Comparison of the behaviour of polymers in supercritical fluids and organic solvents via small-angle neutron scattering

Abstract

Small-angle neutron scattering has been used to study the effect of temperature and pressure on the phase behaviour of semidilute solutions of polymers dissolved in organic and supercritical solvents. Above the theta temperature (T Θ ), these systems exhibit a "good solvent" domain, where the molecules expand beyond the unperturbed dimensions in both organic solvents and in CO 2 . However, this transition can be made to occur at a critical "theta pressure" (P Θ ) in CO 2 and this represents a new concept in the physics of polymer-solvent systems. For T < T Θ , and P < P Θ , the system enters the "poor solvent" domain, where diverging concentration fluctuations prevent the chains from collapsing and allow them to maintain their unperturbed dimensions.

Critical flocculation density of dilute water-in-CO2 emulsions stabilized with block copolymers

“…In addition to lowering the UCSD and the theta density for the homopolymer in bulk CO 2 , increasing the temperature has been found to have a pronounced effect on the solvation of stabilizing tails in CO 2 , as observed both theoretically [32,64] and experimentally [38,63]. On the basis of Monte Carlo simulations, Luna-Barcenas and coworkers [32] reported that the mean square end-to-end distance of a Lennard-Jones polymer chain in an L-J solvent increased monotonically as the temperature was increased at constant density.…”

“…Yet another factor for the observed decrease in the CFD at elevated temperatures is the weakening of the dipole-dipole interactions between the PFOMA tails as temperature is increased. Temperature has been shown to have a pronounced effect on the phase behavior for both PFOA [29,56] and PDMS [31,63] homopolymers. These studies indicated a decrease in both the UCSD and the theta density as the temperature was increased, and the same trend was observed for the PFOMA homopolymer in this study (Fig.…”

“…On the basis of Monte Carlo simulations, Luna-Barcenas and coworkers [32] reported that the mean square end-to-end distance of a Lennard-Jones polymer chain in an L-J solvent increased monotonically as the temperature was increased at constant density. Using SANS, Melnichenko et al [63] measured the effect of temperature on the radius of gyration (R g ) for PDMS in bulk CO 2 . The results indicated that above the theta condition, R g increased linearly as the temperature was increased at a constant CO 2 density of 0.95 g/ml.…”

Effect of branching on the interfacial properties of nonionic hydrocarbon surfactants at the air–water and carbon dioxide–water interfaces

“…This behavior has been investigated by optical microscopy [14], turbidimetry [78][79][80], SANS [81,82], and Monte Carlo simulations [83]. When the density is held constant, the C-W c o decreases slightly as the temperature is elevated up to 70°C.…”

Polystyrene/decahydronaphthalene/propane phase equilibria and polymer conformation properties from intrinsic viscosities

“…The study of conformational properties (i.e., hydrodynamic radius) of polymers in supercritical fluids has been an area of active research. Some commonly used supercritical fluids (ScF) for polymers include carbon dioxide (CO 2 ),1–4 ethane (C2),1, 3, 5, 6 and propane (C3)1, 3, 5, 7–9 due to their relatively low‐critical temperatures and pressures. The solubility of polystyrene (PS) in these three supercritical fluids is well known 1, 5, 10.…”