All issues / Volume 8 (2014) / Issue 7 (July)
This is an editorial article. It has no abstract.
The study of excimer laser treatment of polystyrene surface was performed. The influence of laser fluence and number of laser pulses on surface chemistry and morphology was determined. The surface morphology and roughness were studied with atomic force microscopy. Surface wettability and aging studies were characterized by the water contact angle measurements. Surface oxygen concentration and chemistry were evaluated from X-ray photoelectron spectroscopy and zeta potential measurements. The optimal polystyrene treatment parameters for the most regular pattern were determined. The foils with optimal ripple pattern were subsequently sputtered with gold nano-layers of 100 nm thickness. It was found that the surface roughness of PS strongly depends on number of pulses. The aging study revealed that the higher contact angle achieve the samples treated with higher laser fluence. The deposition of gold nano-layer increases the surface roughness of nano-patterned surface. It was proved that the oxygen concentration is significantly influenced by the KrF laser exposure.
Graphene oxide (GO) sheets were chemically grafted with thermotropic liquid crystalline epoxy (TLCP). Then we fabricated composites using TLCP-g-GO as reinforcing filler. The mechanical properties and thermal properties of composites were systematically investigated. It is found that the thermal and mechanical properties of the composites are enhanced effectively by the addition of fillers. For instance, the composites containing 1.0 wt% of TLCP-g-GO present impact strength of 51.43 kJ/m2, the tensile strength of composites increase from 55.43 to 80.85 MPa, the flexural modulus of the composites increase by more than 48%. Furthermore, the incorporation of fillers is effective to improve the glass transition temperature and thermal stability of the composites. Therefore, the presence of the TLCP-g-GO in the epoxy matrix could make epoxy not only stronger but also tougher.
A novel synthesis of 4-toluene 9H-carbazole-9-carbodithioate (TCzC) was chemically synthesized and characterized by Fourier Transform Infrared (FTIR), proton nuclear magnetic resonance (1H-NMR), and carbon nuclear magnetic resonance (13C-NMR) spectroscopies. Specific (Csp) and double layer capacitances (Cdl) of the electro-coated poly(carbazole) and poly(TCzC) films were obtained on glassy carbon electrode (GCE) by impedimetric method with DC potential from –0.1 to +1.0 V by increasing potential of 0.2 V. The polymers were characterized by Cyclic voltammetry (CV), Fourier transform infrared reflectance-attenuated total reflection spectroscopy (FTIR-ATR), Atomic force microscopy (AFM), and Electrochemical impedance spectroscopy (EIS). The use of additional variable (DC potential) helped to disambiguate the equivalent circuit model of R(C(R(Q(RW))))(CR). Simulation results were compared with experimental data. In this study, substituted group effects of CS2 and tosyl on carbazole polymer were investigated by EIS technique. CS2 group together with tosyl group in the structure of carbazole decreased the specific capacitance value (Csp = 0.43 mF•cm–2) compared to PCz (Csp = 1.44 mF•cm–2). Electropolymerization formation was seriously affected by substituted groups of CS2 and tosyl on conjugation system because of the electron donor and acceptor ability.
In order to improve the bonding between henequen fibers (Agave fourcroydes) and High Density Polyethylene (HDPE), they were treated in an ethylene-dielectric barrier discharge (DBD) plasma operating at atmospheric pressure. A 23 factorial experimental design was used to study the effects of the plasma operational parameters, namely, frequency, flow rate and exposure time, over the fiber tensile mechanical properties and its adhesion to HDPE. The fiber-matrix Interfacial Shear Strength (IFSS) was evaluated by means of the single fiber pull-out test. The fiber surface chemical changes were assessed by photoacoustic Fourier transform infrared spectroscopy (PAS-FTIR) and the changes in surface morphology with scanning electron microscopy (SEM). The results indicate that individual operational parameters in the DBD plasma treatment have different effects on the tensile properties of the henequen fibers and on its bonding to HDPE. The SEM results show that the plasma treatment increased the roughness of the fiber surface. The FTIR result seems to indicate the presence of a hydrocarbon-like polymer film, bearing some vinyl groups deposited onto the fibers. These suggests that the improvement in the henequen-HDPE bonding could be the result of the enhancement of the mechanical interlocking, due the increment in roughness, and the possible reaction of the vinyl groups on the film deposited onto the fiber with the HDPE.
A series of diblock copolymers (poly(n-butylacrylate)-co-poly(2-hydroxyethyl acrylate))-b-poly(glycidyl methacrylate) ((PnBA-co-PHEA)-b-PGMA), containing a random copolymer block PnBA-co-PHEA, were successfully synthesized by atom transfer radical polymerization (ATRP). After being chemically grafted onto carbon fibers, the photosensitive methacrylic groups were introduced into the random copolymer, giving a series of copolymers (poly(n-butylacrylate)-co-poly(2-methacryloyloxyethyl acrylate))-b-poly(glycidyl methacrylate)((PnBA-co-PMEA)-b-PGMA). Dynamic mechanical analysis indicated that the random copolymer block after ultraviolet (UV) irradiation was a lightly crosslinked polymer and acted as an elastomer, forming a photo-crosslinked network structure at the interface of carbon fiber/epoxy composites. Microbond test showed that such an interfacial network structure greatly improved the cohesive strength and effectively controlled the deformation ability of the flexible interlayer. Furthermore, three kinds of interfacial network structures, i) physical crosslinking by H-bonds, ii) chemical crosslinking by photopolymerization, and iii) interpenetrating crosslinked network by photopolymerization and epoxy curing reaction were received in carbon fiber/epoxy composite, depending on the various preparation processes.
Partially bio-based thermoplastic elastomers (bio-TPE) were designed and prepared by physical blending a commercial grade poly(hydroxyalkanoate)s (PHBM, Metabolix) and poly(ethylene-co-vinyl acetate) (EVA). The PHBM is miscible with EVA90 which has a vinyl acetate (VA) content of 90 wt% while it is not miscible with EVA at low VA content (!70 wt%). The PHBM/EVA90 blends exhibit high tensile strength and typical thermoplastic elastomeric characteristics e.g. high elongation at break (>800%), good strain-recovery (>60%) and melt processability. The spherulite growth rate of PHBM decreases with increasing EVA90 content. Consequently, a large number of fine PHBM spherulites were formed in the blends. The spherulites act as physical crosslink-points leading to a thermoreversable network in the blends. Such network and elastic EVA90 molecules result in the thermoplastic and elastomeric characteristics of the PHBM/EVA90 blends.
A dual-switchable surface between hydrophobic and superhydrophobic has been fabricated successfully by combining reversible addition-fragmentation chain transfer polymerization (RAFT) polymeric technology and thiol-NCO click chemistry. Well-defined block copolymer, poly(7-(6-(acryloyloxy) hexyloxy) coumarin)-b-poly(N-Isopropylacryl amide), was synthesized by RAFT, and then the block copolymer was grafted onto the surface of SiO2 modified by toluene disocynate (TDI) via thiol-NCO click chemistry. The results of nuclear magnetic resonance (NMR) and Fourier Transform Infrared (FTIR) spectroscopies confirmed that the block copolymer (Number average molecular weight (Mn) = 9400, polydispersity index (PDI) = 1.22) has been synthesized successfully. The static contact angle (CA) of the surface prepared by SiO2/P (7-6-AC)-b-PNIPAAm switches from 98±2 to 137±2° by adjusting the temperature. Furthermore, the contact angle can also oscillate between 137±2 and 157±2° on the irradiation of UV light at 365 and 254 nm, respectively. The dual-switchable surfaces exhibit high stability between hydrophilicity and superhydrophobicity. Therefore, the method provides a new method to fabricate the dual-stimuli-responsive surface with tunable wettability, reversible switching, and also be easily extended to other dual-responsive surfaces. This ability to control the wettability by the adjustment of the temperature and UV light has applications in a broad range of fields.