Adsorption of nonionic surfactants and model HEUR associative thickeners on oligomeric acid-stabilized poly(methyl methacrylate) latices

Abstract

Abstract The adsorption and competitive adsorption of nonionic oxynonylphenols (average oxyethylene units 12, 40 and 100), and model hydrophobically-modified ethoxylate urethane (HEUR) thickeners onto model poly(methyl methacrylate-methacrylic acid) P(MMA-MAA) latices were studied in terms of hydrophobicity of adsorbates (hydrophobe size and concentration), oxyethylene chain length, pH, and latex surface acid concentration. The adsorption isotherms of the nonionic surfactants on oligomeric acid-stabilized P(MMA-MAA) latices can be described by the Langmuir equation. For nonionic surfactants, the pH value had a significant effect on adsorption behavior. At pH 6, the amount of the surfactants adsorbed increases as the surface-acid concentration increases (e.g. 15–20% higher than that on acid monomer-free latex for NPO(EtO) 12 H). At pH 9.5, the adsorption of NP(EtO) 12 H decreases with increasing surface acid concentration. This reverse in trend, however, was not observed with the surfactants having higher oxyethylene content, and at both neutral and alkaline conditions, greater adsorption on acid-stabilized latices than on acid-monomer-free latices was observed with all HEUR thickeners studied. This was supported by electrokinetic measurements. The competitive adsorption between the nonionic surfactant C 9 H 19 C 6 H 4 O(EtO) 12 H and model HEUR associative thickeners onto model P(MMA-MAA) latices was investigated in relation to the structure of the HEURs. Structural variables include terminal-hydrophobe size and the architecture of the internal connecting unit. The amount of surfactant adsorbed is unaffected by the presence of poly(oxyethyle)e), but is significantly reduced as the effective size of the terminal hydrophobe of the thickener and the concentration of the HEUR hydrophobe are increased.