NMP 2008
 |
XiaoBo Gong |
ADVISOR:
Ted Davis |
High Resolution Cryo-SEM of the Nanostructure of PB-BEO Diblock Copolymer Solutions
Authors:
Xiaobo Gong, L. E. Scriven & H. T. Davis
Collaborators: Sangwoo Lee & Frank S. Bates
The phase behavior of poly(ethylene oxide)-poly(butadiene) (PEO-PB) diblock
copolymers mixed with water was studied using combined technique of high
pressure freezing and high resolution cryogenic scanning electron microscopy
(cryo-SEM). Two-component mixtures were investigated as a function of block
composition and copolymer concentration. At low concentrations they form
spherical (S) and cylindrical (C) micelles, and self-intersecting bilayers
known as vesicles (B). Increasing the concentration leads to ordered structures,
notably lamellae (L), hexagonally packed cylinders (H), and arrangements
of spherical nanodomains on cubic (bcc, fcc) lattices. At higher molecular
weights, a random network phase (N) was identified over a sizable portion
of the phase portrait, located between hexagonally ordered cylinders and
ordered lamellae. This new structure, along with branching of cylindrical
micelles, bear a striking similarity to experimentally observed and theoretically
predicted phase behavior in certain ternary water/oil/surfactant systems.
These findings demonstrate that block copolymer surfactants are characterized
by at least four structural building blocks - spheres, cylinders, bilayers,
and branched cylinders - above a threshold molecular weight.
Read Xiaobo Gong's current CV.