热诱导金属/聚合物膜系图案化控制的研究

近年来 ,在简单体系上形成复杂规则的图案已引起诸多学者的注意 ,其中以聚合物为母体的体系发展了模板、局部紫外照射和激光诱导等一系列技术 ,从而得到可控的表面图案[1～ 6] .本文用激光刻蚀法对溅射在聚合物膜上的金属薄膜进行处理 ,在热诱导情况下使金属 /聚合物膜系表面产生了规则的图案 .薄膜热应力的可控释放作用和激光刻蚀造成的区域局限作用被认为是诱导这种可控图案产生的两种基本要素 .通过控制激光刻蚀区域 ,可控制薄膜表面形貌变化 ,从而实现可控的图案化设计 .1　实验部分1.1　原料及仪器　聚苯乙烯 (PS) :北京燕山石油化工…     

Thickness of hydroxyapatite nanocrystal controls mechanical properties of the collagen-hydroxyapatite interface

Collagen-hydroxyapatite interfaces compose an important building block of bone structures. While it is known that the nanoscale structure of this elementary building block can affect the mechanical properties of bone, a systematic understanding of the effect of the geometry on the mechanical properties of this interface between protein and mineral is lacking. Here we study the effect of geometry, different crystal surfaces, and hydration on the mechanical properties of collagen-hydroxyapatite interfaces from an atomistic perspective, and discuss underlying deformation mechanisms. We find that the presence of hydroxyapatite significantly enhances the tensile modulus and strength compared with a tropocollagen molecule alone. The stiffening effect is strongly dependent on the thickness of the mineral crystal until a plateau is reached at 2 nm crystal thickness. We observe no significant differences due to the mineral surface (Ca surface vs OH surface) or due to the presence of water. Our result shows that the hydroxyapatite crystal with its thickness confined to the nanometer size efficiently increases the tensile modulus and strength of the collagen-hydroxyapatite composite, agreeing well with experimental observations that consistently show the existence of extremely thin mineral flakes in various types of bones. We also show that the collagen-hydroxyapatite interface can be modeled with an elastic network model which, based on the results of atomistic simulations, provides a good estimate of the surface energy and other mechanical features.     

Instabilities and pattern miniaturization in confined and free elastic-viscous bilayers

We present an analysis of the instabilities engendered by van der Waals forces in bilayer systems composed of a soft elastic film (<10 microm) and a thin (<100 nm) viscous liquid film. We consider two configurations of such systems: (a) Confined bilayers, where the bilayer is sandwiched between two rigid substrates, and (b) free bilayers, where the viscous film is sandwiched between a rigid substrate and the elastic film. Linear stability analysis shows that the time and length scales of the instabilities can be tuned over a very wide range by changing the film thickness and the material properties such as shear modulus, surface tension, and viscosity. In particular, very short wavelengths comparable to the film thickness can be obtained in bilayers, which is in contrast to the instability wavelengths in single viscous and elastic films. It is also shown that the instabilities at the interfaces of the free bilayers are initiated via an in-phase "bending" mode rather than out-of-phase "squeezing" mode. The amplitudes of deformations at both the elastic-air and elastic-viscous interfaces become more similar as the elastic film thickness decreases and its modulus increases. These findings may have potential applications in the self-organized patterning of soft materials.     

Superficial wrinkles in stretched, drying gelatin films

When a thin film of initially hydrated gelatin is allowed to dry from the surface, superficial changes in the structure of the material affect the local mechanical properties of the drying region. If the film is simultaneously subjected to large strain deformation (above 20%), a periodic pattern of wrinkles appears on the surface of the gelatin along the length of the sample in the direction of the applied force. These wrinkles are uniformly distributed on the surface of the gelatin with a wavelength that is much smaller than the sample thickness, which changes with sample composition, aging time, and deformation rate. We investigate these patterns via in situ environmental scanning electron microscopy (ESEM) and provide a theory for their origin.     

Interfacial rheology and structure of tiled graphene oxide sheets

The hydrophilic nature of graphene oxide sheets can be tailored by varying the carbon to oxygen ratio. Depending on this ratio, the particles can be deposited at either a water-air or a water-oil interface. Upon compression of thus-created Langmuir monolayers, the sheets cover the entire interface, assembling into a strong, compact layer of tiled graphene oxide sheets. With further compression, the particle layer forms wrinkles that are reversible upon expansion, resembling the behavior of an elastic membrane. In the present work, we investigate under which conditions the structure and properties of the interfacial layer are such that free-standing films can be obtained. The interfacial rheological properties of these films are investigated using both compressional experiments and shear rheometry. The role of surface rheology in potential applications of such tiled films is explored. The rheological properties are shown to be responsible for the efficiency of such layers in stabilizing water-oil emulsions. Moreover, because of the mechanical integrity, large-area monolayers can be deposited by, for example, Langmuir-Blodgett techniques using aqueous subphases. These films can be turned into transparent conductive films upon subsequent chemical reduction.     

Topographical and Electrical Stimulation of Neuronal Cells through Microwrinkled Conducting Polymer Biointerfaces

The development of smart biointerfaces combining multiple functions is crucial for triggering a variety of cellular responses. In this work, wrinkled organic interfaces based on the conducting polymer poly(3,4‐ethylene dioxythiophene) doped with poly(styrene sulfonate) are developed with the aim to simultaneously convey electrical and topographical stimuli to cultured cells. The surface wrinkling of thin films on heat‐shrink polymer sheets allows for rapid patterning of self‐assembled anisotropic topographies characterized by micro/sub‐microscale aligned wrinkles. The developed interfaces prove to support the growth and differentiation of neural cells (SH‐SY5Y, human neuroblastoma) and are remarkably effective in promoting axonal guidance, by guiding and stimulating the neurite growth in differentiating cells. Electrical stimulation with biphasic pulses delivered through the conductive wrinkled interface is found to further promote the neurite growth, demonstrating the suitability of such interfaces as platforms for conveying multiple stimuli to cells and tissues.     

Surface Wrinkling Induced by Photofluidization of Low Molecular Azo Glasses

Photoinduced surface wrinkling is demonstrated for a low molecular azo compound confined between a substrate and a thin inorganic elastic layer. The wrinkling process is investigated by time‐resolved light scattering as well as by two‐dimensional autocorrelation analysis of microscopic images. It is shown that the temporal evolution of the wrinkling pattern is directly controlled by the amount of photons absorbed by the sample and that there is no significant dependence of the equilibrium wavelength on irradiation intensity. Finally, the comparison of thermal and photoinduced wrinkling revealed that photoinduced wrinkles are characterized by a narrower mode distribution and less coarsening.     

Characterisation of pure or coated metal surfaces with streaming potential measurements

In the field of corrosion prevention, the characterisation of metal surfaces is useful to obtain information about the necessary preparation of the surface and about the quality of thin coatings of coupling and protective agents. Electrokinetic measurements can be used to determine the properties of modified polymer surfaces, metal sheets, and different surface preparations. However, it was necessary first to create special conditions for measuring the streaming potential, such as electrical isolation of the sample sheets together with the use of inert systems, as shown by the example of aluminium. According to the usual procedure the metal was first coated with a thin layer of a coupling agent. The effect of this adhesive agent depends on the degree of its adsorption by the metal surface. The quality of this layer can be characterised by streaming potential measurements, which can show the degree of coverage, the adhesive strength of the coated layer, and the effective chemical properties of the treated surface. These results were confirmed by wetting measurements. The production of surfaces which allow us to couple a coating varnish to the adhesive agent in good quality was demonstrated. Received: 24 June 1996 / Revised: 30 January 1997 / Accepted: 30 January 1997     

Nonlinear behavior during semi-quantitative analysis of thin organic layers by laser desorption mass spectrometry

Characterization of the surface coverage and thickness of an organic thin film is particularly important in organic electronics and optoelectronics. For surface coverage down to the submonolayer level there is still a need for characterization methods which are easily applicable. In the present work we report on the evaluation of laser desorption mass spectrometry (LD-MS) for its use in thickness determination of organic thin films. Whereas LD-MS is well established as a soft ionization method for small molecules, its capability for use in quantitative analysis is nearly unexplored. We carried out experiments with two different molecules, 7,7,8,8-tetracyanoquinodimethane and hexabenzocoronene, in a series of experiments with increasing surface coverage. The obtained data were analyzed by plotting the LD signal intensities versus the relative layer thickness and they reveal a nonlinear behavior, which can be classified into regions of different desorption/ionization efficiencies. Visualization by atomic force microscopy reveals that the first efficiency change corresponds to the transition between incomplete and complete coverage of the metal surface by analyte molecules. A second transition is observed at high layer thickness where the signal intensity stays constant, independent of further thickness increments, and this is attributed to the limited penetration depth of the laser beam. The intermediate region between the two transitions shows a linear behavior and can thus be used for semi-quantitative thickness measurements. The efficiency change observed at the point of complete surface coverage is particularly useful for thin layer preparation of organic field effect transistors, where complete surface coverage is a minimum requirement.     

Instabilities of nematic liquid crystal films

We discuss instabilities exhibited by free surface nematic liquid crystal (NLC) films of nanoscale thickness deposited on solid substrates, with a focus on surface instabilities that lead to dewetting. Such instabilities have been discussed extensively; however, there is still no consensus regarding the interpretation of experimental results, appropriate modeling approaches, or instability mechanisms. Instabilities of thin NLC free surface films are related to a wider class of problems involving dewetting of non-Newtonian fluids. For nanoscale films, the substrate–film interaction, often modeled by a suitable disjoining pressure, becomes relevant. For NLCs, one can extend the formulation to include the elastic energy of the NLC film, leading to an ‘effective’ disjoining pressure, playing an important role in instability development. Focusing on thin film modeling within the framework of the long-wave asymptotic model, we discuss various instability mechanisms and outline problems where new research is needed.     

Single molecule magnets: from thin films to nano-patterns

Single molecule magnets (SMM) are a class of molecules exhibiting magnetic properties similar to those observed in conventional bulk magnets, but of molecular origin. SMMs have been proposed as potential candidates for several technological applications that require highly controlled thin films and patterns. Here we present an overview of the most important approaches for thin film growth and micro(nano)-patterning of SMM, giving special attention to Mn(12) based molecules. We present both conventional approaches to thin film growth (Langmuir-Blodgett, chemical approach, dip and dry, laser evaporation), patterning (micro-contact printing, deposition on patterned surface, moulding of homogeneous films) and new methods specifically developed for SMM (lithographically controlled wetting, lithographically controlled de-mixing).     

Interfacial chemistries for nanoscale transfer printing

We describe a patterning technique that uses self-assembled monolayers and other surface chemistries for guiding the transfer of material from relief features on a stamp to a substrate. This purely additive contact printing technique is capable of nanometer resolution. Pattern transfer is fast and it occurs at ambient conditions. We illustrate the versatility of this method by printing single-layer metal patterns with feature sizes from a few tens of microns to a few tens of nanometers. We also demonstrate its use for patterning, in a single step, metal/dielectric/metal multilayers for functional thin film capacitors on plastic substrates.     

Towards advanced circuit board materials: adhesion of copper foil to ultra‐high molecular weight polyethylene composite

Polyethylene based composites are attractive materials for advanced circuit board applications because of their unique combination of properties: low dielectric constant and loss factor, light weight, high flexural modulus and low thermal expansion coefficient controlled in all spatial directions. This investigation describes a process to consolidate chopped fibers of ultra‐high molecular weight polyethylene concurrently with its bonding to a copper foil. Bonding is affected by a thin sheet of low‐density polyethylene, incorporating a crosslinking agent with a concentration gradient across the sheets thickness. In this single step process, the composite material is formed and bonded to the metal foil, achieving good adhesion without the use of extraneous glue. Copyright © 2002 John Wiley & Sons, Ltd.     

Phase diagrams of nonionic foam films: construction by means of disjoining pressure versus thickness curves

The thickness h of foam films can be measured as a function of the disjoining pressure Pi using a thin film pressure balance. Experimental Pi-h curves of foam films stabilized with nonionic surfactants measured at various concentrations resemble the p-V(m) isotherms of real gases measured at various temperatures (p is the pressure and V(m) is the molar volume of the gas). This observation led us to adopt the van der Waals approach for describing real gases to thin foam films, where the thickness h takes the role of V(m) and the disjoining pressure Pi replaces the ordinary pressure p. Our analysis results in a phase diagram for a thin foam film with spinodal, binodal as well as a critical point. The thicker common black film corresponds to the gas phase and the compact Newton black film for which the two surfaces are in direct contact corresponds to the dense liquid. We show that the tuning parameter for the phase behavior of the film is the surface charge density, which means that Pi-h curves should not be referred to as isotherms. In addition to the equilibrium properties the driving force for the phase transition from a common black film to a Newton black film or vice versa is calculated. We discuss how this transition can be controlled experimentally.     

A “self‐pinning” adhesive based on responsive surface wrinkles

Surface wrinkles are interesting since they form spontaneously into well‐defined patterns. The mechanism of formation is well‐studied and is associated with the development of a critical compressive stress that induces the elastic instability. In this work, we demonstrate surface wrinkles that dynamically change in response to a stimulus can improve interfacial adhesion with a hydrogel surface through the dynamic evolution of the wrinkle morphology. We observe that this control is related to the local pinning of the crack separation pathway facilitated by the surface wrinkles during debonding, which is dependent on the contact time with the hydrogel. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2010     

Status and perspectives in thin films and patterning of spin crossover compounds

Spin crossover compounds are a class of functional materials able to switch their spin state upon external stimuli. They were proposed as potential candidates for several technological applications that require highly controlled thin films and patterns. Here we present a critical overview of the most important approaches for thin film growth and patterning of spin-crossover compounds, giving special attention to Fe(ii) based molecules, which are the most studied materials. We present both conventional approaches to thin film growth (Langmuir-Blodgett, constructive chemical approach, spin coating, drop casting and vacuum sublimation) and patterning (combined top-down/bottom-up method, soft and unconventional lithography). We critically discuss the application of thin film growth and fabrication techniques highlighting the most critical aspects and the perspectives opened by the recent progress.     

Molecular dynamics simulation of thermomechanical properties of montmorillonite crystal. 1. Isolated clay nanoplate

The structure and mechanical properties of clay nanoparticles is a subject of growing interest because of their numerous applications in engineering. We present the results of molecular dynamics simulation for a single nanoplate of pyrophyllite - a 2:1 clay mineral consisting of two tetrahedral sheets of SiO4 and an intervening octahedral AlO6 sheet. Simulations were performed in the temperature interval from 5 to 750 K using the ionic-type potentials of Cygan et al. On this basis the temperature dependences of structural parameters, characterizing both tetrahedral and octahedral sheets as well as single lamella, have been studied. Two slightly different structures were observed in this wide temperature interval. The mechanical properties of the nanoplate were calculated from stress-strain diagrams, which have been obtained at relatively slow rates of deformation (for molecular simulations). Using different types of loading, we calculated the full elasticity tensor and estimated the influence of temperature on its components. We estimated also the bending and torsion stiffnesses of the nanoplate as specific characteristics of this type of particle. Because the nanoplate is atomically thin, a reasonable determination of the thickness is a nontrivial problem, both in the modeling of mechanical properties and in physical interpretation of the obtained data. We propose a procedure for its calculation.     

Large-area patterning of coinage-metal thin films using decal transfer lithography

We describe two new procedures that appear to hold significant promise as means for patterning thin-film microstructures of the coinage metals (Cu, Ag, Au). A feature central to both is the modification of their surfaces to promote the adhesive transfer of PDMS thin-film microstructures, a material suitable for use as resist layers in large-area patterning, using Decal Transfer Lithography (DTL). The present work provides a significant extension of the capabilities of DTL patterning, providing general protocols that can be used to transfer decal resists to essentially any substrate surface. The first method involves the functionalization of a surface, specifically those of gold and silver films with a thiol-terminated silane coupling agent, (mercaptopropyl)trimethoxysilane. This self-assembled monolayer, when hydrolyzed to its silanol form, provides a robust adhesion-promoting layer suitable for use in DTL patterning. The second method exploits the surface chemistry provided by the deposition of a nanoscale silicon dioxide thin-film capping layer using e-beam evaporation. This procedure provides an exceptional method for patterning large-area, thin-film microstructures of Cu-one compatible with micrometer-scale design rules-that are essentially defect free. Both surface modification strategies enable high-quality poly(dimethylsiloxane) decal transfers, and as the current work shows, these structures are suitable for large-area micrometer-sized patterning of gold, silver, and copper thin films via both wet-etching and lift-off procedures.     

Crystalline,Highly Oriented MOF Thin Film: the Fabrication and Application

The thin film of metal‐organic frameworks (MOFs) is a rapidly developing research area which has tremendous potential applications in many fields. One of the major challenges in this area is to fabricate MOF thin film with good crystallinity, high orientation and well‐controlled thickness. In order to address this challenge, different appealing approaches have been studied intensively. Among various oriented MOF films, many efforts have also been devoted to developing novel properties and broad applications, such as in gas separator, thermoelectric, storage medium and photovoltaics. As a result, there has been a large demand for fundamental studies that can provide guidance and experimental data for further applications. In this account, we intend to present an overview of current synthetic methods for fabricating oriented crystalline MOF thin film and bring some updated applications. We give our perspective on the background, preparation and applications that led to the developments in this area and discuss the opportunities and challenges of using crystalline, highly oriented MOF thin film.