Microfluidic SAXS Study of Lamellar and Multilamellar Vesicle Phases of Linear Sodium Alkylbenzenesulfonate Surfactant with Intrinsic Isomeric Distribution.
Microfluidic SAXS Study of Lamellar and Multilamellar Vesicle Phases of Linear Sodium Alkylbenzenesulfonate Surfactant with Intrinsic Isomeric Distribution.
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DOI：
10.1021/acs.langmuir.6b01240
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发表时间：
2016-06
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影响因子：
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通讯作者：
A. Poulos;Manuela Nania;P. Lapham;Ruhina M. Miller;Andrew J. Smith;H. Tantawy;Joel Caragay;J. Gummel;O. Ces;E. Robles;J. Cabral
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作者：
A. Poulos;Manuela Nania;P. Lapham;Ruhina M. Miller;Andrew J. Smith;H. Tantawy;Joel Caragay;J. Gummel;O. Ces;E. Robles;J. Cabral
采用微流控小角X射线散射（SAXS）技术研究了普遍存在的线性烷基苯磺酸钠（NaLAS）表面活性剂浓水溶液（45 wt %）在70 °C下的结构和流动行为。NaLAS是一种由20多种表面活性剂分子组成的复杂混合物，具有胶束相（L1）和层状相（Lα）共存的特点。制造新型微流体装置以确保耐压性和耐热性、处理粘性流体的能力以及低SAXS背景。偏光显微镜观察表明，NaLAS溶液在微通道中表现出壁面滑移，速度分布接近活塞流。微流控SAXS证明了该系统的结构空间异质性，特征长度尺度为50 nL。使用统计流SAXS分析，我们确定了胶束相和多个共存的层状相，连续分布的d间距在37.5和39.5 μ m之间。此外，我们表明，NaLAS层状相的取向强烈影响由一个单一的微流体收缩。双层在进入收缩时平行于速度场排列，在离开收缩时垂直于速度场排列。另一方面，在相同的流动条件下，多层囊泡相不受影响。我们的研究结果表明，尽管NaLAS固有的组成复杂性，微流控SAXS可以严格阐明其结构和流动响应。
The structure and flow behavior of a concentrated aqueous solution (45 wt %) of the ubiquitous linear sodium alkylbenzenesulfonate (NaLAS) surfactant is investigated by microfluidic small-angle X-ray scattering (SAXS) at 70 °C. NaLAS is an intrinsically complex mixture of over 20 surfactant molecules, presenting coexisting micellar (L1) and lamellar (Lα) phases. Novel microfluidic devices were fabricated to ensure pressure and thermal resistance, ability to handle viscous fluids, and low SAXS background. Polarized light optical microscopy showed that the NaLAS solution exhibits wall slip in microchannels, with velocity profiles approaching plug flow. Microfluidic SAXS demonstrated the structural spatial heterogeneity of the system with a characteristic length scale of 50 nL. Using a statistical flow-SAXS analysis, we identified the micellar phase and multiple coexisting lamellar phases with a continuous distribution of d spacings between 37.5 and 39.5 Å. Additionally, we showed that the orientation of NaLAS lamellar phases is strongly affected by a single microfluidic constriction. The bilayers align parallel to the velocity field upon entering a constriction and perpendicular to it upon exiting. On the other hand, multilamellar vesicle phases are not affected under the same flow conditions. Our results demonstrate that despite the compositional complexity inherent to NaLAS, microfluidic SAXS can rigorously elucidate its structure and flow response.