(188h) Effect of Particle Size and Anisotropy On Yield Stress and Dynamic Modulus in Latex

The control of particle size and its morphology are critical in producing high quality latex for applications in digital images, coatings, adhesives, impact modifiers, and medical diagnostics. Understanding the development of non-equilibrium morphologies where the possible number of particle structures is large is a challenge. Semi-batch emulsion polymerization in the presence of seed particles that eliminates the particle nucleation stage and with the regulated concentration of monomer in the reaction system represents an effective tool to investigate the particle growth mechanisms. The studies on diffusion-controlled nucleation and growth of particle nuclei and the molecular diffusion of monomer from the aqueous phase to the particle–water interface are two examples in investigating polymerization mechanisms and kinetics.

In our study, latex emulsions were prepared by a semi-continuous emulsion polymerization from styrene/n-butyl methacrylate with dodecaneethiol, a chain transfer agent and decanediol diacrylate, a branching agent and ammonium persulfate, an initiator. Nonlinear rheology and yielding behavior of repulsive and attractive spheres and anisotropic particles are examined and analyzed in terms of barriers constraining motion. The barriers are due to inter-particle bonds or cages constraining translational or rotational motion. The effects of particle shape, anisotropy, size and inter-particle interaction on yield stress and dynamic modulus are explored.