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We report a small angle neutron scattering (SANS) study of semi-dilute aqueous solutions of sodium carboxymethyl cellulose (NaCMC), in the presence of mono-(Na +) and divalent salts (Mg 2+ , Ca 2+ , Zn 2+ , Ba 2+). A degree of substitution of 1.3 is selected to ensure that, in salt-free solution, the polymer is molecularly dissolved with conformation well described by polyelectrolyte scaling theory in semi-dilute regime. We find that Na + and Mg 2+ salt addition yield H-type phase behaviour, while Ca 2+ , Zn 2+ , and Ba 2+ instead yield L-type behaviour, in decreasing order of the salt concentration associated with demixing. Charge screening by addition of Na + induces the progressive disappearance of the characteristic polyelectrolyte correlation peak and eventually yields scattering profiles with a q −1 dependence over nearly three decades in wavenumber q. By fitting a descriptive model to data with excess Na + , we obtain a correlation length ξ'= 1030c −0.72 p [Å] with polymer concentration c p [g L −1 ]. Addition of Mg 2+ , which does not interact specifically with carboxylate groups, yields an analogous screening behaviour to that of Na + , albeit at lower salt concentrations, in line with its higher ionic strength. At low salt concentration, addition of specifically interacting Ca 2+ , Zn 2+ , and Ba 2+ yield a comparatively greater screening of the polyelectrolyte screening and, at concentrations above the phase boundary, results in excess scattering at low q, compatible with the formation of clusters of 10s nm in size. This behaviour is interpreted as due to the reduction in charge density along the chain, promoting association, clustering and eventual phase separation. Overall, drawing analogies with NaCMC at lower degree of substitution, where hydrophobic association takes place, our findings provide a framework to describe the solution conformation and phase behaviour of NaCMC in salt-free and salt solutions.

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.

We investigate the formation of poly(vinyl alcohol) microparticles by the selective extraction of aqueous polymer solution droplets, templated by microfluidics and subsequently immersed in a non-solvent bath. The role of polymer molecular mass (18-105 kg mol-1), degree of hydrolysis (88-99%) and thus solubility, and initial solution concentration (0.01-10% w/w) are quantified. Monodisperse droplets with radii ranging from 50 to 500 μm were produced at a flow-focusing junction with carrier phase hexadecane and extracted into ethyl acetate. Solvent exchange and extraction result in droplet shrinkage, demixing, coarsening and phase-inversion, yielding polymer microparticles with well-defined dimensions and internal microstructure. Polymer concentration, varied from below the overlap concentration c* to above the concentrated crossover c**, as estimated by viscosity measurements, was found to have the largest impact on the final particle size and extraction timescale, while polymer mass and hydrolysis played a secondary role. These results are consistent with the observation that the average polymer concentration upon solidification greatly exceeds c**, and that the internal microparticle porosity is largely unchanged. However, reducing the initial polymer concentration to well below c* (approximately 100×) and increasing droplet size yields thin-walled (100's of nm) capsules which controllably crumple upon extraction. The symmetry of the process can be readily broken by imposing extraction conditions at an impermeable surface, yielding large, buckled, cavity morphologies. Based on these results, we establish robust design criteria for polymer capsules and particles, demonstrated here for poly(vinyl alcohol), with well-defined shape, dimensions and internal microstructure.

This is a repository copy of Spontaneous formation of multilamellar vesicles from aqueous micellar solutions of sodium linear alkylbenzene sulfonate (NaLAS).