Departamento de Estructura de la Materia, Física Térmica y Electrónica, Universidad Complutense de Madrid, 28040 Madrid, Spain; GISC-Grupo Interdisciplinar de Sistemas Complejos, 28040 Madrid, Spain.
Departamento de Química Física, Universidad Complutense de Madrid, Avda. Complutense s/n, Madrid 28040, Spain.
J Colloid Interface Sci. 2022 May 15;614:378-388. doi: 10.1016/j.jcis.2022.01.110. Epub 2022 Jan 24.
A broad range of phenomena, such as emulsification and emulsion stability, foam formation or liquid evaporation, are closely related to the dynamics of adsorbing colloidal particles. Elucidation of the mechanisms implied is key to a correct design of many different types of materials.
Microspheres forced to rotate near a fluid interface exhibit a roto-translational hydrodynamic mechanism that is hindered by capillary torques as soon as the particles protrude the interface. Under these conditions, the time evolution in the ratio of moving spheres provides a direct description of the adsorption kinetics, while microscopy monitoring of particle acceleration\deceleration informs about the adsorption\desorption dynamics. In this work, the proposed strategy is applied at an air/water interface loaded with spherical magnetic particles negatively charged, forced to rotate by the action of a rotating magnetic field.
The proposed method enables the adsorption/desorption dynamics to be followed during the earliest phase of the process, when desorption of a small fraction of particles is detected, as well as to estimate approximated values of the adsorption/desorption constants. The results obtained show that the addition of a monovalent salt or a cationic (anionic) surfactant promotes (inhibits) both adsorption and formation of permanent bonds between particles.
从乳化和乳状液稳定性到泡沫的形成或液体的蒸发等一系列现象都与吸附胶体颗粒的动力学密切相关。阐明所涉及的机制是正确设计许多不同类型材料的关键。
当颗粒突出界面时，微球在靠近流体界面的强制旋转过程中表现出一种转动-平移流体动力学机制，这种机制会受到毛细扭矩的阻碍。在这些条件下，移动球体的比例随时间的演化直接描述了吸附动力学，而对颗粒加速/减速的显微镜监测则提供了吸附/解吸动力学的信息。在这项工作中，所提出的策略应用于加载有带负电荷的球形磁性颗粒的空气/水界面，这些颗粒在旋转磁场的作用下被迫旋转。
所提出的方法能够在过程的最早阶段跟踪吸附/解吸动力学，当检测到一小部分颗粒解吸时，以及估计吸附/解吸常数的近似值。所得到的结果表明，单价盐或阳离子（阴离子）表面活性剂的添加会促进（抑制）颗粒之间的吸附和形成永久性键合。
