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Abstract
Polymeric thickeners are important ingredients to adjust flow properties and stability of formulations. The effect of polymeric additives on dispersion properties is rather complex (viscosity of the continuous phase, adsorption and depletion effects, interaction with other ingredients). Therefore optimum formulation requires extensive experimental investigations. A new multisample approach is presented using analytical centrifugation (STEP-Technology), which allows for an accelerated characterisation of separation stability. The potential of multisample analytical centrifugation for formulation design was demonstrated investigating the effect of particle (calcium carbonate, silica) and polymer (polyacryl amide) concentration on dispersion properties of different stabilised suspensions. The quality of dispersion – flocculated or stable dispersion – can be judged based on shape and evolution of the transmission profiles or by comparison of the speed of separation. Accordingly the optimum concentration for stabilisation of lime dispersions by an anionic surfactant was identified. Stability of the surfactant stabilised lime dispersions can be markedly enhanced by low concentrations of polymeric thickener. Effect of addition of non-adsorbing thickener with high molecular mass very sensibly depends on concentration (integral effect of depletion and increasing viscosity). For the quartz dispersion investigated stabilisation at low polymer concentration by viscosity effect, followed by destabilisation at intermediate concentration due to depletion flocculation and stabilisation at higher concentration by viscosity, eventually by depletion stabilisation was experienced. In summary analytical centrifugation can be successfully used for screening purposes in dispersion product development. Different samples can be directly compared in short time.
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