Matthews Lauren, Schmetterer Maria
ESRF, The European Synchrotron, 71 Avenue des Martyrs, Grenoble 38043, France.
School of Chemistry, University of Bristol, Cantock's Close, Bristol BS8 1TS, U.K.
Langmuir. 2024 Feb 27;40(8):4207-4217. doi: 10.1021/acs.langmuir.3c03271. Epub 2024 Feb 14.
Glycerol is a nonaqueous polar solvent and is of interest in many industrial areas due to its beneficial properties, such as green production and biocompatibility. Our previous works have shown the presence of a fibrillar phase on the microscale that consists of lamellar sodium dodecyl sulfate (SDS) crystals containing interstitial glycerol on the nanoscale. The phase is gel-like at room temperature and demonstrates shear-thinning behavior upon application of a shear. Initially, small-angle X-ray scattering coupled with rheology (rheo-SAXS) measurements were performed to elucidate the structural transition of the gel phase under an applied shear, but it became clear that the aging process of the gel has a profound impact on both the gel nanostructure and also the mechanical properties. For younger gels, both the dissolution of SDS crystallites and the alignment of the fibrillar phase were seen. However, in the aged gels, an unexpected foam was formed at shear rates > 700 s. The microscopic structure of the foam phase was imaged using polarizing light microscopy and brightfield and darkfield optical microscopy. The nanostructure of the foam phase was investigated using rheo-SAXS. The foam phase was shown to be stabilized by the presence of SDS crystallites at the air-liquid interface, and the stability of the foam is high with foam persisting even = 3 months after formation. These results highlight the importance of investigating green nonaqueous media and the gel aging process, both of which are interesting not only on a fundamental level but also for a range of industrial applications, from personal care products and cosmetics to food science.
甘油是一种非水极性溶剂，因其具有绿色生产和生物相容性等有益特性，在许多工业领域备受关注。我们之前的研究表明，在微观尺度上存在一种纤维状相，其由纳米尺度上含有间隙甘油的层状十二烷基硫酸钠（SDS）晶体组成。该相在室温下呈凝胶状，施加剪切力时表现出剪切变稀行为。最初，进行了小角X射线散射与流变学（流变小角X射线散射）测量，以阐明施加剪切力时凝胶相的结构转变，但很明显，凝胶的老化过程对凝胶纳米结构和机械性能都有深远影响。对于较年轻的凝胶，可以看到SDS微晶的溶解和纤维状相的排列。然而，在老化的凝胶中，在剪切速率>700 s时会形成意想不到的泡沫。使用偏光显微镜、明场和暗场光学显微镜对泡沫相的微观结构进行成像。使用流变小角X射线散射研究泡沫相的纳米结构。结果表明，泡沫相通过气液界面处SDS微晶的存在而稳定，泡沫的稳定性很高，即使在形成后3个月仍能持续存在。这些结果突出了研究绿色非水介质和凝胶老化过程的重要性，这两者不仅在基础层面上有趣，而且对于从个人护理产品、化妆品到食品科学等一系列工业应用也很重要。
