UV protection and coatings for plastics are important in many applications. The cladding of low m... more UV protection and coatings for plastics are important in many applications. The cladding of low microwave (MW) absorption composite coatings on high MW transparent plastic substrates is a challenge due to their disparate dielectric properties. Moreover, an uneven heat energy conversion within the composite creates an additional hurdle in producing a coating with good surface integrity. In this study, a protocol was developed to overcome these difficulties based on a hybrid approach. The adverse effect of temperature mismatch between the coating and substrate was reduced through a two-way susceptor-aided heating mechanism. Low MW absorbing sol–gel derived composite coatings consisting of silicon dioxide (SiO2) and titanium dioxide (TiO2) were successfully cladded on the surface of MW and visual light transparent polycarbonate to produce a clear protective coating with UV-resistance. Nanoindentation tests were conducted to assess the effectiveness of the proposed protocol. Significant...
Silanization processes with perfluoroalkyl silanes have been demonstrated to be effective in deve... more Silanization processes with perfluoroalkyl silanes have been demonstrated to be effective in developing advanced materials with many functional properties, including hydrophobicity, water repellency, and self-cleaning properties. However, practical industrial applications of perfluoroalkyl silanes are limited by their extremely high cost. On the basis of our recent work on photoredox catalysis for amidation with perfluoroalkyl iodides, its application for surface chemical modification on filter paper, as an illustrative example, has been developed and evaluated. Before photocatalytic amidation, the surface is functionalized with amine functional groups by silanization with 3-(trimethoxysilyl)propylamine. All chemically modified surfaces have been fully characterized by attenuated total reflection infrared (ATR-IR), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy with energy-dispersive spectroscopy (SEM-EDS), and three-dimensional (3D) profiling to confirm the successful silanization and photocatalytic amidation. After surface modification of the filter papers with perfluoroalkanamide, they show high water repellency and hydrophobicity with contact angles over 120°. These filter papers possess high wetting selectivity, which can be used to effectively separate the organic and aqueous biphasic mixtures. The perfluoroalkanamide-modified filter papers can be used for separating organic/aqueous biphasic mixtures over many cycles without lowering the separating efficiency, indicating their reusability and excellent durability.
The International Journal of Advanced Manufacturing Technology, 2020
Microwave (MW) sintering offers higher heating rate, rapid processing, reduced energy consumption... more Microwave (MW) sintering offers higher heating rate, rapid processing, reduced energy consumption, and reduced sintering temperature. However, the technique is not fully understood, difficult to control, and often relies on experience and trial-and-error approach. Consequently, hot spots, uneven heating, thermal runaway, and shape distortion develop in sintered compacts. Therefore, developing a model that can simulate the sintering process, enhance predictability, and determine the critical sintering conditions is essential. Multiphysics finite element (FE) modelling of hybrid MW sintering of a magnesium alloy AZ61 compact was undertaken in this study. The FE model coupled the electromagnetic, heat conduction, and densification equations. The model utilised parameters related to the furnace, compact, and susceptor to predict the spatial distribution of electric field, thermal response, and densification in the compact. A power-based sintering criterion was developed to predict the sintering of the compact and estimate its critical sintering energy. Modelling results showed that heating time, compact size, and thickness of the susceptor are critical to the sintering process. It was also shown that the susceptor not only mediated the sintering of the compact but also homogenised its temperature and densification. Thus, MW sintering of the compact was predicted to occur at 500°C for 8 to 10 min with a predicted relative density of about 0.98. Experimental MW sintering data showed good concurrence with the developed model. These results are useful for controlling the MW sintering process, eliminating trial-and-error, and determining the critical sintering conditions.
This review is intended to provide an overview of the design and fabrication of ionic liquid-base... more This review is intended to provide an overview of the design and fabrication of ionic liquid-based ionic electroactive polymer (IL-iEAP) transducers for advanced applications in biological and electronic fields. The iEAP is a class of smart materials that can perform sensing or actuating functions by controlling the movement of cations and anions in the active layer. This type of material can deform under low voltage stimulation and generate electrical signals when undergoing mechanical deformation because of ion redistribution. Numerous research attention has been focused on studying the deformation mechanisms and the potential for actuation, sensing, and energy harvesting applications. Compared to the traditional water-based iEAP, the non-volatile IL-iEAP delivers a wider electrochemical window and a more stable actuation performance. In this paper, the classification of iEAP with different actuation mechanisms is first outlined, followed by introducing various preparation methods...
Micro/nano-fabrication technology via two-photon polymerization (TPP) nanolithography is a powerf... more Micro/nano-fabrication technology via two-photon polymerization (TPP) nanolithography is a powerful and useful manufacturing tool that is capable of generating two dimensional (2D) to three dimensional (3D) arbitrary micro/nano-structures of various materials with a high spatial resolution. This technology has received tremendous interest in cell and tissue engineering and medical microdevices because of its remarkable fabrication capability for sophisticated structures from macro- to nano-scale, which are difficult to be achieved by traditional methods with limited microarchitecture controllability. To fabricate precisely designed 3D micro/nano-structures for biomedical applications via TPP nanolithography, the use of photoinitiators (PIs) and photoresists needs to be considered comprehensively and systematically. In this review, widely used commercially available PIs are first discussed, followed by elucidating synthesis strategies of water-soluble initiators for biomedical applic...
Diamondoids are cage-like hydrocarbon materials with unique characteristics such as low dielectri... more Diamondoids are cage-like hydrocarbon materials with unique characteristics such as low dielectric constants, negative electron affinity, large steric bulk, and electron-donating ability. They are widely used for advanced functional materials in nanocomposite science. Surface modification of diamondoids also produces functional derivatives that broaden its applications. This article provides a concise review of the fundamentals of diamondoids, including their origin and functionalization, electronic structure, optical properties, and vibrational characteristics. The recent advances of diamondoids and their derivatives in applications, such as nanocomposites and thin film coatings, are presented. The fabrication of diamondoid-based nanostructured devices, including electron emitters, catalyst sensors, and light-emitting diodes, are also reviewed. Finally, the future developments of this unique class of hydrocarbon materials in producing a novel nanostructure system using advanced nan...
Electroactive hydrogels have received increasing attention due to the possibility of being used i... more Electroactive hydrogels have received increasing attention due to the possibility of being used in biomimetics, such as for soft robotics and artificial muscles. However, the applications are hindered by the poor mechanical properties and slow response time. To address these issues, in this study, supramolecular ionic polymer–carbon nanotube (SIPC) composite hydrogels were fabricated via in situ free radical polymerization. The polymer matrix consisted of carbon nanotubes (CNTs), styrene sulfonic sodium (SSNa), β-cyclodextrin (β-CD)-grafted acrylamide, and ferrocene (Fc)-grafted acrylamide, with the incorporation of SSNa serving as the ionic source. On applying an external voltage, the ions accumulate on one side of the matrix, leading to localized swelling and bending of the structure. Therefore, a controllable and reversible actuation can be achieved by changing the applied voltage. The tensile strength of the SIPC was improved by over 300%, from 12 to 49 kPa, due to the reinforce...
Four-dimensional (4D) printable light-powered materials have emerged as a new generation of mater... more Four-dimensional (4D) printable light-powered materials have emerged as a new generation of materials for the development of functional devices. The design of these types of materials is mostly based on the trans-cis transformation of azobenzene moieties in a liquid crystalline elastomer (LCE) matrix, in which the motion is triggered by ultraviolet (UV) irradiation. In this paper, we first report on a direct laser printable photoresist for producing light-powered 4D structures with enhanced mechanical properties and near-infrared (NIR) responsive mechanical deformation. The reported nanocomposite design is based on the photothermal effects of gold nanorods (AuNRs), which can induce the nematic-to-isotropic (N-to-I) transition of LCE upon exposure to NIR irradiation. The miscibility between AuNRs and LCE is enhanced by thiolfunctionalization. Appropriate printing parameters are determined, and nanocomposites containing 0-3 wt.% of AuNR loading are fabricated via femtosecond two-photon direct laser writing (DLW). The effects of the AuNR loading fraction and laser power on the light-powered actuating performance are evaluated. It is found that the nanocomposite with AuNR loading of 3 wt.% demonstrates the maximum percentage (20 %) of elongation under an NIR laser power of 2 W. An increase in laser power can lead to faster deformation but slower restoration. The nanocomposites demonstrate relatively good stability. Even after 300 actuation cycles, 80 % of the elongation magnitude can be retained. In addition, an improvement of 80 % in the complex modulus of the nanocomposites, due to the inclusion of AuNRs, is observed.
International Communications in Heat and Mass Transfer, 2019
The application of developed thermal models has demonstrated that parameters, such as power, scan... more The application of developed thermal models has demonstrated that parameters, such as power, scanning velocity and spot diameter of laser beams have considerable effects on the formation of weld pools. The properties of the weld metal are heavily dependent on the solidification microstructure, and an accurate prediction of the weld pool solidification requires consideration in both the thermodynamics and kinetics of solidification. The computations we presented for a transient three-dimensional model show the aspects of weld pool formation and solidification in a quantitative manner. Our focus was the examination of heat transfer and fluid flow analysis in laser micro-welding of thin stainless-steel sheet (SUS304) using the computational fluid dynamics (CFD) approach. In this research work, a useful linkage between the laser micro-welding parameters and the geometry of the microweld can be derived from the results, and informative guidance was achieved as to how the width, depth and length of the weld pool differ during laser micro-welding as a function of spot diameter, scanning velocity and laser power. The simulation results have been compared with two sets of experimental data to predict the weld bead geometry and solidification pattern made on thin stainless steel sheet using a continuous wave (CW) fibre laser. The reasonable agreement between the simulated and experimental results, demonstrates the reliability of the computed model, and the results can be used to determine the laser microwelding conditions necessary to achieve an appropriate target microstructure. However, the results allow estimation of acceptable ranges of welding variables, to attain the required micro-weld geometry.
The demands for achieving microencapsulated phase-change materials (MEPCMs) with high thermal-ene... more The demands for achieving microencapsulated phase-change materials (MEPCMs) with high thermal-energy storage ability have motivated increasing research interest in inorganic filler-modified MEPCMs. However, challenges for such MEPCMs still exist in the pursuit of good compatibility of inorganic particles with the core or shell material. Here, a novel type of octadecylamine-grafted graphene oxide (GO-ODA)-modified MEPCMs using melamine-formaldehyde (MF) resin as the shell material and the mixture of GO-ODA and n-octadecane as the core material was fabricated via in-situ polymerization. The alkylated GO with a thickness of ~ 1 nm was confirmed to be highly compatible with the core material. The as-prepared MEPCMs with a regular spherical shape were dispersed without any agglomeration, and the size decreased with increasing the filling amounts of GO-ODA. The incorporation of GO-ODA
Biomechanics and modeling in mechanobiology, Jan 5, 2018
Cell contraction regulates how cells sense their mechanical environment. We sought to identify th... more Cell contraction regulates how cells sense their mechanical environment. We sought to identify the set-point of cell contraction, also referred to as tensional homeostasis. In this work, bovine aortic endothelial cells (BAECs), cultured on substrates with different stiffness, were characterized using traction force microscopy (TFM). Numerical models were developed to provide insights into the mechanics of cell-substrate interactions. Cell contraction was modeled as eigenstrain which could induce isometric cell contraction without external forces. The predicted traction stresses matched well with TFM measurements. Furthermore, our numerical model provided cell stress and displacement maps for inspecting the fundamental regulating mechanism of cell mechanosensing. We showed that cell spread area, traction force on a substrate, as well as the average stress of a cell were increased in response to a stiffer substrate. However, the cell average strain, which is cell type-specific, was ke...
It has been commonly discovered that reducing particle size always accompanies with undesirable d... more It has been commonly discovered that reducing particle size always accompanies with undesirable deterioration of drug encapsulation efficiency in double emulsion based techniques. However, a clear optimization strategy for process variables to minimize this negative impact has been rarely reported. To fill this gap, we have successfully developed an optimization strategy for silica xerogel/polymer composite nanoparticles prepared by our recently developed gelation‐emulsion method. To develop this strategy, interactive effects of multiple process variables were investigated through a four‐factor three‐level experimental design by considering all screened dominant process variables influencing particle size and encapsulation efficiency, including sonication time of second emulsion (t2), sonication power of the second emulsion (P2), total volume of the second emulsion (V2) and volume ratio of aqueous phase and primary emulsion (r). The optimization strategy for fabricating the target p...
The tensile properties of polypropylene (PP) composites filled separately with three kinds of gra... more The tensile properties of polypropylene (PP) composites filled separately with three kinds of graphene nano-platelets (GNPs) with different size were measured using a universal materials tester at room temperature and rate of extension of 50 mm/min. It was found that the values of the Young's modulus of the composites increased, the values of the tensile yield strength and tensile fracture of the composites increased slightly while the values of the tensile elongation at break decreased with increasing the GNPs weight fraction. The reinforcement of the composites could be attributed to the relatively big interfacial area and good interfacial adhesion between the matrix and the GNPs.
Abstract The effects of the filler size and content on thermal properties and thermal stability o... more Abstract The effects of the filler size and content on thermal properties and thermal stability of polypropylene (PP) composites filled with four different sizes of multi-walled carbon nanotubes (MWCNTs) were investigated through thermogravimetric analysis. The results showed that the values of the decomposition temperature increased with increasing weight fraction and length–diameter ratio of the filler, while increased with decreasing filler diameter. The values of the residues increased approximately linearly with increasing filler weight fraction. The values of maximum mass loss rate decreased roughly with increasing filler weight fraction, while the influence of the filler diameter and length–diameter ratio on the maximum mass loss rate was insignificant. The thermal stability improvement might be attributed to the barrier function of the MWCNTs. This study provides a basis for further development of MWCNTs reinforced polymer composites with desirable thermal properties for potential application as energy materials.
The hydroxyapatite/graphene (HAP/Gr) composite was electrodeposited on Ti using the electrophoret... more The hydroxyapatite/graphene (HAP/Gr) composite was electrodeposited on Ti using the electrophoretic deposition process to obtain uniform bioactive coating with improved mechanical strength and favorable corrosion stability in simulated body fluid (SBF). Incorporation of Gr was verified by Raman spectroscopy, X-ray diffraction, Fourier transform infrared spectroscopy, thermogravimetric analysis, and X-ray photoelectron analysis. The HAP/Gr composite coating exhibited reduced surface cracks, nearly double the hardness, and elastic modulus increased by almost 50% compared to pure HAP coating, as estimated by a nanoindentation test. The bioactive HAP/Gr composite coating provided a newly formed apatite layer in SBF with enhanced corrosion stability, as evidenced by electrochemical impedance spectroscopy. The thermal stability of the HAP/Gr coating was improved in comparison to the pure HAP coating, and the Ca/P ratio was closer to the stoichiometric value. No antibacterial activity against S. aureus or E. coli could be verified. The HAP/Gr composite coating was classified as noncytotoxic when tested against healthy peripheral blood mononuclear cells (PBMC).
Hydroxyapatite (HAP) is the most suitable biocompatible material for bone implant coatings; its b... more Hydroxyapatite (HAP) is the most suitable biocompatible material for bone implant coatings; its brittleness, however, is a major obstacle, and the reason why research focuses on creating composites with biopolymers. Organosolv lignin (Lig) is used for the production of composite coatings, and these composites were examined in this study. Titanium substrate is a key biomedical material due to its well-known properties, but infections of the implantation site still impose a serious threat. One approach to prevent infection is to improve antimicrobial properties of the coating material. Silver doped hydroxyapatite (Ag/HAP) and HAP coatings on titanium were obtained by an electrophoretic deposition method in order to control deposited coating mass and morphology by varying applied voltage and deposition time. The effect of lignin on microstructure, morphology and thermal behavior of biocomposite coatings was investigated. The results showed that higher lignin concentrations protect the HAP lattice during sintering, improving coating stability. The corrosion stability was evaluated in simulated body fluid (SBF) at 37 °C. Newly formed plate-shaped carbonate-HAP was
Two-photon polymerization direct laser writing (TPP DLW) is an emerging technology for producing ... more Two-photon polymerization direct laser writing (TPP DLW) is an emerging technology for producing advanced functional devices with complex three-dimensional (3D) micro-structures. Tremendous efforts have been devoted to developing two-photon polymerizable photo-sensitive nanocomposites with tailored properties. Light-induced reconfigurable smart materials such as liquid crystalline elastomers (LCEs) are promising materials. However, due to the difficulties in designing two-photon polymerizable liquid crystal monomer (LCM) nanocomposite photoresists, it is challenging to fabricate true 3D LCE micro-structures. In this paper, we report the preparation of photo-sensitive LCE nanocomposites containing photothermal nanomaterials, including multiwalled carbon nanotubes, graphene oxide and gold nanorods (AuNRs), for TPP DLW. The printability of the LCE nanocomposites is assessed by the fidelity of the micro-structures under different laser writing conditions. DLW of GO/LCM photoresist has s...
Journal of Thermoplastic Composite Materials, 2017
The thermal properties and thermal stability of polypropylene (PP) composites separately filled w... more The thermal properties and thermal stability of polypropylene (PP) composites separately filled with graphene nanoplatelets (GNPs) with three different sizes were measured using a differential scanning calorimetry and a thermal gravimetric analyser. The results showed that the values of the melting temperature of the composites were higher than that of the unfilled PP; the thermal stability increased with increasing the weight fraction and lateral dimension of GNPs in the case of low filler concentration, while the effect of the GNPs thickness on the thermal stability was insignificant; the onset decomposition temperature increased with increasing the GNPs lateral dimension, while the maximum thermal decomposition rate increased first and then decreased with increasing the GNPs weight fraction. The thermal stability improvement should be attributed to the sheet barrier function of the GNPs.
Abstract Biodegradable polymer–inorganic composites particles can provide significant advantages ... more Abstract Biodegradable polymer–inorganic composites particles can provide significant advantages while avoiding the shortcomings of using polymer or inorganic particles alone as drug delivery vehicles. Most of the existing fabrication methods for polymer nanoparticles and silica xerogel nanoparticles are not applicable for composite nanoparticles. To overcome these difficulties, a novel gelation–emulsion method was successfully developed through the integration of sol–gel and modified double emulsion processes, in which gelation of the silica solution was enabled in nanodroplets generated in the modified emulsion process. Spherical vancomycin loaded silica xerogel/polymer core–shell composite nanoparticles with a tunable size and good drug encapsulation efficiency were fabricated through this novel method. By changing the process variables of the modified double emulsion process in terms of the second sonication time and PVA concentration, the average diameter of the composite nanoparticles could be adjusted in the range of 192–569 nm, with a maximum encapsulation efficiency up to 82.2%. With the introduction of silica xerogel as the primary core material by the sol–gel process, the prepared composite nanoparticles exhibited a higher encapsulation efficiency, lower burst drug release and longer drug complete release time than the polymer nanoparticles by 110%, 37.5% and 230%, respectively, enabling these composite nanoparticles to be better candidates for long-term sustained drug release applications. Formation mechanisms of the composite nanoparticles with respect to the second sonication time and PVA concentration were also discussed.
UV protection and coatings for plastics are important in many applications. The cladding of low m... more UV protection and coatings for plastics are important in many applications. The cladding of low microwave (MW) absorption composite coatings on high MW transparent plastic substrates is a challenge due to their disparate dielectric properties. Moreover, an uneven heat energy conversion within the composite creates an additional hurdle in producing a coating with good surface integrity. In this study, a protocol was developed to overcome these difficulties based on a hybrid approach. The adverse effect of temperature mismatch between the coating and substrate was reduced through a two-way susceptor-aided heating mechanism. Low MW absorbing sol–gel derived composite coatings consisting of silicon dioxide (SiO2) and titanium dioxide (TiO2) were successfully cladded on the surface of MW and visual light transparent polycarbonate to produce a clear protective coating with UV-resistance. Nanoindentation tests were conducted to assess the effectiveness of the proposed protocol. Significant...
Silanization processes with perfluoroalkyl silanes have been demonstrated to be effective in deve... more Silanization processes with perfluoroalkyl silanes have been demonstrated to be effective in developing advanced materials with many functional properties, including hydrophobicity, water repellency, and self-cleaning properties. However, practical industrial applications of perfluoroalkyl silanes are limited by their extremely high cost. On the basis of our recent work on photoredox catalysis for amidation with perfluoroalkyl iodides, its application for surface chemical modification on filter paper, as an illustrative example, has been developed and evaluated. Before photocatalytic amidation, the surface is functionalized with amine functional groups by silanization with 3-(trimethoxysilyl)propylamine. All chemically modified surfaces have been fully characterized by attenuated total reflection infrared (ATR-IR), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy with energy-dispersive spectroscopy (SEM-EDS), and three-dimensional (3D) profiling to confirm the successful silanization and photocatalytic amidation. After surface modification of the filter papers with perfluoroalkanamide, they show high water repellency and hydrophobicity with contact angles over 120°. These filter papers possess high wetting selectivity, which can be used to effectively separate the organic and aqueous biphasic mixtures. The perfluoroalkanamide-modified filter papers can be used for separating organic/aqueous biphasic mixtures over many cycles without lowering the separating efficiency, indicating their reusability and excellent durability.
The International Journal of Advanced Manufacturing Technology, 2020
Microwave (MW) sintering offers higher heating rate, rapid processing, reduced energy consumption... more Microwave (MW) sintering offers higher heating rate, rapid processing, reduced energy consumption, and reduced sintering temperature. However, the technique is not fully understood, difficult to control, and often relies on experience and trial-and-error approach. Consequently, hot spots, uneven heating, thermal runaway, and shape distortion develop in sintered compacts. Therefore, developing a model that can simulate the sintering process, enhance predictability, and determine the critical sintering conditions is essential. Multiphysics finite element (FE) modelling of hybrid MW sintering of a magnesium alloy AZ61 compact was undertaken in this study. The FE model coupled the electromagnetic, heat conduction, and densification equations. The model utilised parameters related to the furnace, compact, and susceptor to predict the spatial distribution of electric field, thermal response, and densification in the compact. A power-based sintering criterion was developed to predict the sintering of the compact and estimate its critical sintering energy. Modelling results showed that heating time, compact size, and thickness of the susceptor are critical to the sintering process. It was also shown that the susceptor not only mediated the sintering of the compact but also homogenised its temperature and densification. Thus, MW sintering of the compact was predicted to occur at 500°C for 8 to 10 min with a predicted relative density of about 0.98. Experimental MW sintering data showed good concurrence with the developed model. These results are useful for controlling the MW sintering process, eliminating trial-and-error, and determining the critical sintering conditions.
This review is intended to provide an overview of the design and fabrication of ionic liquid-base... more This review is intended to provide an overview of the design and fabrication of ionic liquid-based ionic electroactive polymer (IL-iEAP) transducers for advanced applications in biological and electronic fields. The iEAP is a class of smart materials that can perform sensing or actuating functions by controlling the movement of cations and anions in the active layer. This type of material can deform under low voltage stimulation and generate electrical signals when undergoing mechanical deformation because of ion redistribution. Numerous research attention has been focused on studying the deformation mechanisms and the potential for actuation, sensing, and energy harvesting applications. Compared to the traditional water-based iEAP, the non-volatile IL-iEAP delivers a wider electrochemical window and a more stable actuation performance. In this paper, the classification of iEAP with different actuation mechanisms is first outlined, followed by introducing various preparation methods...
Micro/nano-fabrication technology via two-photon polymerization (TPP) nanolithography is a powerf... more Micro/nano-fabrication technology via two-photon polymerization (TPP) nanolithography is a powerful and useful manufacturing tool that is capable of generating two dimensional (2D) to three dimensional (3D) arbitrary micro/nano-structures of various materials with a high spatial resolution. This technology has received tremendous interest in cell and tissue engineering and medical microdevices because of its remarkable fabrication capability for sophisticated structures from macro- to nano-scale, which are difficult to be achieved by traditional methods with limited microarchitecture controllability. To fabricate precisely designed 3D micro/nano-structures for biomedical applications via TPP nanolithography, the use of photoinitiators (PIs) and photoresists needs to be considered comprehensively and systematically. In this review, widely used commercially available PIs are first discussed, followed by elucidating synthesis strategies of water-soluble initiators for biomedical applic...
Diamondoids are cage-like hydrocarbon materials with unique characteristics such as low dielectri... more Diamondoids are cage-like hydrocarbon materials with unique characteristics such as low dielectric constants, negative electron affinity, large steric bulk, and electron-donating ability. They are widely used for advanced functional materials in nanocomposite science. Surface modification of diamondoids also produces functional derivatives that broaden its applications. This article provides a concise review of the fundamentals of diamondoids, including their origin and functionalization, electronic structure, optical properties, and vibrational characteristics. The recent advances of diamondoids and their derivatives in applications, such as nanocomposites and thin film coatings, are presented. The fabrication of diamondoid-based nanostructured devices, including electron emitters, catalyst sensors, and light-emitting diodes, are also reviewed. Finally, the future developments of this unique class of hydrocarbon materials in producing a novel nanostructure system using advanced nan...
Electroactive hydrogels have received increasing attention due to the possibility of being used i... more Electroactive hydrogels have received increasing attention due to the possibility of being used in biomimetics, such as for soft robotics and artificial muscles. However, the applications are hindered by the poor mechanical properties and slow response time. To address these issues, in this study, supramolecular ionic polymer–carbon nanotube (SIPC) composite hydrogels were fabricated via in situ free radical polymerization. The polymer matrix consisted of carbon nanotubes (CNTs), styrene sulfonic sodium (SSNa), β-cyclodextrin (β-CD)-grafted acrylamide, and ferrocene (Fc)-grafted acrylamide, with the incorporation of SSNa serving as the ionic source. On applying an external voltage, the ions accumulate on one side of the matrix, leading to localized swelling and bending of the structure. Therefore, a controllable and reversible actuation can be achieved by changing the applied voltage. The tensile strength of the SIPC was improved by over 300%, from 12 to 49 kPa, due to the reinforce...
Four-dimensional (4D) printable light-powered materials have emerged as a new generation of mater... more Four-dimensional (4D) printable light-powered materials have emerged as a new generation of materials for the development of functional devices. The design of these types of materials is mostly based on the trans-cis transformation of azobenzene moieties in a liquid crystalline elastomer (LCE) matrix, in which the motion is triggered by ultraviolet (UV) irradiation. In this paper, we first report on a direct laser printable photoresist for producing light-powered 4D structures with enhanced mechanical properties and near-infrared (NIR) responsive mechanical deformation. The reported nanocomposite design is based on the photothermal effects of gold nanorods (AuNRs), which can induce the nematic-to-isotropic (N-to-I) transition of LCE upon exposure to NIR irradiation. The miscibility between AuNRs and LCE is enhanced by thiolfunctionalization. Appropriate printing parameters are determined, and nanocomposites containing 0-3 wt.% of AuNR loading are fabricated via femtosecond two-photon direct laser writing (DLW). The effects of the AuNR loading fraction and laser power on the light-powered actuating performance are evaluated. It is found that the nanocomposite with AuNR loading of 3 wt.% demonstrates the maximum percentage (20 %) of elongation under an NIR laser power of 2 W. An increase in laser power can lead to faster deformation but slower restoration. The nanocomposites demonstrate relatively good stability. Even after 300 actuation cycles, 80 % of the elongation magnitude can be retained. In addition, an improvement of 80 % in the complex modulus of the nanocomposites, due to the inclusion of AuNRs, is observed.
International Communications in Heat and Mass Transfer, 2019
The application of developed thermal models has demonstrated that parameters, such as power, scan... more The application of developed thermal models has demonstrated that parameters, such as power, scanning velocity and spot diameter of laser beams have considerable effects on the formation of weld pools. The properties of the weld metal are heavily dependent on the solidification microstructure, and an accurate prediction of the weld pool solidification requires consideration in both the thermodynamics and kinetics of solidification. The computations we presented for a transient three-dimensional model show the aspects of weld pool formation and solidification in a quantitative manner. Our focus was the examination of heat transfer and fluid flow analysis in laser micro-welding of thin stainless-steel sheet (SUS304) using the computational fluid dynamics (CFD) approach. In this research work, a useful linkage between the laser micro-welding parameters and the geometry of the microweld can be derived from the results, and informative guidance was achieved as to how the width, depth and length of the weld pool differ during laser micro-welding as a function of spot diameter, scanning velocity and laser power. The simulation results have been compared with two sets of experimental data to predict the weld bead geometry and solidification pattern made on thin stainless steel sheet using a continuous wave (CW) fibre laser. The reasonable agreement between the simulated and experimental results, demonstrates the reliability of the computed model, and the results can be used to determine the laser microwelding conditions necessary to achieve an appropriate target microstructure. However, the results allow estimation of acceptable ranges of welding variables, to attain the required micro-weld geometry.
The demands for achieving microencapsulated phase-change materials (MEPCMs) with high thermal-ene... more The demands for achieving microencapsulated phase-change materials (MEPCMs) with high thermal-energy storage ability have motivated increasing research interest in inorganic filler-modified MEPCMs. However, challenges for such MEPCMs still exist in the pursuit of good compatibility of inorganic particles with the core or shell material. Here, a novel type of octadecylamine-grafted graphene oxide (GO-ODA)-modified MEPCMs using melamine-formaldehyde (MF) resin as the shell material and the mixture of GO-ODA and n-octadecane as the core material was fabricated via in-situ polymerization. The alkylated GO with a thickness of ~ 1 nm was confirmed to be highly compatible with the core material. The as-prepared MEPCMs with a regular spherical shape were dispersed without any agglomeration, and the size decreased with increasing the filling amounts of GO-ODA. The incorporation of GO-ODA
Biomechanics and modeling in mechanobiology, Jan 5, 2018
Cell contraction regulates how cells sense their mechanical environment. We sought to identify th... more Cell contraction regulates how cells sense their mechanical environment. We sought to identify the set-point of cell contraction, also referred to as tensional homeostasis. In this work, bovine aortic endothelial cells (BAECs), cultured on substrates with different stiffness, were characterized using traction force microscopy (TFM). Numerical models were developed to provide insights into the mechanics of cell-substrate interactions. Cell contraction was modeled as eigenstrain which could induce isometric cell contraction without external forces. The predicted traction stresses matched well with TFM measurements. Furthermore, our numerical model provided cell stress and displacement maps for inspecting the fundamental regulating mechanism of cell mechanosensing. We showed that cell spread area, traction force on a substrate, as well as the average stress of a cell were increased in response to a stiffer substrate. However, the cell average strain, which is cell type-specific, was ke...
It has been commonly discovered that reducing particle size always accompanies with undesirable d... more It has been commonly discovered that reducing particle size always accompanies with undesirable deterioration of drug encapsulation efficiency in double emulsion based techniques. However, a clear optimization strategy for process variables to minimize this negative impact has been rarely reported. To fill this gap, we have successfully developed an optimization strategy for silica xerogel/polymer composite nanoparticles prepared by our recently developed gelation‐emulsion method. To develop this strategy, interactive effects of multiple process variables were investigated through a four‐factor three‐level experimental design by considering all screened dominant process variables influencing particle size and encapsulation efficiency, including sonication time of second emulsion (t2), sonication power of the second emulsion (P2), total volume of the second emulsion (V2) and volume ratio of aqueous phase and primary emulsion (r). The optimization strategy for fabricating the target p...
The tensile properties of polypropylene (PP) composites filled separately with three kinds of gra... more The tensile properties of polypropylene (PP) composites filled separately with three kinds of graphene nano-platelets (GNPs) with different size were measured using a universal materials tester at room temperature and rate of extension of 50 mm/min. It was found that the values of the Young's modulus of the composites increased, the values of the tensile yield strength and tensile fracture of the composites increased slightly while the values of the tensile elongation at break decreased with increasing the GNPs weight fraction. The reinforcement of the composites could be attributed to the relatively big interfacial area and good interfacial adhesion between the matrix and the GNPs.
Abstract The effects of the filler size and content on thermal properties and thermal stability o... more Abstract The effects of the filler size and content on thermal properties and thermal stability of polypropylene (PP) composites filled with four different sizes of multi-walled carbon nanotubes (MWCNTs) were investigated through thermogravimetric analysis. The results showed that the values of the decomposition temperature increased with increasing weight fraction and length–diameter ratio of the filler, while increased with decreasing filler diameter. The values of the residues increased approximately linearly with increasing filler weight fraction. The values of maximum mass loss rate decreased roughly with increasing filler weight fraction, while the influence of the filler diameter and length–diameter ratio on the maximum mass loss rate was insignificant. The thermal stability improvement might be attributed to the barrier function of the MWCNTs. This study provides a basis for further development of MWCNTs reinforced polymer composites with desirable thermal properties for potential application as energy materials.
The hydroxyapatite/graphene (HAP/Gr) composite was electrodeposited on Ti using the electrophoret... more The hydroxyapatite/graphene (HAP/Gr) composite was electrodeposited on Ti using the electrophoretic deposition process to obtain uniform bioactive coating with improved mechanical strength and favorable corrosion stability in simulated body fluid (SBF). Incorporation of Gr was verified by Raman spectroscopy, X-ray diffraction, Fourier transform infrared spectroscopy, thermogravimetric analysis, and X-ray photoelectron analysis. The HAP/Gr composite coating exhibited reduced surface cracks, nearly double the hardness, and elastic modulus increased by almost 50% compared to pure HAP coating, as estimated by a nanoindentation test. The bioactive HAP/Gr composite coating provided a newly formed apatite layer in SBF with enhanced corrosion stability, as evidenced by electrochemical impedance spectroscopy. The thermal stability of the HAP/Gr coating was improved in comparison to the pure HAP coating, and the Ca/P ratio was closer to the stoichiometric value. No antibacterial activity against S. aureus or E. coli could be verified. The HAP/Gr composite coating was classified as noncytotoxic when tested against healthy peripheral blood mononuclear cells (PBMC).
Hydroxyapatite (HAP) is the most suitable biocompatible material for bone implant coatings; its b... more Hydroxyapatite (HAP) is the most suitable biocompatible material for bone implant coatings; its brittleness, however, is a major obstacle, and the reason why research focuses on creating composites with biopolymers. Organosolv lignin (Lig) is used for the production of composite coatings, and these composites were examined in this study. Titanium substrate is a key biomedical material due to its well-known properties, but infections of the implantation site still impose a serious threat. One approach to prevent infection is to improve antimicrobial properties of the coating material. Silver doped hydroxyapatite (Ag/HAP) and HAP coatings on titanium were obtained by an electrophoretic deposition method in order to control deposited coating mass and morphology by varying applied voltage and deposition time. The effect of lignin on microstructure, morphology and thermal behavior of biocomposite coatings was investigated. The results showed that higher lignin concentrations protect the HAP lattice during sintering, improving coating stability. The corrosion stability was evaluated in simulated body fluid (SBF) at 37 °C. Newly formed plate-shaped carbonate-HAP was
Two-photon polymerization direct laser writing (TPP DLW) is an emerging technology for producing ... more Two-photon polymerization direct laser writing (TPP DLW) is an emerging technology for producing advanced functional devices with complex three-dimensional (3D) micro-structures. Tremendous efforts have been devoted to developing two-photon polymerizable photo-sensitive nanocomposites with tailored properties. Light-induced reconfigurable smart materials such as liquid crystalline elastomers (LCEs) are promising materials. However, due to the difficulties in designing two-photon polymerizable liquid crystal monomer (LCM) nanocomposite photoresists, it is challenging to fabricate true 3D LCE micro-structures. In this paper, we report the preparation of photo-sensitive LCE nanocomposites containing photothermal nanomaterials, including multiwalled carbon nanotubes, graphene oxide and gold nanorods (AuNRs), for TPP DLW. The printability of the LCE nanocomposites is assessed by the fidelity of the micro-structures under different laser writing conditions. DLW of GO/LCM photoresist has s...
Journal of Thermoplastic Composite Materials, 2017
The thermal properties and thermal stability of polypropylene (PP) composites separately filled w... more The thermal properties and thermal stability of polypropylene (PP) composites separately filled with graphene nanoplatelets (GNPs) with three different sizes were measured using a differential scanning calorimetry and a thermal gravimetric analyser. The results showed that the values of the melting temperature of the composites were higher than that of the unfilled PP; the thermal stability increased with increasing the weight fraction and lateral dimension of GNPs in the case of low filler concentration, while the effect of the GNPs thickness on the thermal stability was insignificant; the onset decomposition temperature increased with increasing the GNPs lateral dimension, while the maximum thermal decomposition rate increased first and then decreased with increasing the GNPs weight fraction. The thermal stability improvement should be attributed to the sheet barrier function of the GNPs.
Abstract Biodegradable polymer–inorganic composites particles can provide significant advantages ... more Abstract Biodegradable polymer–inorganic composites particles can provide significant advantages while avoiding the shortcomings of using polymer or inorganic particles alone as drug delivery vehicles. Most of the existing fabrication methods for polymer nanoparticles and silica xerogel nanoparticles are not applicable for composite nanoparticles. To overcome these difficulties, a novel gelation–emulsion method was successfully developed through the integration of sol–gel and modified double emulsion processes, in which gelation of the silica solution was enabled in nanodroplets generated in the modified emulsion process. Spherical vancomycin loaded silica xerogel/polymer core–shell composite nanoparticles with a tunable size and good drug encapsulation efficiency were fabricated through this novel method. By changing the process variables of the modified double emulsion process in terms of the second sonication time and PVA concentration, the average diameter of the composite nanoparticles could be adjusted in the range of 192–569 nm, with a maximum encapsulation efficiency up to 82.2%. With the introduction of silica xerogel as the primary core material by the sol–gel process, the prepared composite nanoparticles exhibited a higher encapsulation efficiency, lower burst drug release and longer drug complete release time than the polymer nanoparticles by 110%, 37.5% and 230%, respectively, enabling these composite nanoparticles to be better candidates for long-term sustained drug release applications. Formation mechanisms of the composite nanoparticles with respect to the second sonication time and PVA concentration were also discussed.
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Papers by Gary Tsui