The Flory-Huggins interaction parameter, , is often used in the literature to describe the binary interactions of polymer blends, yet to what extent does this widespread analysis yield valuable thermodynamic insight? In this work we think critically about and creatively about alternatives. Making use of a simple lattice theory to model binary polymer mixtures, we follow a different, less ambiguous route and show connections between the microscopic characteristic parameters of a system and its macroscopic thermodynamic behavior. To this end we analyze experimental data, including results from neutron scattering experiments, cloud point curves, and pressure-volume-temperature (PVT) surfaces for a series of blends, including deuterated polystyrene/poly-(tetramethyl bisphenol A polycarbonate) (dPS/TMPC), deuterated polystyrene/poly(vinyl methyl ether) (dPS/ PVME), polystyrene/polybutadiene (PS/PB), deuterated polystyrene/poly(p-methylstyrene) (dPS/PpMS), polypropylene/ deuterated head-to-head polypropylene (PP/dhhPP), polystyrene/deuterated polystyrene (PS/dPS), polystyrene/ polychlorostyrene (PS/PCS), deuterated poly(methylbutylene)/poly(ethylbutylene) (dPMB/PEB), and poly(ethylmethylsiloxane)/deuterated poly(dimethylsiloxane) (PEMS/dPDMS). We conclude by suggesting that there is a temperature-and concentration-independent parameter which may prove to be a more characteristic indicator of blend behavior than .
We employ a molecular mean-field theory to quantitatively understand the sizes, surfactant surface coverage, and size fluctuations of gold nanocrystals decorated with thiol surfactants of different chain lengths. Our model assumes that surfactant-coated nanoparticles are equilibrium structures. We find that packing constraints experienced by the surfactant tails are less significant for more curved (smaller) particles. This effect enables us to rationalize the experimental observations/deductions that the thiol coverage per unit area increases with decreasing particle size. The reduction of surface coverage with increasing size also explains the fact that size polydispersity increases with increasing nanoparticle size. We find that increasing the length of the surfactants results in larger nanoparticles.
We examine the effects of pressure on polymer blend miscibility for two polyolefin blends as well as for blends of polystyrene (PS) and polybutadiene (PB). Each of the blends studied exhibits an upper critical solution temperature (UCST), and for the PS/PB blend we report experimental results on the pressure dependence of the UCST for different molecular weight combinations. We make use of the Born-Green-Yvon integral equation theory to exploit the connection between the pressure dependence of the UCST and the sign of the volume change on mixing, leading us to predict that through judicious choice of polymer molecular weights the response of the UCST to pressure may be controlled.
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