| Abstract
| - The effect of hydrostatic pressure on the lower critical ordering transition (LCOT) wasinvestigated by in situ small angle neutron scattering on symmetric and asymmetric diblock copolymersof perdeuterated polystyrene and poly(n-butyl methacrylate). These systems exhibit a transition fromthe disordered to ordered state upon heating. Similar to the lower critical solution transition (LCST) inpolymer mixtures, the LCOT is entropically driven and is accompanied by an increase in volume ondemixing of the copolymer blocks. As a consequence, application of hydrostatic pressure markedlyincreases the temperature at which the transition from the disordered to the ordered state occurs. Smallangle neutron scattering studies as a function of temperature and pressure show that the pressuredependence of the LCOT, ΔTLCOT/ΔP, is up to +147 °C/kbar (1.45 ± 0.07 °C/MPa), roughly 1 order ofmagnitude greater than that seen at elevated pressures for diblock copolymers exhibiting an upper criticalordering transition (UCOT). Additionally, SANS data obtained at various pressures were superimposedto generate master curves for the peak intensity, peak position, and full width at half-maximum (fwhm).This suggests an equivalence between temperature and pressure of the thermodynamic behavior of systemsthat exhibit the LCOT.
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