SANS Study of Polymer−Supercritical Fluid Solutions:  Transitions from Liquid to Supercritical Fluid Solvent Quality

Abstract

Phase behavior and small-angle neutron scattering (SANS) measurements are reported for poly(ethylene-co-1-butene) (PEB) dissolved in pentane, pentane plus ethane, and supercritical ethane to pressures of 2000 bar and temperatures of 130 and 150 °C. The solution microstructure and solvent quality are probed using the high-concentration isotopic labeling technique at the mixture critical concentration to determine the variation of intra-and intermolecular correlations on approach to the phase boundary with isothermal changes in pressure. The SANS results for the three solutions show that the intramolecular radius of gyration remains close to the unperturbed value over the entire pressure range investigated. However, the intermolecular correlation length changes dramatically as the phase boundary is approached and is approximately 3 times larger in ethane as compared to pentane even at 1000 bar from the phase boundary. The intermolecular correlation length data suggest that ethane is a poorer quality solvent than pentane at conditions close to the phase boundary even though both solvents have similar mass densities.

Moisture Absorption and Absorption Kinetics in Polyelectrolyte Films: Influence of Film Thickness

“…The second explanation for the difference between liquid and vapor absorption is that the solvent quality is influenced by the entropic nature of the absorbate. Recently, for n -alkane systems, the state of the fluid was found to have a significant influence on the polymer solubility, with liquids being better solvents than supercritical fluids …”

SANS study of the self-organization of gradient copolymers with ligand groups in supercritical CO2

“…SANS has been used to study polymer conformations in liquid and supercritical CO 2 [26][27][28][29][30][31][32][33][34][35] and in other supercritical fluids. 36,37 This technique is suited to study the structure of complex fluids under pressure due to the high transmission of the materials used in the construction of pressure vessels. Aggregation properties of several kinds of polymers (homopolymers, 28 graft 28 and block 26,27,[29][30][31][32][33][34][35] copolymers) in scCO 2 have been studied by SANS except gradient copolymers which were rarely studied by SANS, only in aqueous solutions [15][16][17] and never in scCO 2 .…”

High pressure cell for Bio-SANS studies under sub-zero temperatures or heat denaturing conditions

“…HP-SANS cells with a broad range of pressure and temperature capabilities find applications in the studies of biomembranes, critical to many cellular processes (for a review on HP instrumentation in this context see [7]). Other examples of applications include studies on the self-assembly of the so-called patchy colloidal particles [14,47], or studies of polymer-supercritical fluids [13].…”

“…With the present design, the neutron path length through the cell can increase by several percent for path lengths less than 3.0 mm at 300 MPa internal cell pressure, due to the elastic deformation caused by the windows pushing against the end caps. The window displacement can be easily determined as a function of pressure and temperature [13] using a high-resolution indicator gauge (Starrett Co., model . Alternatively, the amount of elastic deformation can be significantly reduced if the end caps are machined from a metal that is harder than Nitronic 50 ® , such as a grade of Inconel ® (austenitic nickel-chromiumbased superalloys).…”