Changli Lü

High refractive index organic–inorganic nanocomposites: design, synthesis and application

Organic–inorganic nanocomposites with high refractive index (RI) are typically constructed by integrating high RI inorganic nanoscale building blocks into a processable, transparent organic matrix. These nanocomposites combine the numerous advantages of organic and inorganic components, and have many promising applications in optical design and advanced optoelectronic fabrication. A substantial amount of work has been performed in this area. This Feature article summarizes the general design principles and different fabrication approaches of high RI nanocomposites, and reviews recent research advances and some important optical applications of these nanocomposites.

Preparation and characterization of ZnS–polymer nanocomposite films with high refractive index

Novel ZnS–poly(urethane-methacrylate macromer) n(PUMM) nanocomposite films with high refractive index were prepared by incorporating thiophenol (PhSH)–4-thiomethyl styrene (TMSt)-capped ZnS nanoparticles into a urethane-methacrylate macromer (UMM), followed by spin-coating and ultraviolet radiation initiated free radical polymerization. PhSH–TMSt-capped colloidal ZnS solution was synthesized by reacting zinc acetate with H2S in N,N-dimethylformamide. UMM macromer was synthesized by reacting 2-hydroxyethyl methacrylate (HEMA) with isocyanate group terminated polythiourethane oligomer which was obtained from polyaddition of 2,2′-dimercaptoethyl sulfide (MES) with 2,4-tolylene diisocyanate (TDI). Thiol-capped ZnS nanoparticles were characterized and found to be 2.0–5.0 nm in diameter with a cubic phase structure. The chemical composition of these ZnS nanoparticles was determined to be Zn2+ n∶ S2− n∶ RS− n= 1 ∶ 0.6 ∶ 0.6 using chemical analysis methods. The weight fraction of ZnS nanoparticles in the films was measured by TGA, and it accords well with that of theoretical calculation. FTIR and DSC studies show that ZnS nanoparticles were successfully immobilized into the polymer matrix and the resulting nanocomposite films have a good thermal stability. TEM images indicate that the ZnS nanoparticles were uniformly dispersed in the polymer matrix and the particles remained their original size (2–5 nm) before incorporation into the polymer matrix. The XPS depth profiling technique demonstrates that the ZnS nanoparticles were also dispersed homogeneously in the depth scales of the polymer matrix. The nanocomposite films show high optical transparency in the visible region (T > 95% at 550 nm) and high refractive index in the range of 1.645–1.796 at 632.8 nm as the content of thiol-capped ZnS nanoparticles linearly increased from 0 to 86 wt%.

High refractive index thin films of ZnS/polythiourethane nanocomposites

High refractive index optical thin films of nano-ZnS/polythiourethane (PTU) composites have been prepared via immobilization of thiophenol (PhSH)/mercaptoethanol (ME)-capped ZnS nanoparticles into a PTU matrix. PhSH/ME-capped ZnS particles with a diameter of 2–6 nm were synthesized by reacting zinc acetate with H2S in N,N-dimethylformamide. The nanocomposite films with high refractive index were prepared by adding an isocyanate group terminated PTU oligomer, which was synthesized by polyaddition of 2,2′-dimercaptoethylsulfide (MES) and isophorone diisocyanate (IPDI), to a DMF solution containing colloidal ZnS particles, and followed by spin-coating and multi-step heat curing. FTIR studies show that the ZnS nanoparticles were successfully immobilized into the polymer matrix. TGA results indicates that the nanocomposite films have a good thermal stability and the weight fraction of ZnS particles in the films is well in accordance with that of theoretical calculations. TEM studies suggest that the ZnS nanoparticles with a diameter of 2–6 nm were well dispersed in the PTU matrix and maintained their original size before immobilization. The refractive index of the transparent ZnS/PTU nanocomposite films was in the range from 1.574 to 1.848 at 632.8 nm, which linearly increased with the content of PhSH/ME-capped ZnS from 0 to 97 wt%.

Biomimetic polyimide nanotube arrays with slippery or sticky superhydrophobicity

In this paper, we report the fabrication of superhydrophobic polyimide (PI) nanotube arrays with different topographies, which possess slippery or sticky superhydrophobicity. The PI nanotube arrays were fabricated by the porous alumina membrane molding method. We regulated three kinds of solvent evaporation and drying processes, which controlled different congregated and noncongregated topographies of PI nanotube arrays. Large scale comb-like congregated topography possesses a small sliding angle (SA<5 degrees), small scale comb-like congregated topography possesses a medium sliding angle (SA is about 30 degrees), noncongregated topography possesses a large sliding angle (strong adhesive force to water droplet). Moreover, the as-prepared superhydrophobic PI nanotube arrays have remarkable resistivity to acid, weak base, high temperature (up to 350 degrees C) and various organic solvents. Our work provides a facile and promising strategy to fabricate superhydrophobic surfaces with controlled sliding angles by utilizing self-organization effect, and such high performance superhydrophobic PI nanotube arrays can be used as coating materials in various harsh conditions.

White light emission from Mn2 + doped ZnS nanocrystals through the surface chelating of 8-hydroxyquinoline-5-sulfonic acid

White light emitting semiconductor nanocrystals (NCs) have been successfully synthesized from 8-hydroxyquinoline-5-sulfonic acid (HQS) decorated manganese doped ZnS NCs through fine tuning the surface-coordination emission and dopant emission of the NC host. The HQS functionalized manganese doped ZnS NCs (QS-ZnS:Mn), with a cubic crystal structure, have the same diameter of about 4.0 nm as ZnS:Mn NCs without HQS. The intensity of the surface-coordination emission peak increased with increasing HQS content or augmenting excited wavelength. The emission of white light was achieved by carefully controlling the dosage of HQS in NCs and appropriately tuning the excited wavelength. The color coordinates (0.35, 0.34) for the efficient white light emitting NCs were very close to the ideal Commission Internationale de lEclairage (CIE) chromaticity coordinates for pure white light (0.33, 0.33). The photoluminescence (PL) decay study revealed that the white light emitting NCs exhibited maximum lifetime values at different emission peaks for different NC samples. The study results also indicated that the HQS molecules were attached to the surface of ZnS:Mn NCs in a single coordination fashion due to the steric hindrance effect of the special spherical surface of NCs, which made the QS-ZnS:Mn NCs possess stable and high fluorescent properties in different organic solvents as compared with the conventional small molecule complexes.

The research on syntheses and properties of novel epoxy/polymercaptan curing optical resins with high refractive indices

Abstract A novel thioether glycidyl resin bis[3-(2,3-Epoxypropylthio)phenyl]-sulfone (BEPTPhS) with high refractive index was synthesized by condensation of bis(3-mercaptophenyl)sulfone (BMPS) with epichlorohydrin. Its structure was characterized by FTIR, MS and NMR. It was the first time that trimercaptothioethylamine (TMTEA) was used as curing agent to cure epoxy resins. Optical resins possessing high refractive index were prepared by curing diglycidyl ether of bisphenol A (DGEBA) with the mixture of TMTEA and ethylendiamine (EDA) and by curing BEPTPhS/DGEBA with TMTEA. The research on the optical properties of resins of DGEBA cured by the mixtures of TMTEA and EDA indicated that these resins possess higher refractive index (nd>1.60), lower dispersity (νd>34), high impact strength (IPS>30xa0kJxa0m−2) and higher transmittance. The nd, νd and density of these resins varied linearly with the EDA content in the curing agent mixtures. The optimum ratio of the EDA content to that of TMTEA is 20:80 (molar ratio), at this ratio the cured resin has the optimum optical properties (nd20=1.61, vd=35.4). The cured resins of BEPTPhS/TMTEA have a high refractive index (the highest is nd=1.67). The optical, physical and thermal properties of the cured optical resins of BEPTPhS/TMTEA were discussed in this paper.

A facile one-pot route to transparent polymer nanocomposites with high ZnS nanophase contents via in situ bulk polymerization

Transparent polymer nanocomposites with high ZnS nanophase contents were prepared by a facile one-pot route. Compared with other methods, this method is easier to control. The structure, morphology, thermal and optical properties of the obtained nanocomposites were characterized. The results showed that the ZnS nanoparticles with an average size of 3 nm were dispersed uniformly in the polymer matrix. The ZnS nanoparticles and the polymer matrix were linked by covalent-bonds, which improved the nanocomposite’s thermal behavior and mechanical properties. Due to the controlled structure and ZnS content, the nanocomposites had good transparency and the refractive index was continuously adjustable.

Preparation and properties of transparent bulk polymer nanocomposites with high nanophase contents

Transparent bulk polymer nanocomposites with high contents of ZnS nanoparticles (NPs) were prepared by free radical initiated in-situ bulk polymerization of N,N-dimethylacrylamide (DMAA), styrene (St) and divinylbenzene (DVB) using 2,2′-azobisisobutyronitrile (AIBN) as initiator in the presence of 2-mercaptoethanol (ME) capped ZnS NPs. The structure and properties of the nanocomposites were studied. Sphalerite ZnS NPs with average size of about 3nm were dispersed homogeneously in polymer matrices. The ME capped ZnS nanophase reached 30 wt%, while the bulk nanocomposites still exhibited good transparency in the visible light range. TGA study showed that the nanocomposite materials had excellent thermal stability below 245 °C. Dynamic mechanical analysis and pencil hardness studies showed that the materials had good mechanical properties. However, with the increase of the ME capped ZnS content, the glass transition temperature of the nanocomposites decreased probably due to the plasticizing effect of the ME capped ZnS NPs. Refractive indices of the nanocomposite materials increased from 1.536 for the matrix to 1.584 upon increasing the weight fraction of the ME capped ZnS NPs to 30 wt%.

APhen-functionalized nanoparticles–polymer fluorescent nanocomposites via ligand exchange and in situ bulk polymerization

A series of APhen-functionalized ZnS nanoparticles (NPs)–polymer transparent nanocomposites with tunable fluorescent emission were prepared via ligand exchange and in situ bulk polymerization. The APhen-ZnS NPs were synthesized from the mercaptoethanol (ME)-capped ZnS nanoparticles (ME–ZnS NPs) and 5-amino-1,10-phenanthroline (APhen) by a ligand-exchange process. The APhen–ZnS NPs still had a cubic crystal structure and a diameter of about 3.0 nm as before functionalization of ME–ZnS NPs. The fluorescent emission of APhen–ZnS NPs exhibited a red shift at 550 nm as compared to ME–ZnS NPs (423 nm) and APhen (473 nm). The APhen–ZnS NPs were incorporated into different polymer matrix by in situ bulk polymerization. TEM results showed that the NPs were uniformly dispersed in the polymer matrix without aggregation. It was found that the nanocomposites exhibited a dependence of photoluminescence properties on the concentration of NPs in polymer and the composition of polymer. As the methacrylic acid (MAA) and glycidyl methacrylate (GMA) as co-monomers were introduced in polymer matrix, the emission peaks of APhen–ZnS NPs–polymer nanocomposites had a blue shift. These transparent nanocomposites with tunable photoluminescence can be potentially used for the fabrication of optical and optoelectronic devices.

Fabrication of thermo-responsive polymer functionalized reduced graphene oxide@Fe3O4@Au magnetic nanocomposites for enhanced catalytic applications

A novel strategy was developed to fabricate thermo-responsive copolymer functionalized reduced graphene oxide@Fe3O4@Au magnetic nanocomposites (Au NPs@GFDP) for highly efficient catalysis. Superparamagnetic Fe3O4 nanoparticles (NPs) on reduced graphene oxide (RGO@Fe3O4) were obtained via a one-pot chemical functionalization method. RGO@Fe3O4 was coated with dopamine (DA) to generate polydopamine (PDA) modified RGO@Fe3O4 (GFD) through a combination of mussel inspired chemistry of dopamine in a weakly alkaline aqueous solution. The thermo-responsive polymer of poly(N-isopropylacrylamide-co-2,3-epithiopropyl methacrylate) P(NIPAM-co-ETMA) (P) was synthesized via a reversible addition fragmentation chain transfer (RAFT) polymerization and was facilely grafted onto the surface of GFD through a Michael addition reaction. The final gold nanoparticle (Au NP) functionalized GFDP nanocomposites were obtained through in situ reduction of gold precursors in GFDP solution using the episulfide groups of P(NIPAM-co-ETMA) as a ligand. The Au NPs@GFDP nanocomposite exhibited excellent dispersibility and stability in aqueous solutions. More importantly, the obtained nanocomposite also displayed easy recyclability because of the existence of Fe3O4 NPs and a higher catalytic efficiency for the reduction of nitrophenols over the Au NPs@RGO@Fe3O4 and Au NPs@GO without polymer modification. Au NPs@GFDP modified with PNIPAM also exhibited excellent temperature-responsive behavior for the catalytic reduction of nitrophenol. Therefore, the strategy described in this work may be of great potential for various industrial catalytic applications.