posted on 2021-02-05, 17:36authored bySwarit Dwivedi, Jitendra Mata, Samir H. Mushrif, Alan L. Chaffee, Akshat Tanksale
Methanol–Water (mw) mixtures,
with or without a solute,
display a nonideal thermodynamic behavior, typically attributed to
the structure of the microphase. However, experimental observation
of the microphase structures at the molecular length scale has been
a challenge. We report the presence of molecular clusters in mw and
formaldehyde–methanol–water (fmw) mixtures using small-angle
neutron scattering (SANS) experiments and molecular dynamics (MD)
simulations. Hydrophobic clusters of methanol in mw and formaldehyde–methanol
in fmw mixtures were observed at low methanol compositions (xm ≤ 0.3). A three-dimensional hydrogen-bonded
network of water with the solute is observed at xm = 0.5. Linear chains of methanol surrounding the formaldehyde
and water molecules were observed at high methanol compositions (xm ≥ 0.7). The calculated size of the
molecular clusters (r ≈ 0.5 nm, spherical)
from the SANS data and their volume fraction closely matched the MD
simulation results.