Structural characterization, bandgap energy, and mechanic deformation studies of polyacrylamide (PAAm) nanocomposite hydrogels doped with homogeneously-distributed multiwalled carbon nanotubes (MWCNTs)

Hydrogels doped with carbon nanotubes (CNTs) have been widely used in many areas due to the superior properties of both hydrogels and CNTs. The synthesis of homogeneously-distributed CNTs-hydrogel nanocomposites is an important research topic because the quality of the dispersion in the structure affects all observed and measured properties. In the literature, high electrical and mechanical properties of CNTs can only be transferred to the elastic hydrogels if their homogeneous distribution in the composite networks is achieved by adding functional groups. In this work, we synthesized polyacrylamide (PAAm) hydrogels doped with homogeneously-distributed multi-walled carbon nanotubes (MWCNTs) by free-radical crosslinking copolymerization in phosphate-buffered saline (PBS) solution without any functional groups. The contents of MWCNTs varied from 0.1 to 2.5 vol% with no aggregation in the PAAm hydrogel networks. The agglomeration of MWCNTs in PAAm hydrogels was prevented by rapid polymerization with catalyzer, tetramethylethylenediamine (TEMED) effect. The homogeneous distributions of MWCNTs were observed by scanning electron microscopy (SEM). UV-Vis spectroscopy was used to investigate optical properties, bandgap energies, dispersibility, refractive index, resonance and non-resonance ratios for hydrogels doped with various MWCNTs contents. Here bandgap energies of composite hydrogels were calculated by Tauc’s relation. The results showed that bandgap energies of hydrogel composite decreased as MWCNTs contents increased. The mechanic deformation tests of the composites were also performed and it was observed that when MWCNTs increased, the elastic modulus of hydrogel composites increased. These well-dispersed composites are a potential candidate in different areas due to the higher electrical and mechanical properties of MWCNTs.