MICROGELS IN COATING TECHNOLOGY - STRUCTURE AND RHEOLOGICAL PROPERTIES

Monodispersed spherical particles (0.1 mu m diameter in the latex phas e) of microgels with different crosslinking densities have been synthe sized by emulsion polymerization. The theological properties of suspen sions of these particles have been studied over a wide concentration r ange. It is shown that the viscosity (especially at low shear rate) an d the dynamic moduli undergo a strong transition when the concentratio n is such that the particles are closely packed. Increasing the crossl inking density of the spheres leads to an increase of the elastic modu lus when the concentration is above this critical concentration. The a ddition of linear species can be used to adjust the theological proper ties of the suspensions. Two competing effects are involved. Either th e viscosity of the suspending medium is increased or the particles und ergo an osmotic deswelling from the linear chains. Molecular weight an d concentration of the linear chains can be chosen to promote the desi red trend.