Thompson K L, Fielding L A, Mykhaylyk O O, Lane J A, Derry M J, Armes S P
Department of Chemistry , University of Sheffield , Brook Hill, Dainton Building , Sheffield , UK S3 7HF . Email:
Department of Chemical and Biological Engineering , The University of Sheffield , Mappin Street , Sheffield , UK S1 3JD.
Chem Sci. 2015 Jul 1;6(7):4207-4214. doi: 10.1039/c5sc00598a. Epub 2015 May 7.
Thermo-responsive vermicious (or worm-like) diblock copolymer nanoparticles prepared directly in -dodecane polymerisation-induced self-assembly (PISA) were used to stabilise water-in-oil Pickering emulsions. Mean droplet diameters could be tuned from 8 to 117 μm by varying the worm copolymer concentration and the water volume fraction and very high worm adsorption efficiencies (∼100%) could be obtained below a certain critical copolymer concentration (∼0.50%). Heating a worm dispersion up to 150 °C led to a worm-to-sphere transition, which proved to be irreversible if conducted at sufficiently low copolymer concentration. This affords a rare opportunity to directly compare the Pickering emulsifier performance of worms and spheres. It is found that the former nanoparticles are markedly more efficient, since worm-stabilised water droplets are always smaller than the equivalent sphere-stabilised droplets prepared under identical conditions. Moreover, the latter emulsions are appreciably flocculated, whereas the former emulsions proved to be stable. SAXS studies indicate that the mean thickness of the adsorbed worm layer surrounding the water droplets is comparable to that of the worm cross-section diameter determined for non-adsorbed worms dispersed in the continuous phase. Thus the adsorbed worms form a monolayer shell around the water droplets, rather than ill-defined multilayers. Under certain conditions, demulsification occurs on heating as a result of a partial worm-to-sphere morphological transition.
通过在正十二烷中进行聚合诱导自组装（PISA）直接制备的热响应蠕虫状（或蠕虫样）二嵌段共聚物纳米颗粒用于稳定油包水型皮克林乳液。通过改变蠕虫状共聚物浓度和水相体积分数，平均液滴直径可在8至117μm之间调节，并且在一定临界共聚物浓度（约0.50%）以下可获得非常高的蠕虫吸附效率（约100%）。将蠕虫状分散体加热至150°C会导致蠕虫向球形转变，如果在足够低的共聚物浓度下进行，这一转变被证明是不可逆的。这提供了一个难得的机会来直接比较蠕虫状颗粒和球状颗粒作为皮克林乳化剂的性能。研究发现，前者纳米颗粒的效率明显更高，因为蠕虫状颗粒稳定的水滴总是小于在相同条件下由球状颗粒稳定的等效水滴。此外，后者乳液明显絮凝，而前者乳液被证明是稳定的。小角X射线散射（SAXS）研究表明，围绕水滴吸附的蠕虫状层的平均厚度与分散在连续相中的未吸附蠕虫状颗粒的横截面直径相当。因此，吸附的蠕虫状颗粒在水滴周围形成单层壳，而不是不确定的多层结构。在某些条件下，加热会导致部分蠕虫向球形的形态转变，从而发生破乳。
