254 results found
White RP, Aoki Y, Higgins JS, et al., 2020, Thermodynamics of model PαMSAN/dPMMA blend: a combined study by SANS, ellipsometry, and locally correlated lattice (LCL) theory, Macromolecules, Vol: 53, Pages: 7084-7095, ISSN: 0024-9297
We combine experiment and theory to elucidate how small, local, structural changes can impact miscibility in polymer blends. Small-angle neutron scattering (SANS) experiments yield both the phase boundaries and the temperature dependence of the second derivative of the free energy of mixing. We demonstrate here, for the first time, that a fundamental characterization of pure component properties can be achieved through ellipsometry measurements on films of pure polymers (thickness ∼200 nm) to provide key data on the volume (or thickness)–temperature relationships; this development is significant given the scarcity of precise pressure–volume–temperature (PVT) data on pure polymers and blends. The experimental measurements allow us to undertake a detailed thermodynamic analysis of mixing using the locally correlated lattice (LCL) theory, which has been shown to be effective in rationalizing blend miscibility in terms of the pure component properties. We focus here on polymer blends of poly(α-methyl styrene-co-acrylonitrile) (PαMSAN) with deuterated poly(methyl methacrylate) (dPMMA), which differ in the degree of tacticity in the dPMMA component (atactic or syndiotactic), leading to an increase in miscibility for the latter. By combining LCL analysis of pure and mixed systems, we are able to connect tacticity changes to shifts in local nonbonded interactions, in free volume, and in thermal expansion coefficients, which in turn impact the thermodynamic compatibility of the blend components.
Arrighi V, Higgins JS, 2020, Local effects of ring topology observed in polymer conformation and dynamics by neutron scattering-a review, Polymers, Vol: 12, ISSN: 2073-4360
The physical properties of polymers depend on a range of both structural and chemical parameters, and in particular, on molecular topology. Apparently simple changes such as joining chains at a point to form stars or simply joining the two ends to form a ring can profoundly alter molecular conformation and dynamics, and hence properties. Cyclic polymers, as they do not have free ends, represent the simplest model system where reptation is completely suppressed. As a consequence, there exists a considerable literature and several reviews focused on high molecular weight cyclics where long range dynamics described by the reptation model comes into play. However, this is only one area of interest. Consideration of the conformation and dynamics of rings and chains, and of their mixtures, over molecular weights ranging from tens of repeat units up to and beyond the onset of entanglements and in both solution and melts has provided a rich literature for theory and simulation. Experimental work, particularly neutron scattering, has been limited by the difficulty of synthesizing well-characterized ring samples, and deuterated analogues. Here in the context of the broader literature we review investigations of local conformation and dynamics of linear and cyclic polymers, concentrating on poly(dimethyl siloxane) (PDMS) and covering a wide range of generally less high molar masses. Experimental data from small angle neutron scattering (SANS) and quasi-elastic neutron scattering (QENS), including Neutron Spin Echo (NSE), are compared to theory and computational predictions.
Higgins JS, Cabral JT, 2020, A thorny problem? spinodal decomposition in polymer blends, Macromolecules, Vol: 53, Pages: 4137-4140, ISSN: 0024-9297
Aoki Y, Sharratt W, Wang H, et al., 2020, Effect of tacticity on the phase behavior and demixing of p alpha MSAN/dPMMA blends investigated by SANS, Macromolecules, Vol: 53, Pages: 445-457, ISSN: 0024-9297
We investigate the effect of polymer tacticity on the phase behavior 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 the blend’s interaction parameter). One-phase (equilibrium) and time-resolved, spinodal demixing experiments were analyzed by 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″ ≡ ∂2ΔGm/∂ϕ2) 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 = 7.4 Å, slightly larger than 6.9 Å reported for lower syndiotacticity dPMMA. Consideration of thermal fluctuations is required for the self-consistent analysis of the nontrivial 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 demixing length scale of Λ ≈ 40 nm is obtained, in agreement with the theory for deeper quenches, but deviates at shallower quenches, whose origin we discuss. CHC correctly describes demixing length and time scales, except for quenches into the vicinity of the spinodal boundary. Our data demonstrat
O'Connell RA, Porter AE, Higgins JS, et al., 2019, Phase behaviour of poly(2, 6-diphenyl-p-phenylene oxide) (PPPO) in mixed solvents, Polymer, Vol: 180, ISSN: 0032-3861
The solution phase behaviour of poly(2, 6-diphenyl-p-phenylene oxide) (PPPO) is investigated by a combination of turbidimetry, infrared spectroscopy, dynamic light scattering and densitometry, combined with calorimetry and X-ray scattering. We select dichloromethane (DCM) and heptane as, respectively, representative good and poor solvents for the polymer. This ternary system results in a miscibility gap which can be utilised for the design and fabrication of PPPO porous materials, membranes and scaffolds via phase inversion. We establish the phase diagram and resolve the kinetic solidification condition arising from the intersection between the coexistence and glass transition curves. PPPO exhibits a high 230 ∘C and is found to crystallise at 336 ∘C, and melt at 423, 445 ∘C with a double endotherm. The kinetics of demixing and (buoyancy-driven) stratification are quantified by optical imaging and the PPPO-rich phase analysed by SAXS/WAXS to resolve both amorphous and crystalline phases. Equipped with this knowledge, we demonstrate the controlled formation of nodular, bicontinuous and cellular morphologies by non-solvent induced demixing.
Aoki Y, Wang H, Sharratt W, et al., 2019, Small angle neutron scattering study of the thermodynamics of highly interacting PαMSAN/dPMMA blends, Macromolecules, Vol: 52, Pages: 1112-1124, ISSN: 0024-9297
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 (Mw) 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, G00 (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 G00 with temperature, to yield the spinodal, and inspection of Kratky plots to yield the binodal. For PαMSAN, a is determined to be 10.1±0.4 ˚A. Unsurprisingly, this system deviates strongly from Flory-Huggins expectations, exhibiting a minimal Mw dependence of the phase boundaries and φ-dependence of effective interaction parameter (˜χ). Comparison of G00 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.
Wang H, Aoki Y, Sharratt W, et al., 2019, SANS study of the thermodynamics and demixing of highly interacting PaMSAN/dPMMA blends, APS March Meeting 2019
Arrighi V, Gagliardi S, Ganazzoli F, et al., 2018, Effect of chain length and topological constraints on segmental relaxation in cyclic PDMS, Macromolecules, Vol: 51, Pages: 7209-7223, ISSN: 0024-9297
We present a detailed investigation of local dynamics of linear and cyclic poly(dimethylsiloxane) (PDMS) covering a wide range of molar masses. To aid interpretation of the experimental data, QENS measurements in the time scale from 2 to 200 ps and at Q = 0.3 to 1.8 Å–1 are complemented by theoretical calculations. These make use of a methodology developed by us elsewhere applicable to both simple chain models and real chains and applied here, for the first time, to cyclic PDMS. Analysis of the incoherent dynamic structure factor at T < Tm shows that the rotational motion of the methyl groups is unaffected by polymer topology. At higher temperatures, the QENS data are described by a model that consists of two dynamic contributions: methyl group rotation and segmental motion, the latter described by a stretched exponential function. Relaxation times of both linear and cyclic PDMS increase with increasing molar mass. Several features predicted by theory are also reproduced by the experimental data. We show, unambiguously, that rings have higher relaxation times for the segmental motion compared to linear chains of the same number of monomer units. Theoretical calculations support the idea that such slowing down of local dynamics is due to the topological constraint imposed by the ring closure, a constraint which becomes negligible for very large molar masses. Our calculations suggest that due to its albeit small conformational rigidity, cyclic PDMS undergoes an additional constraint which further increases the relaxation time, producing a shallow maximum for N ≈ 50 repeat units. A similar feature is also observed in the experimental QENS data. Values of activation energy, Ea, are derived from analysis of the temperature dependence of the quasi-elastic broadening and are found to be in agreement with viscosity measurements reported in the literature. Although the pronounced molar mass dependence of Ea for linear PDMS is certainly linked to the pres
Cabral JP, Higgins JS, 2018, Spinodal nanostructures in polymer blends: on the validity of the Cahn-Hilliard length scale prediction, Progress in Polymer Science, Vol: 81, Pages: 1-21, ISSN: 0079-6700
Spinodal decomposition of partially miscible polymer blends has the potential to generate well-defined polymeric nanostructured materials, with precise control of length scale and connectivity, and applications ranging from membranes and scaffolds to photovoltaics. In this review, we briefly summarize the theoretical basis for describing spinodal decomposition in binary polymer blends, and the parameters that determine the accessible demixing length scales and the timescales over which they develop. We then examine experimentally the validity of the classical Cahn-Hilliard (CH) theory prediction for the initial spinodal length scale, where G′′ is the second derivative of the free energy of mixing with respect to composition, and k is the ‘square gradient’ parameter, accounting for changes in free energy arising from concentration gradients. Benefitting from the perspective of over 40 years of neutron and light scattering data, and noting (remaining) misconceptions in the literature when analyzing phase separation, we examine a large collection of Λ measurements, and independent -G′′(T) and k experimental estimates. Overall, we find the CH prediction for Λ to be remarkably accurate for all blends and self-consistent conditions examined. We then summarize design considerations for generating polymeric materials via spinodal decomposition, bound by thermodynamics of available polymer systems, coarsening kinetics governed by rheology, as well as by engineering constraints. The fulfillment of the potential of this approach in the development of real functional materials demands, however, improved thermodynamic theories for polymer blends, able to quantitatively predict G′′(T) and k in terms of molecular structure and interactions.
DeFelice J, Higgins JS, Lipson JEG, 2017, The effects of branching and deuterium labeling on blend miscibility, POLYMER, Vol: 114, Pages: 149-160, ISSN: 0032-3861
Higgins JS, 2016, Neutron Scattering from Polymers: Five Decades of Developing Possibilities, ANNUAL REVIEW OF CHEMICAL AND BIOMOLECULAR ENGINEERING, VOL 7, Vol: 7, Pages: 1-28, ISSN: 1947-5438
White RP, Lipson JEG, Higgins JS, 2012, How Pure Components Control Polymer Blend Miscibility, MACROMOLECULES, Vol: 45, Pages: 8861-8871, ISSN: 0024-9297
White RP, Lipson JEG, Higgins JS, 2012, New Correlations in Polymer Blend Miscibility, MACROMOLECULES, Vol: 45, Pages: 1076-1084, ISSN: 0024-9297
Chua Y-C, Chan A, Wong H-C, et al., 2010, Thermodynamics of TMPC/PSd/Fullerene Nanocomposites SANS Study, MACROMOLECULES, Vol: 43, Pages: 9578-9582, ISSN: 0024-9297
Higgins JS, Lipson JEG, White RP, 2010, Neutron scattering as an insight to polymer mixtures, ABSTRACTS OF PAPERS OF THE AMERICAN CHEMICAL SOCIETY, Vol: 240, ISSN: 0065-7727
White RP, Lipson JEG, Higgins JS, 2010, Effect of Deuterium Substitution on the Physical Properties of Polymer Melts and Blends, MACROMOLECULES, Vol: 43, Pages: 4287-4293, ISSN: 0024-9297
Higgins JS, Lipson JEG, White RP, 2010, A simple approach to polymer mixture miscibility, PHILOSOPHICAL TRANSACTIONS OF THE ROYAL SOCIETY A-MATHEMATICAL PHYSICAL AND ENGINEERING SCIENCES, Vol: 368, Pages: 1009-1025, ISSN: 1364-503X
Cabral JT, Higgins JS, 2009, Small Angle Neutron Scattering from the Highly Interacting Polymer Mixture TMPC/PSd: No Evidence of Spatially Dependent chi Parameter, MACROMOLECULES, Vol: 42, Pages: 9528-9536, ISSN: 0024-9297
Saiani A, Novak A, Rodier L, et al., 2007, Origin of multiple melting endotherms in a high hard block content polyurethane: Effect of annealing temperature, MACROMOLECULES, Vol: 40, Pages: 7252-7262, ISSN: 0024-9297
Tambasco M, Lipson JEG, Higgins JS, 2006, Blend miscibility and the Flory-Huggins interaction parameter: A critical examination, MACROMOLECULES, Vol: 39, Pages: 4860-4868, ISSN: 0024-9297
Gretton-Watson SP, Alpay E, Steinke JHG, et al., 2006, Multi-functional monomer derived hyperbranched poly(methyl methacrylate): Kinetic modelling and experimental validation, CHEMICAL ENGINEERING SCIENCE, Vol: 61, Pages: 1421-1433, ISSN: 0009-2509
Sakai VG, Higgins JS, Trusler JPM, 2006, Cloud curves of polystyrene or poly(methyl methacrylate) or poly(styrene-co-methyl methacrylate) in cyclohexanol determined with a thermo-optical apparatus, JOURNAL OF CHEMICAL AND ENGINEERING DATA, Vol: 51, Pages: 743-748, ISSN: 0021-9568
Immanuel CD, Steinke JHG, Higgins JS, 2006, An integrated model-based analysis of polymer chemistry and polymerisation reactors, MACROMOLECULAR SYMPOSIA, Vol: 243, Pages: 225-232, ISSN: 1022-1360
Gretton-Watson SP, Alpay E, Steinke JHG, et al., 2005, Hyperbranched polymers. Synthesis, modeling, experimental validation, and rheology of hyperbranched poly(methyl methacrylate) derived from a multifunctional monomer (MFM) route, Industrial & Engineering Chemistry Research, Vol: 44, Pages: 8682-8693, ISSN: 0888-5885
Higgins JS, Tambasco M, Lipson JEG, 2005, Polymer blends; stretching what we can learn through the combination of experiment and theory, 40th International Symposium on Macromolecules, Publisher: PERGAMON-ELSEVIER SCIENCE LTD, Pages: 832-843, ISSN: 0079-6700
Gagliardi S, Arrighi V, Ferguson R, et al., 2005, On the difference in scattering behavior of cyclic and linear polymers in bulk, JOURNAL OF CHEMICAL PHYSICS, Vol: 122, ISSN: 0021-9606
Tambasco M, Lipson JEG, Higgins JS, 2004, New routes to the characterization and prediction of polymer blend properties, MACROMOLECULES, Vol: 37, Pages: 9219-9230, ISSN: 0024-9297
Cereghetti PM, Kind R, Higgins JS, 2004, Tacticity effects on the barriers to rotation of the ester methyl group in poly (methyl methacrylate): A deuteron magnetic resonance study, JOURNAL OF CHEMICAL PHYSICS, Vol: 121, Pages: 8068-8078, ISSN: 0021-9606
Bucknall DG, Higgins JS, Butler SA, 2004, Real-time neutron reflectivity study of the early stages of diffusion into and dissolution of glassy polymers, JOURNAL OF POLYMER SCIENCE PART B-POLYMER PHYSICS, Vol: 42, Pages: 3267-3281, ISSN: 0887-6266
Wacharawichanant S, Thongyai S, Tanodekaew S, et al., 2004, Spinodal decomposition as a probe to measure the effects on molecular motion in poly(styrene-co-acrylonitrile) and poly(methyl methacrylate) blends after mixing with a low molar mass liquid crystal or commercial lubricant, POLYMER, Vol: 45, Pages: 2201-2209, ISSN: 0032-3861
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