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Protein conformational changes are often induced when bound to surfaces and can modulate colloidal stability of protein coated particles in dispersion. We evaluated bovine serum albumin (BSA) adsorbed onto polystyrene particles at room temperature. A z-axis translating laser light scattering device (ZATLLS) measured the sedimentation velocity of protein-coated particles tracking aggregation characteristics compared with non-coated ones. Sedimentation velocities of particles moving in the dispersion, and the resulting viscosity and density of the residual solution following sedimentation determined aggregate size in the dispersion using Stoke's law. Our experiments objectively show that albumin-coated polystyrene forms aggregates. Interestingly, coating particles with protein slows the sedimentation velocity which should correspond to a more dispersed system, but it leads to higher aggregate sizes due to the larger influence of proteins in solution raising solution viscosity. Protein-bound particles were observed to fall out of solution in a more controlled and steady manner compared with uncoated particles. [ABSTRACT FROM AUTHOR]

Sedimentation is a limiting factor for the shelf life of filled paints and adhesive resins, and requires consideration when optimizing a resin's formulation for an end application. Static settling experiments have been performed using a bis-GMA-based photocurable resin system by varying some characteristics of the filler particles (size and composition) and of the resin (viscosity and composition). The recorded batch settling curves, mudline height vs. time, displayed the standard sedimentation shape. In particular, the mudline movement rate was constant in the initial period of sedimentation. The variations of this constant mudline velocity as a function of the settling conditions has been compared to sedimentation model predictions. A close correspondence has been obtained between the data and a model describing the sedimentation behavior of non-aggregated rigid spheres at high concentration in the Stokes regime. In particular, the constant mudline velocity is proportional to the square of the particle diameter. This result can be used as a way to limit the settling phenomenon in filled resin systems, by choosing a particle diameter as small as possible. As a validation of this result, no visually observable settling was seen in 50%-filled resin systems for a period more than 4 months at room temperature using 5.1-μm poly(methyl methacrylate-co-ethylene glycol dimethacrylate) particles as filler. [ABSTRACT FROM AUTHOR]