Conductive, self-healing, and adhesive hydrogels are of great significance in wearable electronic devices. The most important properties of conductive self-healing hydrogels are the efficient recovery of both electrical and mechanical properties at room temperature and prolonged durability. In this work, we developed a novel double-network hydrogel consisting of poly(4styrene sulfonate-co-methyl-uracil-imidazolium) chloride (PSS-MUI), gelatin, and ferric ions (Fe 3+ ). Here, the MUI serves as a supramolecular crosslinker, while ferric ions act as ionic crosslinkers between gelatin and PSS functional groups. The hydrogel demonstrated excellent stretchability and outstanding ionic conductivity. The reversible nature of dynamic hydrogen bonding and ionic and metal coordination interactions rendered the hydrogel selfhealing ability, strong adhesion, and rapid electrical performance recovery. Variation in the Fe 3+ concentration proved to influence the time window of hydrogel processability and allowed tuning the hydrogel mechanical and ion-conducting properties. The optimal Fe 3+ ion concentration for use in a processable, ion-conducting hydrogel was found to be 2 wt %. During repeated stretching, the hydrogel showed only small changes in its electrical resistance. An electric circuit was successfully assembled onto a flexible polyurethane (PU) substrate where the power supply, light-emitting diode, and resistor were connected with the hydrogel, serving as a conductive wire. Upon breakage of the wire, simple extrusion of the hydrogel precursor into the gap yielded instant repair of the circuit. Thus, the hydrogel demonstrated suitability for use in flexible electronic devices.

Fibers were electrospun from a solution comprised of oppositely charged polyelectrolytes, in efforts to achieve highly confined macromolecular packaging. A stoichiometric ratio of poly(allylamine hydrochloride) and poly(acrylic acid) solution was mixed in an ethanol-water co-solvent. Differential scanning calorimetry (DSC) analysis of electrospun fibers demonstrated no indication of glass transition, Tg. Infrared spectroscopy (FTIR) analysis of the fibers as a function of temperature, demonstrated an amidation process at lower temperature compared to cast film. Polarized FTIR indicated a preference of the functional groups to be perpendicular to the fiber axis. These results imply formation of mixed phase fibers with enhanced conditions for intermolecular interactions, due to the highly aligned and confined assembly of the macromolecules. The tunable intermolecular interactions between the functional groups of the polyelectrolytes, impact pH-driven, reversible swelling-deswelling of the fibers. The degree of ionization of PAA at pH 5.5 and pH 1.8 varied from 85% to 18%, correspondingly, causing transformation of ionic interactions to hydrogen bonding between the functional groups. The chemical change led to a massive water diffusion of 500% by weight and to a marked increase of 400% in fiber diameter, at a rate of 0.50 μm s(-1). These results allow for manipulation and tailoring of key fiber properties for tissue engineering, membranes, and artificial muscle applications.

Wrought by nature's wondrous hand, surface topographies are discovered on all length scales in living creatures and serve a variety of functions. Inspired by floral striations, here we developed a scalable means of fabricating custom-tailored photonic cellulose films that contained both cholesteric organization and microscopic wrinkly surface topography. Free-standing films were prepared by molding cellulose nanocrystal ink onto an oriented wrinkled template through evaporation-assisted nanoimprinting lithography, yielding morphology-induced light scattering at a short wavelength as well as optically tunable structural color derived from the helical cellulose matrix. As a result, the interplay between the two photonic structures, grating-like surface and chiral bulk, led to selective scattering of circularly polarized light with specific handedness. Moreover, the wrinkled surface relief on cholesteric cellulose films could be precisely controlled, enabling engineered printing of microscopic patterned images.

Thermal conductivity (TC) enhancement of an insulating polymer matrix at low filler concentration is possible through the loading of a high aspect ratio, thermally conductive single filler. Unfortunately, the dispersion of high-aspect-ratio particles greatly influences the rheological behavior of the polymer host at relatively low volume fractions, which makes further polymer processing or mixing difficult. A possible remedy is using two (hybrid) fillers, differing in their aspect ratios: (1) a plate-like filler, which sharply increases both viscosity and TC, and (2) an isotropic filler, which gradually increases these properties. We examine this hypothesis in a thermosetting silicone rubber by loading it with different ratios, (1)/(2), of graphene nanoplatelets (GNPs) (1) and graphite powder (2). We constructed a “phase diagram” delineating two composite processability regions: solid-like (moldable) or fluid-like (pourable). This diagram may be employed to tailor the mixture’s viscosity to a desired TC value by varying the fillers’ volume fraction. The phase diagram highlights the low volume fraction value, above which the composite is solid-like (low processability) for a single high-aspect-ratio nanofiller. By using hybrid filling, one can overcome this limit and prepare a fluid-like composite at a desired TC, not accessible by the single nanofiller. Thus, it provides an indicative tool for polymer processing, especially in applications such as the encapsulation of electronic devices. This approach was demonstrated for a heat source (resistor) potted by silicon rubber graphene–graphite composites, for which a desired TC was obtained in both solid- and liquid-like regions.

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