Anyfantakis Manos, Geng Zheng, Morel Mathieu, Rudiuk Sergii, Baigl Damien
Department of Chemistry, Ecole Normale Supérieure-PSL Research University, 24 rue Lhomond, F-75005, Paris, France.
Sorbonne Universités, UPMC Univ Paris 06, PASTEUR, F-75005, Paris, France.
Langmuir. 2015 Apr 14;31(14):4113-20. doi: 10.1021/acs.langmuir.5b00453. Epub 2015 Apr 2.
We study the effect of surfactants on the deposits formed after the evaporation of colloidal suspension drops, at initial concentrations lower than the critical micellar concentrations, for various particle/surfactant mixtures. We show that the surfactant-mediated interactions between particles and the liquid-gas (LG) and liquid-solid (LS) interfaces, rather than the flow patterns, primarily define the morphology of the dry deposit in a robust and reproducible manner. For like-charged particle/surfactant mixtures, most of the particles form a ring-shaped deposit (according to the so-called "Coffee-Ring Effect"), but some particles can also be deposited inside the ring in a way that is modulated by electrostatic interactions between the particles and the LS interface. For oppositely charged systems, surfactant adsorption to the particle surface strongly affects particle-LG interface interactions, which in turn control the deposition pattern. For low surfactant concentrations, coffee-rings are systematically observed. For intermediate concentrations, the charge of surfactant-decorated particles becomes nearly neutral, and their hydrophobicity is enhanced, which promotes particle trapping at the LG interface. A particle skin is formed and its deposition upon drying leads to homogeneous disk-like patterns. For high surfactant concentrations, particle charge is reversed, and coffee-rings are observed again. Notably, this ring-disk-ring evolution of the deposition behavior as a function of surfactant concentration is observed in a variety of mixtures, regardless of particle absolute charge and surface chemistry as well as of surfactant charge and hydrophobicity. Its apparent universal character makes it a promising strategy for a robust control of particle deposition from evaporating drops.
我们研究了表面活性剂对胶体悬浮液滴蒸发后形成的沉积物的影响，这些悬浮液滴的初始浓度低于临界胶束浓度，涉及各种颗粒/表面活性剂混合物。我们表明，颗粒与液 - 气（LG）和液 - 固（LS）界面之间由表面活性剂介导的相互作用，而非流动模式，主要以一种稳健且可重复的方式决定了干沉积物的形态。对于带同种电荷的颗粒/表面活性剂混合物，大多数颗粒形成环形沉积物（根据所谓的“咖啡环效应”），但一些颗粒也能以一种受颗粒与LS界面之间静电相互作用调节的方式沉积在环内。对于带相反电荷的体系，表面活性剂在颗粒表面的吸附强烈影响颗粒 - LG界面相互作用，进而控制沉积模式。对于低表面活性剂浓度，系统地观察到咖啡环。对于中等浓度，表面活性剂修饰颗粒的电荷变得几乎中性，且其疏水性增强，这促进了颗粒在LG界面处的捕获。形成了颗粒外皮，其干燥时的沉积导致均匀的盘状图案。对于高表面活性剂浓度，颗粒电荷反转，再次观察到咖啡环。值得注意的是，在各种混合物中都观察到了这种沉积行为随表面活性剂浓度的环 - 盘 - 环演变，无论颗粒的绝对电荷和表面化学性质以及表面活性剂的电荷和疏水性如何。其明显的普遍性使其成为一种有前景的策略，可用于稳健控制蒸发液滴中的颗粒沉积。
