Moleular level (PFGNMR) study of rheology modifiers interactions to nanoparticles

K. Beshah
The DOW Chemical Co., US

Keywords: Rheology modifiers, latex particles, coatings, PFGNMR, shear thinning

Summary:

Hydrophobically modified ethoxylated urethane resins (HEUR) have been used to control viscosity of nanoparticle dispersions. Extensive work has been done and published over the past three decades on the associative nature of these polymers in water. A molecular based study that showed the interaction between the rheology modifier (RM) and the nanoparticles was conspicuously missing. The major reason for this is the inability to detect the low level hydrophobic signals in an overwhelming signals of aqueous phase materials of the dispersions. We have developed PFGNMR techniques that enable the elimination of unwanted low Mw signals based on their higher diffusion coefficients to detect the desired HEUR signals (higher Mw)without any perturbation of the composite. With this technique, we are able to probe RM-nanoparticle interactions as a function of HEUR end group and nanoparticle surface hydrophobicity. The method is used to obtain adsorption isotherms of the composite in-situ providing unperturbed dynamic equilibrium systems. Our observation has led to a new model of RM-latex interaction that sheds light on the elusive mechanism of high shear viscosity (10,000 s-1) of RM-latex composites. The implications of these molecular level interactions to shear thinning rheology of RM-latex composites will be discussed.