The　critical　reverse　micelle　concentrations　of　C12-s-C12ṡ2Br　(s　=　2,　3,　4,　5,　6,　8,　12)　in　n-heptane/n-hexanol　solutions,　cmcI　s,　have　been　determined　by　absorption　spectrum　method　using　iodine　as　probe.　The　values　of　cmcI　s　are　smaller　than　those　of　the　critical　micelle　concentrations　(cmcaq　s)　in　aqueous　solution　and　reach　a　maximum　at　s　=　4,　which　is　similar　to　the　variation　of　cmcaq　with　s.　The　variation　of　cmcI　with　s　is　attributed　to　the　alteration　in　the　spacer　chain　conformation,　i.e.　when　the　spacer　is　short　enough,　it　may　adopt　stretch　configuration　and　when　the　spacer　is　long,　it　tends　to　bend　towards　the　continuous　oil　phase　to　achieve　a　more　densely　packing　of　the　quaternary　ammonium　heads　on　the　surface　of　the　core.　©　2006　Elsevier　Inc.　All　rights　reserved.