GOALI: SURFACTANT-MEDIATED ELECTROPHORETIC PROPERTIES OF APOLAR DISPERSIONS

摘要#1160138Sven H.Behrens的智力价值移动离子和表面电荷普遍存在于水和其他极性液体中，但在非极性液体中应该不起作用，因为在非极性液体中，电荷解离的能量成本通常太大，无法进行热激活。与这一传统智慧背道而驰的是，一些表面活性剂添加剂可以将非极性液体的电导率提高许多个数量级，并促进浸泡的固体表面或悬浮胶体颗粒的带电。由此产生的利用外加电场引导粒子运动的能力是至关重要的，例如对于液体调色剂和电泳显示器，但目前还不了解粒子带电的机制或定向电场的影响。基于PI在测量和建模静电相互作用方面的经验，并在惠普团队开发下一代彩色电泳显示器的大力支持下，研究人员提议揭开非极性表面活性剂溶液中粒子电荷和场驱动运动的基本原理。该项目的工作假设是，表面活性剂同时通过至少三种方式影响非极分散体的电行为：通过酸碱相互作用促进表面电荷，通过在表面活性剂聚集体内增溶表面反离子，通过电荷歧化在溶液中形成胶束离子。他们的目的是用一套独创的实验技术来解开这些机制，分别获取主体溶液中和粒子表面上的电荷，粒子-粒子和粒子-场的相互作用，以及吸附的表面活性剂和残余水分的量。使用不同表面特征的颗粒和具有系统变化的结构的表面活性剂将使研究人员找到难以捉摸的答案，即是什么使某些表面活性剂在赋予给定颗粒类型的电荷和电泳迁移率方面比其他表面活性剂更有效。充电反应和表面活性剂吸附的热力学模型将与他们的实验进行对比测试。更广泛的影响，拟议的研究将极大地扩大对非极性液体和浸泡固体表面充电过程的理解。应用范围从燃料运输中的安全措施和电泳显示器和电子皮肤的设计，到与食品配方和护肤霜相关的固体颗粒乳状液的稳定，以及石油回收和漏油补救。这项研究直接触及我们在日常生活中对我们周围表面活性剂的理解，并可以很容易地用非专家可以接触到的例子来说明。基于这种教育潜力，PI与学龄前儿童到一年级学生合作，在一所以非裔美国人为主的学校(97%)，通过实践科学研讨会，旨在增强这些年幼儿童的自然好奇心。与课堂教师的持续密切合作通过使用相关科学材料加强课堂活动，使这些讲习班更具影响力；最成功的演示被记录在科学演示工具包中，并提供适当的材料和说明，供教师在以后几年独立于国际和平研究所使用。PI还通过向他的实验室招募女性学生来支持大学层面的多样性，该实验室在任何给定的时间都有女性占多数，并有让非裔美国本科生参与其研究的历史。

Abstract#1160138Sven H. Behrens Intellectual Merit Mobile ions and electric surface charges are ubiquitous in water and other polar liquids, but should play no role in apolar liquids, where the energetic cost of charge dissociation is typically too large for thermal activation. Defying this conventional wisdom, some surfactant additives can raise the conductivity of apolar liquids by many orders of magnitude and promote electrical charging of immersed solid surfaces or of suspended colloidal particles. The resulting ability to direct particle motion with applied electric fields is crucial, e.g. for liquid toners and electrophoretic displays but neither the mechanism of particle charging nor the effect of the directing field are currently understood. Building on the PI's experience in measuring and modeling electrostatic interactions, and with strong support from the Hewlett-Packard team developing the next generation of color electrophoretic displays, the investigators propose to unravel the fundamental principles of particle charge and field-driven motion in apolar surfactant solutions. The working hypothesis in this project is that surfactants simultaneously influence the electric behavior of apolar dispersions in at least three ways: by promoting surface charging via acid-base interaction, by solubilizing surface counterions inside of surfactant aggregates, and by forming micellar ions in the solution bulk via charge disproportionation. They aim at disentangling these mechanisms with an original suite of experimental techniques accessing separately the charge contained in the bulk solution and on the particle surface, the particle-particle and particle-field interaction, as well as the amount of adsorbed surfactant and residual water. Using particles of different surface characteristics and surfactants with systematically varied architecture will allow the investigators to find the elusive answer to the question what makes some surfactants more effective than others at imparting charge and electrophoretic mobility on a given particle type. Thermodynamic models for the charging reaction and surfactant adsorption will be tested against their experiments. Broader Impact The proposed study should significantly expand the understanding of charging processes in apolar liquids and on immersed solid surfaces. Applications range from safety measures in fuel transportation and the design of electrophoretic displays and electronic skins to the stabilization of emulsions with solid particles relevant for food formulation and skin care creams as well as for oil recovery and oil spill remediation. The research directly touches on our understanding of surfactants surrounding us in everyday life, and can easily be illustrated with examples accessible to non-experts.Building on this educational potential, the PI works with pre-schoolers through first graders in a predominantly (97%) African-American school via hands-on science workshops designed to reinforce the natural curiosity in these young children. An ongoing close collaboration with the classroom teachers makes these workshops more impactful by enhancing classroom activities with related science materials; and the most successful demonstrations are captured in science demo kits with appropriate materials and instructions for the teachers to use in later years independently of the PI. The PI also supports diversity at the collegiate level by recruiting female students to his lab, which has had a majority of women at any given time, and has a history of involving African American undergraduates in its research.