For environmentally-switchable adhesive systems to be reused repeatedly, the adhesive strength must not deteriorate after each adhesion cycle. An important criterion to achieve this goal is that the integrity of the interface must be retained after each adhesion cycle. Furthermore, in order to have practical benefits, reversing the adhesion must be a relatively rapid process. Here, a double-network hydrogel of poly(methacrylic acid) and poly[oligo(ethylene glycol)methyl ether methacrylate] is shown to undergo adhesive failure during pH-switchable adhesion with a grafted (brush) layer of polycationic poly[2-(diethyl amino)ethyl methacrylate], and can be reused at least seven times. The surfaces are attached at pH 6 and detached at pH 1. A single-network hydrogel of poly(methacrylic acid), also exhibits pH-switchable adhesion with poly[2-(diethyl amino)ethyl methacrylate] but cohesive failure leads to an accumulation of the hydrogel on the brush surface and the hydrogel can only be reused at different parts of that surface. Even without an environmental stimulus (i.e. attaching and detaching at pH 6), the double-network hydrogel can be used up to three times at the same point on the brush surface. The single-network hydrogel cannot be reused under such circumstances. Finally, the time taken for the reuse of the double-network hydrogel is relatively rapid, taking no more than an hour to reverse the adhesion.

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The adhesion at the aqueous interface between a polyacid hydrogel and a grafted polycation layer (brush) is shown to be reversible on the addition of sodium chloride, which screens the charges on the gel and brush. Furthermore it is shown that a double-network hydrogel both exhibits adhesive failure and stronger adhesion with the brush than a simple poly(methacrylic acid) [PMAA] hydrogel, whereas the PMAA gel undergoes cohesive failure on detachment. The adhesive force at the hydrogel-brush interface significantly increases after adding dilute salt solution (of 0.001 M). Once the concentration of salt solution is raised above 0.05 M, both the adhesive force and work done in detaching both single-and doublenetwork hydrogels from the brush surface are notably reduced. This result confirms that reversible adhesion between a hydrogel and polymer brush in salt solutions is possible, although a double-network gel is required for adhesive failure.

Selenium oxide thin films are highly transparent optical layers proper for optoelectronic technology. However, SeO2 films are rarely studied and observed suffering from clustery surface morphology, low light absorbability and low dielectric constant. For this reason herein, in an attempt to enhance its properties, platinum nanosheets (10-50 nm) are used as plasmonic substrates to grow transparent selenium oxide thin films. The films are deposited onto glass and Pt substrates using thermal evaporation technique under a vacuum pressure of 10-5 mbar. Both films of the glass/SeO2 and Pt/SeO2 are characterized by the techniques of X-ray diffraction, scanning electron microscopy, energy dispersive X-ray spectroscopy, optical spectrophotometry and impedance spectroscopy. While no significant effect of Pt nanosheets on the amorphous nature of structure of SeO2 is observed, remarkable enhancements in the light absorbability by 50 times and in dielectric constant by three times are achieved. In addition, Pt nanosheets form plasmonic interfaces resulting in improving the plasmon frequency, drift mobility and free carrier density of the films. Pt/SeO2 films showed plasmon frequency larger than 6.0 GHz and free carrier density of 1018 cm-3. Moreover, analysis of the terahertz cutoff frequency and impedance spectra have shown that the Pt/SeO2 interfaces can also be employed as terahertz receivers and as low pass filters suitable for 5G/6G technologies.