Williams Ashley P, Sokolova Anna V, Faber Jonathan M, Butler Calum S G, Starck Pierre, Ainger Nick J, Tuck Kellie L, Dagastine Raymond R, Tabor Rico F
School of Chemistry, Monash University, Clayton VIC 3800, Australia.
Australian Centre for Neutron Scattering, ANSTO, Lucas Heights, NSW 2234, Australia.
Langmuir. 2024 Jan 9;40(1):211-220. doi: 10.1021/acs.langmuir.3c02380. Epub 2023 Dec 28.
Surfactants provide detergency, foaming, and texture in personal care formulations, yet the micellization of typical industrial primary and cosurfactants is not well understood, particularly in light of the polydisperse nature of commercial surfactants. Synergistic interactions are hypothesized to drive the formation of elongated wormlike self-assemblies in these mixed surfactant systems. Small-angle neutron scattering, rheology, and pendant drop tensiometry are used to examine surface adsorption, viscoelasticity, and self-assembly structure for wormlike micellar formulations comprising cocoamidopropyl betaine, and its two major components laurylamidopropyl betaine and oleylamidopropyl betaine, with sodium alkyl ethoxy sulfates. The tail length of sodium alkyl ethoxy sulfates was related to their ability to form wormlike micelles in electrolyte solutions, indicating that a tail length greater than 10 carbons is required to form wormlike micelles in NaCl solutions, with the decyl homologue unable to form elongated micelles and maintaining a low viscosity even at 20 wt % surfactant loading with 4 wt % NaCl present. For these systems, the incorporation of a disperse ethoxylate linker does not enable shorter chain surfactants to elongate into wormlike micelles for single-component systems; however, it could increase the interactions between surfactants in mixed surfactant systems. For synergy in surfactant mixing, the nonideal regular solution theory is used to study the sulfate/betaine mixtures. Tail mismatch appears to drive lower critical micelle concentrations, although tail matching improves synergy with larger relative reductions in critical micelle concentrations and greater micelle elongation, as seen by both tensiometric and scattering measurements.
表面活性剂在个人护理配方中提供去污、发泡和质地功能，但典型工业主表面活性剂和助表面活性剂的胶束化尚未得到很好的理解，特别是考虑到商业表面活性剂的多分散性质。据推测，协同相互作用驱动了这些混合表面活性剂体系中细长蠕虫状自组装体的形成。小角中子散射、流变学和悬滴张力测定法用于研究由椰油酰胺丙基甜菜碱及其两种主要成分月桂酰胺丙基甜菜碱和油酰胺丙基甜菜碱与烷基乙氧基硫酸钠组成的蠕虫状胶束配方的表面吸附、粘弹性和自组装结构。烷基乙氧基硫酸钠的尾链长度与其在电解质溶液中形成蠕虫状胶束的能力相关，这表明在氯化钠溶液中形成蠕虫状胶束需要尾链长度大于10个碳，癸基同系物无法形成细长胶束，即使在存在4 wt%氯化钠且表面活性剂负载量为20 wt%时仍保持低粘度。对于这些体系，在单组分体系中引入分散乙氧基连接基并不能使短链表面活性剂伸长形成蠕虫状胶束；然而，它可以增加混合表面活性剂体系中表面活性剂之间的相互作用。为了研究表面活性剂混合中的协同作用，使用非理想正规溶液理论来研究硫酸盐/甜菜碱混合物。尾链不匹配似乎会导致较低的临界胶束浓度，尽管尾链匹配会改善协同作用，临界胶束浓度的相对降低幅度更大，胶束伸长程度更高，这在张力测定和散射测量中都可以看到。
