jz7b01008_si_liveslides.zip (11.04 MB)
Role of Solvent Water in the Temperature-Induced Self-Assembly of a Triblock Copolymer
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posted on 2017-06-29, 14:23 authored by Achintya Kundu, Pramod Kumar Verma, Minhaeng ChoWater-soluble triblock
copolymers have received much attention
in industrial applications and scientific fields. We here show that
femtosecond mid-IR pump–probe spectroscopy is useful to study
the role of water in the temperature-induced self-assembly of triblock
copolymers. Our experimental results suggest two distinct subpopulations
of water molecules: those that interact with other water molecules
and those involved in the hydration of a triblock copolymer surface.
We find that the vibrational dynamics of bulk-like water is not affected
by either micellation or gelation of triblock copolymers. The increased
population of water interacting with ether oxygen atoms of the copolymer
during the unimer to micelle phase transition is important evidence
for the entropic role of water in temperature-induced micelle formation
at a low copolymer concentration. In contrast, at the critical gelation
temperature and beyond, the population of surface-associated water
molecules interacting with ether oxygen atoms decreases, which indicates
important enthalpic control by water. The present study on the roles
of water in the two different phase transitions of triblock copolymers
sheds new light on the underlying mechanisms of temperature-induced
self-aggregation behaviors of amphiphiles that are ubiquitous in nature.