Adsorption of surfactant molecules onto the surface of colloidal particles: Case of like-charged species
Adsorption of surfactant molecules onto the surface of colloidal particles: Case of like-charged species
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DOI：
10.1016/j.colsurfa.2023.132142
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发表时间：
2023
期刊：
影响因子：
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通讯作者：
E. L. Correia;S. Thakur;Aanahita Ervin;E. Shields;Sepideh Razavi
中科院分区：
文献类型：
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作者：
E. L. Correia;S. Thakur;Aanahita Ervin;E. Shields;Sepideh Razavi
纳米颗粒和表面活性剂的混合体系具有广泛的应用，从消费品和医药到喷墨打印和石油回收。粒子间的相互作用可以调整在表面活性剂的存在下，并取决于两个物种的表面电荷，颗粒的润湿性，表面活性剂的溶解度，和溶液的条件，如电解质浓度和pH值。带相反电荷的颗粒和表面活性剂的情况下已被广泛研究的文献中，主要是调整颗粒的润湿性。与此相反，在系统中的带电物质，如带负电荷的颗粒和阴离子表面活性剂的行为仍然知之甚少，与相互矛盾的发现，在以前的研究中报道的表面活性剂的吸附。通过进行全面的调查，在本研究中，我们揭示了影响表面活性剂在颗粒表面吸附的因素，包括促进和阻止表面活性剂在颗粒表面吸附的因素，并揭示了控制这种行为的潜在机制。以二氧化硅纳米粒子为荷电粒子，十二烷基硫酸钠（SDS）为表面活性剂，硝酸钾为盐，氢氧化钾和硝酸调节pH值，考察了不同操作条件下表面活性剂对二氧化硅纳米粒子表面特性的影响。通过迁移率测量获得颗粒的zeta电位沿着与溶液电导率。利用这些信息，溶液的德拜长度和粒子的表面电荷密度被估计。有人发现，解释的结果仅仅基于zeta电位数据可能不会揭示SDS吸附到颗粒表面上，因为在某些情况下，没有增压效果可以检测到。然而，将视角转移到电荷密度表明，SDS在2-5的pH值范围内增加了颗粒的电荷密度，对应于邻位和偕位硅烷醇基团解离的pH条件。这种效果在1和10 mM之间的中等总离子强度下更明显，其中发现SDS活性更高并且德拜长度足够短。粒子的电荷密度的增加归因于SDS通过熵驱动的相互作用到粒子表面上的尾部向下吸附。这些发现为带电混合颗粒/表面活性剂系统提供了有价值的见解，并为科学界澄清了这个复杂且以前没有定论的话题。
Mixed systems of nanoparticles and surfactants have a broad range of applications from consumer products and medicine to inkjet printing and oil recovery. The interparticle interactions can be tuned in presence of surfactants and are dependent on surface charge of both species, particle’s wettability, surfactant solubility, and solution conditions such as electrolyte concentration and pH. The case of oppositely charged particles and surfactants has been extensively examined in the literature, primarily to tune the wettability of particles. In contrast, the behavior in systems of like-charged species such as negatively charged particles and anionic surfactants remains poorly understood, with conflicting findings reported in previous studies on the adsorption of surfactants. By conducting a comprehensive investigation, in this study we shed light on the factors that influence the adsorption of surfactant onto the particle surface, both promoting and preventing it, and unravel the underlying mechanisms governing such behavior. Silica nanoparticles were used as the negatively charged particle, sodium dodecyl sulfate (SDS) was used as the surfactant and potassium nitrate was used as the salt, while the pH was adjusted by potassium hydroxide and nitric acid, to investigate the effect of surfactants on the surface characteristics of the silica nanoparticles under various operating conditions. The zeta potential of particles along with the solution conductivity were obtained via mobility measurements. Using this information, the solution’s Debye length and the particle’s surface charge density were estimated. It was found that interpreting the outcome solely based on the zeta potential data might not reveal the adsorption of SDS onto the particle surface as no supercharging effect could be detected in some cases. However, shifting the perspective to charge density shows that SDS increased the particles charge density for pH values in the range of 2–5, corresponding to the pH conditions at which vicinal and geminal silanol groups are dissociated. This effect was more pronounced at moderate total ionic strengths between 1 and 10 mM, where SDS activity was found to be higher and the Debye length was sufficiently short. The increase in the particle’s charge density was attributed to the tail-down adsorption of SDS onto the particle surface via entropically-driven interactions. These findings offer valuable insights into like-charged mixed particle/surfactant systems and bring clarity to the scientific community regarding this complex and previously inconclusive topic.