Tao Jiang

Graphene-Enabled Superior and Tunable Photomechanical Actuation in Liquid Crystalline Elastomer Nanocomposites.

Programmable photoactuation enabled by graphene: Graphene sheets aligned in liquid crystalline elastomers are capable of absorbing near-infrared light. They thereafter act as nanoheaters and provide thermally conductive pathways to trigger the nematic-to-isotropic transition of elastomers, leading to macroscopic mechanical deformation of nanocomposites. Large strain, high actuation force, high initial sensitivity, fast reversible response, and long cyclability are concurrently achieved in nanocomposites.

Carbon Nanotube Industrial Applications

Since carbon nanotube was discovered by S. Ijima in 1991, it has become one of the main academic research subjects. Carbon nanotube is the thinnest tube human can make presently. It has advantages in lightweight, high strength, high toughness, flexibility, high surface area, high thermal conductivity, good electric conductivity and chemical stability. Carbon nanotube can be applied to manufacture smaller transistors or electronic devices. Samsung Korea has made carbon nanotube into Field Emission Display. When the technology is matured and the cost is reduced, it will replace traditional bulky cathode ray tube (CRT) screen. Carbon nanotube has high toughness, so it can be made into highstrength composite with other materials. Thus, carbon nanotube is a material with high economic value and very worth researching. Besides, carbon nanotube has both conductor and semiconductor properties. Therefore, for electronic circuit, the semiconductor property of carbon nanotube enables its application to field emission transistor (FET) gate electrode, which has 100 times higher electric conductivity than silicon semiconductor when voltage is applied and 1000 times higher operational frequency than current Complementary MetalOxide Semiconductor (CMOS). The conductor property makes carbon nanotube have similar thermal conductivity to diamond and superior current carrying capacity to copper and gold. For the application of display, its long-term reliability is very excellent [Iijima, 1991, Lee et. al., 1977]. In order to create new material systems with superior properties, various nanoparticle morphologies have been used as reinforcing fillers in elastomeric matrices. These nanometerscale reinforcing particles include spherical particles such as silica or titania [McCarthy et. al., 1997, Kohjiya et. al., 2005], platelets such as layered silicates [Osman et. al., 2001, Joly et. al., 2002, Varghese & Karger-Kocsis, 2003, Kim et. al., 2004, Arroyo et. al., 2003, Bala et. al., 2004, Jeon et. al., 2004], carbon [Gauthier et. al., 2005] or clay fibers [Bokobza & Chauvin, 2005] and multiwall or singlewall carbon nanotubes[Barraza et.

Judicious selection of bifunctional molecules to chemically modify graphene for improving nanomechanical and thermal properties of polymer composites

Covalently-functionalised graphene (FG) was successfully obtained by grafting m-isopropenyl-α, α′-dimethyl benzyl isocyanate (m-TMI) to graphene oxide (GO) followed by the chemical and solvothermal reduction of GO. The FG sheets were hydrophobic and stable in polar solvents such as N,N-dimethylformamide. The reactive vinyl-benzyl groups of m-TMI attached to FG copolymerised with methyl methacrylate to produce graphene/poly(methyl methacrylate) (PMMA) composites. The FG sheets were well dispersed in PMMA and formed strong interfacial bonds with the matrix, contributing to large increases in elastic modulus (+72.9%) and indentation hardness (+51.2%) at 1% loading by weight. The incorporation of FG into PMMA changed its elastic-plastic behaviour; hence, a decrease in the plasticity index and an increase in recovery resistance were observed for the resulting composites due to the increased portion related to the elastic work. The onset decomposition temperature and glass transition temperature of neat PMMA increased by 100 °C and 12.7 °C, respectively, by the addition of 1 wt% FG. Herein, in situ copolymerisation of monomers and well-suspended FG promotes the exfoliation of graphene associated with strong chemical bonding with the polymer matrix. This report provides a promising and facile method for fabricating high-performance polymeric composites.

Core/shell rubber toughened polyamide 6: an effective way to get good balance between toughness and yield strength

We have recently shown that by adding 10 to 30 wt% core/shell toughener with a low density polyethylene (LDPE) core and a polybutadiene-g-maleic anhydride (PB-g-MAH) rubber shell to polyamide 6 (PA6), the impact strength of PA6 matrix can be significantly increased by 600–1000%. However, this is at the expense of quite large losses in elastic modulus of 10–25% and tensile yield strength of 30–55%, especially at high core/shell rubber loading (e.g., 30 wt%). In this study, we have redressed this problem by replacing the LDPE core with a polypropylene (PP) core, which has both higher elastic modulus and yield strength than that of LDPE, forming a new core/shell (PP/PB-g-MAH) toughener. When this core/shell toughener containing 5 wt% PB-g-MAH is blended with PA6 in the weight ratios of 10/90 and 30/70, the Izod impact strengths are 390 and 480 J m−1 (which are 330 and 550% increases compared to neat PA6), and the modulus are 2.37 and 2.13 GPa, and yield strength are 60.2 and 54 MPa, respectively (which represent only 6 and 15% loss of modulus, and 5 and 13% decrease in yield strength relative to neat PA6). These improved results confirm that although the decrease of tensile modulus cannot be avoided with increasing impact strength, increasing the elastic modulus and yield strength of the core material in the rigid core/soft rubber shell toughener is an effective way to obtain a good balance of elastic modulus, tensile yield strength and impact strength.

Facile fabrication of bactericidal and antifouling switchable chitosan wound dressing through a 'click'-type interfacial reaction.

A facile approach to functionalize chitosan (CS) non-woven surface with the bactericidal and antifouling switchable moieties is presented. Azlactone-cationic carboxybetaine ester copolymer was firstly prepared, then chemically attached onto CS non-woven surface through the fast and efficient click-type interfacial reaction between CS primary amines and azlactone moieties. The CS non-woven surface functionalized with cationic carboxybetaine esters is able to kill bacteria effectively. Upon the hydrolysis of carboxybetaine esters into zwitterionic groups, the resulting zwitterionic surface can further prevent the attachment of proteins, platelets, erythrocytes and bacteria. This CS non-woven that switches from bactericidal performance during storage to antifouling property before its service has great potential in wound dressing applications.

Adsorption Behavior of High Stable Zr-Based MOFs for the Removal of Acid Organic Dye from Water

Zirconium based metal organic frameworks (Zr-MOFs) have become popular in engineering studies due to their high mechanical stability, thermostability and chemical stability. In our work, by using a theoretical kinetic adsorption isotherm, we can exert MOFs to an acid dye adsorption process, experimentally exploring the adsorption of MOFs, their external behavior and internal mechanism. The results indicate their spontaneous and endothermic nature, and the maximum adsorption capacity of this material for acid orange 7 (AO7) could be up to 358 mg·g−1 at 318 K, estimated by the Langmuir isotherm model. This is ascribed to the presence of an open active metal site that significantly intensified the adsorption, by majorly increasing the interaction strength with the adsorbates. Additionally, the enhanced π delocalization and suitable pore size of UiO-66 gave rise to the highest host–guest interaction, which further improves both the adsorption capacity and separation selectivity at low concentrations. Furthermore, the stability of UiO-66 was actually verified for the first time, through comparing the structure of the samples before and after adsorption mainly by Powder X-ray diffraction and thermal gravimetric analysis.

A Si-doped flexible self-supporting comb-like polyethylene glycol copolymer (Si-PEG) film as a polymer electrolyte for an all solid-state lithium-ion battery

Herein, a self-supporting comb-like Si-PEG copolymer with flexible Si–O–C bonds in the main chain and pending short PEG chains as the side chain was synthesized to improve the low temperature performance and overcome the quandary between good mechanical and electrochemical properties of the polymer electrolyte in lithium-ion batteries. The tensile strength of Si-PEG polymer electrolytes (SPH15) is 0.8 MPa at 30 °C, which is high enough to inhibit the growth of lithium dendrites. The ion conductivities of Si-PEG (SPH15) are 1.2 × 10−4 S cm−1 at 30 °C and 3.2 × 10−5 S cm−1 at 10 °C, which are one order of magnitude higher than those for PEG-based copolymer electrolytes without Si doping. The assembled LiFePO4/SPH15/Li half batteries can deliver the specific capacities of 84 mA h g−1 at 10 °C and present 75% capacity retention after 500 charge–discharge cycles at 0.5C.

Preparation of poly(cyclooctene)-g-poly(ethylene glycol) (PCOE-g-PEG) graft copolymers with tunable PEG side chains via ROMP and its protein adsorption and platelet adhesion properties

In our previous work [H. Shi, D. Shi et al., Polymer Chemistry 2(2011)679-684], polycyclooctene-g-PEG (PCOE-g-PEG) copolymers were synthesized via ring opening metathesis polymerization (ROMP) from PEG functionalized cyclic olefin macromonomers and cyclooctene. The grafting degree and the grafting site were easily controlled through the grafting through approach. The PCOE-g-PEG film surface was imparted excellent anti-protein adsorption properties. In that work, the molecular weight of PEG side chain was fixed at 750 g/mol and the neat PEG content in the copolymer was lower than 50 wt.%. In this work, both the effects of PEG side chain lengths (350 to 1000 g/mol) at a fixed PEG content (50 wt.%) and the neat PEG content (30 wt.% to 70 wt.%) at a fixed PEG molecular weight (750 g/mol) on the anti-protein adsorption and anti-platelet adhesion properties are studied. It is shown that the copolymer with 60 wt.% PEG side chains of 750 g/mol, where both PEG and PCOE form continuous morphology, is optimal to reduce the adsorption of both the bovine serum albumin (BSA) and platelet. When the PEG content reaches 70 wt.%, phase inversion happens. PEG is the continuous phase but PCOE becomes the dispersed phase. The surface roughness of the casting PCOE-g-PEG film increases. In this case, both BSA adsorption and platelet adhesion will slightly increase comparing to the sample with 60 wt.% PEG.

Preparation and Characterization of Polyurethanes with Cross-Linked Siloxane in the Side Chain by Sol-Gel Reactions

A series of novel polyurethanes containing cross-linked siloxane in the side chain (SPU) were successfully synthesized through a sol-gel process. The SPU was composed of 0%–20% N-(n-butyl)-3-aminopropyltriethoxysilane (HDI-T) modified hexamethylene diisocynate homopolymer. The effects of HDI-T content on both the structure and properties of SPU were investigated by Fourier transform infrared spectroscopy (FT-IR), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), mechanical properties tests, gel content test, water contact angle measurement and water absorption test. FT-IR, XPS and XRD results confirmed the successful incorporation of HDI-T onto polyurethanes and the formation of Si–O–Si. The surface roughness and the Si content of SPU enhanced with the increase of HDI-T content. Both crystallization and melting temperature shifted to a lower point after the incorporation of HDI-T. The hydrophobicity, tensile strength, Young’s modulus and pencil hardness overall increased with the increasing of HDI-T content, whereas the thermal stability and the elongation at break of SPU slightly decreased.

Nanostructures: Graphene‐Enabled Superior and Tunable Photomechanical Actuation in Liquid Crystalline Elastomer Nanocomposites (Adv. Mater. 41/2015)

Actuated materials undergo shape and dimension changes in response to external stimuli and thus convert various forms of input energies into mechanical work. On page 6376, Y. Yang, Z. Lin, and co-workers report novel near-infrared responsive composites consisting of uniformly aligned graphene in a liquid-crystalline elastomer matrix. Large deformation amplitude, high driving force, fast reversible response, and long cyclability can be achieved by tuning the characteristics of graphene in these nanocomposites. Such materials have potential applications in robotics, artificial muscles, switches, motors, sensors, and micromechanical systems.