SANS study of hydrophobic effects on pressure-induced micro- and macrophase separations of block copolymers

• Published in: Physica. B, Condensed matter Vol. 385; pp. 749 - 751
• Main Authors: Osaka, N., Okabe, S., Karino, T., Hirabaru, Y., Aoshima, S., Shibayama, M.
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 01.11.2006
• Subjects: Block copolymers; Hydrophobic effects; Hydrostatic pressure; Microphase separation; Microphase separation; Hydrophobic effects; 61.12.Ex; 82.35.Jk; Hydrostatic pressure; 82.70.Uv; 64.75.+g; Block copolymers
• ISSN: 0921-4526; 1873-2135
• DOI: 10.1016/j.physb.2006.06.051

Hydrophobic effects on pressure-induced microphase separation of block copolymers were investigated by using small-angle neutron scattering (SANS). A block copolymer, pEOEOVE- b-pMOVE aqueous solution, which shows LCSTs (at 40 and 60 ∘ C , for pEOEOVE and pMOVE homopolymers, respectively) was used. A phase diagram was obtained by tracing light-transmittance at 632.8 nm by increasing temperature ( T) at various pressures ( P), which was a convex-upward function. The change in the slope of the phase boundary curve could be explained by volume change associated with mixing as well as “iceberg” formation. SANS revealed that a microphase separation took place by pressurizing or increasing temperature. At 28 ∘ C , the correlation length was observed to show continuous increase with divergence at 350 MPa. This result showed that the block copolymers at 28 ∘ C underwent macrophase separation and the transition was a second-order transition. At 45 ∘ C , under atmospheric pressure, the SANS curve suggested formation of a BCC lattice structure with micelles composed of a central core of pEOEOVE. By pressurizing, the SANS peak related to the microphase separation disappeared, meaning dissolution of block copolymers. However, by further pressurizing, another peak re-appeared at 250 MPa. This peak indicates the microphase separation of block copolymers is different from those observed under low pressures.