Multiple relaxation modes in suspensions of colloidal particles bridged by telechelic polymers.

We build a Brownian dynamics simulation model to study the linear rheology of latex particles interacting with telechelic polymers (for example, so-called “HEUR” polymers), with the latter modeled as Finitely Extensible Nonlinear Elastic (FENE) dumbbells with ends that stick to Brownian colloidal spheres. We identify from this model four relaxation modes, including (1) a single chain relaxation time, <italic>τ′FENE</italic>, which is closely related to <italic>τFENE</italic>, the relaxation time of a free chain predicted using the FENE model, but is around 1.4 times longer because of surface constraints on polymer configuration; (2) a loop translational-rotational relaxation time, <italic>τloop</italic>, produced by migration of the chain over the particle surface, allowing it to further relax its orientational conformation while still trapped on the particle surface; (3) a bridge formation/breakage relaxation time, <italic>τbridge</italic>; and (4) one or more colloidal particle cluster relaxation times. We show that <italic>τloop</italic> scales as the square of particle radius. <italic>τbridge</italic> is the same as the lifetime of a bridge and increases exponentially with the adsorption energy of a telechelic hydrophobic sticker to the latex particle surface. The one or more long particle cluster relaxation modes are influenced by the diffusion coefficient of the latex particles, the polymer concentration, and the volume fraction of latex particles. These multiple relaxation times help explain the observed rheological behavior of water-borne coatings and differ from the rheology of reversible networks composed of only telechelic HEUR chains, which frequently show single-relaxation-time behavior. [ABSTRACT FROM AUTHOR]