Swelling ratios of N-n-propylacrylamide (NNPA) and N-cyclopropylacrylamide (NCPA) gels in a sodium dodecyl sulfate aqueous solution and transition temperatures of poly(N-isopropylacrylamide) and poly-NNPA in several surfactant aqueous solutions were measured. The swelling behaviors of the gels and the transition temperatures of the polymer solutions are affected by the addition of small amount of surfactants, resulting from the association of the surfactant and the polymer chain. The addition effect of surfactant is strongly dependent on the alkyl chain length of polymer and surfactant. The results in the present work reveal that hydrophobic interaction between polymer chain and surfactant is a chief driving force of the association for anionic surfactant/nonionic gel (polymer) systems.
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