Near-infrared Responsive MoS₂/Poly（N-isopropylacrylamide） Hydrogels:Synthesis And Application

Following the exciting study of graphene,MoS2,another graphene-like two-dimensional layered inorganic nanosheets,has attracted tremendous attention due to its unique physical and chemical properties.Chemically exfoliate MoS2 combines hydrophilic nature and good photothermal properties,so it might be a good candidate to be used as a photothermal heater in composite material,which is remain to be explored.Accordingly,this thesis mainly focuses on the synthesis of Near-infrared responsive MoS2/Poly(N-isopropylacrylamide)hydrogels and their application on microvalves.The main results obtained are listed as below:(1)To achieve the remote control over the swelling/deswelling transition,chemically exfoliated MoS2 nanosheets with photothermal properties were successfully incorporated into the Poly(N-isopropylacrylamide)(PNIPAM)hydrogel by in situ polymerization.Energy dispersive X-ray spectroscopy(EDS)mapping and X-ray photoelectron spectroscopy(XPS)spectrum demonstrated that the MoS2 was homogeneous wrapped inside the PNIPAM network.Raman spectra demonstrated the existence of 1T MoS2 in the composite hydrogel.(2)The MoS2/PNIPAM composite hydrogel inherited the thermal-responsive properties from PNIPAM hydrogel.Different from the other photothermal nanomaterials,MoS2 had no oxygen-containing functional group to form hydrogen bonds with H2 O or PNIPAM chains.Besides,the hydrophilic nature of the chemical exfoliated MoS2 prevented the introduction of additional hydrophobic forces to PNIPAM.Therefore,there was no obvious change of lower critical solution temperature(LCST),swelling ratio and hysteresis.(3)Furthermore,different from the conventional thermal-responsive PNIPAM hydrogel,the MoS2/PNIPAM composite hydrogel here showed a reversible volumetric change in response to near-infrared(NIR)illumination.Based on this new composite hydrogel,a microfluidic device actuated remotely by NIR laser was also demonstrated.(4)To solve the problem of low concentration of MoS2 in MoS2/PNIPAM composite hydrogel,the MoS2 nanosheets were functionalized with mercaptosuccinic acid(MSA).The surface functionalized MoS2 nanosheets showed better dispersibility and comparable photothermal properties to MoS2 nanosheets.Then,MoS2-MSA/PNIPAM composite hydrogel was successfully fabricated.The overall loading of MoS2 in MoS2-MSA/PNIPAM composite hydrogel increased fivefold,and the corresponding NIR responsiveness was improved due to the increase of photothermal heater.