Competing fracture in kinetically controlled transfer printing

Transfer printing by kinetically switchable adhesion to an elastomeric stamp shows promise as a powerful micromanufacturing method to pickup microstructures and microdevices from the donor substrate and to print them to the receiving substrate. This can be viewed as the competing fracture of two interfaces. This paper examines the mechanics of competing fracture in a model transfer printing system composed of three laminates: an elastic substrate, an elastic thin film, and a viscoelastic member (stamp). As the system is peeled apart, either the interface between the substrate and thin film fails or the interface between the thin film and the stamp fails. The speed-dependent nature of the film/stamp interface leads to the prediction of a critical separation velocity above which separation occurs between the film and the substrate (i.e., pickup) and below which separation occurs between the film and the stamp (i.e., printing). Experiments verify this prediction using films of gold adhered to glass, and the theoretical treatment extends to consider the competing fracture as it applies to discrete micro-objects. Temperature plays an important role in kinetically controlled transfer printing with its influences, making it advantageous to pickup printable objects at the reduced temperatures and to print them at the elevated ones.     

Adhesive and mechanical properties of soft nanocomposites: Model studies with blended latex films

We used a unique approach based on contact mechanics to quantify the adhesive and linear viscoelastic properties of latex films approximately 100 μm thick. The latex films were formed from a mixture of two particle types and form stable films consisting of rigid and compliant regions. We used atomic force microscopy to verify that these regions remained well dispersed on the length scale of the original particle size. The properties of the films were determined by ?_h, the volume fraction of the stiffer component. For ?_h < 0.45, the films were quite adhesive, with viscoelastic properties determined by the compliant matrix material. Adhesive interactions between the film and indenter enabled us to oscillate the indenter in the direction normal to the film surface while maintaining a constant contact area, allowing us to determine the frequency dependence of the dynamic moduli of the films. Stiffer films with higher volume fractions of hard particles were characterized by indentation measurements, from which we were able to determine the time dependence of the relaxation modulus of the latex films. All results were consistent with a power‐law form of the relaxation modulus with an exponent of 0.25. The magnitude of the relaxation modulus increased by a factor of 3000 as the volume fraction of hard particles increased from 0 to 0.89. For low values of ?_h, the composition dependence of the film stiffness was similar to the concentration dependence of the viscosity of spherical particle suspensions. A much weaker concentration dependence was observed for the highest values of ?_h, where the properties of the films were dominated by the stiffer component. © 2001 John Wiley & Sons, Inc. J Polym Sci Part B: Polym Phys 39: 3090–3102, 2001     

Geometric Model Describing the Banded Morphology of Particle Films Formed by Convective Assembly

Nanoparticle films coated on smooth substrates by convective assembly from dilute suspensions in dip‐coating configuration are known to have discrete film morphologies. Specifically, the film morphology is characterized by alternating bands of densely packed particles and bands of bare substrate. Convective assembly is a frontal film‐growth process that occurs at the three‐phase contact line formed by the substrate, the suspension in which it is submersed, and the surrounding air. The bands are parallel to this contact line and can be either monolayered or multilayered. Monolayered bands result whenever the substrate is withdrawn from the suspension at a rate too high for particles to assemble into a continuous film. We report a new insight to the mechanism behind this banding phenomenon, namely, that inter‐band spacing is strongly influenced by the constituent particle size. We therefore propose a geometric model relating the inter‐band spacing to the particle size. By making banded films with systematically varied particle sizes (silica/zeolite, 20 to 500 nm), we are able to quantitatively validate our model. Furthermore, the model correctly predicts that multilayered banded films have higher inter‐band spacings than monolayered banded films comprising the same particles.     

Surface force spectroscopy of elastomeric nanoscale films

We studied nanomechanical properties for a series of ultrathin films of elastomeric materials from polyisoprene rubbers and tri‐block styrene‐butadiene‐styrene copolymer, SEBS. As we observed, the Hertzian approximation for elastic mechanical deformation of double layer films can be used for the analysis of force‐distance data at modest indentation depths and film thickness higher than 3 nm. For thinner films, the influence of solid substrate becomes very significant. On the other hand, the applicability of the Hertzian approximation is limited by the rate dependent elastomeric deformation. We demonstrated that Johnson modification of the contact mechanics model that includes a viscoelastic contribution could be utilized to obtain reasonable fitting of loading data for elastomeric materials.     

Quartz crystal microbalance studies of the contact between soft, viscoelastic solids

Mechanical contact between a viscoelastic lens and a viscoelastic film has been probed by means of a quartz crystal microbalance operated in the impedance analysis mode. The frequency shift induced by the formation of the contact decreases with increasing film thickness because of the finite penetration depth of the acoustic shear wave. The dependence of frequency and bandwidth on film thickness and contact area is described within a sheet-contact model, which can be employed to quantitatively analyze mechanical contact in a wide range of materials problems. The model was tested by bringing a quartz crystal coated with an elastomeric gel into contact with a hemispherical cap of a similar gel. Both gels consisted of the thermoreversible gel Kraton G swollen in mineral oil. The experiments support the model well.     

Ultrathin Carbon Film Electrodes from Vacuum‐Carbonised Cellulose Nanofibril Composite

A novel way to produce ultrathin transparent carbon layers on tin‐doped indium oxide (ITO) substrates is developed. The ITO surface is coated with cellulose nanofibrils (from sisal) via layer‐by‐layer electrostatic binding with poly(diallyldimethylammonium chloride) or PDDAC acting as the binder. The cellulose nanofibril‐PDDAC composite film is then vacuum‐carbonised at 500 °C. The resulting carbon films are characterised by atomic force microscopy (AFM), small angle X‐ray scattering (SAXS), wide‐angle X‐ray scattering (WAXS), and Raman methods. Smooth carbon films with good adhesion to the ITO substrate are formed. The electrochemical characterisation of the carbon films is based on the oxidation of hydroquinone and the reduction of benzoquinone in aqueous phosphate buffer media. A modest effect of the cellulose nanofibril‐PDDAC film on the rate of electron transfer is observed. The effect of the film on the rate of electron transfer after carbonisation is more dramatic. For a 40‐layer cellulose nanofibril‐PDDAC film after carbonisation a two‐order of magnitude change in the rate of electron transfer occurs presumably due to a better interaction of the hydroquinone/benzoquinone system with the electrode surface.     

Dewetting of thin liquid films near soft elastomeric layers

Thin liquid film instabilities driven by van der Waals forces and in the proximity of soft elastomeric layers are considered in this work through two model problems: (i) a liquid film resting on an elastomeric layer and (ii) a liquid film bounded from one side by a rigid substrate and from the other side by an elastomeric layer. The elastomeric layers are modeled as linear viscoelastic solids, van der Waals forces are assumed to act only in the liquid, and lubrication theory and linear stability analysis are applied. For a liquid film resting on an elastomeric layer, substrate deformability has a destabilizing effect, as evidenced by an increase in the maximum growth rate and range of unstable wavenumbers. The destabilization worsens for thicker solid layers and is due to a lowering of the effective liquid-air interfacial tension. For an elastomeric layer resting on a liquid film, layer deformability has a stabilizing effect for thin layers but a destabilizing effect for thicker layers, with the former due to an enhancement and the latter due to a reduction of the effective solid-air interfacial tension. The results presented here suggest the possibility of exploiting the dewetting of thin liquid films to create topographically patterned surfaces on soft polymeric solids.     

Creating patterned carbon nanotube catalysts through the microcontact printing of block copolymer micellar thin films

We report a route for synthesizing patterned carbon nanotube (CNT) catalysts through the microcontact printing of iron-loaded poly(styrene-block-acrylic acid) (PS-b-PAA) micellar solutions onto silicon wafers coated with thin aluminum oxide (Al(2)O(3)) layers. The amphiphilic block copolymer, PS-b-PAA, forms spherical micelles in toluene that can form quasi-hexagonal arrays of spherical PAA domains within a PS matrix when deposited onto a substrate. In this report, we dip a poly(dimethylsiloxane) (PDMS) molded stamp into an iron-loaded micellar solution to create a thin film on the PDMS features. The PDMS stamp is then put in contact with a substrate, and uniaxial compressive stress is applied to transfer the micellar thin film from the PDMS stamp onto the substrate in a defined pattern. The polymer is then removed by oxygen plasma etching to leave a patterned iron oxide nanocluster array on the substrate. Using these catalysts, we achieve patterned vertical growth of multiwalled CNTs, where the CNTs maintain the fidelity of the patterned catalyst, forming high-aspect-ratio standing structures.     

基板界面对PS/PMMA溶液共混物溶剂挥发成膜相结构的影响

研究了PS PMMA的共混物溶液溶剂蒸发成膜时的基板界面效应 .利用扫描电子显微镜 (SEM)研究了PS PMMA(5 5 ) (W W) THF高分子共混物溶液在不同基板上通过溶剂挥发成膜的相形态结构 .通过FTIR及ATR FTIR检测了共混物薄膜及其表面的共混组成 .研究结果表明 ,成膜基板对高分子共混物溶液成膜后的相形态有很重要的影响 .控制共混物溶液体系成膜过程中的动力学因素 ,可以调控出所设想的各种复杂的相结构形态     

Improving surface quality of polyethylene terephthalate film for large area flexible electronic applications

Lamination is a method utilized to protect flexible electroluminescence device against environmental hazards, such as dust, moisture, and water vapor. The materials are typically joined together using adhesive or cohesion of the materials during the lamination process. Polyethylene terephthalate (PET) is commonly used as the substrate film where electroluminescence patterns are printed. However, PET film has a relatively low surface energy and high contact angle, which would cause relatively weak laminating strength. This paper discusses the use of atmospheric plasma as a surface treatment method to modify PET and laminating films’ interface to improve bonding and laminating quality. Experimental results revealed that atmospheric plasma process reduced the contact angle of both PET and laminating films. Functional groups favoring hydrophilicity were found on the films’ interface after the atmospheric plasma treatment. These effects consequently increased surface energies of both films and favored bonding between the films. The treated films thus had increased laminating strength by approximately six times without compromising the transparency quality.     

Application of the Scanning Kelvin Probe for the study of the corrosion resistance of interfacial thin organosilane films at adhesive/metal interfaces

The Scanning Kelvin Probe is introduced as a real time non-destructive in situ technique for the detection of de-adhesion at adhesive/metal oxide interfaces. Iron substrates and an epoxy adhesive served as model systems. Iron surfaces were coated with ultra-thin organosilane plasma polymer films from a microwave discharge and 3-(trimethoxysilyl)-propylamine films from dilute water based solutions. Surface and film characterisation was done by means of atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS) and infrared reflection absorption spectroscopy (IRRAS). The effect of these interfacial films on the stability of the adhesive/metal joint was studied in corrosive environments. The Scanning Kelvin Probe allows the measurement of electrode potentials at buried polymer/metal interfaces with a spatial resolution of about 100 m. The electrode potential characterises the reactivity of the interface. Moreover, by the variation of the oxygen partial pressure in the measurement chamber, local anodes and cathodes underneath the polymer can be distinguished. The kinetics of electrochemical de-adhesion can be effectively slowed down by thin 3-(trimethoxysilyl)-propylamine films at the interface. The effect of the adhesion promoter can be further improved when a thin SiO_x layer, which inhibits electron transfer reactions, and is deposited on the iron surface prior to coating with the adhesion promoter.This paper is dedicated to Mike Owen on occasion of his winning the DeBruyn medal, the first silicon chemist to do so.     

Microstructured silicone substrate for printable and stretchable metallic films

Stretchable electronics (i.e., hybrid inorganic or organic circuits integrated on elastomeric substrates) rely on elastic wiring. We present a technique for fabricating reversibly stretchable metallic films by printing silver-based ink onto microstructured silicone substrates. The wetting and pinning of the ink on the elastomer surface is adjusted and optimized by varying the geometry of micropillar arrays patterned on the silicone substrate. The resulting films exhibit high electrical conductivity (～11?000 S/cm) and can stretch reversibly to 20% strain over 1000 times without failing electrically. The stretchability of the ≥200 nm thick metallic film relies on engineered strain relief in the printed film on patterned PDMS.     

Development of a colloidal lithography method for patterning nonplanar surfaces

A colloidal lithography method has been developed for patterning nonplanar surfaces. Hexagonal noncontiguously packed (HNCP) colloidal particles 127 nm-2.7 μm in diameter were first formed at the air-water interface and then adsorbed onto a substrate coated with a layer of polymer adhesive ～17 nm thick. The adhesive layer plays the critical role of securing the order of the particles against the destructive lateral capillary force generated by a thin film of water after the initial transfer of the particles from the air-water interface. The soft lithography method is robust and very simple to carry out. It is applicable to a variety of surface curvatures and for both inorganic and organic colloidal particles.     

Scratching behavior of elastomeric poly(dimethylsiloxane) coatings

Scratch testing has been performed on elastomeric poly(dimethylsiloxane) (PDMS) coatings on stainless steel with a spherical indenter. The friction coefficient (horizontal‐to‐normal force ratio) during scratching decreases with increasing normal load. This result can be explained by assuming that during scratching the contact area is determined by elastic deformation and the horizontal force is proportional to the contact area. With increasing driving speed, the friction coefficient increases, but the rate of increase decreases; this suggests that the scratching of the PDMS coating is a rate process and that the viscoelastic property of the coating influences its frictional behavior. Below a critical normal load, which increases with the coating thickness, the PDMS coating recovers elastically after being scratched so that there are no scratch marks left behind. Above the critical normal load, the coating is damaged by a combination of delamination at the coating/substrate interface and through‐thickness cracking. When the coating is damaged, there is an increase in the friction coefficient, and the friction force displays significant fluctuations. Furthermore, the critical normal load increases with the driving speed; this implies that time is needed to nucleate damage. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 1530–1537, 2002     

Nonlinear evolution of thin liquid films dewetting near soft elastomeric layers

The nonlinear evolution of thin liquid films dewetting near soft elastomeric layers is examined in this work. Evolution equations are derived by applying the lubrication approximation and assuming that van der Waals forces in the liquid cause the dewetting and that the solid can be described as a linear viscoelastic material. Two cases are examined: (i) a liquid layer resting on an elastomer bounded from below by a rigid substrate, and (ii) an elastomer overlying a thin liquid film bounded from below by a rigid substrate. Linear stability analysis is carried out to obtain asymptotic relations which are then compared against solutions of the full characteristic equations. In the liquid-on-solid case, numerical solutions of the evolution equations show that van der Waals forces cause thinning of the liquid film and thickening of the elastomeric solid beneath film depressions. Inclusion of a short-range repulsive force suggests that regular patterns may form in which ridges of fluid rest on depressions in the solid. In the solid-on-liquid case, the van der Waals forces cause the solid layer to break up before the liquid film can dewet. The results presented here support the idea that the dewetting of thin liquid films might be exploited to create topographically patterned surfaces on soft polymeric solids.     

Detection of mechanical effects of adhesive thin films on substrate using the modulated-temperature dilatometry (MT DIL)

The work is aimed to develop the diagnostic method for testing the state of surface coated with the wear-resistant films. Thin wear-resistant ceramic films based on titanium such as TiN, TiCN, TiAlN are deposited on working surface of cutting tools or machine elements in order to improve their tribological properties. The operation life depends mainly on the residual stresses occurring in films and the kinetics of their relaxation as a function of temperature and time. The value of the stresses is influenced by the technological conditions of film deposition and the physical and chemical properties of the substrate and film. The paper has demonstrated the usability of the modulated-temperature dilatometry (MT DIL) for recording the changes in mechanical effects of the adhesive film on the substrate as a function of temperature and time. The substrates where in the shape of cylindrical rod, 30 mm length and 3 mm diameter and of the ribbon 30 mm in length, 2 mm in wide and 120 μm thick. The thickness of the coatings was from 2 to 3 μm. The films deposition were performed using the physical vapour deposition (PVD) technique.     

Supported particle track etched polyimide membranes: a grazing incidence small-angle X-ray scattering study

Particle track etched polyimide membranes on silicon substrates covered with a native oxide layer are investigated. Preparation steps similar to the common classical particle track etched membrane production, giving rise to free-standing membranes, are successfully applied to the supported membranes. Polyimide films are used as a starting material for a template preparation based on high energy ion irradiation. The film/membrane structure is probed at different length scales by grazing incidence small-angle X-ray scattering at each individual preparation step. In addition, characterization with atomic force microscopy, variable-angle spectroscopic ellipsometry, Fourier transform infrared transmission, and attenuated total reflection spectroscopy is performed. An amount of 6 +/- 1 vol % pores inside the polyimide film is detected. The pores are oriented perpendicular to the substrate surface and have a conical shape, yielding a slightly reduced pore size at the substrate/film interface.     

Study of poly[bis(p-toluene sulfonate) diacetylene] films prepared by a modification of the Langmuir–Blodgett technique

Coherent this films of poly[bis(p-toluene sulfonate) diacetylene] were successfully formed by modified Langmuir–Blodgett techniques using two methods: (i) Photopolymerization of the monomer film at the gas/liquid interface and then transfer to a solid substrate, and (ii) transfer of the monomer film to the solid substrate and subsequent photopolymerization on the substrate itself. The films thus obtained were characterized by traditional force–area isotherms while on pure water subphases. Segments were transferred at either 1 or 10 dyn/cm surface pressure, in different stages of photopolymerization, to glass or germanium substrates. The films on the substrate were characterized by the methods of multiple attenuated-internal-reflection infrared spectroscopy, ellipsometry, contact-potential measurement, and laser Raman spectroscopy. Our results show that the films are multimolecular and about 100 Å thick. Of special interest were the observation of significant anisotropy of oriented dipoles and the ability to obtain excellent spectral data for these very thin oriented films. Raman spectroscopic features are similar to those observed for the bulk polymer, even in the low-frequency region. Polarized Raman spectroscopy confirmed the presence of local anisotropy in these films.     

Plasma Polymerization on Metals

An ellipsometric technique is described for accurately measuring the film thickness of plasma-polymerized polymers on metallic substrates. The index of refraction n and absorption index Kof the plasma polymer film can also be studied by ellipsometry. Films of plasma polystyrene and polyepichlorohydrin were deposited on evaporated aluminum substrates and their thickness and optical constants determined. Plasma polystyrene films from 20 to 1600 Å thick have optical constants n = 1.63 and K =0 independent of film thickness. Plasma polyepichlorohydrin films over the same range of thickness give n ? 1.70 and K? 0.01. By utilizing the ellipsometric method the effect of plasma polymer film thickness on surface energy properties was determined. Advancing contact angle measurements and surface energy analysis detail the polar γSV^P dispersion γSV^Pcontributions to the solid-vapor surface tension γSV = γSV^d + γSV^P Polystyrene and polyepichlorohydrin films on etched aluminum. For thin plasma polystyrene films (600 Å), anomalies in the calculated surface energy are discussed and related to possible surface nonuniformity caused by film growth. Thicker films of plasma polystyrene are shown to have normal surface energy properties as does plasma poly-epichlorohydrin over the entire range of film thickness measured. The adhesive and cohesive properties of plasma polystyrene and polyepichlorohydrin films are discussed as estimated from a lap-shear bond strength study. Etched aluminum coated with various thicknesses of these two polymers and bonded with an epoxy-phenolic adhesive shows a decreasing shear strength with increasing plasma film thickness but begins to level off at ～1600 psi for films >1600 Å thick.     

A new patterning method using photocatalytic lithography and selective atomic layer deposition

We report a new patterning method using photocatalytic lithography of alkylsiloxane self-assembled monolayers and selective atomic layer deposition of thin films. The photocatalytic lithography is based on the fact that the decomposition rate of the alkylsiloxane monolayers in contact with TiO2 is much faster than that with SiO2 under UV irradiation in air. The photocatalytic lithography, using a quartz plate coated with patterned TiO2 thin films, was done to prepare patterned monolayers of the alkylsiloxane on Si substrates. A ZrO2 thin film was selectively deposited onto the monolayer-patterned Si substrate by atomic layer deposition.