Abstract
Photo-thermo-mechanochemical (P-T-MCh) nanocomposites provide a mechanical and/or chemical output (MCh) in response to a photonic (P) input, with the thermal (T) flux being the coupling factor. The nanocomposite combines a photon absorbing nanomaterial with a thermosensitive hydrogel matrix. Conjugated (absorbing in the near infrared (NIR, 750–850 nm) wavelength range) polymer (polyaniline, PANI) nanostructures are dispersed in cross-linked thermosensitive (poly(N-isopropylacrylamide), PNIPAM) hydrogel matrices, giving the nanocomposite P-T-MCh properties. Since PANI is a conductive polymer, electromagnetic radiation (ER) such as radiofrequency (30 kHz) and microwaves (2.4 GHz) could also be used as an input. The alternating electromagnetic field creates eddy currents in the PANI, which produces heat through the Joule effect. A new kind of “product” nanocomposite is then produced, where ER drives the mechanochemical properties of the material through thermal coupling (electromagnetic radiation thermomechanochemical, ER-T-MCh). Both optical absorption and conductivity of PANI depend on its oxidation and protonation state. Therefore, the ER-T-MCh materials are able to react to the surroundings properties (pH, redox potential) becoming a smart (electromagnetic radiation thermomechanochemical) (sER-T-MCh) material. The volume changes of the sER-T-MCh materials are reversible since the size and shape is recovered by cooling. No noticeable damage was observed after several cycles. The mechanical properties of the composite materials can be set by changing the hydrogel matrix. Four methods of material fabrication are described.
Highlights
Composite materials are made of two materials, one dispersed in the other, which are present as two different phases [1]
If a species with strong near infrared absorption could be incorporated into the material, the absorbed radiation will be dissipated as heat triggering the coil to globule transition of the thermosensitive polymer, effectively giving the P-T-mechanical and/or chemical output (MCh) property to the new material
Crosslinked thermosensitive hydrogels of poly(n-isopropyacrylamide) nanoporous hydrogels were prepared by free radical polymerization of NIPAM (0.5 M) and 10 mM BIS as crosslinker agent, using ammonium persulfate (APS) (0.001 g/mL) and TEMED (10 μL/mL) as redox initiator and activator, respectively
Summary
Composite materials are made of two materials, one dispersed in the other (called the matrix), which are present as two different phases [1]. If a species (material or molecule) with strong near infrared absorption could be incorporated into the material, the absorbed radiation will be dissipated as heat triggering the coil to globule transition of the thermosensitive polymer, effectively giving the P-T-MCh property to the new material. Wu et al used NIR radiation to heat gels loaded with aggregated gold nanoparticles, showing an almost constant absorbance up to 820 nm [15] Since both the gold nanostructures and the hydrogel could be made by soft chemistry methods, the nanocomposite could be made by in situ formation of either component, together with the other preformed material. It is noteworthy that some of the P-T-MCh nanocomposites could be driven by other electromagnetic radiation (making them ER-T-MCh) Both gold and carbon nanostructures present large electronic conductivities. To the best of our knowledge, no ER-T-MCh materials based on Au or C nanomaterials and driven by electromagnetic radiation (microwaves, radiofrequency) have been described
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