posted on 2021-02-08, 19:07authored byNikolaos
A. Burger, Antonios Mavromanolakis, Gerhard Meier, Patrick Brocorens, Roberto Lazzaroni, Laurent Bouteiller, Benoit Loppinet, Dimitris Vlassopoulos
We
utilize dynamic light scattering (DLS) and passive microrheology
to examine the phase behavior of a supramolecular polymer at very
high pressures. The monomer, 2,4-bis(2-ethylhexylureido)toluene (EHUT),
self-assembles into supramolecular polymeric structures in the nonpolar
solvent cyclohexane by means of hydrogen bonding. By varying the concentration
and temperature at atmospheric pressure, the formation of the viscoelastic
network (at lower temperatures) and predominantly viscous phases,
based on self-assembled tube and filament structures, respectively,
has been established. The associated changes in the rheological properties
have been attributed to a structural thickness transition. Here, we
investigate the effects of pressure variation from atmospheric up
to 1 kbar at a given concentration. We construct a temperature–pressure
diagram that reveals the predominance of the viscoelastic network
phase at high pressures. The transition from the viscoelastic network
organization of the tubes to a weaker viscous-dominated structure
of the filaments is rationalized by using the Clapeyron equation,
which yields an associated volume change of about 8 Å3 per EHUT molecule. This change is further explained by means of
Molecular Dynamics simulations of the two phases, which show a decrease
in the molecular volume at the filament-tube transition, originating
from increased intermolecular contacts in the tube with respect to
the filament. These findings offer insights into the role of pressure
in stabilizing self-assemblies.