posted on 2012-06-12, 00:00authored byKoffi
L. Dagnon, Kadhiravan Shanmuganathan, Christoph Weder, Stuart J. Rowan
Biomimetic, stimuli-responsive nanocomposites were made
using either
poly(styrene-co-butadiene) (SBR) or polybutadiene
(PBD) as the hydrophobic, low-modulus matrix and hydrophilic cellulose
whiskers isolated from tunicates (TW) as the high-modulus filler.
These materials were prepared using a template approach, which involves
the formation of a percolating TW network and filling this template
with either of the matrix polymers. Dynamic mechanical analysis (DMA)
studies of the dry nanocomposite films reveal that the incorporation
of TWs into the rubbery polymers increases the tensile storage modulus E′ significantly. The reinforcement is attributed
to the formation of a three-dimensional TW network within the SBR
and PBD matrices. The incorporation of the TWs did not affect the
main relaxation temperature of the matrix SBR polymer, suggesting
weak nanofiller–polymer interactions. Thus, the reinforcement
is primarily on account of the nanofiller–nanofiller interactions,
which involve hydrogen bonding. Interestingly, submersion of these
hydrophobic matrix nanocomposites in water results in dramatic softening,
consistent with disengagement of the TW network as a consequence of
competitive hydrogen bonding with water. The kinetics of the modulus
change and the amount of water uptake were shown to depend on the
TW content. Given the hydrophobic nature of the matrices, it is proposed
that the TWs create a percolating network of hydrophilic channels
within the hydrophobic SBR and PBD matrices.