1 research outputs found
Demonstration of a Novel Charge-Free Reverse Wormlike Micelle System
We
demonstrate a novel charge-free reverse wormlike micelle (RWLM)
consisting of a ternary mixture of a nonionic amphiphilic block copolymer,
fatty acid alkyl ester oil, and water under ambient conditions. Nonionic
amphiphile tetra-[poly(oxyethylene)-poly(oxybutylene)]pentaerythrityl
ether (TEBPE) self-assembled into spheroid-type micelles in nonaqueous
media isopropyl myristate (IPM) with viscosity comparable to that
of IPM. The addition of water increases viscosity only slightly up
to a certain concentration of water and then drastically, demonstrating
the sphere-to-wormlike micelle transition as confirmed by small-angle
X-ray scattering. Further increase in water decreases the viscosity
after attaining a maximum value. The zero shear viscosity (η<sub>0</sub>) of the 10 wt % TEBPE/IPM system reached the maximum at 2.6
wt % water and ca. 56 Pa·s, which is ∼fivefold higher
than that of water. Dynamic rheological measurements on the highly
viscous solutions confirmed the viscoelastic behavior and could be
described by the Maxwell model. Conductivity, measured in the presence
of a conductive probe, 1-ethyl-3-methylimidazolium tetrafluoroborate,
was found to be higher for viscous samples compared to the nonviscous
samples, suggesting the static percolation caused by the RWLM formation.
Decrease in η<sub>0</sub> and conductivity beyond a maximum
suggests the shortening of reverse micelles. A similar behavior has
been observed in other fatty acid alkyl ester oils of different alkyl
chain lengths. Note that most of the RWLM systems previously reported
are based on phosphatidylcholine (PC). Formulation and structure–properties
related to non-PC-based RWLMs have been rarely explored. Non-PC-based
RWLMs using chemically stable and low-cost synthetic molecules can
be applied not only in pharmaceuticals and cosmetics but also in a
wide range of applications including drag reduction agents for nonaqueous
fluids and as a template for nanomaterial synthesis