Thompson K L, Mable C J, Cockram A, Warren N J, Cunningham V J, Jones E R, Verber R, Armes S P
Department of Chemistry, The University of Sheffield, Dainton Building, Brook Hill, Sheffield, South Yorkshire S3 7HF, UK.
Soft Matter. 2014 Nov 21;10(43):8615-26. doi: 10.1039/c4sm01724b.
RAFT-mediated polymerisation-induced self-assembly (PISA) is used to prepare six types of amphiphilic block copolymer nanoparticles which were subsequently evaluated as putative Pickering emulsifiers for the stabilisation of n-dodecane-in-water emulsions. It was found that linear poly(glycerol monomethacrylate)-poly(2-hydroxypropyl methacrylate) (PGMA-PHPMA) diblock copolymer spheres and worms do not survive the high shear homogenisation conditions used for emulsification. Stable emulsions are obtained, but the copolymer acts as a polymeric surfactant; individual chains rather than particles are adsorbed at the oil-water interface. Particle dissociation during emulsification is attributed to the weakly hydrophobic character of the PHPMA block. Covalent stabilisation of these copolymer spheres or worms can be readily achieved by addition of ethylene glycol dimethacrylate (EGDMA) during the PISA synthesis. TEM studies confirm that the resulting cross-linked spherical or worm-like nanoparticles survive emulsification and produce genuine Pickering emulsions. Alternatively, stabilisation can be achieved by either replacing or supplementing the PHPMA block with the more hydrophobic poly(benzyl methacrylate) (PBzMA). The resulting linear spheres or worms also survive emulsification and produce stable n-dodecane-in-water Pickering emulsions. The intrinsic advantages of anisotropic worms over isotropic spheres for the preparation of Pickering emulsions are highlighted. The former particles are more strongly adsorbed at similar efficiencies compared to spheres and also enable smaller oil droplets to be produced for a given copolymer concentration. The scalable nature of PISA formulations augurs well for potential applications of anisotropic block copolymer nanoparticles as Pickering emulsifiers.
可逆加成-断裂链转移（RAFT）介导的聚合诱导自组装（PISA）用于制备六种两亲性嵌段共聚物纳米粒子，随后将其作为假定的Pickering乳化剂进行评估，以稳定水包正十二烷乳液。结果发现，线性聚（甲基丙烯酸甘油酯）-聚（甲基丙烯酸2-羟丙酯）（PGMA-PHPMA）二嵌段共聚物球体和蠕虫状粒子在用于乳化的高剪切均质条件下无法保持稳定。虽然获得了稳定的乳液，但共聚物起到了聚合物表面活性剂的作用；是单条链而非粒子吸附在油水界面。乳化过程中粒子解离归因于PHPMA嵌段的弱疏水性。在PISA合成过程中加入乙二醇二甲基丙烯酸酯（EGDMA），可以很容易地实现这些共聚物球体或蠕虫状粒子的共价稳定。透射电子显微镜（TEM）研究证实，所得的交联球形或蠕虫状纳米粒子在乳化过程中保持稳定，并产生真正的Pickering乳液。或者，用疏水性更强的聚（甲基丙烯酸苄酯）（PBzMA）取代或补充PHPMA嵌段也可以实现稳定。所得的线性球体或蠕虫状粒子在乳化过程中也能保持稳定，并产生稳定的水包正十二烷Pickering乳液。突出了各向异性蠕虫状粒子相对于各向同性球体在制备Pickering乳液方面的固有优势。与球体相比，前者粒子在吸附效率相近的情况下吸附更强，并且在给定的共聚物浓度下还能产生更小的油滴。PISA配方的可扩展性预示着各向异性嵌段共聚物纳米粒子作为Pickering乳化剂具有潜在的应用前景。
