Ray Debes, Kumar Sugam, Aswal Vinod Kumar, Kohlbrecher Joachim
Solid State Physics Division, Bhabha Atomic Research Centre , Mumbai 400 085, India.
Laboratory for Neutron Scattering, Paul Scherrer Institut , CH-5232 PSI Villigen, Switzerland.
Langmuir. 2018 Jan 9;34(1):259-267. doi: 10.1021/acs.langmuir.7b03429. Epub 2017 Dec 20.
The evolution of the interaction between an anionic nanoparticle and a nonionic surfactant and their resultant phase behavior in aqueous solution in the presence of electrolyte and ionic surfactants have been studied. The mixed system of anionic silica nanoparticles (Ludox LS30) with nonionic surfactant decaethylene glycol monododecylether (C12E10) forms a highly stable clear phase over a wide concentration range of surfactant. Small-angle neutron scattering (SANS) and dynamic light scattering data show that the surfactant micelles adsorb on the surface of the nanoparticle, resulting in micellar-decorated nanoparticle structures. With the addition of a small amount of electrolyte into this system, the stability gets disturbed substantially and turns to a two-phase (turbid) system. The evolution of interaction in this system has been examined, and it was found that micelle-induced long-range depletion attraction (modeled by a double Yukawa potential) between nanoparticles leads to their aggregation. Interestingly, the addition of anionic surfactant sodium dodecyl sulfate (SDS) in this two-phase system transforms it to a transparent one-phase state, suppressing the depletion-mediated aggregation of nanoparticles. This is attributed to the formation of anionic C12E10-SDS mixed micelles, and it is their repulsive micelle-micelle interaction that disrupts the depletion phenomenon. On the other hand, the addition of cationic surfactant dodecyl trimethylammonium bromide (DTAB) to the turbid LS30-C12E10 electrolyte system shows no change in the turbidity arising from an aggregated nanoparticle system. The driving interaction, in this case, is different from that of the surfactant-mediated depletion attraction; it is due to the attraction between the nanoparticles mediated by the presence of oppositely charged DTAB micelles between them, resulting in a charge-driven bridging aggregation of nanoparticles. Each of these multicomponent systems has been investigated using contrast variation SANS measurements for different contrast conditions where the role of individual components (nanoparticle or surfactant) in the mixed system has been selectively studied. These results thus show that nanoparticle-surfactant micelle interactions can be tuned by the presence of electrolyte and/or choice of surfactant combination.
研究了阴离子纳米颗粒与非离子表面活性剂之间的相互作用及其在电解质和离子表面活性剂存在下在水溶液中的相行为演变。阴离子二氧化硅纳米颗粒（Ludox LS30）与非离子表面活性剂十二烷基十乙二醇醚（C12E10）的混合体系在表面活性剂的宽浓度范围内形成高度稳定的澄清相。小角中子散射（SANS）和动态光散射数据表明，表面活性剂胶束吸附在纳米颗粒表面，形成胶束修饰的纳米颗粒结构。向该体系中加入少量电解质后，稳定性受到严重干扰，转变为两相（浑浊）体系。研究了该体系中相互作用的演变，发现纳米颗粒之间的胶束诱导长程耗尽吸引（由双 Yukawa 势模拟）导致它们聚集。有趣的是，在该两相体系中加入阴离子表面活性剂十二烷基硫酸钠（SDS）可将其转变为透明的单相状态，抑制纳米颗粒的耗尽介导聚集。这归因于阴离子 C12E10-SDS 混合胶束的形成，是它们的胶束-胶束排斥相互作用破坏了耗尽现象。另一方面，向浑浊的 LS30-C12E10 电解质体系中加入阳离子表面活性剂十二烷基三甲基溴化铵（DTAB），纳米颗粒聚集体系产生的浑浊度没有变化。在这种情况下，驱动相互作用与表面活性剂介导的耗尽吸引不同；这是由于纳米颗粒之间存在带相反电荷的 DTAB 胶束介导的吸引，导致纳米颗粒的电荷驱动桥连聚集。使用对比变化 SANS 测量对不同对比条件下的这些多组分体系进行了研究，其中选择性地研究了混合体系中各个组分（纳米颗粒或表面活性剂）的作用。因此，这些结果表明，纳米颗粒-表面活性剂胶束相互作用可以通过电解质的存在和/或表面活性剂组合来调节。
