Stabilization of Supramolecular Polymer Phase at High Pressures

Abstract

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(2ethylhexylureido)toluene (EHUT), self-assembles into supramolecular polymeric structures in the non-polar solvent cyclohexane, by means of hydrogen bonding. By varying concentration and temperature at atmospheric pressure, the formation of 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. We construct a temperature-pressure diagram that reveals the predominance of the viscoelastic network phase at high pressures. The transition from viscoelastic network organization of the tubes to a weaker viscous-dominated

Competition between shear and biaxial extensional viscous dissipation in the expansion dynamics of Newtonian and rheo-thinning liquid sheets

“…This monomer has the ability to self-associate by means of hydrogen bonding in an apolar solvent (dodecane) forming supramolecular polymers. [41][42][43][44][45][46][47] As schematically shown in Fig. 1, EHUT molecules self-assemble into small and long rod-like structures whose cross section is solvent-and temperaturedependent.…”

Competition between shear and biaxial extensional viscous dissipation in the expansion dynamics of Newtonian and rheo-thinning liquid sheets

“…As non-Newtonian system, we choose wormlike micellar solutions (WLM) made of 2, 4-bis (2-ethylhexylureido) toluene, abbreviated as EHUT, dispersed in dodecane. This monomer has the ability to self-associate by means of hydrogen bonding in an apolar solvent (dodecane) forming supramolecular polymers [41][42][43][44][45][46][47] . As schematically shown in Figure 1, EHUT molecules self-assemble into small and long rod-like structure whose cross-section is solvent-and temperature-dependent.…”

Dynamics and Rheology of Supramolecular Assemblies at Elevated Pressures

“…In this work, we present a methodology to measure the high-pressure linear viscoelasticity (HP-LVE) of a supramolecular polymer in apolar solvents ( n -dodecane and cyclohexane) by means of passive DLS-microrheology in the single scattering limit. This limit can be reached if the refractive index contrast of the examined solution is low and scattering is mainly due to the added tracer particles (at very low fraction), as reported for similar systems , and for DNA-star solutions and gels . However, passive microrheology in this limit has not been explored at high pressures; therefore, we focus here on probing the dynamic structure (intermediate scattering function) of supramolecular polymer solutions at high pressures and extracting their LVE properties.…”

“…Pressure is often considered to be the “forgotten thermodynamic variable”, in part because precise experiments at high pressures are challenging; however, its impact can be significant and has been widely considered in various situations in science and technology. − It may induce microstructural changes in soft materials with consequences for their phase behavior and, especially, dynamics. Typical examples include but are not limited to polymer melts and solutions, glass-forming liquids, colloidal dispersions, self-assemblies, biomaterials, and other technologically relevant materials such as bitumen. − Focusing on rheology, a substantial increase in the viscosity of branched polyethylenes with increasing pressure was already reported in the late 1950s . Extensive studies, primarily with capillary rheology and polyolefins, have revealed the role of pressure in increasing viscosity and reducing the wall slip velocity. − The use of rotational instruments offers the advantage of giving access to the entire linear viscoelastic (LVE) spectrum as well as nonlinear viscometric material functions, but is limited to relatively low pressures (typically not exceeding 20 MPa, although some commercial rheometer vendors offer options that claim to reach 100 MPa, mostly with liquids). ,, Recently, the pressure-dependent viscosity (up to 100 MPa) in hydrogels of the host–guest type was investigated with Couette geometry in a commercial device .…”

“…The particle is chosen such that is does not adsorb on the test sample (here, a supramolecular polymer) and does sense its fluctuations (having a size larger than that of the test material). Typically, the MSD is measured by dynamic light scattering (DLS) techniques. ,− Different specialized sample cells for handling elevated pressures have been developed and utilized in neutron or X-ray scattering facilities or in conjunction with static or dynamic light scattering setups. ,− DLS-based microrheological LVE data were reported in the past, and very recently, a comprehensive study reported the design and implementation of a versatile experimental setup to obtain reliable data with fracturing fluids at pressures of up to 200 MPa . Both investigations , used passive microrheology based on diffusive wave spectroscopy (DWS).…”