Coil-globule transitions drive discontinuous volume conserving deformation in locally restrained gels

Abstract

The equilibrium volume of a thermoresponsive polymer gel changes dramatically across a temperature due to the coil–globule transitions of the polymers. When cofacially oriented nanosheets are embedded in such a gel, the composite gel deforms at the temperature, without changing the volume, and the response time is considerably shorter. We here theoretically predict that the deformation of the composite gel results from the fact that the nanosheets restrain the deformation of some polymers, while other polymers deform relatively freely. The unrestrained polymers collapse due to the coil–globule transitions and this generates the solvent flows to the restrained regions. The response time of this process is rather fast because solvent molecules travel only by the distance of the size of a nanosheet, instead of permeating out to the external solution. This concept may provide insight in the physics of composite gels and the design of thermoresponsive gels of fast response.

Versatile Approach to Well-Defined Oligofluorenes and Polyfluorenes with Low Dispersity

“…Temperature-dependent absorption and emission measurements in the mTHF solution confirmed the expected increase of the critical transition temperature from the amorphous phase to the β-phase as a function of the number of repeat units according to the Sanchez model. We note that only few studies exist on the coil-to-globule transition for more rigid polymers, while there is an abundance of studies on flexible polymers. − A major difference of more rigid polymers is that they first expand before collapsing, as evidenced by the bathochromic shift of the transition energies. This behavior has been predicted in simulations yet is not always appreciated in the community.…”

Temperature Dependence of Polymer Network Diffusion

“…Our findings demonstrate a nontrivial similarity between the statics and dynamics of polymer networks. Furthermore, our findings provide new insights into the so-called diffusio-mehcanical (or stress-diffusion) coupling [32][33][34][35] and further advance practical applications of stimuli-responsive gels, such as sensors and actuators [3,4], because the swelling dynamics can determine the swelling response time.…”

Enthalpic and Entropic Contributions to Fast Lithium Ion Conduction in Solid-State Aqueous Polymer Electrolytes

“…Such high water content is also found in the temperature-induced water uptake in a proton exchange membrane at high temperatures. 18,19 Also, Widstrom et al 20 discussed a water-rich phase forming in high-molecular-weight polymer/water-in-salt systems. The virtual spheres of various sizes are inserted into the spaces between the polymers to identify the water tubes along with their size estimates.…”