Influence of surfactant addition on the rheological properties of aqueous Welan matrices

Rheological characterization of polysaccharide–surfactant matrices for cosmetic O/W emulsions

“…However, a strong increase in the shear-thinning character of the scleroglucan solution appears around c p = 0.4% w/w, since at higher concentrations the index n exponent becomes lower than 0.1, meaning that the density of intermolecular interactions and associations becomes quite significant and, hence, a typical weak gel network is developed. The values of η 0 calculated for this biopolymer are similar to others obtained from polysaccharides such as welan matrices [7].…”

“…Both instruments were equipped with parallel plates geometry with rough surfaces (Bohlin 25-mm diameter and Haake 35-mm diameter, 1-mm gap) for the steady shear flow, to eliminate wall-slip phenomena, and with the cone-plate geometry (60 mm diameter, 1 • angle) for the oscillatory tests performed in the Haake RS150. An oil film was deposited on the interface sample/air in order to overcome the evaporation of water from the borders of the measuring systems [7].…”

“…The interactions between these additives may influence some properties of the system such as the interfacial tension, the optical properties, the viscosity, and other rheological parameters [1,4,7]. When these interactions take place in the continuous phase of an emulsion, there could be a lack of surfactant at the interface and, consequently, this might affect the continuous-phase viscosity, a fact that might lead to poor mechanical properties and stability.…”

“…There are different mechanisms by which these polymers can stabilize an emulsion. Thus, the formation of an extended hydrogel network reflects into high viscosity of the continuous phase at low shear, thus slowing down the droplet motion [1,6,7]; such a polymeric structure surrounds the oil droplets, ensuring effective steric hindrance of their coalescence [5,6]. Another contribution to the stabilization is provided by nonadsorbing depletion mechanism, due to the pronounced hydrophilicity, low flexibility, and low surface activity of these polymers [5,9].…”

“…In particular, they are frequently employed to stabilize aqueous suspensions or O/W emulsions [6][7][8]. There are different mechanisms by which these polymers can stabilize an emulsion.…”