Four types of submicron Ag-coated Cu particles with different Ag contents were prepared as sintering paste fillers,and the Ag contents of the particles were measured to be 10,20,30,and 40 wt.%.Four types of particles(...Four types of submicron Ag-coated Cu particles with different Ag contents were prepared as sintering paste fillers,and the Ag contents of the particles were measured to be 10,20,30,and 40 wt.%.Four types of particles(in order of increasing Ag content:A10,A20,A30,and A40)were surface-modified with stearic acid,to suppress the Ag shell dewetting and improve sinterability.The surface-modified particles were mixed with a polyol-based solvent to fabricate a resin-free paste.Subsequently,the pastes were screen-printed onto a slide glass and sintered at 250°C in a nitrogen atmosphere for 1-10 min to form an electrode.The electrical resistivity of the sintered film as a function of sintering time was measured using a four-point probe.All the four surface-modified Cu@Ag particles with different Ag contents exhibited decreased electrical resistivity.Particularly,the largest difference in values after and before the surface modification was observed for A40 with the highest Ag content;the electrical resistivities of the initial and surface-modified particles were 1.51×10^(-4) and 6.67×10^(-5)Ω·cm,respectively,after sintering for 10 min.The findings of this study confirmed that the surface modification using stearic acid effectively suppressed the dewetting of the Ag shell and improved the sinterability of the submicron Cu@Ag particles.展开更多
Hydrogen-bonded polymer complex films with the thickness ranging from 50 nm to 2400 nm were prepared by layer-by-layer （LbL） assembly of poly（2-ethyl-2-oxazoline） （PEOX） and poly（acrylic acid） （PAA）. The dew...Hydrogen-bonded polymer complex films with the thickness ranging from 50 nm to 2400 nm were prepared by layer-by-layer （LbL） assembly of poly（2-ethyl-2-oxazoline） （PEOX） and poly（acrylic acid） （PAA）. The dewetting behavior of PEOX/PAA films under hydrothermal condition was investigated. It was found that the dewetting occurred at solid-liquid interface, and the typical morphologies such as holes, irregular cellular structure, and droplets were observed. Atomic force microscopy （AFM） revealed the initial rupture of the film. Microscopic Raman and infrared （IR） imaging demonstrated that the PEOX and PAA chains remained association during the dewetting process.展开更多
In this work, monodisperse giant polymersomes are fabricated by dewetting of water-in-oil-in-water double emulsion droplets which are assembled by amphiphilic block copolymer molecules in a microfluidic device. The de...In this work, monodisperse giant polymersomes are fabricated by dewetting of water-in-oil-in-water double emulsion droplets which are assembled by amphiphilic block copolymer molecules in a microfluidic device. The dewetting process can be tuned by solvation between solvent and amphiphilic block copolymer to get polymersomes with controllable morphology. Good solvent （chloroform and toluene） hinders dewetting process of double emulsion droplets and gets acornlike polymersomes or patched polymersomes. On the other hand, poor solvent （hexane） accelerates the dewetting process and achieves complete separation of inner water phase from oil phase to form complete bilayer polymersomes. In addition, twin polymersomes with bilayer membrane structure are formed by this facile method. The formation mechanism for different polymersomes is discussed in detail.展开更多
We have investigated the influence of the adsorption process on the dewetting behavior of the linear polystyrene film （LPS）, the 3-arm star polystyrene film （3SPS） and the ring polystyrene film （RPS） on the sila...We have investigated the influence of the adsorption process on the dewetting behavior of the linear polystyrene film （LPS）, the 3-arm star polystyrene film （3SPS） and the ring polystyrene film （RPS） on the silanized Si substrate. Results show that the adsorption process greatly influences the dewetting behavior of the thin polymer films. On the silanized Si substrate, the 3SPS chains exhibit stronger adsorption compared with the LPS chains and RPS chains; as a result, the wetting layer forms more easily. For LPS films, with the decrease of annealing temperature, the kinetics of polymer film changes from exponential behavior to slip dewetting. As a comparison, the stability of 3SPS and RPS films switches from slip dewetting to unusual dewetting kinetic behavior. The adsorbed nanodroplets on the solid substrate play an important role in the dewetting kinetics by reducing the driving force of dewetting and increase the resistant force of dewetting. Additionally, Brownian dynamics （BD） simulation shows that the absolute values of adsorption energy （ε） gradually increase from linear polymer （-0.3896） to ring polymer （-0.4033） and to star polymer （-0.4264）, which is consistent with the results of our adsorption experiments.展开更多
The effects of film thickness and composition ratio on the morphology evolution of polystyrene （PS）/poly（vinyl methyl ether） （PVME） blend thin films were investigated. Diverse morphology evolutions including dro...The effects of film thickness and composition ratio on the morphology evolution of polystyrene （PS）/poly（vinyl methyl ether） （PVME） blend thin films were investigated. Diverse morphology evolutions including droplet-matrix structure, hole emergence, bicontinuous structure formation, percolation-to-droplet transition could be observed under annealing in two-phase region, depending on film thickness and composition ratio. The mechanism for these morphology variations was related to the complex effects of phase separation, dewetting and preferential wetting. The comparison between the thickness of bottom PVME layer and the twice of gyration radius 2Rg（PVME） played a dominant role in morphology control. Only when the PS/PVME film had specific film thickness and compositional symmetry, phase separation and dewetting could happen in sequence.展开更多
A novel solvent-sensitive fluorescent actuator with reversibility has been obtained from carbon dots （CDs） inverse opals, which is prepared via infiltrating CDs solution into the interstice of colloidal crystal temp...A novel solvent-sensitive fluorescent actuator with reversibility has been obtained from carbon dots （CDs） inverse opals, which is prepared via infiltrating CDs solution into the interstice of colloidal crystal template, thermal polymerization of CDs materials and removing the colloidal template. The as-prepared CDs inverse opal actuator shows a bending angle of 75° in 10.2 s, bending rate of 7.35 （°）.s-1. In particular, the fluorescence intensity of the films varies during the actuating process. The actuating behavior is attributed to the inhomogeneous swelling/shrinking of the film, which originates from the gradient dewetting by solvent evaporation and hydrogen-bonding interaction between the solvent molecules and oxygen/hydrogen ions of CDs side chain. The CDs inverse opal actuator has the advantages of quick response, good repeatability and strong fluorescence, which gives an important insight into the design and manufacture of novel and advanced solvent-actuators.展开更多
Silver(Ag) nanostructures demonstrate outstanding optical, electrical, magnetic, and catalytic properties and are utilized in photonic, energy, sensors, and biomedical devices.The target application and the performanc...Silver(Ag) nanostructures demonstrate outstanding optical, electrical, magnetic, and catalytic properties and are utilized in photonic, energy, sensors, and biomedical devices.The target application and the performance can be inherently tuned by control of configuration, shape, and size of Ag nanostructures. In this work, we demonstrate the systematical fabrication of various configurations of Ag nanostructures on sapphire(0001) by controlling the Ag deposition thickness at different annealing environments in a plasma ion coater. In particular, the evolution of Ag particles(between 2 and 20 nm),irregular nanoclusters(between 30 and 60 nm), and nanocluster networks(between 80 and 200 nm) are found be depended on the thickness of Ag thin film. The results were systematically analyzed and explained based on the solid-state dewetting,surface diffusion, Volmer–Weber growth model, coalescence,and surface energy minimization mechanism. The growth behavior of Ag nanostructures is remarkably differentiated at higher annealing temperature(750 ℃) due to the sublimation and temperature-dependent characteristic of dewetting process.In addition, Raman and reflectance spectra analyses reveal that optical properties of Ag nanostructures depend on their morphology.展开更多
Isocyanate-treated graphite oxides （iGOs） were well-dispersed into the polystyrene （PS） thin films and formed a novel network structure. With control in fabrication, an iGOs-web layer was horizontally embedded nea...Isocyanate-treated graphite oxides （iGOs） were well-dispersed into the polystyrene （PS） thin films and formed a novel network structure. With control in fabrication, an iGOs-web layer was horizontally embedded near the surface of the films and thus formed a composite slightly doped by iGOs. This work demonstrated that the iGOs network can remarkably depress the dewetting process in the polymer matrix of the composite, while dewetting often leads to rupture of polymer films and is considered as a major practical limit in using polymeric materials above their glass transition temperatures （Tg）. Via annealing the 50-120 nm thick composite and associated neat PS films at temperatures ranging from 35℃ to 70 ℃ above Tg, surface morphology evolution of the films was monitored by atomic force microscopy （AFM）. The iGOs-doped PS exhibited excellent thermal stability, i.e., the number of dewetting holes was greatly reduced and the long-term hole growth was fairly restricted. In contrast, the neat PS film showed serious surface fluctuation and a final rupture induced by ordinary dewetting. The method developed in this work may pave a road to reinforce thin polymer films and enhance their thermal stability, in order to meet requirements by technological advances.展开更多
Coarse-grained molecular dynamics simulations were carried out to investigate the dewetting behavior of a polymer thin film on partial wetting solid surface at the early stage of the dewetting process. Spontaneous dew...Coarse-grained molecular dynamics simulations were carried out to investigate the dewetting behavior of a polymer thin film on partial wetting solid surface at the early stage of the dewetting process. Spontaneous dewetting is initiated by removing a band of strip from both the ends of the liquid polymer film which has achieved equilibrium. The solid-liquid interaction and temperature were varied to show their influence on the dewetting dynamics during dewetting as well as the shape evolution of the liquid polymer film. As is consistent with the results obtained in previous researches, the liquid film recedes at a constant speed initially with different solid-liquid couplings and tempe- ratures. Furthermore, smaller coupling parameters or higher temperatures tend to accelerate the recession speed of the liquid film and shorten the constant-speed recession duration. Obvious rims were not always observed. Both coupling parameter and temperature can influence the emergence of the rims.展开更多
We investigate the influence of an external electric field on the dewetting behavior of nitrogen-water systems between two hydrophobic plates using molecular dynamics simulations. It is found that the critical distanc...We investigate the influence of an external electric field on the dewetting behavior of nitrogen-water systems between two hydrophobic plates using molecular dynamics simulations. It is found that the critical distance of dewetting increases obviously with the electric field strength, indicating that the effective range of hydrophobic attraction is extended. The mechanism behind this interesting phenomenon is related to the rearrangement of hydrogen bond networks between water molecules induced by the external electric field. Changes in the hydrogen bond networks and in the dipole orientation of the water molecules result in the redistribution of the neutral nitrogen molecules, especially in the region close to the hydrophobic plates. Our findings may be helpful for understanding the effects of the electric field on the long-range hydrophobic interactions.展开更多
The thermodynamic conditions for dewetting of a liquid solder drop on copper thin films were examined under a hot-stage optical microscope in a flowing protective atmosphere.Dewetting of liquid solder was found to dep...The thermodynamic conditions for dewetting of a liquid solder drop on copper thin films were examined under a hot-stage optical microscope in a flowing protective atmosphere.Dewetting of liquid solder was found to depend strongly on the copper film thickness and preceded by spalling of Cu 6 Sn 5 intermetallic compounds.However,the loss of interfacial bonding by spalling was not sufficient to cause immediate dewetting of solder drops if the wetting tip was still strongly bonded to the copper film.By introducing a pinning force on the wetting front,a sufficient condition was found from a force balance analysis for dewetting of the liquid solder drop,in general agreement with the experimental results.展开更多
Molecular dynamics simulation is applied to study the instability and rupture process of ultra-thin water films on a solid substrate. Results show the small disturbance of the film will develop linearly due to the spi...Molecular dynamics simulation is applied to study the instability and rupture process of ultra-thin water films on a solid substrate. Results show the small disturbance of the film will develop linearly due to the spinodal instability, whereas the interaction between solid and liquid has less influences on the initial growth. Then the rupture occurs and the rim recedes with a dynamic contact angle. The radius of the rim. varies with time as the square root of t, which is consistent with the macroscopic theory available. Stronger interaction between solid and liquid will postpone rupture time decline the dynamic contact angle and raise the density of water near the interface between solid and liquid.展开更多
To understand the influences of nanoparticles on dewetting in ultra-thin films, both linear stability the- ory and numerical simulations are performed in the present study, with the consideration of oscillatory struct...To understand the influences of nanoparticles on dewetting in ultra-thin films, both linear stability the- ory and numerical simulations are performed in the present study, with the consideration of oscillatory structural （OS） forces. Long scale approximation is utilized to simplify the hydrodynamic and diffusion equations to a nonlinear system for film thickness and nanoparticle concentration. Results show that the presence of nanoparticles generally suppresses the dewetting process. Two physical mechanisms responsi- ble for this phenomenon are addressed in the present study. When the oscillatory structural forces are relatively smaller, the essential feature of film evolution is similar to the case of particle-free flow. The reduction of the linear growth rate and the postponement of film rupturing can be attributed to the increment of the viscosity due to the presence of nanoparti- cles. On the other hand, when the intensity of the OS forces becomes stronger, the stepwise thinning of film can be ob- served which prevents the film from rupture. Numerical sim- ulations indicate that this phenomenon is caused by the ex- istence of a stable zone due to the oscillatory nature of the structural forces. Another interesting finding is that the non- uniformity of the distribution of nanoparticle concentration might destabilize a spinodally stable film, and trigger the oc- currence of film dewetting.展开更多
The capability to manipulate liquid shape at the microscale has enabled numerous microfluidic devices.Due to its simple electric actuation,electrowetting-on-dielectric has been widely used in a variety of microfluidic...The capability to manipulate liquid shape at the microscale has enabled numerous microfluidic devices.Due to its simple electric actuation,electrowetting-on-dielectric has been widely used in a variety of microfluidic applications that require reversible liquid-shape modulation.However,its use of dielectric and hydrophobic layers raised operation voltage,caused reliability issues,and increased fabrication cost.As an alternative mechanism,ionic-surfactant-mediated electro-dewetting has recently been demonstrated to enable digital microfluidics in air with a much lower voltage,higher reliability,and simpler chip fabrication.However,electro-dewetting for liquid-shape manipulation has remained poorly explored due to its limited contact-angle changes.Here,we investigated electro-dewetting in oil by testing various droplet liquids and hydrophilic substrate materials.To guide device development,cationic surfactants with varying hydrocarbon chain lengths and concentrations are tested.Acontact-angle change of 100◦is obtained for electro-dewetting of a dimethyl sulfoxide droplet in hexadecane with mere 4 V.To evaluate the utility of electro-dewetting in oil,proof-ofconcept devices are assembled to explore the potential in optical applications such as reflective displays and liquid lenses.Compatible with various liquids and substrates,electro-dewetting with the liquid-in-oil configuration opens a door for simpler and more reliablemicrofluidic devices.展开更多
In this paper we report a multifunctional nanostructured surface on glass that, for the first time, combines a wide range of optical, wetting and durability properties, including low omnidirectional reflectivity, low ...In this paper we report a multifunctional nanostructured surface on glass that, for the first time, combines a wide range of optical, wetting and durability properties, including low omnidirectional reflectivity, low haze, high transmission, superhydrophobicity, oleophobicity, and high mechanical resistance. Nanostructures have been fabricated on a glass surface by reactive ion etching through a nanomask, which is formed by dewetting ultrathin metal films （〈 10 nm thickness） subjected to rapid thermal annealing （RTA）. The nanostructures strongly reduce the initial surface reflectivity （-4%）, to less than 0.4% in the 390--800 nm wavelength range while keeping the haze at low values （〈 0.9%）. The corresponding water contact angle （0c） is -24.5~, while that on a flat surface is -43.5~. The hydrophilic wetting nanostructure can be changed into a superhydrophobic and oleophobic surface by applying a fluorosilane coating, which achieves contact angles for water and oil of -156.3~ and -116.2~, respectively. The multicomponent composition of the substrate （Coming~ glass） enables ion exchange through the surface, so that the nanopillars＇ mechanical robustness increases, as is demonstrated by the negligible changes in surface morphology and optical performance after 5,000-run wipe test. The geometry of the nanoparticles forming the nanomask depends on the metal material, initial metal thickness and RTA parameters. In particular we show that by simply changing the initial thickness of continuous Cu films we can tailor the metal nanoparticles＇ surface density and size. The developed surface nanostructuring does not require expensive lithography, thus it can be controlled and implemented on an industrial scale, which is crucial for applications.展开更多
In this paper,we study linearly first and second order in time,uniquely solvable and unconditionally energy stable numerical schemes to approximate the phase field model of solid-state dewetting problems based on the ...In this paper,we study linearly first and second order in time,uniquely solvable and unconditionally energy stable numerical schemes to approximate the phase field model of solid-state dewetting problems based on the novel"scalar auxiliary variable"(SAV)approach,a new developed efficient and accurate method for a large class of gradient flows.The schemes are based on the first order Euler method and the second order backward differential formulas(BDF2)for time discretization,and finite element methods for space discretization.The proposed schemes are proved to be unconditionally stable and the discrete equations are uniquely solvable for all time steps.Various numerical experiments are presented to validate the stability and accuracy of the proposed schemes.展开更多
We propose an accurate and energy-stable parametric finite element method for solving the sharp-interface continuum model of solid-state dewetting in three-dimensional space.The model describes the motion of the film/...We propose an accurate and energy-stable parametric finite element method for solving the sharp-interface continuum model of solid-state dewetting in three-dimensional space.The model describes the motion of the film/vapor interface with contact line migration and is governed by the surface diffusion equation with proper boundary conditions at the contact line.We present a weak formulation for the problem,in which the contact angle condition is weakly enforced.By using piecewise linear elements in space and backward Euler method in time,we then discretize the formulation to obtain a parametric finite element approximation,where the interface and its contact line are evolved simultaneously.The resulting numerical method is shown to be well-posed and unconditionally energystable.Furthermore,the numerical method is generalized to the case of anisotropic surface energies in the Riemannian metric form.Numerical results are reported to show the convergence and efficiency of the proposed numerical method as well as the anisotropic effects on the morphological evolution of thin films in solid-state dewetting.展开更多
An approach for the wafer-level synthesis of size- and site-controlled amorphous silicon nanowires （α-SiNWs） is presented in this paper. Microscale Cu pattern arrays are precisely defined on SiO2 films with the hel...An approach for the wafer-level synthesis of size- and site-controlled amorphous silicon nanowires （α-SiNWs） is presented in this paper. Microscale Cu pattern arrays are precisely defined on SiO2 films with the help of photolithography and wet etching. Due to dewetting, Cu atoms shrink to the center of patterns during the annealing process, and react with the SiO2 film to open a diffusion channel for Si atoms to the substrate, α-SiNWs finally grow at the center of Cu patterns, and can be tuned by varying critical factors such as Cu pattern volume, SiO2 thickness, and annealing time. This offers a simple way to synthesize and accurately position a SiNW array on a large area.展开更多
We propose a θ-L approach for solving a sharp-interface model about simulating solid-state dewetting of thin films with isotropic/weakly anisotropic surface energies.The sharp-interface model is governed by surface d...We propose a θ-L approach for solving a sharp-interface model about simulating solid-state dewetting of thin films with isotropic/weakly anisotropic surface energies.The sharp-interface model is governed by surface diffusion and contact line migration.For solving the model,traditional numerical methods usually suffer from the severe stability constraint and/or the mesh distribution trouble.In the θ-L approach,we introduce a useful tangential velocity along the evolving interface and utilize a new set of variables(i.e.,the tangential angle 6 and the total length L of the interface curve),so that it not only could reduce the stiffness resulted from the surface tension,but also could ensure the mesh equidistri-bution property during the evolution.Furthermore,it can achieve second-order accuracy when implemented by a semi-implicit linear finite element method.Numerical results are reported to demonstrate that the proposed θ-L approach is efficient and accurate.展开更多
Anisotropic dewetting polydimethylsiloxane （PDMS） surfaces, which consist of groove-like micro/ nanostructures （so-called hierarchical structures）, are fabricated using an ultrashort pulsed laser. The contact angl...Anisotropic dewetting polydimethylsiloxane （PDMS） surfaces, which consist of groove-like micro/ nanostructures （so-called hierarchical structures）, are fabricated using an ultrashort pulsed laser. The contact angles （CAs） are measured parallel to the microgrooves, which are always larger than those measured perpendicular to the microgrooves, exhibiting a superhydrophobic anisotropy of approximately 4°on these fabricated PDMS surfaces at optimized parameters. These pulsed-laser irradiated surfaces exhibit enhanced hydrophobicity with CAs that increase from 116°to 156°while preserving the anisotropic dewetting. Additionally, the wettability of the surfaces with different morphologies is investigated. The temporal evolution of the wettability of the pulsed-laser irradiated PDMS surface is also observed within the first few hours after pulsed laser irradiation.展开更多
基金supported by the National Research Foundation of Korea(NRF)grant funded by the Korea government(MSIT)(No.2021R1A2C1007400)supported,partly,by the National R&D Program through the National Research Foundation of Korea(NRF)funded by the Ministry of Science and ICT(Nos.NRF-2020M3H4A3106383,NRF2020M3H4A3081764)+1 种基金supported,partly,by ETRI(No.21YB1610)supported by a Korea Institute for Advancement of Technology(KIAT)grant funded by the Korea Government(MOTIE)(No.P0008458,HRD Program for Industrial Innovation)。
文摘Four types of submicron Ag-coated Cu particles with different Ag contents were prepared as sintering paste fillers,and the Ag contents of the particles were measured to be 10,20,30,and 40 wt.%.Four types of particles(in order of increasing Ag content:A10,A20,A30,and A40)were surface-modified with stearic acid,to suppress the Ag shell dewetting and improve sinterability.The surface-modified particles were mixed with a polyol-based solvent to fabricate a resin-free paste.Subsequently,the pastes were screen-printed onto a slide glass and sintered at 250°C in a nitrogen atmosphere for 1-10 min to form an electrode.The electrical resistivity of the sintered film as a function of sintering time was measured using a four-point probe.All the four surface-modified Cu@Ag particles with different Ag contents exhibited decreased electrical resistivity.Particularly,the largest difference in values after and before the surface modification was observed for A40 with the highest Ag content;the electrical resistivities of the initial and surface-modified particles were 1.51×10^(-4) and 6.67×10^(-5)Ω·cm,respectively,after sintering for 10 min.The findings of this study confirmed that the surface modification using stearic acid effectively suppressed the dewetting of the Ag shell and improved the sinterability of the submicron Cu@Ag particles.
基金financially supported by the National Natural Science Foundation of China(No.51373032)
文摘Hydrogen-bonded polymer complex films with the thickness ranging from 50 nm to 2400 nm were prepared by layer-by-layer （LbL） assembly of poly（2-ethyl-2-oxazoline） （PEOX） and poly（acrylic acid） （PAA）. The dewetting behavior of PEOX/PAA films under hydrothermal condition was investigated. It was found that the dewetting occurred at solid-liquid interface, and the typical morphologies such as holes, irregular cellular structure, and droplets were observed. Atomic force microscopy （AFM） revealed the initial rupture of the film. Microscopic Raman and infrared （IR） imaging demonstrated that the PEOX and PAA chains remained association during the dewetting process.
基金financially supported by the National Natural Science Foundation of China(No.50633030,Innovation Group:50921062)
文摘In this work, monodisperse giant polymersomes are fabricated by dewetting of water-in-oil-in-water double emulsion droplets which are assembled by amphiphilic block copolymer molecules in a microfluidic device. The dewetting process can be tuned by solvation between solvent and amphiphilic block copolymer to get polymersomes with controllable morphology. Good solvent （chloroform and toluene） hinders dewetting process of double emulsion droplets and gets acornlike polymersomes or patched polymersomes. On the other hand, poor solvent （hexane） accelerates the dewetting process and achieves complete separation of inner water phase from oil phase to form complete bilayer polymersomes. In addition, twin polymersomes with bilayer membrane structure are formed by this facile method. The formation mechanism for different polymersomes is discussed in detail.
基金financially supported by the National Natural Science Foundation of China (Nos.51473168,21234007,21674114,51503048,51573131 and 21374077)the grant of Guizhou Education University (No.107003001455)the Natural Science Foundation of Guizhou Province (No.QKHJC[2017]1137)
文摘We have investigated the influence of the adsorption process on the dewetting behavior of the linear polystyrene film （LPS）, the 3-arm star polystyrene film （3SPS） and the ring polystyrene film （RPS） on the silanized Si substrate. Results show that the adsorption process greatly influences the dewetting behavior of the thin polymer films. On the silanized Si substrate, the 3SPS chains exhibit stronger adsorption compared with the LPS chains and RPS chains; as a result, the wetting layer forms more easily. For LPS films, with the decrease of annealing temperature, the kinetics of polymer film changes from exponential behavior to slip dewetting. As a comparison, the stability of 3SPS and RPS films switches from slip dewetting to unusual dewetting kinetic behavior. The adsorbed nanodroplets on the solid substrate play an important role in the dewetting kinetics by reducing the driving force of dewetting and increase the resistant force of dewetting. Additionally, Brownian dynamics （BD） simulation shows that the absolute values of adsorption energy （ε） gradually increase from linear polymer （-0.3896） to ring polymer （-0.4033） and to star polymer （-0.4264）, which is consistent with the results of our adsorption experiments.
基金financially supported by the National Natural Science Foundation of China(No.51403026)
文摘The effects of film thickness and composition ratio on the morphology evolution of polystyrene （PS）/poly（vinyl methyl ether） （PVME） blend thin films were investigated. Diverse morphology evolutions including droplet-matrix structure, hole emergence, bicontinuous structure formation, percolation-to-droplet transition could be observed under annealing in two-phase region, depending on film thickness and composition ratio. The mechanism for these morphology variations was related to the complex effects of phase separation, dewetting and preferential wetting. The comparison between the thickness of bottom PVME layer and the twice of gyration radius 2Rg（PVME） played a dominant role in morphology control. Only when the PS/PVME film had specific film thickness and compositional symmetry, phase separation and dewetting could happen in sequence.
基金the Ministry of Science and Technology of China(Nos.2016YFA0200803 and2016YFB0402004)the National Natural Science Foundation of China(Nos.51673207 and 51373183)Scientific Research Fund of Hunan Provincial Science and Technology Department(No.09236)
文摘A novel solvent-sensitive fluorescent actuator with reversibility has been obtained from carbon dots （CDs） inverse opals, which is prepared via infiltrating CDs solution into the interstice of colloidal crystal template, thermal polymerization of CDs materials and removing the colloidal template. The as-prepared CDs inverse opal actuator shows a bending angle of 75° in 10.2 s, bending rate of 7.35 （°）.s-1. In particular, the fluorescence intensity of the films varies during the actuating process. The actuating behavior is attributed to the inhomogeneous swelling/shrinking of the film, which originates from the gradient dewetting by solvent evaporation and hydrogen-bonding interaction between the solvent molecules and oxygen/hydrogen ions of CDs side chain. The CDs inverse opal actuator has the advantages of quick response, good repeatability and strong fluorescence, which gives an important insight into the design and manufacture of novel and advanced solvent-actuators.
基金the National Research Foundation of Korea(no.2011-0030079 and 2016R1A1A1A05005009)the research grant of Kwangwoon University in 2016
文摘Silver(Ag) nanostructures demonstrate outstanding optical, electrical, magnetic, and catalytic properties and are utilized in photonic, energy, sensors, and biomedical devices.The target application and the performance can be inherently tuned by control of configuration, shape, and size of Ag nanostructures. In this work, we demonstrate the systematical fabrication of various configurations of Ag nanostructures on sapphire(0001) by controlling the Ag deposition thickness at different annealing environments in a plasma ion coater. In particular, the evolution of Ag particles(between 2 and 20 nm),irregular nanoclusters(between 30 and 60 nm), and nanocluster networks(between 80 and 200 nm) are found be depended on the thickness of Ag thin film. The results were systematically analyzed and explained based on the solid-state dewetting,surface diffusion, Volmer–Weber growth model, coalescence,and surface energy minimization mechanism. The growth behavior of Ag nanostructures is remarkably differentiated at higher annealing temperature(750 ℃) due to the sublimation and temperature-dependent characteristic of dewetting process.In addition, Raman and reflectance spectra analyses reveal that optical properties of Ag nanostructures depend on their morphology.
基金the start-up fund of Y.G.from both University of Michigan-Shanghai Jiao Tong University Joint InstituteSchool of Materials Science and Engineering at SJTU+4 种基金the National Science Foundation of China for financial support through the General Program(No.2157408)the foundation of Shanghai Sailing Plan(No,16YF1406100)the National Youth 1000 Talent Program of Chinathe Shanghai 1000 Talent Planthe Scientific Research Foundation for the Returned Overseas Chinese Scholars,State Education Ministry of China
文摘Isocyanate-treated graphite oxides （iGOs） were well-dispersed into the polystyrene （PS） thin films and formed a novel network structure. With control in fabrication, an iGOs-web layer was horizontally embedded near the surface of the films and thus formed a composite slightly doped by iGOs. This work demonstrated that the iGOs network can remarkably depress the dewetting process in the polymer matrix of the composite, while dewetting often leads to rupture of polymer films and is considered as a major practical limit in using polymeric materials above their glass transition temperatures （Tg）. Via annealing the 50-120 nm thick composite and associated neat PS films at temperatures ranging from 35℃ to 70 ℃ above Tg, surface morphology evolution of the films was monitored by atomic force microscopy （AFM）. The iGOs-doped PS exhibited excellent thermal stability, i.e., the number of dewetting holes was greatly reduced and the long-term hole growth was fairly restricted. In contrast, the neat PS film showed serious surface fluctuation and a final rupture induced by ordinary dewetting. The method developed in this work may pave a road to reinforce thin polymer films and enhance their thermal stability, in order to meet requirements by technological advances.
基金Supported by the National Natural Science Foundation of China(Nos.20774036 50930001+1 种基金 20933001)the Program for New Century Excellent Talents in University of China and Fok Ying Tung Education Foundation(No.114018)
文摘Coarse-grained molecular dynamics simulations were carried out to investigate the dewetting behavior of a polymer thin film on partial wetting solid surface at the early stage of the dewetting process. Spontaneous dewetting is initiated by removing a band of strip from both the ends of the liquid polymer film which has achieved equilibrium. The solid-liquid interaction and temperature were varied to show their influence on the dewetting dynamics during dewetting as well as the shape evolution of the liquid polymer film. As is consistent with the results obtained in previous researches, the liquid film recedes at a constant speed initially with different solid-liquid couplings and tempe- ratures. Furthermore, smaller coupling parameters or higher temperatures tend to accelerate the recession speed of the liquid film and shorten the constant-speed recession duration. Obvious rims were not always observed. Both coupling parameter and temperature can influence the emergence of the rims.
基金Project supported by the National Natural Science Foundation of China (Grant No. 11875237)。
文摘We investigate the influence of an external electric field on the dewetting behavior of nitrogen-water systems between two hydrophobic plates using molecular dynamics simulations. It is found that the critical distance of dewetting increases obviously with the electric field strength, indicating that the effective range of hydrophobic attraction is extended. The mechanism behind this interesting phenomenon is related to the rearrangement of hydrogen bond networks between water molecules induced by the external electric field. Changes in the hydrogen bond networks and in the dipole orientation of the water molecules result in the redistribution of the neutral nitrogen molecules, especially in the region close to the hydrophobic plates. Our findings may be helpful for understanding the effects of the electric field on the long-range hydrophobic interactions.
基金supported by the National Natural Science Foundation of China(No.50501022)the National Basic Research Program of China(No.2004CB619306)
文摘The thermodynamic conditions for dewetting of a liquid solder drop on copper thin films were examined under a hot-stage optical microscope in a flowing protective atmosphere.Dewetting of liquid solder was found to depend strongly on the copper film thickness and preceded by spalling of Cu 6 Sn 5 intermetallic compounds.However,the loss of interfacial bonding by spalling was not sufficient to cause immediate dewetting of solder drops if the wetting tip was still strongly bonded to the copper film.By introducing a pinning force on the wetting front,a sufficient condition was found from a force balance analysis for dewetting of the liquid solder drop,in general agreement with the experimental results.
基金the National Natural Science Foundation of China(Nos.10472062 and 10772107)Shanghai Leading Academic Discipline Project(No.Y0103)
文摘Molecular dynamics simulation is applied to study the instability and rupture process of ultra-thin water films on a solid substrate. Results show the small disturbance of the film will develop linearly due to the spinodal instability, whereas the interaction between solid and liquid has less influences on the initial growth. Then the rupture occurs and the rim recedes with a dynamic contact angle. The radius of the rim. varies with time as the square root of t, which is consistent with the macroscopic theory available. Stronger interaction between solid and liquid will postpone rupture time decline the dynamic contact angle and raise the density of water near the interface between solid and liquid.
基金supported by the National Natural Science Foundation of China (10872122)Doctoral Fund of Ministry of Education of China (20103108110004)+1 种基金Program for Changjiang Scholars and Innovative Research Team in University (IRT0844)Shanghai Program for Innovative Research Team in Universities
文摘To understand the influences of nanoparticles on dewetting in ultra-thin films, both linear stability the- ory and numerical simulations are performed in the present study, with the consideration of oscillatory structural （OS） forces. Long scale approximation is utilized to simplify the hydrodynamic and diffusion equations to a nonlinear system for film thickness and nanoparticle concentration. Results show that the presence of nanoparticles generally suppresses the dewetting process. Two physical mechanisms responsi- ble for this phenomenon are addressed in the present study. When the oscillatory structural forces are relatively smaller, the essential feature of film evolution is similar to the case of particle-free flow. The reduction of the linear growth rate and the postponement of film rupturing can be attributed to the increment of the viscosity due to the presence of nanoparti- cles. On the other hand, when the intensity of the OS forces becomes stronger, the stepwise thinning of film can be ob- served which prevents the film from rupture. Numerical sim- ulations indicate that this phenomenon is caused by the ex- istence of a stable zone due to the oscillatory nature of the structural forces. Another interesting finding is that the non- uniformity of the distribution of nanoparticle concentration might destabilize a spinodally stable film, and trigger the oc- currence of film dewetting.
文摘The capability to manipulate liquid shape at the microscale has enabled numerous microfluidic devices.Due to its simple electric actuation,electrowetting-on-dielectric has been widely used in a variety of microfluidic applications that require reversible liquid-shape modulation.However,its use of dielectric and hydrophobic layers raised operation voltage,caused reliability issues,and increased fabrication cost.As an alternative mechanism,ionic-surfactant-mediated electro-dewetting has recently been demonstrated to enable digital microfluidics in air with a much lower voltage,higher reliability,and simpler chip fabrication.However,electro-dewetting for liquid-shape manipulation has remained poorly explored due to its limited contact-angle changes.Here,we investigated electro-dewetting in oil by testing various droplet liquids and hydrophilic substrate materials.To guide device development,cationic surfactants with varying hydrocarbon chain lengths and concentrations are tested.Acontact-angle change of 100◦is obtained for electro-dewetting of a dimethyl sulfoxide droplet in hexadecane with mere 4 V.To evaluate the utility of electro-dewetting in oil,proof-ofconcept devices are assembled to explore the potential in optical applications such as reflective displays and liquid lenses.Compatible with various liquids and substrates,electro-dewetting with the liquid-in-oil configuration opens a door for simpler and more reliablemicrofluidic devices.
文摘In this paper we report a multifunctional nanostructured surface on glass that, for the first time, combines a wide range of optical, wetting and durability properties, including low omnidirectional reflectivity, low haze, high transmission, superhydrophobicity, oleophobicity, and high mechanical resistance. Nanostructures have been fabricated on a glass surface by reactive ion etching through a nanomask, which is formed by dewetting ultrathin metal films （〈 10 nm thickness） subjected to rapid thermal annealing （RTA）. The nanostructures strongly reduce the initial surface reflectivity （-4%）, to less than 0.4% in the 390--800 nm wavelength range while keeping the haze at low values （〈 0.9%）. The corresponding water contact angle （0c） is -24.5~, while that on a flat surface is -43.5~. The hydrophilic wetting nanostructure can be changed into a superhydrophobic and oleophobic surface by applying a fluorosilane coating, which achieves contact angles for water and oil of -156.3~ and -116.2~, respectively. The multicomponent composition of the substrate （Coming~ glass） enables ion exchange through the surface, so that the nanopillars＇ mechanical robustness increases, as is demonstrated by the negligible changes in surface morphology and optical performance after 5,000-run wipe test. The geometry of the nanoparticles forming the nanomask depends on the metal material, initial metal thickness and RTA parameters. In particular we show that by simply changing the initial thickness of continuous Cu films we can tailor the metal nanoparticles＇ surface density and size. The developed surface nanostructuring does not require expensive lithography, thus it can be controlled and implemented on an industrial scale, which is crucial for applications.
基金The work is supported by the National Natural Science Foundation of China(No.11401467)China Postdoctoral Science Foundation(No.2013M542334.and No.2015T81012)Natural Science Foundation of Shaanxi Province(No.2015JQ1012).The work is also supported in part by funding from King Abdullah University of Science and Technology(KAUST)through the grant BAS/1/1351-01-01.
文摘In this paper,we study linearly first and second order in time,uniquely solvable and unconditionally energy stable numerical schemes to approximate the phase field model of solid-state dewetting problems based on the novel"scalar auxiliary variable"(SAV)approach,a new developed efficient and accurate method for a large class of gradient flows.The schemes are based on the first order Euler method and the second order backward differential formulas(BDF2)for time discretization,and finite element methods for space discretization.The proposed schemes are proved to be unconditionally stable and the discrete equations are uniquely solvable for all time steps.Various numerical experiments are presented to validate the stability and accuracy of the proposed schemes.
基金supported by Singapore MOE grant MOE2019-T2-1-063(R-146-000-296-112)supported by the Singapore MOE grant R-146-000-285-114.
文摘We propose an accurate and energy-stable parametric finite element method for solving the sharp-interface continuum model of solid-state dewetting in three-dimensional space.The model describes the motion of the film/vapor interface with contact line migration and is governed by the surface diffusion equation with proper boundary conditions at the contact line.We present a weak formulation for the problem,in which the contact angle condition is weakly enforced.By using piecewise linear elements in space and backward Euler method in time,we then discretize the formulation to obtain a parametric finite element approximation,where the interface and its contact line are evolved simultaneously.The resulting numerical method is shown to be well-posed and unconditionally energystable.Furthermore,the numerical method is generalized to the case of anisotropic surface energies in the Riemannian metric form.Numerical results are reported to show the convergence and efficiency of the proposed numerical method as well as the anisotropic effects on the morphological evolution of thin films in solid-state dewetting.
基金This work was supported by the National Basic Research Program of China （Nos. 2011CB707601, 2011CB707605, and 2012CB934102）, the National Science and Technology Supporting Program （No. 2012BAJ11B01）, the Creative Research of National Natural Science Foundation of China （No. 61021064）, and the National Natural Science Foundation of China （Nos. 60936001, 91123037 and 81201358）.
文摘An approach for the wafer-level synthesis of size- and site-controlled amorphous silicon nanowires （α-SiNWs） is presented in this paper. Microscale Cu pattern arrays are precisely defined on SiO2 films with the help of photolithography and wet etching. Due to dewetting, Cu atoms shrink to the center of patterns during the annealing process, and react with the SiO2 film to open a diffusion channel for Si atoms to the substrate, α-SiNWs finally grow at the center of Cu patterns, and can be tuned by varying critical factors such as Cu pattern volume, SiO2 thickness, and annealing time. This offers a simple way to synthesize and accurately position a SiNW array on a large area.
基金This work was partially supported by the National Natural Science Foundation of China under Grant Nos.11871384(W.J.),12001034(W.H.),12001221(Y.W.),and 91630207(W.H.)the Fundamental Research Funds for the Central Universities under Grant CCNU19TD010(Y.W.)the Natural Science Foundation of Hubei Province under Grant Nos.2018CFB466(W.J.)and 2020CFB221(Y.W.).
文摘We propose a θ-L approach for solving a sharp-interface model about simulating solid-state dewetting of thin films with isotropic/weakly anisotropic surface energies.The sharp-interface model is governed by surface diffusion and contact line migration.For solving the model,traditional numerical methods usually suffer from the severe stability constraint and/or the mesh distribution trouble.In the θ-L approach,we introduce a useful tangential velocity along the evolving interface and utilize a new set of variables(i.e.,the tangential angle 6 and the total length L of the interface curve),so that it not only could reduce the stiffness resulted from the surface tension,but also could ensure the mesh equidistri-bution property during the evolution.Furthermore,it can achieve second-order accuracy when implemented by a semi-implicit linear finite element method.Numerical results are reported to demonstrate that the proposed θ-L approach is efficient and accurate.
基金supported by the National Natural Science Foundation of China(Nos.61178024 and 11374316)the National Basic Research Program of China(No.2011CB808103)Q.Zhao acknowledges research funding from the Shanghai Pujiang Program(No.10PJ1410600)
文摘Anisotropic dewetting polydimethylsiloxane （PDMS） surfaces, which consist of groove-like micro/ nanostructures （so-called hierarchical structures）, are fabricated using an ultrashort pulsed laser. The contact angles （CAs） are measured parallel to the microgrooves, which are always larger than those measured perpendicular to the microgrooves, exhibiting a superhydrophobic anisotropy of approximately 4°on these fabricated PDMS surfaces at optimized parameters. These pulsed-laser irradiated surfaces exhibit enhanced hydrophobicity with CAs that increase from 116°to 156°while preserving the anisotropic dewetting. Additionally, the wettability of the surfaces with different morphologies is investigated. The temporal evolution of the wettability of the pulsed-laser irradiated PDMS surface is also observed within the first few hours after pulsed laser irradiation.
