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Effects of pH, temperature and shear on the structure–property relationship of lamellar hydrogels from microbial glucolipids probed by in situ rheo-SAXS
Soft Matter ( IF 2.9 ) Pub Date : 2020/02/25 , DOI: 10.1039/c9sm02494h Ghazi Ben Messaoud 1, 2, 3, 4, 5 , Patrick Le Griel 1, 2, 3, 4, 5 , Daniel Hermida-Merino 6, 7, 8, 9 , Niki Baccile 1, 2, 3, 4, 5
Soft Matter ( IF 2.9 ) Pub Date : 2020/02/25 , DOI: 10.1039/c9sm02494h Ghazi Ben Messaoud 1, 2, 3, 4, 5 , Patrick Le Griel 1, 2, 3, 4, 5 , Daniel Hermida-Merino 6, 7, 8, 9 , Niki Baccile 1, 2, 3, 4, 5
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Lipid lamellar hydrogels are a class of soft materials composed of a defectuous lipid lamellar phase, where defects are classically stabilized by polymer or surfactant inclusions in lipid membranes. We have recently shown that bolaform microbial glucolipids, composed of a single glucose headgroup and a C18:0 fatty acid, with the carboxylic acid group located opposite to glucose, spontaneously form lamellar hydrogels at room temperature below pH 8. In this work, we combine rheology with small angle X-ray scattering (SAXS), rheo-SAXS, to correlate, in situ, the structural and mechanical properties of microbial glycolipid lamellar hydrogels upon application of three different stimuli: pH, temperature and a shear rate. In all cases we find unusual structural features of the lamellar phase if compared to classical phospholipid lamellar structures: reducing pH from alkaline to acidic induces a sol-to-gel transition during which an increasing elastic modulus is associated with an oscillatory evolution of lamellar d(100) spacing; temperature above Tm and increasing shear induce the formation of spherulitic crumpled domains, instead of a classically-expected lamellar-to-vesicle or lamellar-to-onion phase transitions.
中文翻译：
pH，温度和剪切对原位流变-SAXS探测微生物糖脂层状水凝胶的结构-性能关系的影响
脂质层状水凝胶是一类由有缺陷的脂质层状相组成的软质材料，其中的缺陷通常通过脂质膜中的聚合物或表面活性剂夹杂物得以稳定。我们最近发现，由单个葡萄糖头基和C18：0脂肪酸组成且与葡萄糖相反的羧酸基团的棒状微生物糖脂在室温下低于pH 8时自发形成层状水凝胶。在这项工作中，我们结合了流变学与小角度X射线散射（SAXS），rheo-SAXS进行原位关联，微生物糖脂层状水凝胶在三种不同刺激条件下的结构和力学性能：pH，温度和剪切速率。在所有情况下，与经典的磷脂层状结构相比，我们都发现了层状相的不同寻常的结构特征：将pH从碱性降低到酸性会导致溶胶-凝胶转变，在此期间弹性模量的增加与层状d的振荡演化有关（ 100）间距; 高于T m的温度和增加的剪切力会引起球状皱折畴的形成，而不是经典预期的层状到囊状或层状到洋葱的相变。
更新日期：2020-03-12
中文翻译：
pH，温度和剪切对原位流变-SAXS探测微生物糖脂层状水凝胶的结构-性能关系的影响
脂质层状水凝胶是一类由有缺陷的脂质层状相组成的软质材料，其中的缺陷通常通过脂质膜中的聚合物或表面活性剂夹杂物得以稳定。我们最近发现，由单个葡萄糖头基和C18：0脂肪酸组成且与葡萄糖相反的羧酸基团的棒状微生物糖脂在室温下低于pH 8时自发形成层状水凝胶。在这项工作中，我们结合了流变学与小角度X射线散射（SAXS），rheo-SAXS进行原位关联，微生物糖脂层状水凝胶在三种不同刺激条件下的结构和力学性能：pH，温度和剪切速率。在所有情况下，与经典的磷脂层状结构相比，我们都发现了层状相的不同寻常的结构特征：将pH从碱性降低到酸性会导致溶胶-凝胶转变，在此期间弹性模量的增加与层状d的振荡演化有关（ 100）间距; 高于T m的温度和增加的剪切力会引起球状皱折畴的形成，而不是经典预期的层状到囊状或层状到洋葱的相变。
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