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Hans Hasse (1455325)

Jadran Vrabec (1514461)

Jan Sehrt (2087545)

Jonathan Walter (2087548)

The conformation transition of poly­(<i>N</i>-isopropylacrylamide)
hydrogel as a function of the methanol mole fraction in water/methanol
mixtures is studied both experimentally and by atomistic molecular
dynamics simulation with explicit solvents. The composition range
in which the conformation transition of the hydrogel occurs is determined
experimentally at 268.15, 298.15, and 313.15 K. In these experiments,
cononsolvency, i.e., collapse at intermediate methanol concentrations
while the hydrogel is swollen in both pure solvents, is observed at
268.15 and 298.15 K. The composition range in which cononsolvency
is present does not significantly depend on the amount of cross-linker.
The conformation transition of the hydrogel is caused by the conformation
transition of the polymer chains of its backbone. Therefore, conformation
changes of single backbone polymer chains are studied by massively
parallel molecular dynamics simulations. The hydrogel backbone polymer
is described with the force field OPLS-AA, water with the SPC/E model,
and methanol with the model of the GROMOS-96 force field. During simulation,
the mean radius of gyration of the polymer chains is monitored. The
conformation of the polymer chains is studied at 268, 298, and 330
K as a function of the methanol mole fraction. Cononsolvency is observed
at 268 and 298 K, which is in agreement with the present experiments.
The structure of the solvent around the hydrogel backbone polymer
is analyzed using H-bond statistics and visualization. It is found
that cononsolvency is caused by the fact that the methanol molecules
strongly attach to the hydrogel’s backbone polymer, mainly
with their hydroxyl group. This leads to the effect that the hydrophobic
methyl groups of methanol are oriented toward the bulk solvent. The
hydrogel+solvent shell hence appears hydrophobic and collapses in
water-rich solvents. As more methanol is present in the solvent, the
effect disappears again

FigShare

Molecular Dynamics and
Experimental Study of Conformation Change of Poly(<i>N</i>-isopropylacrylamide)
Hydrogels in Mixtures of Water and Methanol

Кунцевич, М.П.

Electronic Sumy State University Institutional Repository