Department of Polymer Chemistry, Eindhoven University of Technology, P.O. Box 513, 5600 MB Eindhoven, The Netherlands.
Langmuir. 2010 Sep 21;26(18):14929-36. doi: 10.1021/la1025284.
It is commonly known that Pickering emulsions are extremely stable against coalescence and are, therefore, potentially interesting for the synthesis of new materials, such as colloidosomes, microcapsules, composite particles, foams, and so on. However, for the efficient synthesis of such materials, one also has to consider the colloidal stability against aggregation, which is often neglected. In this study, it is demonstrated that steric stabilization is provided to Pickering emulsion droplets by the adsorption of poly(styrene-block-ethylene-co-propylene) (pS-b-EP) and that it is a requirement for the efficient synthesis of polymeric microcapsules. Monodisperse polystyrene particles of 648 nm are synthesized by soap-free emulsion polymerization. A model Pickering emulsion is then formed by the addition of sodium chloride at a critical concentration of 325 mM and mixing it with either heptane or decane. Subsequently, pS-b-EP is added to the Pickering emulsion to provide steric stabilization. Size exclusion chromatography is used to prove and quantify the adsorption of pS-b-EP onto the Pickering emulsion droplets. A maximum surface coverage of 1.3 mg/m(2) is obtained after 2 h, which is approximately one-third of the adsorption on a pure pS surface. We believe that the presence of polar sulfate groups on the particle, which initially stabilized the particle in water, reduces the adsorption of pS-b-EP. Microcapsules are formed by heating the Pickering emulsion above the glass-transition temperature of the particles. Significant aggregation is observed, if no pS-b-EP is used. The adsorption of pS-b-EP provides steric stabilization to the Pickering emulsion droplets, reduces aggregation significantly, and ultimately leads to the successful and efficient synthesis of pS microcapsules.
众所周知，Pickering 乳液非常稳定，不易聚结，因此对于合成新型材料（如胶体囊泡、微胶囊、复合颗粒、泡沫等）具有潜在的应用价值。然而，为了高效地合成这些材料，人们还必须考虑胶体的聚集稳定性，而这往往被忽视。在本研究中，我们证明了聚（苯乙烯-嵌段-乙烯-共-丙烯）（pS-b-EP）通过吸附为 Pickering 乳液滴提供了空间稳定性，这是高效合成聚合微胶囊的必要条件。通过无皂乳液聚合合成了 648nm 的单分散聚苯乙烯颗粒。然后，通过在临界浓度 325mM 的氯化钠存在下添加这些颗粒，并将其与庚烷或癸烷混合，形成模型 Pickering 乳液。随后，将 pS-b-EP 添加到 Pickering 乳液中以提供空间稳定化。通过尺寸排阻色谱法证明并定量了 pS-b-EP 在 Pickering 乳液滴上的吸附。在 2 小时后，获得了 1.3mg/m2的最大表面覆盖率，这大约是在纯 pS 表面上吸附量的三分之一。我们认为，最初在水中稳定颗粒的粒子上的极性硫酸根基团的存在降低了 pS-b-EP 的吸附。通过将 Pickering 乳液加热到颗粒的玻璃化转变温度以上来形成微胶囊。如果不使用 pS-b-EP，则会观察到明显的聚集。pS-b-EP 的吸附为 Pickering 乳液滴提供了空间稳定化，显著减少了聚集，并最终导致成功高效地合成了 pS 微胶囊。
