Advanced Ceramics , University of Bremen , Am Biologischen Garten 2 , D-28359 Bremen , Germany.
Department of Mechanical Engineering , Federal University of Santa Catarina , 88040-900 Florianópolis , Brazil.
Langmuir. 2019 Aug 27;35(34):11089-11098. doi: 10.1021/acs.langmuir.9b01568. Epub 2019 Aug 15.
In this study, we show that hydrophilic nanoparticles can readily desorb from liquid-liquid interfaces in the presence of surfactants that do not change the wettability of the particles. Our observations are based on a simple theoretical approach to assess the number of adsorbed particles at the surfactant-laden liquid-liquid interface. We test this approach by studying the interfacial self-assembly of equally charged particles and lipids dissolved in separate immiscible phases. Hence, we investigate the interfacial adsorption of aminated silica particles (80 nm) and octadecylamine to the decane/water interface by interfacial tension measurements, which are supplemented by interfacial rheology of the adsorbed interfacial films, scanning electron microscopy images of Langmuir-Blodgett films, and measurements of the three-phase contact angle of the particle surface in the presence of surfactants. The measurements show that particles adsorb at the surfactant-laden interface at all investigated surfactant concentrations and compete with the surfactants for interfacial coverage. Additionally, the wettability of the hydrophilic particles does not change in the presence of the lipids, except for the highest investigated lipid concentration. Comparing the adsorption energies of one particle and of the lipids as a function of the particle contact angle provides an estimate of the tendency for interfacial adsorption of particles from which the particle coverage can be assessed. Based on these findings, equally charged particles and lipids show a competitive behavior at the interface determined by the bulk surfactant concentration and the attachment energies of the particles at the interface. This leads to a simple mechanistic model demonstrating that particles can readily desorb from the interface due to direct displacement by surfactants, which are loosely adsorbed at the oil-facing particle side. This mechanism critically lowers the otherwise high interfacial energy barrier against particle desorption, which otherwise would lead to virtually irreversible particle attachment at the interface.
在这项研究中,我们表明,在不改变颗粒润湿性的情况下,亲水性纳米颗粒很容易从液-液界面解吸。我们的观察结果基于一种简单的理论方法,用于评估吸附在表面活性剂负载液-液界面上的颗粒数量。我们通过研究带相同电荷的颗粒和溶解在不同不混溶相中的脂质在界面处的自组装来检验这种方法。因此,我们通过界面张力测量研究了氨基化二氧化硅颗粒(80nm)和十八胺在癸烷/水界面的吸附,并用吸附界面膜的界面流变学、Langmuir-Blodgett 膜的扫描电子显微镜图像以及在存在表面活性剂时颗粒表面三相接触角的测量进行了补充。测量结果表明,颗粒在所有研究的表面活性剂浓度下都吸附在负载表面活性剂的界面上,并与表面活性剂竞争界面覆盖。此外,亲水颗粒的润湿性在存在脂质的情况下不会改变,除了研究的最高脂质浓度。将一个颗粒的吸附能与脂质的吸附能作为颗粒接触角的函数进行比较,可以估计颗粒从界面吸附的趋势,从而可以评估颗粒的覆盖度。基于这些发现,在界面处,带相同电荷的颗粒和脂质表现出竞争行为,这由体相表面活性剂浓度和颗粒在界面上的附着能决定。这导致了一个简单的机械模型,表明颗粒可以由于被松散吸附在油侧颗粒表面的表面活性剂的直接置换而容易地从界面解吸。这种机制极大地降低了颗粒解吸的高界面能垒,否则会导致颗粒在界面上几乎不可逆地附着。