Abnormal Pressure Dependence of the Phase Boundaries in PEE−PDMS and PEP−PDMS Binary Homopolymer Blends and Diblock Copolymers

Abstract

Both polymer blends and diblock copolymers have been investigated with small-angle neutron scattering (SANS) in varying temperature and pressure fields. Four samples were studied: a polymer blend of near critical composition and the corresponding symmetric diblock copolymer of poly-(ethylethylene) (PEE) and poly(dimethylsiloxane) (PDMS) and two further symmetric diblock copolymers of poly(ethylenepropylene) (PEP) and PDMS differing in their molecular mass. From the SANS results the phase transition temperatures, the Flory-Huggins interaction parameter, the Ginzburg number, and the sizes of the chain were determined. As the transition temperature and the Flory-Huggins parameter are independently determined from the SANS data, the Clausius-Clapeyron equation offers a cross-check of the theoretical background used for SANS analysis. The resulting parameters showed for all samples qualitatively similar behavior. In particular, a quite unusual decrease of the phase boundaries in low increasing pressure regimes was observed. Analysis based on the Clausius-Clapeyron equation shows that the reason for this pressure-induced decrease of the phase boundary is a dominating increase of the entropic Flory-Huggins parameter. The Ginzburg parameter was found constant with pressure. The size of the diblock copolymer chains changes with temperature and pressure. Beyond the chain stretching observed near the ordering temperatures (T ODT) for both decreasing temperature and applied pressure, a discontinuous decrease of the chain size was consistently found at the TODT. The chain size vs temperature was found to follow a scaling behavior with slightly different exponents in the disordered and the ordered regimes consistent with former simulation calculations.

Pressure-Induced Phase Transitions of Hydrophobically Solvated Block-Copolymer Solutions

“…The measure of the miscibility is the so-called Flory interaction parameter, , and the temperature and concentration dependence of MST can be quantitatively discussed with this parameter [10]. Pressure P is also an environmental parameter governing the phase behavior of block copolymers, and a number of works are reported on pressure-induced microphase separation of blockcopolymer systems [11][12][13][14]. Steinhoff et al [12] and Schwahn et al [13] observed a reentrant shift of the order-disorder transition temperature in block-copolymer melts.…”

“…Pressure P is also an environmental parameter governing the phase behavior of block copolymers, and a number of works are reported on pressure-induced microphase separation of blockcopolymer systems [11][12][13][14]. Steinhoff et al [12] and Schwahn et al [13] observed a reentrant shift of the order-disorder transition temperature in block-copolymer melts. However, to our knowledge, there have been no papers that deal with pressure-induced microphase separation of block-copolymer aqueous solutions by focusing on hydrophobic solvation.…”

Thermodynamics and Kinetic Processes of Polymer Blends and Block Copolymers in the Presence of Pressurized Carbon Dioxide

“…[90] Since the UCST/UDOT systems are characterized by endothermic mixing (DH mix > 0), a negative DV mix shifts the UCST/UDOT to a lower temperature, whereas a positive DV mix serves to increase the UCST/UDOT, with increasing P. [90] Both pressure-induced increases [84,[90][91][92][93] and decreases [90,94] in UCST/UDOT have been experimentally observed. Complex P-T relationships wherein the temperature initially decreases and then increases upon pressurization have likewise been reported for UCST/UDOT [95,96] and LCST/LDOT systems. [97,98] …”

Influence of high pressure on higher-order structures of poly(oxyethylene) in its blend with poly(d,l-lactide)

“…Most experiments under pressure have been performed to elucidate the effect of pressure on miscibility of polymer blends [10][11][12][13][14][15]. Almost no researches had been done on the details of nano-structures of PLA/PEG blends under pressure.…”