Wencai Wang

Surface modification of aramid fibers by bio-inspired poly(dopamine) and epoxy functionalized silane grafting.

A novel biomimetic surface modification method for meta-aramid (MPIA) fibers and the improvement on adhesion with rubber matrix was demonstrated. Inspired by the composition of adhesive proteins in mussels, we used dopamine (DOPA) self-polymerization to form thin, surface-adherent poly(dopamine) (PDA) films onto the surface of MPIA fibers simply by immersing MPIA fibers in a dopamine solution at room temperature. An epoxy functionalized silane (KH560) grafting was then carried out on the surface of the poly(dopamine)-coated MPIA, either by a one-step or two-step method, to introduce an epoxy group onto the MPIA fiber surface. The surface composition and microstructure of the modified MPIA was characterized by X-ray photoelectron spectroscopy (XPS), attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR), scanning electron microscopy (SEM), and thermogravimetric analysis (TGA). The results indicated successful grafting of KH560 on the PDA-coated MPIA surface. A single-fiber pull-out test was applied to evaluate the adhesion of MPIA fibers with the rubber matrix. Compared with the untreated MPIA fibers, the adhesion strength between the modified MPIA fibers by one step method with rubber matrix has an increase of 62.5%.

Surface silverized meta-aramid fibers prepared by bio-inspired poly(dopamine) functionalization.

A facile method was developed to fabricate highly electrically conductive aramid fibers. The immobilization of silver nanoparticles on the surface of polymetaphenylene isophthamide (PMIA) fibers was carried out by the functionalization of the PMIA fibers with poly(dopamine), followed by electroless silver plating. The poly(dopamine) (PDA) layer was deposited on the PMIA surface by simply dipping the PMIA substrate into an alkaline dopamine solution. The silver ions can be chemically bound to the catechol and indole functional groups in PDA. The silver ions were reduced into silver nanoparticles by using glucose as the reducing agent, resulting in a distinct silver layer on the PMIA surface. The obtained silver deposit was homogeneous and compact. The chemical composition of the modified PMIA fibers was studied by X-ray photoelectron spectroscopy (XPS) and energy dispersive X-ray spectroscopy (EDS), and the crystalline structure of the silver-coated PMIA fibers was characterized by powder X-ray diffraction (XRD). The topography of the modified PMIA fibers was investigated by scanning electron microscopy (SEM). The four-point probe resistivity meter was used to study the electrical resistivity of the silver-coated PMIA fibers, the results indicated that the electrical resistivity could be as low as 0.61 mΩ·cm, with a controllable silver content, and a satisfactory stability by ultrasonic treatment.

Fabrication of silver-coated silica microspheres through mussel-inspired surface functionalization.

A facile method was developed to prepare silica-silver core-shell composite microspheres with continuous, compact, and conductive silver layers. The procedure involves dopamine oxidative self-polymerization and electroless plating. The poly(dopamine) layer was used as the chemi-sorption sites for silver ions and promoted the silver deposition. The electroless plating procedure involves a combination of surface activation, seeding growth, and deposition. The chemical composition and the crystal structure of the silica-silver core-shell composite microspheres were studied by X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD), respectively. In addition, the surface morphology and chemical composition of each composite microsphere were confirmed by scanning electron microscopy and energy dispersive X-ray spectroscopy. The results demonstrated that the silver layer on the silica surface was continuous and compacted.

Preparation and characterization of polystyrene/Ag core-shell microspheres--a bio-inspired poly(dopamine) approach.

A facile and versatile method using a biopolymer as a chelating agent for silver ions and as a reducing agent for the formation of catalytic sites is proposed to prepare polystyrene (PS)/Ag core-shell microspheres. More specifically, the core-shell microspheres were fabricated by electroless plating after the formation of poly(dopamine) (PDA) on the surface of PS microspheres through insitu spontaneous oxidative polymerization of dopamine. The PS-PDA microspheres were characterized by SEM, XPS, and TGA. The results showed that a uniform PDA layer was formed on the PS microsphere surface and the thickness of the PDA layer could be well controlled by varying the concentration of dopamine solution. The PDA layer was used as a chelating agent for silver ions, as a reducing agent for the formation of catalytic sites by reducing the silver ions into silver nanoparticles, and as an adhesion layer between the PS microspheres and silver layer. SEM and XRD results indicate that the diameter of the silver nanoparticles decreased with the increase in the thickness of the PDA layer. The silver nanoparticles could form a continuous and compact silver layer on the surface of the PS microspheres. Furthermore, the PS-PDA/Ag core-shell microspheres showed a good conductivity of 10S/cm and a low effective density of 1.8 g/cm(3), much lower than the corresponding values for block silver. Finally, hollow silver microspheres could be prepared by removing the PS core through calcination. SEM images showed that the hollow Ag microspheres remained unbroken and retained the spherical shape.

Highly Conductive One-Dimensional Nanofibers: Silvered Electrospun Silica Nanofibers via Poly(dopamine) Functionalization

Using tetraethyl orthosilicate as a main raw material, silica nanofibers (SiNFs) were prepared through the combination of a sol-gel process and an electrospinning technique followed by pyrolysis. Surface modified electrospun SiNFs developed by self-polymerization of polydopamine on the surface (SiNFs-PDA) served as templates for the electroless plating of silver nanoparticles (Ag NPs), using glucose as a reducing agent. The electrical resistivity of silver coated SiNPs-PDA (SiNFs-PDA/Ag) was measured by the four-point probe method and was found to be as low as 0.02 mΩ·cm at room temperature. The morphology of SiNFs-PDA/Ag before and after the blending with silicon rubber indicated a strong interaction between the silver layer and the SiNFs-PDA. The electrical and mechanical properties of the silicon rubber filled with SiNFs-PDA/Ag were studied to demonstrate the conductive performance application of SiNFs-PDA/Ag.

Enhanced dielectric properties and actuated strain of elastomer composites with dopamine-induced surface functionalization

To obtain a dielectric elastomer with excellent dielectric properties and actuated strain, we used bio-inspired dopamine to functionalize the surface of barium titanate (BT) particles. X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), and transmission electron microscopy (TEM) were used to confirm that a poly(dopamine) (PDA) layer of ca. 3.0 nm had been successfully deposited on the surface of the barium titanate particles. With the introduction of the PDA layer, the compatibility between the barium titanate filler and the elastomer matrix (hydrogenated nitrile-butadiene rubber) was significantly improved, which also resulted in the composites displaying better filler dispersion, higher dielectric constant, lower dielectric loss, and higher electric breakdown field compared with composites filled with pristine BT particles. Furthermore, the composites filled with PDA-coated BT (BT–PDA) exhibited higher electromechanical sensitivity (β) than the composites filled with pristine BT, leading to increased actuated strains. Nevertheless, the β of composites filled with pristine BT decreased with increasing content of filler, resulting in decreased actuated strains. Finally, a large actuated strain of 20% without any prestrain was achieved by the composite filled with BT–PDA, which is 54% larger than the largest actuated strain of the polymer without functionalized filler. Moreover, the dopamine functionalization method is simple, efficient, nontoxic, and easy to control, and can be used as a general strategy for improving the dielectric constant, breakdown strength, and actuated strain of dielectric elastomers.

Preparation and characterization of silver nanoparticles immobilized on multi-walled carbon nanotubes by poly(dopamine) functionalization

Multi-walled carbon nanotubes (MWNTs) functionalized with poly(dopamine) (PDA) were found to cause the immobilization of silver nanoparticles on the surface. The PDA functional layer not only improved the dispersion of MWNTs in aqueous solution, but also was used as a platform for subsequent silver nanoparticle immobilization. The surface morphology of the functionalized MWNTs was observed by high-resolution transmission electron microscopy. The results showed that PDA layers with controlled thickness on the nanometer scale were formed on MWNT surfaces by in situ spontaneous oxidative polymerization of dopamine, and that high-density of homogeneously dispersed spherical silver nanoparticles with sizes of 3–4xa0nm were immobilized on their outer surface. The space between spherical silver nanoparticles is less than 10xa0nm. Both X-ray photoelectron spectroscopy and X-ray diffraction results showed that the Ag nanoparticles on the surface of hybrids exist in the zero valent state.

Multi-walled carbon nanotubes/silicone rubber nanocomposites prepared by high shear mechanical mixing

MWCNTs reinforced SiR nanocomposites were prepared through a high-shear mechanical mixing technique, using DCP as a curing agent. Under optimum conditions, the MWCNTs can be dispersed homogeneously in the SiR matrix to improve the mechanical properties of the nanocomposites. The mechanical properties of the nanocomposites such as tensile strength, elongation at break, and hardness were evaluated. In addition, the degree of crystallinity and the supercooling were calculated to characterize the crystallization behavior. From DSC study, it has been determined that the degree of crystallinity Xc and the super cooling ΔT, generally characterize the crystallization behavior of the nanocomposites. A decrease in Xc and ΔT indicate that the crystallization rate of the nanococomposites is increased. After pyrolysis, with the increase of CNT content, the decomposition rate or/and the weight loss of the nanocomposites decreased. The dispersion of carbon nanotubes in silicone rubber was characterized by using SEM. Finally, the effect of carbon nanotubes loading on electrical, thermal conductivity, and the Payne effect was also investigated.

Constructing Covalent Interface in Rubber/Clay Nanocomposite by Combining Structural Modification and Interlamellar Silylation of Montmorillonite

Strong interfacial interaction and nanodispersion are necessary for polymer nanocomposites with expectations on mechanical performance. In this work, montmorillonite (MMT) was first structurally modified by acid treatment to produce more silanol groups on the layer surface. This was followed by chemical modification of γ-methacryloxy propyl trimethoxysilane molecule (KH570) through covalent grafting with the silanol groups. (29)Si and (27)Al magic angle spinning (MAS) NMR results revealed the microstructural changes of MMT after acid treatment and confirmed the increase of silanol groups on acid-treated MMT surfaces. Thermogravimetric analysis indicated an increase in the grafted amount of organosilane on the MMT surface. X-ray diffraction (XRD) showed that the functionalization process changed the highly ordered stacking structure of the MMT mineral into a highly disordered structure, indicating successful grafting of organosilane to the interlayer surface of the crystalline sheets. The styrene-butadiene rubber (SBR)/MMT nanocomposites were further prepared by co-coagulating with SBR latex and grafted-MMT aqueous suspension. During vulcanization, a covalent interface between modified MMT and rubber was established through peroxide-radical-initiated reactions, and layer aggregation was effectively prevented. The SBR/MMT nanocomposites had highly and uniformly dispersed MMT layers, and the covalent interfacial interaction was finally achieved and exhibited high performance.

Design and preparation of bio-based dielectric elastomer with polar and plasticized side chains

A new dielectric elastomer with large actuated strain driven by low electric field was synthesized from di-n-butyl itaconate and isoprene through free radical redox emulsion polymerization. The effect of the copolymerized proportion of poly(di-n-butyl itaconate-co-isoprene) (PDBII) and the dosage of crosslinking agent on the elastic modulus, dielectric properties, and actuated strain of the elastomer were investigated, and a potential dielectric elastomer candidate containing 70 wt% di-n-butyl itaconate was obtained. The permittivity of the PDBII crosslinked by 3.0 phr of dicumyl peroxide was 5.68 at 103 Hz, which was higher than that of commercial acrylic and silicone dielectric elastomers. Without any prestrain, an actuated strain of 20% was obtained at an electric field of 30 kV mm−1. In order to further increase the actuated strain, barium titanate (BaTiO3), a high-dielectric-constant ceramic powder, was utilized to fill the PDBII to form a BaTiO3/PDBII composite. The dielectric constant of the composite increased with increasing content of BaTiO3, and the elastic modulus of the composite was lower than that of the unfilled PDBII, leading to a larger dielectric actuated strain of the composite.