As-made and calcined
forms o
f large-pore (5.3 nm) mesostructured silica with a wormhole
frameworkstructure, denoted MSU-J, have been used to
form rubbery epoxy mesocomposites containing 1.0-12%(w/w) silica. The tensile modulus, strength,
toughness, and extension-at-break
for the mesocomposites
formed
from as-made and calcined
forms o
f MSU-J silica are systematically rein
forced by up to 4.8, 5.7,1.6, and 8.5 times, respectively, in comparison to the pure epoxy polymer. The composites represent the
first examples wherein the rein
forcement bene
fits provided by mesostructured silica particles arecomparable to those provided by ex
foliated organoclay nanolayers at equivalent loadings. Moreover, therein
forcement bene
fits are realized without the need
for organic modi
fication o
f the silica sur
face, andthe increases in tensile properties occur with little or no sacri
fice in optical transparency or thermalstability. The oxygen permeability o
f the mesocomposites prepared
from as-made MSU-J silica increasesdramatically at loadings
![](/images/entities/ge.gi<font color=)
f">5.0% (w/w), whereas the compositions made
from the calcined
form o
f themesostructure show no permeation dependence on silica loading. For instance, the oxygen permeabilityo
f the mesocomposites containing 12% (w/w) as-made MSU-J silica is 6-
fold higher than that o
f thesilica-
free epoxy membrane. Positron annihilation li
fetime spectroscopy established the absence o
f freevolume in the mesocomposites, thus precluding the possibility o
f facile oxygen di
ffusion through the
framework pores o
f the silica. The increase in oxygen permeability is correlated with the partitioning o
fcuring agent between the as-made mesostructure and the liquid prepolymer, which leads to coronas o
fpermeable polymer with reduced chain cross-linking in the vicinity o
f the silica particles. Mesocompositesmade
from calcined
forms o
f the mesostructured silica do not allow
for curing agent partitioning, andthe oxygen permeability is not signi
ficantly in
fluenced by the silica loading.