Birmingham Centre for Energy Storage (BCES), School of Chemical Engineering, University of Birmingham, Edgbaston, Birmingham, West Midlands B15 2TT, United Kingdom; Micromanipulation and Microencapsulation Research Group (MCAP), School of Chemical Engineering, University of Birmingham, Edgbaston, Birmingham, West Midlands B15 2TT, United Kingdom.
Micromanipulation and Microencapsulation Research Group (MCAP), School of Chemical Engineering, University of Birmingham, Edgbaston, Birmingham, West Midlands B15 2TT, United Kingdom.
J Colloid Interface Sci. 2020 May 15;568:155-164. doi: 10.1016/j.jcis.2020.01.115. Epub 2020 Jan 29.
It is hypothesized that poly(vinyl alcohol) (PVOH) as an emulsifier destabilizes the insoluble molecular aggregates by increasing interparticle interactions and their tendency toward agglomeration into large particle aggregates during the encapsulation process of one-step in situ polymerization. Porosity of capsule shells is expected to decrease with reducing agglomeration tendency to allow dense packing of smaller insoluble aggregates. Cross-linking the polymer network further reduces shell permeability to improve the retention of volatile cargos. PVOH also modifies the short-range order of polymer network to bestow improved mechanical properties in addition to the shell thickening effect at appropriate synthesis conditions.
PVOH was used to stabilize a heptane-in-water emulsion as a template for producing capsules via one-step in situ polymerization. Shell morphologies at different PVOH concentrations were compared. Physical freeze-thawing and chemical cross-linking were adopted separately to synthesize capsules with a volatile cargo, and its retention was characterized qualitatively by a solvatochromism-based fluorescent method and quantitative payload calculation. Mechanical properties of capsules were tested with micromanipulation. The effect of graphene oxide (GO) impregnation into capsules was studied with various co-emulsifiers.
When PVOH alone was used as the emulsifier for capsule synthesis, the higher its concentration, the more porous the shell structure was. At very low concentrations, visible pores were eliminated. Freeze-thaw cycles reduced the permeability of capsule shells when visible pores were absent. Chemical cross-linking with poly(acrylic acid) (PAA) significantly improved the retention of volatile cargo heptane. PVOH substantially reduced polymer sediment during capsule synthesis, which eliminated the tedious centrifugation procedure that normally would have followed. Superior mechanical strength of capsules was achieved with PAA cross-linked PVOH at appropriate conditions. The impregnation of aqueously dispersed GO into capsules was also promoted by using PVOH but not hydrocolloid emulsifiers.
假设聚乙烯醇（PVOH）作为乳化剂，通过增加颗粒间的相互作用及其在一步原位聚合包封过程中团聚成大颗粒聚集体的趋势，使不溶性分子聚集体不稳定。预计随着团聚趋势的降低，胶囊壳的孔隙率会降低，从而允许较小的不溶性聚集体更紧密地堆积。进一步交联聚合物网络可以进一步降低壳的渗透性，以提高挥发性货物的保留率。PVOH 还可以改变聚合物网络的短程有序性，从而在适当的合成条件下除了赋予壳增厚效果之外，还可以赋予更好的机械性能。
使用 PVOH 稳定庚烷 - 水乳液作为通过一步原位聚合生产胶囊的模板。比较了不同 PVOH 浓度下的壳形态。分别采用物理冷冻 - 解冻和化学交联来合成含有挥发性货物的胶囊，并通过基于溶剂变色的荧光法定性和定量载药计算来表征其保留率。用微操作法测试了胶囊的机械性能。研究了不同共乳化剂对氧化石墨烯（GO）浸渍胶囊的影响。
当 PVOH 单独用作胶囊合成的乳化剂时，其浓度越高，壳结构的多孔性越大。在非常低的浓度下，可见的孔被消除了。当不存在可见的孔时，冷冻 - 解冻循环会降低胶囊壳的渗透性。用聚丙烯酸（PAA）进行化学交联显著提高了挥发性货物庚烷的保留率。PVOH 大大减少了胶囊合成过程中的聚合物沉淀，从而省去了通常需要的繁琐的离心步骤。在适当的条件下，用 PAA 交联的 PVOH 可实现胶囊的优异机械强度。通过使用 PVOH 也促进了 GO 在水中分散体的浸渍到胶囊中，但不能使用水胶体乳化剂。
