Estimation of the adsorption state of nonionic emulsifier molecules onto styrene–methacrylic acid copolymer particles by in situ ¹H NMR measurements

Abstract.

The adsorption behavior of poly(oxyethylene) nonyl phenyl ether nonionic emulsifier molecules onto polystyrene (PS) and styrene–methacrylic acid copolymer [P(S-MAA)] particles dispersed in D₂O was evaluated by in situ ¹H NMR measurements at room temperature. The resonance due to the protons of the emulsifier molecules was only observed. Normalized NMR integrals of the resonance due to the protons of hydrophobic groups (nonyl and phenyl groups) and the hydrophilic group, poly(oxyethylene) chain, at a certain concentration of the emulsifier decreased with an increase in the total surface area of the PS particles dispersed in the system. The decrease for the hydrophobic groups was much larger than that for the hydrophilic groups. In the dispersion system of P(S-MAA) particles, ionized carboxyl groups at the particle surface decreased the amount of the emulsifier adsorbed.