title: Amide-induced phase separation of hexafluoroisopropanol-water mixtures depending on the hydrophobicity of amides.
abstract: Amide-induced phase separation of hexafluoro-2-propanol (HFIP)-water mixtures has been investigated to elucidate solvation properties of the mixtures by means of small-angle neutron scattering (SANS), (1)H and (13)C NMR, and molecular dynamics (MD) simulation. The amides included N-methylformamide (NMF), N-methylacetamide (NMA), and N-methylpropionamide (NMP). The phase diagrams of amide-HFIP-water ternary systems at 298 K showed that phase separation occurs in a closed-loop area of compositions as well as an N,N-dimethylformamide (DMF) system previously reported. The phase separation area becomes wider as the hydrophobicity of amides increases in the order of NMF < NMA < DMF < NMP. Thus, the evolution of HFIP clusters around amides due to the hydrophobic interaction gives rise to phase separation of the mixtures. In contrast, the disruption of HFIP clusters causes the recovery of the homogeneity of the ternary systems. The present results showed that HFIP clusters are evolved with increasing amide content to the lower phase separation concentration in the same mechanism among the four amide systems. However, the disruption of HFIP clusters in the NMP and DMF systems with further increasing amide content to the upper phase separation concentration occurs in a different way from those in the NMF and NMA systems.
authors.affiliation: Department of Chemistry and Applied Chemistry, Graduate School of Science and Engineering, Saga University, Honjo-machi, Saga 840-8502, Japan. takamut@cc.saga-u.ac.jp
authors.forename: Toshiyuki
authors.initials: T
authors.lastname: Takamuku
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Wada
authors.forename: Chiemi
authors.initials: C
authors.lastname: Kawatoko
authors.forename: Takuya
authors.initials: T
authors.lastname: Shimomura
authors.forename: Ryo
authors.initials: R
authors.lastname: Kanzaki
authors.forename: Munetaka
authors.initials: M
authors.lastname: Takeuchi