Microheterogeneity and Microviscosity of F127 Micelle:
The Counter Effects of Urea
and Temperature
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Abstract
F127
is the most widely studied triblock copolymer and due to the
presence of very long polypropylene oxide (PPO) and polyethylene oxide
(PEO) groups, F127 micelle has different microenvironments clearly
separated into core, corona, and peripheral regions. Urea has been
known to have adverse effects on the micellar properties and causes
demicellization and solvation; on the other hand, rise in temperature
causes micellization and solvent evacuation from the core and corona
regions. In the present study, we have investigated the microheterogeneity
of the core, corona, and peripheral regions of the F127 micelle using
red edge excitation shift (REES) at different temperatures and urea
concentrations and correlated the effect of both on the micellar system.
It was found that the temperature counteracts the effect of urea and
also that the counteraction is more prominent in the core region with
respect to corona, and the peripheral region is least affected. Also,
the core and corona regions are very much heterogeneous, while the
peripheral region is more of a homogeneous nature. Using time-resolved
fluorescence anisotropy, we found that the microviscosity within the
micelles vary in the order of core > corona > peripheral region,
and
urea has a general tendency to reduce the microviscosity, especially
for core and corona regions. On the other hand, rise in temperature
initially increases and then decreases the microviscosity throughout,
and at elevated temperatures the effect of urea is being dominated
by the effect of temperature, thereby establishing the counter effects
of temperature and urea on the F127 micellar system