Composite Films Based on Aligned Carbon Nanotube Arrays and a Poly(N-Isopropyl Acrylamide) Hydrogel

Hybrid materials based on carbon nanotubes (CNTs) and polymers, which integrate the unique characters and functions of these two types of components, have shown improved properties and potential applications in many fields. However, the aggregation of CNTs in the polymer matrix is always a big problem in the preparation of composites. It has been proven that using CNT arrays instead of random CNTs can remarkably improve the dispersion and alignment of CNTs in polymer matrix. As a result, such composites usually exhibit orientation-related extraordinary properties and can be applied as flexible field-emission devices, thermal conducting pads, microelectromechanical devices, chemical vapor sensors, and switchers for ion transportation. Hydrogels, as a type of biocompatible polymers, have wide applications in biological and medical fields. Composites based on hydrogels have shown many exciting properties. An actuation system based on sub-micrometer-sized silicon columns with a hydrogel layer was demonstrated to show humidity-responsive behavior. Preliminary investigations have already shown that CNT/hydrogel composites having potential for biosensors, actuators, and tissue engineering. It has also been reported that bulk CNT/hydrogel composites have improved selectivity in protein electrophoresis separation owing to the hydrophobic effect of the CNTs. As hydrogels are normally temperature-responsive polymers, such composites may also present useful temperature-sensitive properties. However, the hydrophobic CNTs tend to aggregate badly in the hydrophilic hydrogel matrix. Here, we used aligned multiwalled CNT arrays instead of bulk random CNTs to fabricate composite films based on a poly(N-isopropyl acrylic amide) (PNIPAm) hydrogel. PNIPAm was chosen because it is one of the most popular and intensively studied hydrogels, and has found wide applications in many fields. As