title: Pressure-induced reentrant micellization of amphiphilic block copolymers in dilute aqueous solutions.
abstract: The pressure-induced structural changes of a block copolymer, poly(2-ethoxyethoxyethyl vinyl ether)-block-poly(2-hydroxyethyl vinyl ether) (pEOEOVE-b-pHOVE) in aqueous solutions, were studied by means of small-angle neutron scattering (SANS) and dynamic light scattering (DLS) from atmospheric pressure up to 400 MPa. pEOEOVE-b-pHOVE formed a spherical micellar structure above 40 degrees C due to poor solubility of pEOEOVE. Micellization phase diagram was determined by DLS, and a covex-upward pressure-temperature (P-T) phase diagram was obtained having a peak around (P,T)=(150 MPa,48 degrees C). The SANS curves at 50 degrees C were analyzed as a function of P. The micellar core size decreased by pressurizing at low P's (P<or=150 MPa) and then increased by further pressurizing (150 MPa<P<400 MPa). It was confirmed that the water volume fraction in the micellar core was larger at high P's than that at low P's even when the core sizes are the same at both pressure regions. This means that the temperature dependence of hydration is more selective at low pressures than at high pressures, in good accordance with our previous results on concentrated aqueous solutions of block copolymers [Phys. Rev. Lett. 96, 048303 (2006)].
authors.affiliation: Neutron Science Laboratory, Institute for Solid State Physics, The University of Tokyo, Tokai, Ibaraki 319-1106, Japan.
authors.forename: Noboru
authors.initials: N
authors.lastname: Osaka
authors.forename: Sho
authors.initials: S
authors.lastname: Miyazaki
authors.forename: Satoshi
authors.initials: S
authors.lastname: Okabe
authors.forename: Hitoshi
authors.initials: H
authors.lastname: Endo
authors.forename: Aya
authors.initials: A
authors.lastname: Sasai
authors.forename: Ken-ichi
authors.initials: K
authors.lastname: Seno
authors.forename: Sadahito
authors.initials: S
authors.lastname: Aoshima
authors.forename: Mitsuhiro
authors.initials: M
authors.lastname: Shibayama
mesh_terms: D003102:Colloids / Q000737:chemistry*; D003198:Computer Simulation; D057927:Hydrophobic and Hydrophilic Interactions; D008823:Micelles; D008956:Models, Chemical; D044367:Phase Transition; D011108:Polymers / Q000737:chemistry*; D011312:Pressure; D012995:Solubility; D012996:Solutions; D014867:Water / Q000737:chemistry*