Rheology of Industrially Relevant Microgels

Abstract

Microgels are currently used in a broad range of industrial applications and consumer products, including surface coatings, paints, inks, oil recovery, controlled drug delivery, cosmetics, personal care, home care, food, and pharmaceuticals. An essential feature in many of these applications is the rheology of the microgel suspension during processing, storage, and transport, as well as during the application process itself (i.e., at the in-use or end-use stage). Microgel suspensions have a long history of use for rheological control due to their ability to swell in a suitable solvent to give increased viscosity and/or a gel-like consistency. Starches, which are essentially cross-linked carbohydrate polymers, are probably the oldest example of a microgel; they were separated from grains by the ancient Greeks for a variety of uses including foods, adhesives, and even wound healing, where the latter was achieved by mixing with saliva to form a honey-like coating [1].The attraction of microgel suspensions in industrial applications is that their rheology can be controlled to meet the requirements for specific applications by varying composition, cross-link density, particle size, shape, surface properties, and solvent quality. A useful feature of microgels is their responsive nature to their environment; they can swell or deswell by altering solvent quality (through pH, temperature, ions, etc.), thus altering their effective phase volume and consequently the rheological properties of the suspension. The deformable and swellable nature of microgels allows a higher phase volume to be obtained compared to hard spheres of equivalent size. Their deformability also affects their response in shear flow due to their ability to change shape in response to perturbation, particularly at high volume fractions. The composition of microgels can be adapted and customized according to the application, and the microgel additives used have been made out of a wide variety of polymeric materials including natural or modified biopolymer-based components (e.g., polysaccharides, proteins, and starches), and synthesized components such as polyacrylates, poly(styrene sulfonates), poly(vinyl pyridine), and polyurethanes. Microgel Suspensions: Fundamentals and ApplicationsEdited

Tribology of swollen starch granule suspensions from maize and potato

“…Generally, these highly deformable ghost particles are thought to play an important role in many of the characteristic physical properties of starch pastes, solutions, or gel networks such as viscosity, texture, and rheology (Evans & Lips, 1992;Lagarrigue & Alvarez, 2001;Steeneken, 1989). For example, the presence of dilute or highly packed granule ghosts in some semi-solid starch-containing foods such as soups, dressing, custards and sauces leads to "short" texture, thick appearance and sometimes creamy mouthfeel (Stokes, 2011).…”

Biopolymer-based particles as stabilizing agents for emulsions and foams

“…This kind of steric structural barrier is 261 undoubtedly a major factor inhibiting droplet (or bubble) coalescence in systems containing 262 long fibrous particles assembling into entangled networks. 263 stabilizing effect of swollen microgel particles is their generic ability to function as 285 thickening ingredients and structuring agents in bulk aqueous media (Stokes, 2011). In 286 recognition of these multiple functional attributes, it seems reasonable to assert that the role 287 of microgel ingredients is set to become increasingly important in the ongoing development 288 of biopolymer-based stabilizing agents (Dickinson, 2015b(Dickinson, , 2016b.…”

Rheology of emulsion-filled alginate microgel suspensions

“…This suggested a shear thinning behaviour that is a shear-induced break up of interparticulate bridges, which is typically observed in microgel suspensions (Fernández Farrés et al, 2013;Stokes, 2011). The typical flow curve of a shear thinning non-Newtonian fluid generally…”

“…From the comparison of MAPE, it can be inferred that Cross model showed the best fit across suspensions of different viscosities. This was somewhat expected because microgel suspensions typically behave as a non-Newtonian fluid that displays three distinct regions during flow (Larson, 1999;Stokes, 2011). At low and high shear rates, viscosity is independent of shear rate and the suspension behaves as a Newtonian fluid (zero shear and infinite shear plateau).…”

“…Model (4) and (5) are mostly used in food and beverage (Rao, 1993) and has been used to describe the shear dependent viscosity of colloidal microgels (Stokes, 2011) and ionic biopolymer solution (Huh, Choi, & Sharma, 2005). These models are able to describe the shear thinning behaviour of concentrated suspensions (Ewoldt, Winter, Maxey, & McKinley, 2010).…”