Gellan gum fluid gels: influence of the nature and concentration of gel-promoting ions on rheological properties

Abstract

Low-acyl gellan gum fluid gels were obtained using two different gel-promoting cations under the same processing conditions and their rheological properties were investigated.For that reason, stress and frequency sweeps measurements and flow curves tests were carried out. Small amplitude oscillatory shear assays demonstrated that these materials exhibit weak gel behaviour despite the shape of their mechanical spectra being similar to those obtained from strong gels. However, the existence of a weak gel structure was confirmed by the fact that the difference between the elastic and viscous components was of only one order of magnitude. In addition, a reduction in the storage and lost modules and the viscosity as a function of the applied shear was observed with increasing cation concentration. Finally, in order to produce fluid gels, a higher concentration of the monovalent cation was required than when divalent cations were employed in the lowacyl gellan gum fluid gels formulation.

Freeze drying and rehydration of alginate fluid gels

“…They can be prepared using both biological (polysaccharides and proteins) and synthetic polymers (Norton, et al, 1999), and can be produced using typical shear devices, such as a jacketed pin-stirrer, which allows a continuous process. Fluid gels can be temperature and/or ionically set, depending on the hydrocolloid used and to its gelation mechanism (García, et al, 2018a;Wang, et al, 2016). The particle size can be controlled by varying the polymer concentration and the shear rate (García, et al, 2018b;Norton, et al, 1999).…”

“…Fluid gels can be temperature and/or ionically set, depending on the hydrocolloid used and to its gelation mechanism (García, et al, 2018a;Wang, et al, 2016). The particle size can be controlled by varying the polymer concentration and the shear rate (García, et al, 2018b;Norton, et al, 1999).…”

Processable UiO-66 Metal–Organic Framework Fluid Gel and Electrical Conductivity of Its Nanofilm with Sub-100 nm Thickness

“…Rheological measurements of fluid gel revealed the shear-thinning behavior with increasing shear strain rate, which is the characteristic of non-Newtonian fluids (Figure a). , Further measurement of the storage modulus ( G ′) and loss modulus ( G ″) was also carried out as a function of angular frequency (Figure b). The phase angles of both G ′ and G ″ are independent of the frequency, and G ″ remains smaller than G ′ throughout the frequency range, showing characteristic properties of gel state. , It is noted that G ′ and G ″ of the gels decrease with the increasing applied strain and exhibit the flowing-fluid behavior at high strain. , The viscosity of fluid gel was found to be lower by approximately 3 orders of magnitude than that of the nonflowing gel (comparing between Figures a and S2a), suggesting more fluid behavior compared to the nonflowing gel . Therefore, the rheological properties of the fluid gel indicate the suitable viscoelasticity of UiO-66 in the fluid gel state for further fabrication as nanofilms.…”

“…So, we propose that it is feasible to adjust the rheological properties of UiO-66 gel by the synthesis conditions to achieve UiO-66 in a “free-flowing” gel state or fluid gel state. Fluid gel is defined based on its combined gel and fluid characteristics. , Fluid gel exhibits no flow in the steady state (gel), while it tends to flow under an applied shear stress or external force (fluid). , Moreover, fluid gel requires to have low viscosity comparable to general spin-coating solvents for further processing as nanofilm. In addition to the processability, downsizing UiO-66 into nanoparticles in fluid gel is expected to enhance its electrical conductivity and charge diffusion coefficient, which are important to expand the use of UiO-66 for electrocatalysis and energy storage applications.…”

Understanding the encapsulation and release of small molecular weight model actives from alginate fluid gels

“…Over the last two decades a new approach for the production of biopolymer-based microparticles, commonly termed as sheared or fluid gels, has been investigated (Norton et al, 1999;Shewan & Stokes, 2013). Fluid gels are suspensions of gel particles in a non-gelled continuous medium, usually water, produced when a biopolymer solution undergoes gelation whilst subjected to shear (García et al, 2018;Garrec & Norton, 2012;Norton et al, 1999). Fluid gels can be produced continuously using typical shear devices (e.g.…”