Formation of gem-like dispersions of soft crystallites in water by vesicles of a cationic surfactant
Formation of gem-like dispersions of soft crystallites in water by vesicles of a cationic surfactant
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通过阳离子表面活性剂的囊泡在水中形成软晶体的宝石状分散体
DOI：
10.1016/j.colsurfa.2022.129822
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发表时间：
2022
期刊：
影响因子：
--
通讯作者：
Corti, David S.
中科院分区：
文献类型：
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作者：
Hsieh, An-Hsuan;Franses, Elias I.;Corti, David S.
首次发现了由阳离子表面活性剂二十二烷基二甲基溴化铵(DDAB)形成的彩虹状类液体水囊分散体。一些固体微晶、薄膜和胶体晶体会出现虹彩，但在实际上保持液态的体系中还没有观察到彩虹。用目视观察和波长为350-700m nm的光谱比浊法(ST)测定了DDAB重量分数为0.020-0.030的分散体中的囊泡大小和微结构的形成。DDAB囊泡分散体呈彩虹色，w=0.023-0.027，这是由于囊泡自组装形成的“软”微晶所致。根据ST测量结果推算出30~60 nm的有效囊泡半径。还估算了囊泡的体积分数ϕv和它们的有效体积分数ϕv*，它们代表了囊泡周围的双电层。彩虹色分散体的ϕv*值较高，表明它们含有高度重叠的静电双层的相邻小泡，尽管它们的ϕv*值相对较低。因此，小泡之间产生了强烈的静电排斥作用，这可能会驱动“软”微晶的形成，从而形成所观察到的彩虹。然而，这些“柔软”的微晶很容易破碎，但很快就会重生，仍然处于悬浮状态。因此，这些囊泡分散体仍然作为高粘度的整体分散体流动；与其他由刚性胶体组成的胶体晶体的情况相反，作为一个整体，分散体仍然是液体状或“液体宝石”。除了外观美观外，这些DDAB泡囊分散体还可以作为致密二氧化硅悬浮液的有效稳定剂，即使在相对较低的W值时也能防止沉淀。
A first discovery of iridescent liquid-like aqueous vesicle dispersions formed from the cationic surfactant didodecyldimethylammonium bromide (DDAB) is reported. Iridescence arises for some solid crystallites, thin films, and colloidal crystals, but has not yet been observed in systems that in effect remain liquid-like. Visual observations and spectroturbidimetry (ST) at wavelengths of 350–700 nm were used to determine vesicle sizes and microstructure formation in dispersions for DDAB weight fractionswbetween 0.020 and 0.030. The DDAB vesicle dispersions exhibited iridescent colors forw= 0.023–0.027, due to the formation of “soft” crystallites formed by self-assembled vesicles. Effective vesicle radii from 30 to 60 nm were inferred from the ST measurements. The volume fractions of the vesiclesϕvand their effective volume fractionsϕv*, which account for the electrostatic double layers around a vesicle, were also estimated. The high values ofϕv* for the iridescent dispersions indicate that they contain neighboring vesicles with highly overlapping electrostatic double layers, even though their values ofϕvremain relatively low. Hence, strong electrostatic repulsive interactions arise between the vesicles, which probably drive the formation of “soft” crystallites, and thus the observed iridescence. Nevertheless, these “soft” crystallites, which could be easily broken up but were quick to reform, remain suspended. Consequently, these vesicle dispersions still flowed as a bulk dispersion with a high viscosity; the dispersion as a whole remained liquid-like or as a “liquid gem”, in contrast to what occurs to the other colloidal crystals made of rigid colloids. Beside their beautiful appearances, these DDAB vesicle dispersions also act as effective stabilizers of dense silica suspensions against sedimentation even at relatively low values ofw.