Yanbin Cui

Gas barrier properties of polymer/clay nanocomposites

In the field of nanotechnology, polymer nanocomposites (PNCs) have attracted both academic and industrial interest due to their exceptional electrical, mechanical and permeability properties. In this review, we summarize the state-of-the-art progress on the use of platelet-shaped fillers for the gas barrier properties of PNCs. Layered silicate nanoclays (such as montmorillonite and kaolinite) appear to be the most promising nanoscale fillers. These exfoliated nanofillers are able to form individual platelets when dispersed in a polymer matrix. The nanoplatelets do not allow diffusion of small gases through them and are able to produce a tortuous path which works as a barrier structure for gases. The utilization of clays in the fabrication of PNCs with different polymer matrices is explored. Most synthesis methods of clay-based PNCs are covered, including, solution blending, melt intercalation, in situ polymerization and latex compounding. The structure, preparation and gas barrier properties of PNCs are discussed in general along with detailed examples drawn from the scientific literature. Furthermore, details of mathematical modeling approaches/methods of gas barrier properties of PNCs are also presented and discussed.

TLyP-1-conjugated Au-nanorod@SiO2 core-shell nanoparticles for tumor-targeted drug delivery and photothermal therapy

Mesoporous silica-coated Au nanorod (AuNR@SiO2) is one of the most important appealing nanomaterials for cancer therapy. The multifunctions of chemotherapy, photothermal therapy, and imaging of AuNR@SiO2 make it very useful for cancer therapy. In this study, AuNR@SiO2 was functionalized to deliver hydrophobic antitumor drug and to heat the targeted tumor with the energy of near-infrared (NIR). To carry out the function of targeting the tumor, tLyP-1, a kind of tumor homing and penetrating peptide, was engrafted to AuNR@SiO2. The fabricated AuNR@SiO2-tLyP-1 which was loaded with camptothecin (CPT) showed a robust, selective targeting and penetrating efficiency to Hela and MCF-7 cells and induced the death of these cells. When the micromasses of these AuNR@SiO2-tLyP-1 internalized cells were irradiated by NIR illumination, all the cells were killed instantaneously owing to the increased temperature caused by the surface plasma resonance (SPR) of the internalized AuNR@SiO2-tLyP-1. Moreover, the systematic toxicity of CPT-loaded AuNR@SiO2-tLyP-1 on human mesenchymal stem cells (hMSCs) was minimized, because the AuNR@SiO2-tLyP-1 selectively targeted and penetrated into the tumor cells, and little hydrophobic CPT was released into the culture medium or blood. This study indicates that the AuNR@SiO2-tLyP-1 drug delivery system (DDS) has great potential application for the chemo-photothermal cancer therapy.

Cross-links in carbon nanotube assembly introduced by using polyacrylonitrile as precursor.

Individual carbon nanotube (CNT) exhibits extraordinary mechanics. However, the properties of the macroscopic CNT-based structure, such as CNT fibers and films, are far lower than that of individual CNT. One of the main reasons is the weak interaction between tubes and bundles in the CNT assemblies. It is understood that the cross-links in CNT assembly play a key role to improve the performance of CNT-based structure. Different approaches have been taken to create CNT joints. Most of these approaches focus on connecting CNTs by generating new covalent bonding between tubes. In this work, we intend to reinforce the CNT network by locking the contacted CNTs. Polyacrylonitrile (PAN) was used as precursor because PAN can form graphitic structures after carbonization. The freestanding superthin CNT sheet and CNT yarn were used to evaluate the effects of the PAN precursor to form cross-links between CNTs. The tensile strength of CNT yarn is improved when the yarn is partially infiltrated with PAN and consequently carbonated. High-resolution transmission electron microscopy observation of the sheets shows that graphite structures are formed and cross-link CNTs in CNT assembly.

Mimicking a gecko’s foot with strong adhesive strength based on a spinnable vertically aligned carbon nanotube array

To mimic gecko foot adhesion, spinnable vertically aligned carbon nanotube (VACNT) arrays, which have a higher density and cleaner surface than ordinary VACNT arrays, were prepared by a normal chemical vapor deposition (CVD) process that is simple and easy to operate for large-scale fabrication, particularly compared with the low-pressure CVD process. The height of the spinnable VACNT array was tuned by varying the reaction time. The shear adhesion strength of the spinnable VACNT array (0.16 cm2) was increased from 21.4 ± 1.7 to 85.8 ± 8.7 N cm−2 when the length of the spinnable VACNT array increased from 35 to 110 μm. Based on the enhanced van der Waals force induced by the large number of contact points on the high-density spinnable VACNT array, the maximum shear adhesion strength of the spinnable VACNT array (0.16 cm2) is 91.8 N cm−2, which is comparable to that of the CNT-based adhesive (∼100 N cm−2) prepared by the low-pressure CVD process. Moreover, a spinnable VACNT array adhesive was prepared over a large area, and a maximum weight of 3.0 Kg was supported successfully by a spinnable VACNT array adhesive with a contact area of 0.96 cm2.

Copper/Parylene Core/Shell Nanowire Surface Fastener Used for Room-Temperature Electrical Bonding

The traditional bonding technology in electronic assembly relies on high-temperature processes, such as reflow soldering or curing of adhesives, which result in undesired thermal excursions and residual stress at the bonding interface. Therefore, there is an urgent need to attach electronic components on the circuit board with good mechanical and electrical properties at room temperature. In this paper, a room-temperature electrical surface fastener consisting of copper/parylene core/shell nanowire (NW) arrays were prepared, and van der Waals (VDW) forces were utilized to interconnect the core/shell NWs. Interestingly, the Parylene C film becomes conductive due to dielectric breakdown when the thickness of it is miniaturized to nanoscale. Our electrical surface fastener exhibits high macroscopic adhesion strength (∼25 N/cm(2)) and low electrical resistance (∼4.22 × 10(-2) Ω·cm(2)). Meanwhile, a new theoretical model based on VDW forces between the NWs is proposed to explain the adhesion mechanism of the core/shell structure.

Fabrication of cross-linked carbon nanotube foam using polymethylmethacrylate microspheres as templates

Assembling carbon nanotubes (CNTs) into macroscopic and engineered structures with desired configuration and properties is the key step to realize their extensive applications. We devised a simple and scalable method to fabricate three-dimensional CNT foams using polymethylmethacrylate (PMMA) microspheres as templates and polyacrylonitrile (PAN) as a precursor to create crosslinks among CNTs. The porosity and the pore size of the CNT foam can be tuned easily by adjusting the concentration and particle size of the PMMA spheres. The assembled CNT foams have a hierarchically porous structure and the pore size ranges from several nanometers to tens of micrometers. The effect of PAN on crosslinking CNTs was evaluated by using ultrathin freestanding CNT sheets. The structural observations and mechanical property improvement demonstrate that the PAN polymer converts into graphitic structures and accumulates at the joints of CNTs after thermal treatment at 1000 °C, which strengthen CNT assembly.

Optimization of viscosity and thixotropy for organic medium to achieve high photovoltaic conversion efficiency of silicon solar cells

The properties of the silver paste have great influence on the photovoltaic conversion efficiency (Eff) of monocrystalline silicon (Si) solar cells. The organic medium is a very important part of silver paste. In this paper, two main performance parameters of organic medium (viscosity and thixotropic index) are systematically studied. When the thixotropic index of the organic medium is more than 5.50 and the viscosity is between 15 pa·s and 30 pa·s, the silver paste has good thixotropy and appropriate printability. The experimental results indicate that organic medium has appropriate viscosity (20 pa·s) and the highest thixotropic index (9.35) when its composition is as follows: solvents 80.00 wt. %, thickener 3.00 wt. %, thixotropic agents 8.00 wt. %, surfactant 3.00 wt. %, and coupling agent 6.00 wt. %. The silver paste shows appropriate viscosity (270–370 pa·s), high thixotropic index (6.50), and good printability when the percentage of organic medium is about 12.00 wt. %. Using this silver paste, the ...

Carbon nanotube array inducing osteogenic differentiation of human mesenchymal stem cells.

Carbon nanotubes (CNTs) are a kind of nanomaterials which have been shown a promising application for biomedicine. There are a lot of studies to use CNTs to induce the differentiation of mesenchymal stem cells (MSCs). However, the cellular behavior of MSCs on the top layer of CNT array was still not well understood. In this study, we evaluated the morphology, the gene expressions of the osteogenic differentiation related markers, and the gene expressions of collagen type II (Col II, a marker of chondrogenesis), PPARγ (a marker of adipogenesis) and scleraxis (SCX, a marker of tenogenesis) in human mesenchymal stem cells (hMSCs) cultured on multi-walled carbon nanotube (MWCNT) array. The effect of MWCNT array on the mineralization of hMSCs which were cultured in osteogenic differentiation medium (ODM) was further assayed. Our results showed that the hMSCs cultured on MWCNT array spread well, formed numerous spiral shaped cell colons and showed perinuclear morphology. Compared to hMSCs cultured on dish, the gene expression of osteocalcin (OCN) was increased while the gene expressions of collagen type II (Col II), PPARγ and scleraxis (SCX) were decreased in hMSCs which were cultured on MWCNT array without any differentiation factors. Furthermore, compared with hMSCs on dish, the gene expressions of collagen type I (Col I), osteocalcin (OCN), osteopontin (OPN) and RUNX2, and the mineralization of hMSCs on MWCNT array were enhanced when they were cultured in osteogenic differentiation medium (ODM). Our results indicated that MWCNT array was able to promote the osteogenesis of hMSCs.

Carbon nanotube–Cu/parylene nanowire array electrical fasteners with high adhesion strength

The preparation of room-temperature electrical fasteners with high adhesion strength presents a major challenge at the micro- or nanoscale. A carbon nanotube (CNT)–Cu/parylene core/shell nanowire (NW) array room-temperature electrical fastener was therefore prepared, and is described herein. The shear adhesion strength of the CNT–Cu/parylene NW array electrical fastener reached a maximum of 50.72 N/cm2, which is six times higher than that of a metallic NW electrical fastener. A theoretical analysis indicated that the adhesion force of such a fastener can potentially be further improved by increasing the effective contact length between the CNTs and the Cu/parylene NW. The resistance of the fastener is 45.4 Ω, which indicates that it has good electrical conductivity.

Composite Nanowires for Room-Temperature Mechanical and Electrical Bonding

At millimeter dimension or less, the conventional bonding technology in electronic assembly relies heavily on reflow soldering and suffers from severe performance and reliability degradation. Meanwhile, the traditional high temperature bonding process (easily reach 220 °C) tends to result in undesired thermal damage and residual stress at the bonding interface. It is therefore a major challenge to find a means to preparing room-temperature connectors or fasteners with good mechanical and electrical bonding. Very recently, composite nanowires have been used to fabricate room-temperature fasteners. In this chapter, we summarize the state-of-the-art progress on the use of composite nanowires for room-temperature mechanical and electrical bonding. Using anodic aluminum oxide (AAO) and polycarbonate (PC) membrane as templates, the fabrication of Cu/parylene and Cu/polystyrene nanowires was described, while the fabrication of carbon nanotube (CNTs) array used to connect with Cu/parylene nanowires was also introduced. Finally, the performances of the composite nanowires (Cu/parylene, Cu/polystyrene, and CNT-Cu/parylene) used as surface fastener for room-temperature mechanical and electrical bonding were demonstrated.