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. 2020 Mar 11;16(10):2540-2551. doi: 10.1039/c9sm02494h.

Abstract

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.

MeSH terms

  • Elastic Modulus
  • Glucose / analogs & derivatives*
  • Glycolipids / chemistry*
  • Hydrogels / chemistry*
  • Hydrogen-Ion Concentration
  • Phase Transition
  • Rheology
  • Scattering, Small Angle
  • Temperature
  • X-Ray Diffraction
  • Yeasts / chemistry*

Substances

  • Glycolipids
  • Hydrogels
  • Glucose