成的影响。
DOI：
10.1039/c7sm02488f
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发表时间：
2018
期刊：
影响因子：
3.4
通讯作者：
Sharratt WN
中科院分区：
文献类型：
--
作者：
Sharratt WN
我们研究了聚乙烯醇微粒子的形成，通过选择性提取聚合物水溶液滴滴，用微流体模板化，然后浸入无溶剂浴。测定了聚合物分子质量（18-105 kg mol−1）、水解度（88-99%）以及溶解度和初始溶液浓度（0.01-10% w/w）的影响。以十六烷为载体，在流动聚焦结处制备半径为50 ~ 500 μm的单分散液滴，提取到乙酸乙酯中。溶剂交换和萃取导致液滴收缩、脱混、粗化和相转变，产生具有明确尺寸和内部微观结构的聚合物微粒。黏度测量结果表明，聚合物浓度（从低于重叠浓度c*到高于交叉浓度c**）对最终粒径和萃取时间尺度的影响最大，聚合物质量和水解作用次之。这些结果与聚合物凝固时的平均浓度大大超过c**的观察结果一致，并且内部微粒孔隙率基本不变。然而，将初始聚合物浓度降低到远低于c*（约100×），并增加液滴尺寸，可产生薄壁（100纳米）胶囊，其在提取时可控制地皱缩。通过在不透水的表面施加提取条件，可以很容易地打破该过程的对称性，产生大的，弯曲的，腔形态。基于这些结果，我们为聚合物胶囊和颗粒建立了稳健的设计标准，这里展示了聚乙烯醇，具有明确的形状、尺寸和内部微观结构。
We investigate the formation of poly(vinyl alcohol) microparticles by the selective extraction of aqueous polymer solution droplets, templated by microfluidics and subsequently immersed in a non-solvent bath. The role of polymer molecular mass (18–105 kg mol−1), degree of hydrolysis (88–99%) and thus solubility, and initial solution concentration (0.01–10% w/w) are quantified. Monodisperse droplets with radii ranging from 50 to 500 μm were produced at a flow-focusing junction with carrier phase hexadecane and extracted into ethyl acetate. Solvent exchange and extraction result in droplet shrinkage, demixing, coarsening and phase-inversion, yielding polymer microparticles with well-defined dimensions and internal microstructure. Polymer concentration, varied from below the overlap concentration c* to above the concentrated crossover c**, as estimated by viscosity measurements, was found to have the largest impact on the final particle size and extraction timescale, while polymer mass and hydrolysis played a secondary role. These results are consistent with the observation that the average polymer concentration upon solidification greatly exceeds c**, and that the internal microparticle porosity is largely unchanged. However, reducing the initial polymer concentration to well below c* (approximately 100×) and increasing droplet size yields thin-walled (100's of nm) capsules which controllably crumple upon extraction. The symmetry of the process can be readily broken by imposing extraction conditions at an impermeable surface, yielding large, buckled, cavity morphologies. Based on these results, we establish robust design criteria for polymer capsules and particles, demonstrated here for poly(vinyl alcohol), with well-defined shape, dimensions and internal microstructure.
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