Light-Responsive Hybrids Based on Carbon Nanotubes with Covalently Attached PHEMA-g-PCL Brushes

Carbon nanotube (CNT)-based materials allow for the direct conversion of light into heat and then into mechanical force in the so-called photo-mechanical effect. This effect has been observed almost solely in the form of polymer (nano)composites, where CNTs act as active fillers. To overcome the issue with heterogeneous distribution, hybrids based on multiwalled carbon nanotubes (MWCNTs) covalently modified with poly(2-hydroxyethyl methacrylate)-graft-poly(ε-caprolactone) brushes (MWCNTs-PHEMA-g-PCL) were prepared, and their photo-mechanical actuator behavior, without the need for mixing with an elastomer, was proven. The MWCNTs-PHEMA-g-PCL hybrids were synthesized using the surface-initiated reversible addition–fragmentation chain transfer polymerization of 2-hydroxyethyl methacrylate, with subsequent ring-opening polymerization of ε-caprolactone from the pendant hydroxyl groups of PHEMA. It was found that the MWCNTs-PHEMA-g-PCL hybrid material containing 24 wt % MWCNTs possesses the properties of thermoplastic elastomers, while retaining their elastic properties at least up to 100 °C. It exhibits an excellent, fully reversible, repeatable, and fast photo-mechanical actuation behavior.