Synthesis Of Polypyrrole Nanomaterials And Their Applications As Near-Infrared Photoabsorbing Materials

Near-infrared-absorbing materials, which can effectively absorb the near-infrared light(700nm-2.5μm) and convert the near-infrared light which have been widely applied in the fields of energy-saving, environmental and biomedical materials, etc.. At present, two types of NIR absorbing materials have been mainly developed. One is inorganic materials, such as noble metal nanoparticles(Au, Ag, Pd), semiconductors(Cu-based, W-based), metal-oxide semiconductor nanomaterials(ITO,ATO, and AZO) and carbon materials. These materials can absorb part of NIR light, however, these NIR absorbing inorganic materials still have some shortcoming. Metal nanomaterials are expensive, unable to be degraded, poor metabolizers. And carbon materials require surface modification, so the synthesis process is too complicated. The second one is organic materials, such as indocyanine green(ICG), polyaniline, melanin, polypyrrole(PPy), etc. They exhibit excellent biocompatibility, optical stability and excellent NIR shielding properties(range 1000-2700 nm). Polypyrrole as an organic conjugated polymer has excellent NIR absorption properties and biocompatibility, which has significant potential applications in energy environmental protection and bio-treatment. In this paper, we have designed a synthesis for PPy nanoparticles by a modified one-step aqueous dispersion polymerization method and explored PPy applications in NIR shielding films with smart composite microgels. Main works have been listed as follows:Part 1: PPy nanoparticles have been synthesized by a modified one-step aqueous dispersion polymerization method, where the deionized water is used as the solvent, pyrrole is used as the reactant, polyvinyl alcohol(PVA) as a stabilizer and FeCl3 as oxidizing agent. It was characterized by SEM, TEM, FTIR, and UV-vis-NIR ect. As we expected, the prepared PPy nanoparticles(PPy NPs) have a uniform size(~50 nm), good dispersion and exhibits intense NIR absorption. Deionized water dispersion containing PPy NPs(60 μg mL-1) exhibits a temperature increase of 64.5 °C in 6 min under the irradiation of 880 nm laser with the intensity of 0.5 W cm-2. Whereas, deionized water exhibits a temperature increase of 4.7 °C under the other identical conditions. These facts suggest that PPy NPs exhibit higher NIR photoabsorption intensity and photothermal conversion performances.Part 2: We designed and synthesized PPy nanoparticles via mixing with polyacrylic acid(PAA) resin for the preparation of PPy-PAA full-polymer and UV/NIR shielding films. Based on the foundation of the first part, PPy nanoparticles are mixed with polyacrylic acid(PAA) resin for the preparation of PPy-PAA full-polymer films. PPy-PAA films exhibit good transparency in visible region(400-780 nm) but can efficiently absorb UV(305-400 nm) and NIR(780-2500 nm) light, for example, 0.34-mm-thick film with 0.05 wt% PPy can transmit 63.1% visible light but shield 47.2% UV and 80.9% NIR light. When this PPy-PAA film coated glass is used as the window of the sealed black box, the interior air temperature of the box goes up from room temperature of 25.0 °C to 29.2 or 33.9 °C in 1500 s under the irradiation of strong solar light(0.3 or 0.5 W cm-2). Its temperature elevation(4.2 or 8.9 °C) is remarkably lower compared with that(7.3 or 15.7 °C) from quartz glass as window under the other identical condition, resulting from excellent NIR shielding property of PPy. Therefore, PPy nanoparticles have great potential as a novel UV/NIR shielding material for the development of cost-efficient energy-saving full-polymer windows without potential heavy-metal pollution.Part 3: We synthesized chitosan-poly(N-isopropylacrylamide)(CS-PNIPAM) composite temperature-sensitive microgels. Above all, CS-PNIPAM microgels(a mean size ~ 50 nm) have been synthesized by surfactant-free emulsion polymerization route, where the deionized water is used as the solvent, CS and NIPAM is used as the reactant, sodium dodecyl sulfate(SDS) are used as surfactants, and ammonium persulphate(APS) as initiator. Based on the foundation of the microgels, PPy nanoparticles with diameter of 2-5 nm are synthesized by a simple solution polymerization route and the nanoparticles uniform growth/adsorb in CS-PNIPAM microgels surface. The smart composite microgels also exhibit strong absorption in NIR region and volume phase inversion temperature(VPIT) at about 38°C. Furthermore, the as-prepared microgels exhibit excellent photothermal performance under 808 nm laser. The temperature increased from room temperature from 21°C to 115°C with 60 μg mL-1 PPy composite microgels for 6 minuters’ under the irradiation. The temperature elevation(94°C) is remarkably higher compared with that(6.9 °C) from deionized water as solution under the other identical condition. Therefore, PPy-PNIPAM/CS full-polymer smart composite microgels have great potential as a novel NIR absorption materials for the design and development of photothermal treatment.