Gradient Films Research Articles

Fabrication of Two-Dimensional Gradient Layer-by-Layer Films for Combinatorial Biosurface Studies

We have developed a novel gradient fabrication method for combinatorial surface studies that provides the equivalent of 5000 individual polyelectrolyte multilayer (PEM) film physicochemical conditions in a single 7 cm square film. A simple, inexpensive, and versatile automated layering instrument was built, which can generate a gradient of physical properties on a film in 1 dimension laterally by simultaneously changing both the location of polyelectrolyte adsorption and the layering conditions, such as pH or salt concentration of the polyelectrolyte dipping solutions. By rotating the substrate 90° after each deposition cycle, full 2-dimensional gradient combinatorial films were fabricated over many layers, spanning virtually all previous combinations of stable deposition pH and salt conditions for both poly(allylamine hydrochloride) (PAH) and poly(acrylic acid) (PAA), a process which previously required more than 10 000 separate film samples. Surface spatial profiles of film thickness, surface energy (wettability), density (refractive index), and stiffness (modulus) were generated and correlated to assembly conditions. Additionally, step gradient films were generated first by varying the number of bilayers along one axis and pH along the other, which enabled us to measure their combined effect on thickness. To test for biocompatibility, we incubated HEK 293 cells on step gradient films and 2D combinatorial films for 48 h and determined that film assembly conditions played a major role, especially in controlling the stiffness and the density, which could be tailored with deposition pH over a wide range. Optimal growth conditions were discovered not at the extremes of fabrication pH, but instead near PAH pHs of 4–6 and PAA pH around 4, demonstrating that these PEM biosurfaces and this technique are suitable for optimizing high-throughput cellular screening.

Contact instabilities of anisotropic and inhomogeneous soft elastic films

Anisotropy plays important roles in various biological phenomena such as adhesion of geckos and grasshoppers enabled by the attachment pods having hierarchical structures like thin longitudinal setae connected with threads mimicked by anisotropic films. We study the contact instability of a transversely isotropic thin elastic film when it comes in contact proximity of another surface. In the present study we investigate the contact stability of a thin incompressible transversely isotropic film by performing linear stability analysis. Based on the linear stability analysis, we show that an approaching contactor renders the film unstable. The critical wavelength of the instability is a function of the total film thickness and the ratio of the Young's modulus in the longitudinal direction and the shear modulus in the plane containing the longitudinal axis. We also analyze the stability of a thin gradient film that is elastically inhomogeneous across its thickness. Compared to a homogeneous elastic film, it becomes unstable with a longer wavelength when the film becomes softer in going from the surface to the substrate.

Effect of annealing on self-organized gradient film obtained from poly(3-[tris(trimethylsilyloxy)silyl] propyl methacrylate-co-methyl methacrylate)/poly(methyl methacrylate-co-n-butyl acrylate) blend latexes

The effect of annealing on the self-organized morphology and component gradient distribution of films prepared from bimodal latexes blend containing 1:1 silicon-containing acrylate copolymer/silicon-free acrylate copolymer blend was studied using attenuated total reflectance–Fourier transform infrared (ATR-FTIR) spectroscopy, scanning electron microscopy with X-ray energy-dispersive (SEM-EDX) spectrometry, and atomic force microscopy (AFM). The distribution of silicon through the whole thickness of the film as a function of annealing was investigated using confocal Raman spectroscopy (CRS). AFM results show that poly(methyl methacrylate-co-n-butyl acrylate) latex fuses to form a continuous film at 25 °C. The wettability of the acrylate components and the heterogeneous composition of poly(3-[tris(trimethylsilyloxy)silyl] propyl methacrylate-co-methyl methacrylate) result in a graded block film. ATR-FTIR and SEM-EDX measurements reveal silicon-containing components segregate at the film–air interface upon annealing. CRS further shows that the nonlinear model gradient distribution of silicon is obtained, where the content of silicon component is enhanced and it gradually varies in the bulk. When the annealing temperature increases to 120 and 180 °C, blend latexes films demonstrate varying topography and phase images, indicating phase separation is induced by annealing. Furthermore, CRS implies that the destruction of the gradient structure is attributed to the phase separation of the two blend components.

Mechanically alloyed Mg–Ni–Ti and Mg–Fe–Ti powders as hydrogen storage materials

Recent research on coevaporated thin gradient films Mg1−x−zNixTiz have detected, using optical hydrogenography, a compositional region centered around Mg69Ni26Ti5, with low absolute values of the hydride formation enthalpy. These destabilized hydrides would present then sorption kinetics more favorable for their use as hydrogen reservoirs. In order to check if these relevant properties extend to massive samples we attempted an investigation on mechanically alloyed powder mixtures Mg1−x−zNixTiz of similar composition and also on mixtures Mg1−x−zFexTiz, with Fe instead of Ni. Thus, powder mixtures of nominal composition: Mg69M26Ti5, Mg64M26Ti10 and Mg64M31Ti5 (M = Ni, Fe) were milled in a H2 ambient till a steady state, with no further H2 absorption, was attained and the hydriding kinetics was determined from the H2 intake. Each hydrided sample was discharged by increasing the temperature at a given starting H2 pressure and recharged by decreasing the temperature under the same conditions. The resulting P vs T curves were analyzed to extract approximate values of the equilibrium (T,P) data for H2 desorption and absorption. Before and after their cycling in H2 the samples were characterized by X ray diffraction and those containing Fe, by Mössbauer spectroscopy. The results are analyzed in connection with possible mechanisms for the transition metals catalytic action and the influence of the sample microstructure.

Microfluidic Chip for Generating Gradient Polymer Films for Biological Applications

Abstract The behavior of cells, like adhesion or differentiation in case of stem cells, is influenced by the surface the cells are cultivated on. Cells sense the actual properties of the surface as well as gradients of these properties. Here we present the production and usage of a microfluidic chip for generating polymer films possessing gradients of morphology. The polymer surface's properties are defined by the composition of the polymerization mixtures injected into the microfluidic chip. After polymerization and subsequent removal of one part of the microfluidic chip, the surface of the gradient films is accessible for biological experiments on glass slides.

OS1307 種々の濃度勾配を有するNi-Cu合金めっき膜の硬度と微視的構造

Vickers hardness of Ni-Cu alloy films which have composition gradient along thickness direction was investigated. The composition-gradient Ni-Cu films were fabricated on copper substrate by the special electrodeposition technique where electrode potential changed continuously. The films were composed of alternate stack of layers having positive and negative gradients. Total thickness of all the films was 1.2μm. The gradient films differed in both composition gradient dc_<Ni>/dx and amplitude of Ni concentration Δc_<Ni>. The dc_<Ni>/dx and Δc_<Ni> values varied from 5×10^<-6> to 2×10^<-2>nm^<-1> and 0.006 to 0.6, respectively. The composition-gradient Ni-Cu films having high gradient or high Ni concentration amplitude showed higher Vickers hardness than the Ni-Cu multilayered film with defined Ni/Cu interfaces: the maximum hardness of the composition-gradient Ni-Cu films was amounted up to Hv250 while that of the multilayered film was Hv140. The hardness of the composition-gradient Ni-Cu films revealed good correlation with the gradient dc_<Ni>/dx, compared with the Ni concentration amplitude Δc_<Ni>. From this result, the high strength of the composition-gradient Ni-Cu films could be explained not by internal stress induced by lattice mismatch, but by high-density misfit dislocations caused by the composition gradient.

Gradient Technology for High‐Throughput Screening of Interactions between Cells and Nanostructured Materials

We present a novel substrate suitable for the high‐throughput analysis of cell response to variations in surface chemistry and nanotopography. Electrochemical etching was used to produce silicon wafers with nanopores between 10 and 100 nm in diameter. Over this substrate and flat silicon wafers, a gradient film ranging from hydrocarbon to carboxylic acid plasma polymer was deposited, with the concentration of surface carboxylic acid groups varying between 0.7 and 3% as measured by XPS. MG63 osteoblast‐like cells were then cultured on these substrates and showed greatest cell spreading and adhesion onto porous silicon with a carboxylic acid group concentration between 2‐3%. This method has great potential for high‐throughput screening of cell‐material interaction with particular relevance to tissue engineering.

Silicon nitride gradient film as the underlayer of ultra-thin tetrahedral amorphous carbon overcoat for magnetic recording slider

There are higher technical requirements for protection overcoat of magnetic recording slider used in high-density storage fields for the future. In this study, silicon nitride (Si-N) composition-gradient films were firstly prepared by nitriding of silicon thin films pre-sputtered on silicon wafers and magnetic recording sliders, using microwave electron cyclotron resonance plasma source. The ultra-thin tetrahedral amorphous carbon films were then deposited on the Si-N films by filtered cathodic vacuum arc method. Compared with amorphous carbon overcoats with conventional silicon underlayers, the overcoats with Si-N underlayers obtained by plasma nitriding especially at the substrate bias of −150 V, can provide better corrosion protection for high-density magnetic recording sliders.

EFFECT OF FLUORINATED POLYACRYLATE CONTENT ON THE GRADIENT STRUCTURE AND SURFACE PROPERTY OF FLUORINATED/NON-FLUORINATED POLYACRYLATE LATEX BLEND FILMS

In order to obtain the gradient fluorinated/non-fluorinated polyacrylate latex blend films as cheap as possible,the fluorinated polyacrylate emulsion with small particle size was synthesized by bulk emulsion polymerization method,the acrylate copolymer emulsion with big particle size was synthesized by semicontinuous emulsion polymerization method,and then the fluorinated polyacrylate emulsion and the acrylate copolymer emulsion were mixed with a series of ratios(1/9,2/8,3/7,4/6,5/5).The blend latices were dried on clean glass at 20℃ and then annealled at 110℃/210℃ for some time(2~6 h).The effects of the fluorinated polyacrylate content on the gradient structure and surface property of the blend films were discussed.The content of fluorine on the film surface and the film section was analyzed by XPS,SEM-EDX.The surface properties and morphology were characterized by contact angle measurements and AFM.It was found that,while the content of fluorinated polyacrylate latex in the blend system was up to 30 wt%,the small and hard fluorinated polyacrylate particles were selectively gathered on the film-air interface after film-formation at room temperature,and the fluorine content increased from the film-glass interface to the film-air interface gradually in the blend films annealled 2 h at 110℃.The obtained gradient film has low surface free energy as the pure fluorinated polyacrylate and strong adhesion as the pure polyacrylate.The further increasing of fluorinated polyacrylate in the blend system helped the formation and enlargement of gradient structure,but the adhesion of film was decreased a little.The emulsion system with the content of fluorinated polyacrylate latex under 30 wt% was hard to form gradient structure.

Preparation of Cu/ZrW&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;8&lt;/sub&gt; Gradient Films Using Different Targets

The Cu/ZrW2O8gradient films have been deposited on silicon substrates by RF magnetron sputtering with copper and compound targets followed by annealing in argon atmosphere at 750 °C for 3 min. The three different compound targets were B1 (nZrO2:nWO3=1:2.2), B2 (nZrO2:nWO3=1:2.5) and B3 (ZrW2O8), respectively. The as-deposited gradient films were amorphous, while a post-deposition annealing at elevated temperature was required for the development of the cubic ZrW2O8. The structure and surface morphology of the gradient films were then studied using X-ray diffraction (XRD), Scanning Electron Microscopy (SEM) and Energy Dispersive Spectrometer (EDS). The globular and slender rod crystals can be found in annealed films, which are copper and ZrW2O8, respectively. The fine gradient film should be obtained using the target B1.

Toughing of ZrAlN Film through Superlattice Design

Two kinds of magnetron sputtering ZrAlN films containing 23%atAl were deposited. The first was multicomponent ZrAlN film, the second was structure gradient and mulilayer film, named superlattice ZrAlN film. The microstructure was studied by FESEM, TEM , XRD, its mechanical properties were evaluated by nano-indentation method. The fracture toughness of films were determined from the length of ‘radial cracks’ on the applied diamond identer load 1.96N. the results show that, multicomponent ZrAlN film has hardness value of 35GPa, fracutre toughness value of 1.97MPa·m-0.5; while superlattice ZrAlN film has coresponding value of 40.1GPa and 3.17MPa·m-0.5. TEM image illustrates the superlattice ZrAlN film period is 2.5nm, nanoidentation test shows superlattice film has higher elastic recovery parameter and lower plastic work.

Degradation Experiments and Modeling of PLGA Blend and Gradient Films

PLGA blend and gradient films were designed and prepared to improve the late degradation properties of PLGA films. The gradient films were composed of gradual components of PLGA50/50 and PLGA 75/25, and PLGA 50/50, featuring gradual descents from outside parts to inside parts of the films. Degradation processes of biodegradable PLGA blend and gradient films were also predicted by Monte Carlo simulation to understand the mechanism of degradation. The simulation results indicated that the gradient structure prolonged the mass transfer time of the degradable films, and it induced smoother weight loss than single-component or blend films. The degradation behaviors of single-component, blend and gradient films were experimentally investigated to prove the validity of the models by immersing them into PBS. The experiment indicated that the gradient films have the most stable weight loss curves, which were in well accordance with the simulation by Monte Carlo method.

Study on the tribological properties of hard films deposited on biomedical NiTi alloy

Hard films including carbon nitride (CNx), diamond-like carbon (DLC), and titanium nitride (TiN) were respectively deposited on the biomedical NiTi alloy substrate by using reactive direct current magnetron sputtering. A Ti transition layer was pre-deposited in order to strengthen the adhesion between the hard films and NiTi alloy substrate. The tribological properties of the deposited hard films were systematically investigated by using scratch tester and friction wear tester. It was shown that the tribological performance of NiTi alloy substrate was improved effectively after the deposition of gradient films. The deposition of Ti transition layer benefited in increasing the adhesion strength between the NiTi substrate alloy and the inorganic hard films, especially for the CNx film. Among the three types of gradient films, Ti/CNx film possessed the best tribological performance (with the minimum friction coefficient of 0.092 and the maintenance of smooth and intact surface after the friction and wear tests).

Self-Stratification Silicon Gradient Film Prepared by Emulsion Blend Technique

We investigated the effect of film-formation temperature andTg’s difference on the self-stratification gradient silicone film prepared by emulsion blend (poly(3-[tris(trimethyl silyloxy)silyl] propyl methacrylate-co-methyl methacrylate) /poly(butyl acrylate-co-methyl methacrylate) 50/50 by wt) (PTRIS-co-MMA/PBA-co-MMA) technique. The self-stratification film with gradient distribution of silicon was relatively easily obtained when both blend components could fully fuse to form a continuous film. Moreover, proper nonparallelTgs facilitated migration of the silicon component to the film-air interface during the film-formation and hence the gradient distribution was obtained. WhenTgof silicon-free component was 40°C, self-stratification gradient film with concentration of silicon components varying in a gradient-like manner along the overall transaction of the film was fabricated.

Profile Control in Surface Amine Gradients Prepared by Controlled-Rate Infusion

Surface amine gradients that exhibit a wide variety of profiles, including those that incorporate spatially distinct regions having steep and gradual variations in chemical functionality, have been prepared by the sol-gel process using a controlled-rate infusion method. In this work, a substrate that incorporates dimethyl and Si-OH groups is temporally modified with an aminoalkoxysilane (NH(2)(CH(2))(3)Si(OC(2)H(5))(3)) to build a gradient film for which the amine content changes over a 10-20 mm distance. Both X-ray photoelectron spectroscopy (XPS) and contact angle measurements confirm the presence of a chemical gradient across the surface of the film. As expected, a greater density of amine functionalities and lower contact angle were found at the bottom of the gradient relative to the top. The local steepness of the gradient was systematically controlled by changing the rate of infusion. Fast rates of infusion created gradient surfaces where the amine content changed slowly along the surface and never reached saturation, whereas slow rates of infusion formed a surface exhibiting a steep rise in amine content followed by saturation. The steepness of the gradient was also changed at predefined positions along its length by programming the rate of infusion. Gradients prepared using six-step, three-step, and two-step programmed infusion rates are shown. The data fit nicely to a kinetic model that assumes first-order kinetics. The ability to manipulate the gradient profile is particularly vital for applications that rely on mass transport and/or those that require spatial control of gradient properties.

Preparation and characterization of gradient distribution of silicon in emulsion blend films

In this work, a functional gradient polymeric material derived from silicon-containing acrylate blend emulsion film is prepared in two steps. Firstly, 3-[tris(trimethylsilyloxy)silyl] propyl methacrylate (TRIS)-modified acrylate latex is prepared using multiple emulsifiers by the two-stage semicontinuous emulsion copolymerization method. Next, blend latexes composed of TRIS-containing and TRIS-free acrylate latexes are obtained. Detailed studies on the effects of the film-formation temperature and the glass transition temperature (Tg) differences on the compositional gradient film are conducted. Surface energy analysis shows that silicon elements enriched at the film-air (F-A) interface and Tg differences facilitate the fabrication of silicon gradient in emulsion blend films. Scanning electron microscopy-energy dispersive X-ray further reveals that the concentration of silicon components varies in a gradient-like manner along the overall transaction of the film when the film-formation temperature is 55 °C. However, excessive temperature creates the formation of a segmental gradient distribution of silicon in the emulsion blend films.

Oxidation behavior of TiAlZrCr/(Ti,Al, Zr, Cr)N gradient films deposited by multi-arc ion plating

Oxidation behavior of TiAlZrCr/(Ti, Al, Zr, Cr)N gradient films deposited by multi-arc ion plating Shilu ZHAO ∗ and Jun ZHANG School of Mechanism Engineering, Shenyang University, Shenyang 110044, China Changsheng LIU Key Laboratory for Anisotropy and Texture of Materials, Ministry of Education, Northeastern University, Shenyang 110819, China Manuscript received 10 December 2009; in revised form 22 February 2010

Spatiotemporal Evolution of Fixed and Mobile Dopant Populations in Silica Thin-Film Gradients as Revealed by Single Molecule Tracking

Investigations of single molecule diffusion and entrapment within sol−gel-derived silica thin film gradients are reported for the first time. Gradient films were prepared on silica-sublayer-coated substrates by infusion-withdrawal dip-coating [Chem. Mater. 2010, 22, 2970]. This method employs a sol of time- varying composition obtained by slowly mixing two different sols in the deposition reservoir. Tetramethoxysilane (TMOS) and methyltrimethoxysilane (MTMOS) were employed as precursor silanes. Films exhibiting macroscopic, unidirectional gradients in methyl content were obtained. Fourier transform infrared (FTIR) microscopy data provide proof of gradient formation, depicting an increase along the gradient in Si-CH3 absorption at 1275 cm−1 relative to Si−O−Si absorption at 1080 cm−1. Widefield fluorescence videos recorded as a function of position for Nile Red-doped films depict spatially varying populations of immobile and mobile molecules. The immobile fraction is believed to be incorporated in the silica sublayer, while the mobile molecules reside in/on the gradient. Diffusion coefficients, D, measured from single molecule tracking data depict, on average, a gradual increase in molecular mobility between the TMOS and MTMOS ends of the gradient. The mobile fraction is observed to split into two separate populations toward the MTMOS end of the gradient. Simultaneously, the width of the D distribution for the most mobile population is found to increase. Comparison with simulated results suggests that the TMOS end of the film is relatively homogeneous, while the MTMOS end exhibits increased heterogeneity. It is concluded the MTMOS end may incorporate TMOS- and MTMOS-rich “domains”. Plots of mean square displacement in time provide no evidence for confined diffusion, suggesting the molecules move freely between these domains.

Surface modification and characterization of SEBS films obtained by in situ and ex situ oxidization with potassium permanganate

AbstractThe surface morphologies and compositions of the asymmetric films of polystyrene‐b‐poly(ethylene‐co‐butylene)‐b‐polystyrene (SEBS) prepared by in situ and ex situ oxidization with the KMnO4 aqueous solution and KMnO4/H2SO4 mixed solution were investigated by using scanning electron microscope, atomic force microscope (AFM), X‐ray photoelectron spectroscopy (XPS) and attenuated total reflectance infrared spectroscopy (ATR‐FTIR). The effect of the oxidization reagents on morphological changes and the influence of in situ and ex situ preparation methods on surface compositions were discussed. Different from the in situ oxidation by degrading the copolymers to form a gradient film, the ex situ oxidation preferentially degraded the uppermost layer of the film. Although both the KMnO4 oxidation and the KMnO4/H2SO4 oxidation gave hierarchical structures, distinctive differences were found that large ridges and smaller granules were fabricated in the former film and the latter produced large and deep ravines and fine sponge‐like morphologies. Additionally, the oxygen concentration and the oxo‐species implanted by these oxidation treatments were characterized and evaluated to provide a quantitative comparison. Oxygen, as well as manganese was found to be implanted in the surface layer of the oxidized film, forming predominantly OC and OCO groups, as well as a small fraction of OH and MnO compounds. Changes in contact angle of water on these films and total surface oxygen content are related but not directly. The hystereses of water contact angle at a value of 119 ± 3° due primarily to surface roughness and at a value of 63 ± 3° due primarily to chemical heterogeneity are led by different oxidation degrees and oxidation methods. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2010

One-Step Method for Generating PEG-Like Plasma Polymer Gradients: Chemical Characterization and Analysis of Protein Interactions

In this work we report a one-step method for the fabrication of poly(ethylene glycol) PEG-like chemical gradients, which were deposited via continuous wave radio frequency glow discharge plasma polymerization of diethylene glycol dimethyl ether (DG). A knife edge top electrode was used to produce the gradient coatings at plasma load powers of 5 and 30 W. The chemistry across the gradients was analyzed using a number of complementary techniques including spatially resolved synchrotron source grazing incidence FTIR microspectroscopy, X-ray photoelectron spectroscopy (XPS) and synchrotron source near edge X-ray absorption fine structure (NEXAFS) spectroscopy. Gradients deposited at lower load power retained a higher degree of monomer like functionality as did the central region directly underneath the knife edge electrode of each gradient film. Surface derivatization experiments were employed to investigate the concentration of residual ether units in the films. In addition, surface derivatization was used to investigate the reactivity of the gradient films toward primary amine groups in a graft copolymer of poly (L-lysine) and poly(ethylene glycol) (PLL-g-PEG copolymer) which was correlated to residual aldehyde, ketone and carboxylic acid functionalities within the films. The protein adsorption characteristics of the gradients were analyzed using three proteins of varying size and charge. Protein adsorption varied and was dependent on the chemistry and the physical properties (such as size and charge) of the proteins. A correlation between the concentration of ether functionality and the protein fouling characteristics along the gradient films was observed. The gradient coating technique developed in this work allows for the efficient and high-throughput study of biomaterial gradient coating interactions.