Rapid selection of dispersants and evaluation of emulsion stability by analytical centrifugation

摘要

Surface active additives are often applied to stabilize dispersions (emulsions,suspensions) and to modify surface properties.Selection of optimum additive concentration and composition is a crucial step in formulation and in design of technical applications.To this end,a lot of different laboratory methods have been developed,which are in part very sophisticated or on the other end may be very simple but strongly based on individual judgement and experience.Up-to-date related investigations often require a lot of manpower without delivering clear-cut results.A multisample technique based on analytical centrifugation is presented,which allows for an accelerated study of dispersion stability and determination of the velocity of destabilizing processes without dilution,thus avoiding changes of dispersion properties.The kinetics of separation are measured directly in-situ with high time and space resolution. The efficiency of the method proposed for screening and in-depth studies is demonstrated by examples of selection of concentration and composition of additives as well as of preparation conditions for carbon black and lime dispersions.Examples related to emulsion characterization,emulsifier selection,and processing conditions are presented in more detail. The multisample technique is very suitable for screening purposes,to investigate the influence of different preparation conditions and processes,for selection of the most efficient emulsifier or dispersant systems and for quality control.To trace slow destabilizing (aging) processes a combination with common accelerated aging tests is the method of choice.Operation flexibility (centrifugal acceleration,measuring time,temperature) allows one to adapt the measuring conditions to a broad stability range and to investigate temperature effects.