Kinetic theory and the Flory–Huggins approximation

Swelling kinetics of constrained hydrogel spheres

A cross-linked polymer network immersed in a solvent will absorb molecules from its surroundings, leading to transient swelling. Under the constraint of a semi-permeable membrane, the system will swell less and generate a larger internal pressure in return, a system rarely analyzed to date. We use a nonlinear poroelastic theory to model the kinetics of swelling under mechanical constraint. We find the simulation results agree well with our experimental data using hydrogel beads made of a mixture of 3-sulfopropyl acrylate potassium salt and acrylamide, bathed in water. Understanding and predicting the response speed and the actuation stress developed during the swelling of constrained hydrogels can guide the design of polymer-based soft actuators with unusually high strength.

Molecular thermodynamics for food science and engineering

We argue that thanks to molecular modeling approaches, many thermodynamic properties required in Food Science and Food Engineering will be calculable within a few hours from first principles in a near future. These new possibilities will enable to bridge via multiscale modeling composition, process and storage effects to reach global optimization, innovative concepts for food or its packaging. An outlook of techniques and a series of examples are given in this perspective. We emphasize solute chemical potentials in polymers, liquids and their mixtures as they cannot be understood and estimated without theory. The presented atomistic and coarse-grained methods offer a natural framework to their conceptualization in polynary systems, entangled or crosslinked homo- or heteropolymers.

Phase diagrams of monomer and uv-cured difunctional-acrylate-nematic-liquid-crystal systems

This paper deals with the thermal properties of systems made of the difunctional monomer 1,6-hexanedioldiacrylate (HDDA) and the low-molecular-weight liquid crystal E7. Experimental phase diagrams of uv-cured and uncured solutions of HDDA/E7 systems are established with a polarized optical microscope and a differential scanning calorimeter and the data analyzed within a theoretical formalism that combines the Flory-Huggins model of isotropic mixing and the Maier-Saupe model of nematic order. Ultraviolet-curing samples with a difunctional monomer such as HDDA leads to a crosslinked polymer network and consequently an elastic contribution to the free energy is introduced according to the Flory-Rehner theory of rubber elasticity. The amount of liquid crystal segregated is evaluated to assess the efficiency of the phase separation mechanism.

Phase-separated composite films: experiment and theory

A different phase-separation process is capable of producing a composite system consisting of a very thin layer of liquid crystal in contact with a similarly thin layer of polymer. The morphology of the polymer depends on the composition of the prepolymer-liquid crystal mixture and the rate of polymerization. A simple one-dimensional theory is able to describe the essential features of this process.