Small-angle neutron scattering from polymer solutions: 3. Semi-dilute solutions near the lower critical solution temperature

SANS Study of PPPO in Mixed Solvents and Impact on Polymer Nanoprecipitation

We investigate the conformation of poly(2,6-diphenyl-p-phenylene oxide) (PPPO) in good and mixed solvents by small-angle neutron scattering (SANS) across its ternary phase diagram. Dichloromethane was selected as a "good" solvent and heptane as a "poor" solvent whose addition eventually induces demixing and polymer precipitation. Below the overlap concentration c*, the polymer conformation is found to be well described by the polymer-excluded volume model and above by the Ornstein-Zernike expression with a correlation length ξ which depends on the concentration and solvent/nonsolvent ratio. We quantify the decrease in polymer radius of gyration R g , increase in ξ, and effective χ parameter approaching the phase boundary. Upon flash nanoprecipitation, the characteristic particle radius (estimated by scanning electron microscopy, SEM) is found to scale with polymer concentration as well as with nonsolvent content. Significantly, the solution volume per precipitated particle remains nearly constant at all polymer concentrations. Overall, our findings correlate ternary solution structure with the fabrication of polymer nanoparticles by nonsolvent-induced phase separation and precipitation.

Polymer and colloidal models describing structure-function relationships

Colloidal and polymer systems are not only abundant in food but also useful for gaining insights into structure-function relationships of food. Colloid and polymer systems are composed of mesoscopic scale particles dispersed in a liquid. Because of a relatively small potential barrier against aggregation between mesoscopic particles, a small change in temperature, pH, or chemical compositions can trigger aggregation and induce remarkable changes in structure and function of colloidal and polymer systems. An aggregated state is not normally an equilibrium state but a kinetically trapped state also called a jammed state. Various kinetic factors in food processing, such as the rate of changes in temperature, water content, and chemical compositions, must be taken into account to establish a complete state diagram of colloid- and polymer-based food systems.

Flexible chain molecules in the marginal and concentrated regimes: universal static scaling laws and cross-over predictions

We present predictions for the static scaling exponents and for the cross-over polymer volumetric fractions in the marginal and concentrated solution regimes. Corrections for finite chain length are made. Predictions are based on an analysis of correlated fluctuations in density and chain length, in a semigrand ensemble in which mers and solvent sites exchange identities. Cross-over volumetric fractions are found to be chain length independent to first order, although reciprocal-N corrections are also estimated. Predicted scaling exponents and cross-over regimes are compared with available data from extensive off-lattice Monte Carlo simulations [Karayiannis and Laso, Phys. Rev. Lett. 100, 050602 (2008)] on freely jointed, hard-sphere chains of average lengths from N=12-500 and at packing densities from dilute ones up to the maximally random jammed state.