Photothermally Responsive Poly(vinyl alcohol)/Polyaniline Nanoparticle Composite Hydrogels Prepared by a Facile Aqueous Route

Here, we report a facile, reproducible, fully aqueous route to fabricate citric acid–crosslinked poly(vinyl alcohol) (PVA) composite hydrogels incorporating polyaniline nanoparticles (PANI-NP) of ca. 200 nm mean diameter and polydispersity index (PDI) below 0.2, synthesized directly in water. Nanocomposites incorporating 2, 3, and 5% w/w PANI-NP were thoroughly characterized in terms of thickness (obtaining materials of approximately 500 µm), morphology, spectroscopic and thermal properties, surface properties, swelling behavior, and nanomechanical behavior assessed by atomic force microscopy (AFM) operating in Peak Force Quantitative Nanomechanical Mapping (PF-QNM) mode. Incorporation of PANI-NP progressively increased the elastic modulus of the composites (from 794 MPa for neat PVA to values exceeding several GPa at 3–5% w/w loading) and modified swelling capacity to values as low as 140% (from 247% for neat PVA), reflecting nanoscale interfacial interactions. Notably, the hydrogel composites exhibited significant photothermal activity under low-power near-infrared (NIR) LED irradiation (850 nm, 90 mW cm−2), achieving temperature increases of up to 13.7 °C even at low PANI-NP loadings, with a stable and reproducible response across multiple heating–cooling cycles. Overall, this work establishes a straightforward, water-based fabrication platform for structurally stable, photothermally active nanocomposites with promising potential in light-responsive smart material applications.