Real-Time Monitoring of Chemical and Topological Rearrangements in Solidifying Amphiphilic Polymer Co-Networks: Understanding Surface Demixing

Abstract

Amphiphilic polymer co-networks provide a unique route to integrating contrasting attributes of otherwise immiscible components within a bicontinuous percolating morphology and are anticipated to be valuable for applications such as biocatalysis, sensing of metabolites, and dual dialysis membranes. These co-networks are in essence chemically forced blends and have been shown to selectively phase-separate at surfaces during film formation. Here, we demonstrate that surface demixing at the air-film interface in solidifying polymer co-networks is not a unidirectional process; instead, a combination of kinetic and thermodynamic interactions leads to dynamic molecular rearrangement during solidification. Time-resolved gravimetry, low contact angles, and negative out-of-plane birefringence provided strong experimental evidence of the transitory trapping of thermodynamically unfavorable hydrophilic moieties at the air-film interface due to fast asymmetric solvent depletion. We also find that slow-drying hydrophobic elements progressively substitute hydrophilic domains at the surface as the surface energy is minimized. These findings are broadly applicable to common-solvent bicontinuous systems and open the door for process-controlled performance improvements in diverse applications. Similar observations could potentially be coupled with controlled polymerization rates to maximize the intermingling of bicontinuous phases at surfaces, thus generating true three-dimensional, bicontinuous, and undisturbed percolation pathways throughout the material.

Dynamic Covalent Star Poly(ethylene glycol) Model Hydrogels: A New Platform for Mechanically Robust, Multifunctional Materials

“…Figure shows a photograph of the three water-equilibrated gels: the pure tetraPEG DYNAgel, the one modified with 10 mol % with the PDMS derivative, and the other with 50 mol %, displaying aqueous degrees of swelling of 16, 10, and 8, respectively. More importantly, the amphiphilic − character of the modified gels, together with the segmented nature of the PEG and PDMS components, is expected to lead to their aqueous phase separation on the nanoscale which is under investigation.…”

Amphiphilic Polymer Conetwork Gel Films Based on Tetra-Poly(ethylene Glycol) and Tetra-Poly(ε-Caprolactone)

“…The information of phase separation at the surface of the investigated ACN gel films can be combined with the observation that water droplets sit on the dry gel surface before they slowly penetrate the gel and the water droplet spreads. One could argue the presence of hydrophobic domains at the gel-air interface that prevent the transport of solvents, as has been reported by Guzman et al [30,31]. In contrast, toluene immediately spreads and penetrates gel films.…”

“…In situ changes in morphology while changing external parameters were observed using GISAXS [29]. The importance of distinguishing between bulk and surface structure was highlighted by Guzman et al [30,31], who demonstrated that gels from copolymers with a hydrophilic backbone and hydrophobic side chains form a hydrophobic layer at the surface during thin film formation. This hydrophobic layer serves as a barrier for solvent transport in the network.…”

Self‐Healing Functional Surfaces

“…Combining several techniques could be a good alternative to acquire more quantitative or in‐depth knowledge on the surface healing processes, namely on the kinetics of the healing mechanism and time‐frames required for an optimal SHE. Interesting possibilities could be to couple water CA measurements with in‐depth resolved spectroscopy techniques, such as XPS and atomic force microscopy (AFM), which have been used for instance to study the temperature dependence of the surface reorganization of amphiphilic block copolymers in air and in water, or time‐resolved gravimetry and negative out‐of‐plane birefringence, as used by Guzman et al to understand surface demixing on amphiphilic polymer conetworks.…”