Pressure-induced reentrant micellization of amphiphilic block copolymers in dilute aqueous solutions.
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)].
Osaka
Noboru
N
Neutron Science Laboratory, Institute for Solid State Physics, The University of Tokyo, Tokai, Ibaraki 319-1106, Japan.
Miyazaki
Sho
S
Okabe
Satoshi
S
Endo
Hitoshi
H
Sasai
Aya
A
Seno
Ken-ichi
K
Aoshima
Sadahito
S
Shibayama
Mitsuhiro
M
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*