The　state　of　water　in　the　reverse　micelles　of　C12-s-C12ṡ2Br　homologues　has　been　investigated　by　Fourier　transform　infrared　spectroscopy.　The　results　showed　that　the　solubilized　water　had　four　states:　the　quaternary　ammonium　head-group-bound,　the　Br--bound,　the　bulklike,　and　the　free　water.　With　increasing　W0,　the　number　of　bulklike　water　per　surfactant　(nb)　rapidly　increased,　which　indicated　swelling　of　the　reverse　micelle.　The　number　of　the　head-bound　water　per　surfactant　(nN+)　gradually　increased.　This　was　attributed　to　a　reduction　of　the　interfacial　curvature,　which　permitted　more　water　molecules　to　associate　with　the　ionic　heads　of　surfactants　and　also　led　to　a　part　of　n-hexanol　being　expelled　from　the　interface　and　thus　water　filled　up.　Owing　to　the　existence　of　n-hexanol　in　the　interface,　the　head-bound　water　of　the　present　system　was　smaller　than　that　of　AOT　system　at　the　same　W0.　The　number　of　counterion-bound　water　per　surfactant　(nBr-)　remained　unchanged　with　W0.　This　was　due　to　much　smaller　dissociation　of　the　head　of　C12-2-C12ṡ2Br　than　that　of　AOT.　With　increasing　s,　unchanged　nN+　is　attributed　to　the　comprehensive　effects　of　enlarged　head,　which　promotes　the　hydration,　increased　ionization　degree,　and　reduced　size　of　the　water　pool.　Owing　to　increased　ionization　degree,　nBr-　increases　with　s.　©　2007　Elsevier　Inc.　All　rights　reserved.