Surface-Active Properties of Poly(N-alkylsubstituted acrylamide)s and Their Adsorption onto Polystyrene Latex Particles in Water

Abstract

Surface-active properties of copolymers of N,N-dimethylacrylamide (DMA) with n-alkylsubstituted acrylamides, namely as n-butylacrylamide (NBA), n-hexylacrylamide (NHA), n-octylacrylamide (NOA), n-dodecylacrylamide (NDA), and their adsorption onto polystyrene (PS) latex particles were studied at 25°C in water. Surface tension lowering (Δγ) at a concentration of 0.1 g dL−1, where adsorption at air-water interface is close to saturation, increased with the content of N-alkylacrylamide units for respective copolymers containing different N-alkylacrylamide units. The dependence was stronger for copolymers with N-alkylacrylamides bearing the higher alkyl group. The amount of adsorption (Ws) onto PS particles at saturation also increased with the content of N-alkylacrylamide units in the copolymers. Ws linearly increased with Δγ for copolymers with NBA and those with lower contents of NHA and NOA which do not form intramolecular hydrophobic microdomains, whereas copolymers of NDA and those with higher contents of NHA and NOA, which form the microdomains, exhibited large Ws but a small increase with Δγ. Ws were lower and also slightly increased with Δγ for polymers of DMA, N-acryloylpyrrolidine (APR) and N-isopropylacrylamide (IPA). It was deduced that the adsorptions of polymers and copolymers used here at air-water and PS particle-water interfaces are mainly governed by their overall hydrophobicity and that of their alkyl groups of n-alkylacrylamide units, respectively.