Yielding and rheopexy of aqueous xanthan gum solutions

Abstract

Xanthan gum (XG) is widely used in cosmetic and pharmaceutic products (creams, pastes) and in oil industry (drilling fluids) as a stabilizing and/or thickening agent. In literature its rheological behavior is mainly presented as that of a shear-thinning or a yield stress fluid. Here, in order to clarify this rheological behavior we study in detail the flow characteristics during continued flow under given conditions (i.e. controlled stress) for a mass concentration ranging from 0.2 to 5 %. We are thus able to identify the apparent flow curve of the material after short flow duration and the flow curve in steady state (i.e. after long flow duration). The validity of this flow curve, determined from standard rheometry, is confirmed by Magnetic Resonance velocimetry. These materials start to exhibit a yield stress behavior beyond some critical Xanthan or salt concentration. In that case, a significant increase (by a factor up to 5) of the apparent viscosity is observed during flow in some range of stresses, before reaching steady state. This original rheopectic effect might be due, after some time of flow associated with deformation and reconfiguration of the XG molecules, to the progressive formation of intermolecular links such as hydrogen bonds and/or intermolecular association due to acetate residues.

Diversity of Bioinspired Hydrogels: From Structure to Applications

“…Beyond a critical polymer or salt concentration, XG chains aggregate in disordered state determining an increase of viscoelastic parameters, as discussed above (Figure 10a) [175]. Yield stress behavior (liquid-like behavior only above a certain shear stress value) and rheopectic effects (an increase of the apparent viscosity before reaching a steady state) were observed for concentrated solutions of XG at 25 • C [181].…”

“…In aqueous solutions, XG displays high viscosity even at low concentrations [57], making this polysaccharide a valuable thickening or stabilizing agent of high interest in food, agriculture, drilling fluids (coil industry), paint, detergents, cosmetic and pharmaceutic products (creams, pastes), etc. [168,181,182].…”

Acidic aqueous redox flow battery using 12‐phosphotungstic acid and 2,4,5,6‐tetrahydroxybenzene‐1,3‐disulfonic acid as redox couple

“…According to the measurements, the viscosity of PTA before and after the ARFB single‐cell test was 1.69 and 1.72 mm 2 s −1 , while that of TironA was 1.78 and 1.8 mm 2 s −1 . This indicates that there is no significant change in viscosity of PTA and TironA even after the ARFB single‐cell test irrespective of the increase in their concentrations 58,59 …”

“…This indicates that there is no significant change in viscosity of PTA and TironA even after the ARFB single-cell test irrespective of the increase in their concentrations. 58,59 F I G U R E 4 (A) Discharge capacity and SOC profiles and (B) CE and EE of ARFB single cell using 0.1 M PTA and 0.2 M TironA dissolved in 1 M H 2 SO 4 that was operated for 10 cycles. This ARFB single-cell test was performed at 30 mA cm À2 F I G U R E 5 (A) Discharge capacity and SOC profiles and (B) CE and EE of ARFB single cell using 0.25 M PTA and 0.5 M TironA dissolved in 1 M H 2 SO 4 that was operated for 50 cycles.…”

Trends in biopolymer science applied to cosmetics

“…Its linear backbone structure is composed of (1 → 4)-linked-D-glucose with a polysaccharide sidechain containing glucuronic acid residue (1 → 4), a terminal mannose unit and a, connected, second mannose unit (1 → 2). Xanthan gum has a high molecular weight of 2 × 10 6 to 2 × 10 7 g/mol [166,167]. Figure 11 shows the general structure.…”