Gacek Matthew Michael, Berg John C
Department of Chemical Engineering, University of Washington, Seattle, WA, USA.
Department of Chemical Engineering, University of Washington, Seattle, WA, USA.
J Colloid Interface Sci. 2015 Jul 1;449:192-7. doi: 10.1016/j.jcis.2014.11.075. Epub 2014 Dec 8.
The current work examines the role of surfactant hydrophile-lipophile balance (HLB) on the ability for surfactant reverse micelles to impart charge to particles dispersed in an apolar medium, a study motivated by a number of applications that seek to maximize particle charge in such systems. Previous investigations have shown that relative acid-base properties of the particles and surfactants, as well as surfactant concentration and trace water content, all play a major role in the particle charge obtained. However, the ability of a surfactant to stabilize charge in reverse micelles is also an important aspect of creating charge on a particle surface. It has been previously shown that surfactant HLB value is an important parameter in assessing the size of the polar core of the reverse micelles, thereby impacting the total charge that is generated in the bulk solution as determined by conductivity. In the current study, this theory is extended to investigate the impact on particle charging. To accomplish this, the electrophoretic mobility is determined for a series of mineral oxides dispersed in Isopar-L with either Span 20, Span 80, or Span 85. These three surfactants all have the same head group chemistry, but their HLB value ranges from 1.8 to 8.6. It is found that the maximum observed particle electrophoretic mobility does scale directly with the HLB of the accompanying surfactant. This indicates that there is a direct correlation between a surfactant's ability to stabilize charge and its ability to impart charge to a particle. However, the largest HLB surfactant, Span 20, also exhibited a large amount of charge screening or neutralization at larger surfactant concentrations. This highlights the competition between particle charging and micelle-micelle charging that remains one of the largest obstacles to maximizing particle charge in apolar systems.
当前的工作研究了表面活性剂亲水亲油平衡（HLB）对表面活性剂反胶束赋予分散在非极性介质中的颗粒电荷能力的影响，这项研究是由许多旨在使此类体系中的颗粒电荷最大化的应用所推动的。先前的研究表明，颗粒和表面活性剂的相对酸碱性质，以及表面活性剂浓度和微量水含量，在获得的颗粒电荷中都起着主要作用。然而，表面活性剂在反胶束中稳定电荷的能力也是在颗粒表面产生电荷的一个重要方面。先前已经表明，表面活性剂HLB值是评估反胶束极性核大小的一个重要参数，从而影响由电导率测定的本体溶液中产生的总电荷。在当前的研究中，将这一理论扩展以研究对颗粒带电的影响。为了实现这一点，测定了一系列分散在异链烷烃-L中并添加司盘20、司盘80或司盘85的矿物氧化物的电泳迁移率。这三种表面活性剂都具有相同的头基化学性质，但它们的HLB值范围为1.8至8.6。发现观察到的最大颗粒电泳迁移率确实与伴随表面活性剂的HLB值直接相关。这表明表面活性剂稳定电荷的能力与其赋予颗粒电荷的能力之间存在直接关联。然而，HLB值最大的表面活性剂司盘20在较高表面活性剂浓度下也表现出大量的电荷屏蔽或中和现象。这突出了颗粒带电与胶束-胶束带电之间的竞争，这仍然是使非极性体系中的颗粒电荷最大化的最大障碍之一。
