High-pressure neutron scattering and random-phase approximation analysis of a molten Baroplastic diblock copolymer

초록

Through high-pressure, small-angle neutron scattering (SANS) and a random-phase approximation (RPA) theory based on a molecular model, we investigate the origin of the pressure responsiveness of a phase-segregating deuterated polystyrene-block-poly (2-ethyl hexyl acrylate) (dPS-b-PEHA) copolymer melt for use as a material for low-energy processing. The SANS intensities for the copolymer were measured over a temperature range at applied pressures between 0.1 and similar to 83 MPa. The copolymer exhibited an order-disorder transition (ODT) and revealed baroplasticity, where its ODT was suppressed upon pressurization as Delta T-ODT/Delta P approximate to -15.8 K/100 MPa to ease subsequent processing. Theory predicts that a disparity in the self interactions epsilon(jj)'s (Delta epsilon(jj) =epsilon(PS) - epsilon(PEHA)) or a disparity in the compressibilities between blocks precisely yields the observed Delta T-ODT/Delta P. The effective Flory-Huggins chi is argued to consist of the conventional enthalpic chi(H) and entropic chi(S) coming from Delta epsilon(jj) mediated by the copolymer bulk modulus. Pressure strengthens chi(H) due to densification, whereas the augmented bulk modulus reduces chi(S). The diminution of chi(S )is shown to be the source of baroplasticity.

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