Thermal sensitivity of carbon nanotube and graphene oxide containing responsive hydrogels

Abstract

Abstract.Comparative investigations are reported on poly(N-isopropylacrylamide) (PNIPA) gels of various carbon nanotube (CNT) and graphene oxide (GO) contents synthesized under identical conditions. The kind and concentration of the incorporated carbon nanoparticles (CNPs) influence the swelling and stress-strain behaviour of the composites. Practically independently of the filler content, incorporation of CNPs appreciably improves the fracture stress properties of the gels. The time constant and the swelling ratio of the shrinkage following an abrupt increase in temperature of the swelling medium from 20 to 50°C can be adjusted by selecting both the type and the amount of nanoparticle loading. This offers a means of accurately controlling the deswelling kinetics of drug release with PNIPA systems, and could be employed in sensor applications where fast and excessive shrinkage are a significant drawback. Both CNTs and GO enhance the infrared sensitivity of the PNIPA gel, thus opening a route for the design of novel drug transport and actuator systems. It is proposed that the influence of the CNPs depends more on their surface reactivity during the gel synthesis rather than on their morphology. One of the important findings of this study is the existence of a thermally conducting network in the GO filled gels.

Graphene derivatives in responsive hydrogels: Effect of concentration and surface chemistry

“…Similarly to earlier findings [35,36,43], the incorporation of GO effectively improved the mechanical properties and simultaneously decreased the swelling degree (Figure 2a and b). After the post-reduction treatment these properties remained almost unaffected.…”

“…In all cases the shrinkage of the nanocomposite gel disks was less than that of the pure PNIPA gel after 1000 minutes, but the difference, as well as the shape of the shrinkage curves were different for the different systems. In cases where strong interaction is presumed between the CNPs and the polymer matrix (GO@PNIPA and (GO@PNIPA)R) the slower response may be explained by the decrease of the free volume inside the nanocomposite matrix [35,45] that is caused by the increasingly hypernode-like structure. The prolonged shrinkage of the samples suggests a complex process involving the deswelling of the gel matrix, the realignment of the CNP particles and the relaxation of the polymer chains [35,36].…”

“…The pure PNIPA were synthesised from N-isopropylacrylamide (NIPA) monomer (Tokyo Chemical Industry, Japan) and N,N'-methylenebisacrylamide (BA) cross-linker (Sigma Aldrich) in aqueous medium at 20 °C by free radical polymerization, as reported previously [35,36] GO and RGO containing nanocomposite gels (GO@PNIPA and RGO@PNIPA, respectively) were prepared according to the method described earlier [35,36]. The GO loading was varied between 0 and 25 mg GO/g monomer, whereas the highest reachable concentration of RGO was only 11 mg/g monomer due to its poor dispersibility.…”

Poly(N‐isopropylacrylamide)/mesoporous silica thermosensitive composite hydrogels for drug loading and release

“…The PNIPA and PNIPA/MSN‐5 hydrogels both had a porous network structure, with the pore size in the latter case being more uniform. It was proved that the addition of MSN could adjust the pore structure of the gel like other inorganic nanoparticles . The enhanced hole structure of the PNIPA/MSN composite hydrogels relative PNIPA, both at mesoporous (2–50 nm) and macroporous (>50 nm) length scales, was expected to be advantageous for drug loading and drug release.…”

“…The use of chemical crosslinking agents is not ideal for drug delivery systems, tissue engineering, or biological separations as some crosslinking agents are toxic, such as glutaraldehyde, residual chemical crosslinking agent can negatively impact the biocompatibility of hydrogels and their phase transition behavior, limiting their usefulness . The use of inorganic nanomaterials as crosslinkers is an innovative strategy for overcoming the shortcomings of chemical crosslinkers in hydrogel synthesis, this has been proven by many research studies . Mesoporous silica nanoparticles (MSN) are inorganic nanomaterials with well‐defined internal pore structure (pores diameters typically range between 2 and 50 nm depending on the surfactant used in their synthesis).…”