Poly(methyl methacrylate) (PMMA) and poly(α-methyl styrene-co-acrylonitrile) (PαMSAN) form partially miscible blends with lower critical solution temperature (LCST) behaviour. We revisit this system using small angle neutron scattering (SANS), examining the effect of molecular weight (M w) of deuterated PMMA (dPMMA), blend composition (φ) and temperature (T) in the homogeneous region. All data are well described by the Random Phase Approximation (RPA) theory, enabling us to determine thermodynamic and structural parameters, including the correlation length ξ, G (the second derivative of the free energy of mixing with respect to composition), and the statistical segment length a of each component. Phase boundaries are computed by extrapolation of G with temperature, to yield the spinodal, and inspection of Kratky plots to yield the binodal. For PαMSAN, a is determined to be 10.1±0.4Å. Unsurprisingly, this system deviates strongly from Flory-Huggins expectations, exhibiting a minimal M w dependence of the phase boundaries and φ-dependence of effective interaction parameter (χ). Comparison of G with values for other blend systems places PαMSAN/dPMMA in a class of highly interacting blends, expected from Cahn-Hilliard theory to yield small initial phase sizes upon spinodal demixing. This is confirmed experimentally, with an illustrative temperature jump resulting in an initial phase size of 30 nm.
This is a repository copy of Spontaneous formation of multilamellar vesicles from aqueous micellar solutions of sodium linear alkylbenzene sulfonate (NaLAS).
We investigate the effect of polymer tacticity on the phase behaviour and phase separation of polymer mixtures by small angle neutron scattering (SANS). Poly(α-methyl styrene-co-acrylonitrile) (PαMSAN) and deuterated poly(methyl methacrylate) (dPMMA) with two degrees of syndiotacticity, were selected as a model partially miscible blend, as one of the most highly-interacting systems known (defined by the temperature dependence of blend's interaction parameter). One-phase (equilibrium) and time-resolved, spinodal demixing experiments, were analysed by the de Gennes' Random Phase Approximation (RPA) and Cahn-Hilliard-Cook (CHC) theory, respectively. The second derivative of the Gibbs free energy of mixing with respect to composition (G ≡ ∂ 2 ∆G m /∂φ 2) and corresponding χ parameter were obtained from both RPA and CHC analysis, and found to correlate well across the phase boundary. We find that blends with higher PMMA syndiotacticity exhibit greater miscibility, and a steeper G temperature-dependence by ∼40%. The segment length of dPMMA with higher syndiotacticity was found to be a = 7.4Å, slightly larger than 6.9Å reported for lower syndiotacticity dP-MMA. Consideration of thermal fluctuations is required for the self-consistent analysis of the non-trivial evolution of the spinodal peak position q * over time, corroborated by CHC model calculations. The temperature dependence of the mobility parameter, M , can be described by a 'fast mode' average of the diffusion coefficients of the blend constituents, except for quenches originating near the glass transition. A minimum de mixing lengthsc ale of Λ ≈ 40 nm is obtained, in agreement with theory for deeper quenches, but deviates at shallower quenches, whose origin we discuss. CHC correctly describes demixing length and timescales, except for quenches into the vicinity of the spinodal boundary. Our data demonstrate the significant effect of relatively minor polymer microstructure variations on polymer blend behaviour across both sides of the phase boundary.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.