Substrate Withdrawal Research Articles

Spontaneous pattern formation on silica and titania dip-coating films prepared at extremely low substrate withdrawal speeds

Linear patterns were spontaneously formed on the silica and titania dip-coating films prepared from tetramethyl orthosilicate (Si(OCH3)4) and titanium tetraisopropoxide (Ti(OC3H7i)4) solutions, respectively. In both films, the pattern formation occurred at extremely low substrate withdrawal speeds below 1.0 cm min−1, where the film thickness increased with decreasing substrate withdrawal speed for dip-coating. The linear patterns on micrometre scale were arranged perpendicular to the substrate withdrawal direction. The values of RZ (10 point height of irregularities) and S (mean spacing of local peaks) of the patterns increased with decreasing substrate withdrawal speed.

Controlling Inplane Orientation of a Monolayer Colloidal Crystal by Meniscus Pinning

We demonstrate the usage of meniscus pinning by surface relief boundaries to control in-plane orientation of monolayer colloidal crystals without the interruption of grain disorientation. By optimizing the pinning boundary and withdrawal speed, a well controlled linear meniscus contact line offers unidirectional growth of a colloidal crystal-densely packed crystal direction ⟨11⟩ and ⟨10⟩ parallel to linear edge-giving rise to a single domain crystal with only twins and vacancies present as residual defects. The pinning effect works by eliminating the wavy contact line induced by fingering instability which is commonly found in liquid wetting film. It is found that surfactants and colloidal particles play significant roles to enhance edge pinning, increasing the distance traveled by receding bulk meniscus (during substrate withdrawal) before liquid depinning or rupturing.

Effect of type of solvent alcohol and its molar proportion on the drying critical thickness of ZrO2–3 mol% Y2O3 films prepared by the sol–gel method

The effect of the type of the solvent alcohol and its molar proportion on the drying critical thickness of 3mol% Y2O3-stabilized ZrO2 (YSZ) sol–gel films was examined experimentally and modeled analytically. To this end, zirconium n-propoxide was dissolved using different solvent alcohols (ethanol, methanol, and propanol) and different molar proportions of propanol (alcohol-to-alkoxide molar ratios of ~6.5, 11.5, or 16.5), and the resulting sol–gel solutions were dip-deposited at different substrate withdrawal rates until cracking occurred after drying at 100°C. It was found that the drying critical thickness, i.e., the maximum thickness that can be reached without film cracking, was greatest when the solvent alcohol was propanol, despite the tensile strength of the gelled network being the lowest. The use of ethanol and methanol as solvent alcohols results in sol–gel films with greater strength but thinner drying critical thicknesses. The analysis of the results using a drying stress model showed the drying critical thickness to be conditioned by the balance between the evaporation rate and viscosity of the sol–gel solutions, and the experimental data indicated that the predominant factor to take into account when choosing the solvent alcohol is the evaporation rate of the solution. It was also found that the critical thickness increases with increasing molar proportion of solvent alcohol, again despite the decreasing tensile strength of the gelled network. The analytical modeling of the drying stresses indicated that, once the solvent alcohol has been chosen, the determining factor in the drying critical thickness is the viscosity of the sol–gel solutions. Implications for obtaining thicker, crack-free, sol–gel films of YSZ or other oxide ceramics during drying that have greater tensile strength are discussed.

Sol-Gel Derived Sensitive Films for Ammonia Sensors

Sol–Gel Derived Sensitive Films for Ammonia Sensors C. Tyszkiewicz∗, P. Karasinski and R. Rogozinski Department of Optoelectronics, Silesian University of Technology, Krzywoustego 2, 44-100 Gliwice, Poland The sol–gel technology allows the preparation of silica thin films ranging in porosity from dense to highly porous films (50%). Porous silica films can function as a matrix that is able to bind the molecules of pH-sensitive indicators and therefore can be utilized as a sensitive film in construction of intensity based fibre or planar optical sensors for ammonia detection. We report the fabrication and characterization of ammonia sensitive, highly porous silica films deposited on soda-lime glass plates and doped with the bromocresole purple, and bromothymol blue molecules. In this paper we present the influence of the substrate withdrawal speed from sol on a thickness and a refractive index of the undoped silica films, as well as spectral absorbance characteristics of the doped films. An influence of ammonia concentration in air and relative humidity on a transmission of produced sensitive films is also presented.

Spontaneous Formation of Linear Striations and Cell-like Patterns on Dip-Coating Titania Films Prepared from Alkoxide Solutions

Linear striations and cell-like patterns were spontaneously formed on the dip-coating titania films prepared titanium tetraisopropoxide (Ti(OC(3)H(7)(i))(4)) solutions. Such unique patterns on micrometer scale were arranged parallel to the substrate withdrawal direction. The values of R(Z) (10 point height of irregularities) and S (mean spacing of local peaks) of the patterns increased with increasing film thickness depending on the substrate withdrawal speed for dip-coating, the viscosity of the coating solutions, and the distance from the top edge of films. The shape of patterns changed from linear striations to cell-like patterns with increasing viscosity of the coating solutions. Although the heat treatment at 600 degrees C reduced the height (R(Z)) of stripes and cells without the change in spacing (S), the visibility of patterns was enhanced by the increase in refractive index due to the crystallization of films.

Patterning Block Copolymer Aggregates via Langmuir−Blodgett Transfer to Microcontact-Printed Substrates

We demonstrate a new strategy for producing hierarchical polymer nanostructures, which combines nanoscale self-assembly of amphiphilic block copolymers at the air-water interface with microscale templated assembly of the resulting aggregates on chemically patterned substrates. Aggregates are formed via interfacial self-assembly of 141k polystyrene-b-poly(ethylene oxide) (PS-b-PEO, MW = 141k, 11.4 wt % PEO) or a blend of 185k PS-b-PEO (MW = 185k, 18.9 wt % PEO) and PS-coated CdS nanoparticles to form strandlike copolymer or copolymer-nanoparticle aggregates. Using Langmuir-Blodgett (LB) techniques, the aggregates are then transferred to patterned substrates possessing alternating hydrophilic/hydrophobic stripes, obtained by microcontact printing octadecyltrichlorosilane (OTS) on glass. The aggregates are transferred under various conditions of surface pressure, orientation of the patterned substrate, and withdrawal speed. Templated assembly of aggregates into the hydrophilic substrate domains is achieved when the hydrophilic/hydrophobic stripes are oriented perpendicular to the water surface during LB transfer; this is explained by surface energy heterogeneities along the subphase-substrate contact line, which induce selective dewetting and concomitant monolayer rearrangement at the drying front. In contrast, parallel orientation of stripes results in nonselective transfer of the monolayer without registration to the underlying surface pattern. By studying the effect of surface pressure, we show that packing constraints imposed by compression of aggregates to high surface densities prevent the formation of patterned LB films that match the established periodicity of the OTS-patterned glass. As well, it is shown that efficient transfer of aggregates to the patterned glass requires slower substrate withdrawal speeds compared to transfer to unpatterned hydrophilic glass.

Factorial design preparation of transparent conducting oxide thin films

Transparent and conducting properties of Cd 2SnO 4 films deposited onto glass substrates by the dip coating technique have been obtained using a 2 4 factorial design. All films were well adhered onto their substrates, presented porous morphology and inverse spinel structure. Statistical factorial design analysis showed that only substrate withdrawal rate and precursor solution concentration had significant effects on average transmission of the films. Cumulative probability graphs of factorial design model coefficients showed that none of the factor levels have significant effects on resistivity. However the films presented significantly higher resistivities using low withdrawal rates and low concentration levels. This indicates resistivity is a more complex function of the factor variables than transmission. From the factorial design experiments and statistical analysis of their results a highest average transmission of 88% and lowest resistivity of 2.43 × 10 − 4 Ω m were found.

Effects of Individual Layer Thickness on the Microstructure and Optoelectronic Properties of Sol–Gel‐Derived Zinc Oxide Thin Films

Zinc oxide (ZnO) thin films were prepared under different conditions on glass substrates using a sol–gel process. The microstructure of ZnO films was investigated by means of diffraction analysis, and plan‐view and cross‐sectional scanning electron microscopy. It was found that the preparation conditions strongly affected the structure and the optoelectronic properties of the films. A structural evolution in morphology from spherical to columnar growth was observed. The crystallinity of the films was improved and columnar film growth became more dominant as the zinc concentration and the substrate withdrawal speed decreased. The individual layer thickness for layer‐by‐layer homoepitaxy growth that resulted in columnar grains was <20 nm. The grain columns are grown through the entire film with a nearly unchanged lateral dimension through the full film thickness. The columnar ZnO grains are c‐axis oriented perpendicular to the interface and possess a polycrystalline structure. Optical transmittance up to 90% in the visible range and electrical resistivity as low as 6.8 × 10−3·Ω·cm were obtained under optimal deposition conditions.

Inhibition of glucokinase translocation by AMP-activated protein kinase is associated with phosphorylation of both GKRP and 6-phosphofructo-2-kinase/fructose-2,6-bisphosphatase

The rate of glucose phosphorylation in hepatocytes is determined by the subcellular location of glucokinase and by its association with its regulatory protein (GKRP) in the nucleus. Elevated glucose concentrations and precursors of fructose 1-phosphate (e.g., sorbitol) cause dissociation of glucokinase from GKRP and translocation to the cytoplasm. In this study, we investigated the counter-regulation of substrate-induced translocation by AICAR (5-aminoimidazole-4-carboxamide-1-beta-D-ribofuranoside), which is metabolized by hepatocytes to an AMP analog, and causes activation of AMP-activated protein kinase (AMPK) and depletion of ATP. During incubation of hepatocytes with 25 mM glucose, AICAR concentrations below 200 microM activated AMPK without depleting ATP and inhibited glucose phosphorylation and glucokinase translocation with half-maximal effect at 100-140 microM. Glucose phosphorylation and glucokinase translocation correlated inversely with AMPK activity. AICAR also counteracted translocation induced by a glucokinase activator and partially counteracted translocation by sorbitol. However, AICAR did not block the reversal of translocation (from cytoplasm to nucleus) after substrate withdrawal. Inhibition of glucose-induced translocation by AICAR was greater than inhibition by glucagon and was associated with phosphorylation of both GKRP and the cytoplasmic glucokinase binding protein, 6-phosphofructo-2-kinase/fructose-2,6-bisphosphatase (PFK2) on ser-32. Expression of a kinase-active PFK2 variant lacking ser-32 partially reversed the inhibition of translocation by AICAR. Phosphorylation of GKRP by AMPK partially counteracted its inhibitory effect on glucokinase activity, suggesting altered interaction of glucokinase and GKRP. In summary, mechanisms downstream of AMPK activation, involving phosphorylation of 6-phosphofructo-2-kinase/fructose-2,6-bisphosphatase and GKRP are involved in the ATP-independent inhibition of glucose-induced glucokinase translocation by AICAR in hepatocytes.

Adsorption characteristics of zwitterionic diblock copolymers at the silica/aqueous solution interface

The adsorption of a zwitterionic diblock copolymer, poly(2-(diethylamino)ethyl methacrylate)– block–poly(methacrylic acid) (PDEA 59–PMAA 50), at the silica/aqueous solution interface has been characterised as a function of pH. In acidic solution, this copolymer forms core–shell micelles with the neutral PMAA chains being located in the hydrophobic cores and the protonated PDEA chains forming the cationic micelle coronas. In alkaline solution, the copolymer forms the analogous inverted micelles with anionic PMAA coronas and hydrophobic PDEA cores. The morphology of the adsorbed layer was observed in situ using soft-contact atomic force microscopy (AFM): this technique suggests the formation of a thin adsorbed layer at pH 4 due to the adsorption of individual copolymer chains (unimers) rather than micelle aggregates. This is supported by the remarkably low dissipation values and the relatively low degrees of hydration for the adsorbed layers, as estimated using a combination of quartz crystal microbalance with dissipation monitoring (QCM-D) and optical reflectometry (OR). In alkaline solution, analysis of the adsorption data suggests a conformation for the adsorbed copolymers where one block projects normal to the solid/liquid interface; this layer consists of a hydrophobic PDEA anchor block adsorbed on the silica surface and an anionic PMAA buoy block extending into the solution phase. Tapping mode AFM studies were also carried out on the silica surfaces after removal from the copolymer solutions and subsequent drying. Interestingly, in these cases micelle-like surface aggregates were observed from both acidic and alkaline solutions. The lateral dimension of the aggregates seen is consistent with the corresponding hydrodynamic diameter of the copolymer micelles in bulk solution. The combination of the in situ and ex situ AFM data provides evidence that, for this copolymer, micelle aggregates are only seen in the ex situ dry state as a result of the substrate withdrawal and drying process. It remains unclear whether these aggregates are caused by micelle deposition at the surface during the substrate withdrawal from the solution or as a result of unimer rearrangements at the drying front as the liquid recedes from the surface.

Scalable nanotemplate assisted directed assembly of single walled carbon nanotubes for nanoscale devices

The authors demonstrate precise alignment and controlled assembly of single wall nanotube (SWNT) bundles at a fast rate over large areas by combining electrophoresis and dip coating processes. SWNTs in solution are assembled on prepatterned features that are 80nm wide and separated by 200nm. The results show that the direction of substrate withdrawal significantly affects the orientation and alignment of the assembled SWNT bundles. I-V characterization is carried out to demonstrate electrical continuity of these assembled SWNT bundles.

Anisotropic Microstructural Development During the Constrained Sintering of Dip‐Coated Alumina Thin Films

Alumina thin films were manufactured from aqueous slurries by dip coating. Film thickness as function of substrate withdrawal velocity could be correctly modeled by Landau and Levich's theory. Samples were sintered on a rigid substrate at 1350°C for different isothermal times to achieve relative densities from 84% to 97%. Microstructural analysis of polished cross sections revealed a continuous development of pore alignment, as expected by theoretical considerations. With increasing density pores become more anisometric and orientate along the thickness direction. A further preferential orientation of pores was found in the normal plane, apparently due to the coating process. Constraining conditions had less influence on the size and shape of the grains; they tend to become more equiaxed in the constrained plane, presumably due to the biaxial tensile stress state.

Preparation and Characterization of Silica/Polymethylmethacrylate Hybirid Thin Films on Polybutyleneterephthalate Substrates by Sol-Gel Method.

Silica and silica/polymethylmethacrylate (PMMA) hybrid thin films 0.15-0.9 μm in thickness were deposited on polybutyleneterephthalate (PBT) substrates by dip-coating followed by heat-treatment at 170° or 180°C, using perhydropolysilazane (PHPS) and tetraethylorthosilicate (TEOS) as a silica source. A contamination test was carried out using curry as a contaminant; the curry was placed on the thin film samples, heated at 150°C, and then removed with neutral detergent, followed by microscopic observation and color difference measurement. Coating with silica either using TEOS or PHPS was effective in suppressing the contamination, where the latter was found to be more effective than the former. Although the as-prepared silica and silica/PMMA hybrid thin films were crack-free, the films tended to be cracked when subjected to the contamination test, which was more significant for those prepared at higher substrate withdrawal speeds. The cracking tendency, however, was found to decrease when silica was hybridized with PMMA, and no cracks were observed on the contamination test for the sample prepared at PMMA/PHPS mass ratios higher than 1.2. The degree of contamination was minimized at a PMMA/PHPS mass ratio of 0.8, where excellent adhesion was also found between the film and the substrate.

Unique Model of Dormant Infection for Tuberculosis Vaccine Development

Most individuals exposed to Mycobacterium tuberculosis become infected but hinder the infectious process in dormant foci, known as latent tuberculosis. This limited infection usually stimulates strong T-cell responses, which provide lifelong resistance to tuberculosis. However, latent tuberculosis is still poorly understood, particularly because of the lack of a reliable animal model of dormant infection. Here we show that inoculation of mice with a unique streptomycin-auxotrophic mutant of Mycobacterium tuberculosis recapitulates dormant infection. The mutant grows unimpaired in the presence of streptomycin and no longer grows but remains viable for long periods of time after substrate removal, shifting from the log growth phase to the latent stage, as indicated by augmented production of alpha-crystallin. Mice challenged with the mutant and inoculated with streptomycin for approximately 3 weeks developed a limited infection characterized by a low bacteriological burden and the presence of typical granulomas. After substrate withdrawal, the infection was hindered but few microorganisms remained viable (dormant) in the animals' tissues for at least 6 months. In addition, the animals developed both potent T-cell responses to M. tuberculosis antigens, such as early culture filtrate, Ag85B, and ESAT-6, and resistance to reinfection with virulent M. tuberculosis. Therefore, infection of mice or other animals (e.g., guinea pigs) with M. tuberculosis strain 18b constitutes a simple and attractive animal model for evaluation of antituberculosis vaccines in the context of an M. tuberculosis-presensitized host, a prevailing condition among humans in need of a vaccine.

Transplants of fibroblasts expressing BDNF and NT-3 promote recovery of bladder and hindlimb function following spinal contusion injury in rats

We examined whether fibroblasts, genetically modified to express BDNF and NT-3 (Fb-BDNF/NT3) and transplanted into a thoracic spinal injury site, would enhance recovery of bladder function and whether this treatment would be associated with reorganization of lumbosacral spinal circuits implicated in bladder function. Rats received modified-moderate contusion injuries at T8/9, and 9 days later, Fb-BDNF/NT3 or unmodified fibroblasts (OP-controls) were delivered into the cord. Fb-BDNF/NT3 rats recovered from areflexic bladder earlier, showed decreased micturition pressure and fewer episodes of detrusor hyperreflexia, compared to OP-controls. There were also improvements in hindlimb function in the Fb-BDNF/NT3 group although locomotion on a more challenging substrate (grid) and tail withdrawal latency in response to a thermal stimulus showed persisting deficits, little recovery, and no differences between the groups. Immunocytochemistry at L6-S1 revealed changes in density of afferent and descending projections to L6-S1 cord. The density of small dorsal root axons increased in the superficial layers of the dorsal horn in OP-controls but not in Fb-BDNF/NT3, suggesting sprouting of primary afferents following injury that was inhibited by Fb-BDNF/NT-3. In contrast, the trophic factor secreting transplants stimulated sprouting and/or sparing of descending modulatory pathways projecting to the lumbosacral spinal cord. No differences in synaptophysin immunoreactivity were seen in the dorsal horn which suggested that synaptic density was similar but achieved by sprouting of different systems in the two operated groups. Fb-BDNF/NT3 transplanted into injured spinal cord thus improved both bladder and hindlimb function, and this was associated with reorganization of spinal circuitry.

From a microwave flash-synthesized TiO 2 colloidal suspension to TiO 2 thin films

Titanium(IV) oxide thin films have been prepared by dip-coating at ambient temperature from a TiO 2 colloidal suspension. Prior to deposition, this suspension was synthesized by microwave-induced thermal hydrolysis of a titanium tetrachloride aqueous solution in the presence of hydrochloric acid. The effects, on film roughness and film thickness, of substrate, number of layers, substrate withdrawal speed, and heat treatment temperature were investigated on different observation scales. The microwave-born oxide nanoparticles showed good affinity to glass and silicon substrates; 10- to 50-nm-thick thin films, with absorption edge blue-shifted compared to bulk anatase, were obtained through a simple process without the need of heating treatment for crystallization purposes.

Ischemia induces ligand-independent activation of EGFR in model intestinal epithelia: Role of SHC and GRB2 in stress-induced MAPK response

Abstract Introduction: Ischemic stress activates mitogen-activated protein kinases (MAPKs) in intestinal epithelia, a response that directs cell fate after injury. We reported that ischemic stress triggers ligand-independent activation of the epidermal growth factor receptor (EGFR), an event associated with downstream activation of MAPK. This study examines the role of EGFR-associated adaptor proteins SHC and GRB2 in ischemic activation of MAPK. Methods: Human intestinal T84 cells underwent 60min of ischemic stress (ATP depletion) by substrate withdrawal and chemical inhibition of mitochondrial respiration and glycolysis (glucose-free buffer containing 1mM oligomycin-A plus 10mM 2-deoxyglucose). Ischemic stress was terminated by return to glucose-containing buffer (ATP repletion). SHC activation was assessed by immunoprecipitation of SHC and blotting with phosphotyrosine specific Ab. Blots were probed for total SHC to ensure equal loading. SHC interactions with GRB2 were assessed by immunoprecipitation of SHC followed by blotting for GRB2. Results: ERK 1/2 phosphorylation is maximal and EGFR was activated within 20min of ATP repletion. At this time point, levels of SHC tyrosine phosphorylation (indicative of SHC activation) were increased (131% +/− 23%, n=3) without change in total SHC levels. Additionally, the interaction of SHC with GRB2 increased by nearly 3-fold (291 +/− 63.7%, n=3, p Conclusions: Following ischemic stress in model intestinal epithelia, SHC phosphorylation/activation is increased in parallel with increased association with GRB2. We conclude that ischemic stress induces the recruitment of EGFR adaptor proteins SHC and GRB2. These data further support a role for ligand-independent activation of EGFR in post-ischemic activation of MAPK signaling.

Deposition of Cationic Polymer Micelles on Planar SiO2 Surfaces

The deposition of PS-PVPH+ polymer micelles from a pH 1 aqueous solution onto Si wafers has been studied using a simple dip-coating technique. It has been found that the rate of evaporation of the solvent and the rate of withdrawal have a considerable influence on the density and ordering of the adsorbed micelles. The highest density and degree of ordering (as judged by the 2D pair correlation function) is achieved when solvent evaporation dominates the deposition process, but a fairly homogeneous distribution of polymer micelles can be achieved over a distance of at least 3-4 mm by controlling the solvent evaporation rate and the rate of substrate withdrawal. We did not observe any significant effect of added KCl (up to 0.1 M) during the deposition process or soaking in 1 M KCl after deposition. The attachment of these micelles is quite robust, as they cannot be washed off in pH 1 water (with or without KCl) without significant mechanical assistance. However, we did find that the micelles are rather easily caused to dewet and partially aggregate under the influence of 65 degrees C water vapor.

Graphoepitaxial Deposition of Cationic Polymer Micelles on Patterned SiO2 Surfaces

We have studied the deposition of polymer micelles formed from poly(styrene)-block-poly(2-vinylpyridine) (PS-PVPH+) from room-temperature aqueous solutions at pH 1 onto a hydrophilic Si/SiO2 surface with a relief pattern 100 nm deep with variable widths. It has been found that the micelle density is substantially higher and the ordering of the micelles is improved for micelles that adsorb in the 100 nm depressions in the width range of ca. 500-5000 nm. We ascribe these effects to capillary forces that pull the aqueous solution into the canyons where the micelles can be trapped. While the ordering of the micelles can be substantial, they do not form a perfect hexagonal crystal. If the surface is chemically modified by a Au coating, the micelle-surface interaction is strengthened and the degree of ordering is diminished. These results demonstrate that a combination of graphoepitaxy and processing conditions (speed of substrate withdrawal or evaporation of solvent) can be used to make fairly ordered polymer micelle arrays over a space of (at least) several millimeters.

Preparation of PZT(53/47) thick films deposited by a dip-coating process

Crack-free polycrystalline PZT (PbZrTiO 3) thick films up to 15 μm with perovskite structure have been prepared from a dip-coating process. The influence of substrate characteristics, withdrawal speed and ionic concentration of precursor solution on the morphology and microstructure of PZT film was examined. The dielectric, ferroelectric and piezoelectric properties of PZT thick films on Pt/Ti substrate were measured and evaluated. PZT(53/47) thick films on Pt/Ti substrate exhibits a excellent electric properties, e.g. P r: 35 μC/cm 2; E c: 32 kV/cm; ϵ r: 830; tan δ: 0.01–0.03; d 33: 142.