Water-Based Latex Dispersions. 3. Exchange Dynamics of Nonionic Surfactants and Poly(ethylene glycol) on Colloidal Particles with Different Interfacial Properties

Abstract

The residence times at equilibrium of nonylphenol ethoxylate or of poly(ethylene glycol) (PEG) in silica and in latex dispersions (polystyrene and poly(methyl methacrylate-co-ethyl acrylate)) have been determined. By means of self-diffusion nuclear magnetic resonance (NMR) it was found that the surfactant with 84 oxyethylene units (NP100) in mean was “irreversibly adsorbed” on all surfaces, with residence times on the order of seconds. For the surfactant with 10 oxyethylene units (NP10) in mean the residence times were shorter, on the order of milliseconds, on both silica and polystyrene. By using PEGs of different molecular weights instead of the surfactants, it was found that the molecular weight of the PEG chain and the nonylphenol group mutually influenced the residence times of the surfactants. For the short PEG chain (196 g/mol), the residence times were shorter than 10 ms on both silica and on polystyrene. Surprisingly, the residence times were shorter than 10 ms also for the longer PEG chain (4120 g/mol). The main contribution to the slow exchange dynamics was therefore, regardless of the surface polarity, due to the hydrophobic nonylphenol group. However, the PEG chain in NP100 adsorbed with train segments on the surfaces, which, like the nonylphenol group, also prolonged the residence times.