The effects of free polymers on osmotic compression, depletion flocculation and fusion of lamellar liquid-crystalline droplets

The effects of free polymers on the physical properties of lamellar liquid-crystalline dispersions as model systems for active structured liquid detergents have been investigated. Addition of free polymers to lamellar dispersions may lead to osmotic compression (decrease in the volume fraction or lamellar phase), depletion flocculation and fusion of lamellar droplets. Osmotic compression will occur if the size of the polymer coil (e.g. molecular mass) is too large with respect to the lamellar water layer thickness. Depletion flocculation will occur, as found for normal dispersions, at lower polymer concentrations if the molecular mass of the polymer increases. Fusion of lamellar droplets, which results in an increase in lamellar droplet size, occurs at polymer concentrations lower than the polymer concentration at which depletion flocculation is observed. Extensive fusion is observed well above the critical polymer concentration for depletion flocculation. Osmotic compression and fusion result in a decrease in the viscosity of the lamellar dispersions and allow for concentration of the products based on lamellar dispersions while retaining pourability. Depletion flocculation results in physical instability and increased viscosity of the liquid detergents and has to be avoided.