Interaction of water with self-assembled monolayers of alkylsilanes on mica

The interaction of water with self-assembled alkylsilane monolayers on mica substrates has been studied using an atomic force microscope operated in contact, noncontact, and electrical polarization modes. Complete monolayer films were found to be effective in blocking water adsorption. On partially covered surfaces water was found to produce large changes in the conductivity and surface potential of the exposed mica regions. It was also found that water could penetrate films near defects and at island edges.     

Atomic force microscopy study of beta-substituted-T7 oligothiophene films on mica: mechanical properties and humidity-dependent phases

The structural and mechanical properties of Langmuir-Blodgett monolayer and multilayer films of 3",4"-didecyl-5,2'; 5',2"; 5",2'; 5',2"; 5",2''; 5'',2"-heptathiophene-4'-acetic acid on mica have been studied by atomic force microscopy (AFM) as a function of humidity, temperature, and applied force. The molecules orient with the carboxylic acid group pointing toward the mica surface and expose the alkyl side chains to the air interface. As the load applied by the AFM tip increases, the film is compressed easily from an initial height of 2 to 1.2 nm. After compression the films can support much higher loads without loss of height. The state of aggregation of the molecules was found to be sensitive to the environmental humidity, which induced reversible changes. Annealing the samples with monolayer or multilayer films resulted in irreversible changes when the temperature exceeded approximately 100 degrees C.     

Preparation and nanoscale mechanical properties of self-assembled carboxylic acid functionalized pentathiophene on mica

The oligothiophene derivative 4-(5' " '-decyl-[2,2';5',2' ';5' ',2' ";5' ",2' " '] pentathiophen-5-yl)-butyric acid (D5TBA) was synthesized by Stille cross-coupling methods using functionalized thiophene monomers. The structural and mechanical properties of D5TBA self-assembled monolayers on mica have been studied by atomic force microscopy (AFM). The self-assembled films were prepared by immersing the mica in dilute chloroform or tetrahydrofuran (THF) solutions. The films were predominantly of monolayer thickness with molecules packed in nearly upright orientations. In regions covered with multilayers, the molecules in each monolayer were oriented opposite to those in the neighboring ones, that is, with COOH-COOH and CH3-CH3 contact. The nature of the end group in contact with the substrate depended on the solvent used and the degree of hydration of the substrate, with hydrophobic chloroform solvent favoring the methyl end down and hydrophilic THF favoring the acid group end down. The orientation could also be controlled by dipping using the Langmuir-Blodgett technique.     

Reversible collapse of brushlike macromolecules in ethanol and water vapours as revealed by real-time scanning force microscopy

Environment-controlled scanning force microscopy allowed us to study adsorption and desorption of single poly(methacrylate)-graft-poly(n-butyl acrylate) brush molecules on mica in real time. The molecules transform reversibly from a two-dimensional, extended wormlike state to a compact globular state. The dynamics of the conformational transition was sufficiently slow in order to allow its observation by scanning force microscope in real time. The reversible transformation is effected by coadsorption of water or ethanol, the latter introduces the collapse. Adsorbing ethanol and water from the vapour atmosphere results in a change of the surface properties of mica, either favouring adsorption or desorption of the graft polymer. When the extended, tightly adsorbed poly(n-butyl acrylate) brush molecules are exposed to ethanol vapour, the macromolecules swell and contract to form compact globules. Exchanging the ethanol vapour to a humid atmosphere caused the molecules to extend again to a wormlike two-dimensional conformation. Coexistence of collapsed and extended strands within the same molecule indicates a single-molecule first-order transition in agreement with observations on Langmuir films previously reported.     

Multilayer Film Fabrication and Photoelectric Conversion Property of Two Pyrrolidinofullerene Carboxylic Acid Derivatives

Fullerene has many special properties', and our group had successfully introducedfullerene into the photoelectric conversion field by Langmuir-Blodgett technology'. Theonly work of fullerene multilayer films that we have seen was done by J. S. Bae'. In thispaper we tried to introduce fullerene carboxylic acid derivatives into multilayer withoutorganosilicon derivatives and st-IJdied their photoelectric conversion properties. A newway of fabricating fullerene multilayer film was reported her…     

Surface interactions during polyelectrolyte multilayer build-up. 2. The effect of ionic strength on the structure of preformed multilayers

Interactions between surfaces bearing multilayer films of poly(allylamine hydrochloride) (PAH) and poly(styrenesulfonate sodium salt) (PSS) were investigated across a range of aqueous KBr solutions. Three layer films (PAH/PSS/PAH) were preassembled on mica surfaces, and the resulting interactions were measured with the interferometric surface force apparatus (SFA). Increasing the ionic strength of the medium resulted in a progressive swelling of the multilayer films. Interactions in solutions containing more than 10(-3) M KBr were dominated by a long-ranged steric repulsion originating from compression of polyelectrolyte segments extending into solution. In 10(-1) M KBr, repeated measurements at the same contact position showed a considerable reduction of the range and the strength of the steric force, indicating a flattening of the film during initial approach. Furthermore, this flattening was irreversible on the time scale of the experiments, and measurements performed up to 72 h after the initial compression showed no signs of relaxation. These studies aid in understanding the dominant interactions between polyelectrolyte multilayers, including polyelectrolyte films deposited on colloidal particles, which is important for the preparation of colloidally stable nanoengineered particles.     

由聚电解质自组装多层膜制备微孔薄膜

带有相反电荷的聚电解质通过静电作用交替沉积可以得到自组装多层膜,由于这种技术可操作性强,用途广泛,近十几年来已有了大量的研究．聚电解质多层膜在一定条件下可以形成纳米孔和微米孔．Fu等研究了聚丙烯酸和聚乙烯基吡啶组成的氢键自组装多层膜在碱溶液中溶去其中的聚丙烯酸后,剩下的聚乙烯基吡啶重构形成微孔薄膜．Mendelsohn等发现将聚丙烯酸和聚烯丙基胺自组装而成的多层膜浸入pH=2．4左右的溶液中可制备微孔薄膜．但这些方法并不能使强聚电解质多层膜形成多孔结构。     

Novel colorimetric sensor for mercury (Ⅱ) based on layer-by-layer assembly of unmodified silver triangular nanoplates

A simple layer-by-layer deposition technique was used to fabricate the multilayer thin films of unmodified silver triangular nanoplates(AgTNPs).The multilayer of AgTNPs thin films were fabricated by alternate deposition of each anionic sodium citrate stabilized AgTNPs and cationic poly(diallyldimethylammonium chloride).All prepared AgTNPs multilayer thin films were exhibited a strong plasmon band at the wavelength of 667 nm,which confirmed the formation of AgTNPs onto the substrate.The characteristics of the multilayer thin films were investigated using contact angle measurement,UV-visible spectroscopy,X-ray diffraction analysis(XRD),atomic force microscope(AFM)and field emission scanning electron microscope(FESEM).As these films are to be used as a mercury(II)colorimetric sensor,the changes in optical properties of the films were evaluated for various mercury(Ⅱ)concentrations.AgTNPs assembled into thin films showed a strong color shift from blue to mauve and colorless when exposed to mercury(Ⅱ).The constructed multilayer thin films exhibited excellent color changes of mercury(II) with a linear range between 0.5 and 20 ppm.The limit of detection(LOD) and limit of quantitation(LOQ) were 0.45 ± 0.002 and 1.52 ± 0.002 ppm,respectively.The recovery values of AgTNPs multilayer thin films are satisfactory in the range of 100.1%-106.4%when applied to determining mercury(Ⅱ) in water samples.     

Bolaform supramolecular amphiphiles as a novel concept for the buildup of surface-imprinted films

Stable multilayer films were fabricated on the basis of the alternating layer-by-layer assembly of a two-component bolaform supramolecular amphiphile and diazoresins, followed by photochemical cross-linking of the structure. UV-visible spectroscopy and atomic force microscopy revealed a uniform deposition process. Moreover, one component of the supramolecular amphiphile can be removed from the multilayer films after cross-linking between the second component and the diazoresin. The release and uptake of the imprinted supramolecular amphiphile component are shown to be reversible. Furthermore, uptake experiments of different molecules show the selectivity of the imprinted sites for the template molecule. Thus, surface-imprinted films can be formed by employing dissociable two-component supramolecular amphiphiles. This research reveals that supramolecular amphiphiles can be used as a novel concept for the construction of multilayer films, and it also provides a new method of generating surface-imprinted multilayers.     

Large area, molecularly smooth (0.2 nm rms) gold films for surface forces and other studies

Using large-area (cm2) single-crystal mica sheets as the templating substrate, we have created correspondingly large template-stripped (TS) gold films (thickness 82 +/- 2 nm) that appear smooth to within 0.2 nm rms roughness over their entire area. These gold films, created without the use of any releasing solvent, are characterized using AFM, X-ray diffraction, multiple beam interferometric fringes of equal chromatic order (FECO), and contact angle measurements. Being molecularly smooth over large areas and (adjustably) semitransparent, these films are especially suitable for use in the surface force balance (SFB), as shown by measurements of the normal force (F) versus distance (D) profiles between such a flat gold surface and a bare mica surface in water. The F(D) profiles are in good agreement with DLVO theory down to molecular contact and indicate that the gold surface is negatively charged under water.     

Synthesis of novel hybrid films of a layered silicate and alkylammonium cations on rough polymeric surfaces by Langmuir–Blodgett method

Hybrid films of a layered silicate and an amphiphilic alkylammonium (hexadecyltrimethylammonium) cation have been prepared by Langmuir–Blodgett (LB) method and transferred onto a polyamide surface by dip coating. This is the first time that stable LB hybrid monolayer and multilayer films have been formed on rough polymeric surfaces. The films were characterized by X-ray diffraction (XRD), fourier transform infrared spectroscopy (FTIR), atomic force microscopy (AFM) and water contact angle measurements. XRD and FTIR showed that the hybrid multilayer was well-organized and the thickness of one layer was calculated to be 1.6 nm. Furthermore, the layered silicate was determined to be on the substrate side and the amphiphilic molecule layer was exposed to the air side. This provides a novel methodology for the surface modification of polymers.     

Spin Self‐Assembled Clay Nanocomposite Passivation Layers Made from a Photocrosslinkable Poly(vinyl alcohol) and Na+‐Montmorillonite Enhance the Environmental Stability of Organic Thin‐Film Transistors

We investigated the effects of the multilayer polymer‐clay nanohybrid passivation films on the stability of pentacene organic thin‐film transistors (OTFTs) exposed to air and UV irradiation. Well‐ordered multilayer films were deposited by the spin‐assisted layer‐by‐layer assembly method using photocrosslinkable poly(vinyl alcohol) with the N‐methyl‐4(4′‐formylstyryl)pyridinium methosulfate acetal group (SbQ‐PVA) and Na⁺‐montmorillonite in a water‐based solution process. When photocrosslinked, these SbQ‐PVA/clay multilayers were found to serve as excellent barriers to O₂ and UV‐light. Moreover, when used as passivation layers, they enhanced the stability of pentacene OTFT devices exposed to air and UV radiation.     

Imaging structured water and bound polysaccharide on mica surface at ambient temperature

The presence of a water layer on the surface of muscovite mica under ambient conditions is well established. The water molecules are well ordered and seem to be oriented, leading to an icelike monolayer (probably ferroelectric) in epitaxial relation with the mica surface. We have imaged and characterized the height and contact angle of ordered water layer(s) formed by wetting and de-wetting processes on mica surfaces at different states of hydration by tapping mode atomic force microscopy. Implications that the presence of such an ordered water layer may have for imaging of biological samples are also discussed, with consideration of data for the polysaccharide hyaluronan.     

Trapping, pattern formation, and ordering of polyelectrolyte/single-wall carbon nanotube complexes at the air/water and air/solid interfaces

The Langmuir and Langmuir-Blodgett (LB) techniques have been applied in a novel approach to build structurally well-ordered, oriented, and organized assemblies of water-soluble single-wall carbon nanotubes (ws-SWCNTs) at the air/water and air/solid interfaces. The SWCNTs were rendered hydrophilic by complexing them with a quenched polyelectrolyte. We observed that the ws-SWCNT concentration at the air/water interface increases with time condensing into different patterns, among which are isolated soap-froths, rings, and the aggregation of cumuli-like 2D-structures. These patterns were recorded at different compression-expansion stages by Brewster angle microscopy (BAM). From the isotherm measurements, we are able to determine the diffusion process by which ws-SWCNT concentration builds up at the water surface. The corresponding LB films were very stable and could be transferred onto mica substrates easily. Atomic force microscopy (AFM) images revealed that the morphology of these films is surface-pressure dependent, and aligned structures with a nematic-like order formed closely packed mono- or multilayer films. The assembly of 2D-nanostructures by means of this approach offers a great potential for emergent technological applications using modified water-soluble SWCNTs.     

Generation of nanostructures of mica supported lysozyme molecules in aqueous solution by atomic force microscopy

Nanostructures of lysozyme molecules adsorbed to mica were generated by the tip of an atomic force microscope in contact, tapping, and force-distance mode in aqueous solution. In contact mode at high ionic strength and adjusted lysozyme concentration a monolayer of defined pattern and orientation could be formed by the scan process of the tip. A lysozyme monolayer with minimal pattern size of about 60 nm was achieved by line scan. At larger loading forces besides a monolayer also 3D-aggregates of lysozyme molecules could be generated. In force-distance mode the volume of 3D-aggregates grows with increasing generation time, lysozyme concentration in the bulk phase, loading force, and frequency of up- and down-movement of the substrate toward the fixed cantilever. In tapping mode 3D-aggregates could be generated as well. It is postulated that reduction of electrostatic interaction between the oppositely charged lysozyme molecules and mica surface by sufficient high ionic strength is essential for monolayer formation. It is discussed that for the underlying mechanism of monolayer generation in contact mode lysozyme molecules of the bulk phase adsorb to the tip, become pulled off and attach to the mica surface by the scan process of the tip.     

Multilayer Films with Nanocontainers: Redox‐Controlled Reversible Encapsulation of Guest Molecules

Stable multilayer films with cucurbit[8]uril have been fabricated on the basis of the alternating layer‐by‐layer assembly of a novel side‐chain pseudopolyrotaxane and a photoreactive polyanion. The as‐prepared multilayer films exhibit good properties as surface‐imprinted multilayers, because cucurbit[8]uril molecules that are locked inside the multilayers can act as nanocontainers with specific binding to certain guest molecules, and the loading and release of the guest is redox‐controllable and reversible.     

有机HTDIOO分子LB膜结构的AFM研究

利用原子力显微镜（AFM）对有机分子HTDIOO单层和多层LB膜结构进行了观察·实验结果表明，针尖与LB膜表面分子间的相互作用力会对成像的膜结构有影响．当悬臂针尖与LB膜表面分子的相互作用力较大时，针尖会扰动HTDIOO分子在单层LB膜中的有序排列．HTDIOO单层LB膜具有有序结构；而在多层LB膜中，HTDIOO分子则聚集在一起形成了一定的畴结构．     

Real-Time Imaging of the Coil-Globule Transition of Single Adsorbed Poly(2-vinylpyridine) Molecules

Summary: We applied scanning force microscopy to study, in real time, the mobility and reorganisation of single poly(2-vinylpyridine) molecules that were adsorbed on mica and exposed to vapours of ethanol or water. The macromolecules adopted a compact globular conformation in ethanol-saturated vapour and extended to a surface-bound two-dimensional coil in water-saturated vapour. Hence, reversible coil-to-globule conformational transitions of flexible polymer chains were directly visualized with unique molecular resolution.

Left: individual P2VP molecules on mica compacted by exposure to ethanol vapour, right: the same macromolecules extended in water vapour.     

有机HTDIOO分子LB膜结构的AFM研究

利用原子力显微镜（ＡＦＭ）对有机分子ＨＴＤＩＯＯ单层和多层ＬＢ膜结构进行了观察。实验结果表明，针尖与ＬＢ膜表面分子间的相互作用力会对成像的膜结构有影响。当悬臂针尖与ＬＢ膜表面分子的相互作用力较大时，针尖会扰动ＨＴＤＩＯＯ分子在单层ＬＢ膜中的有序排列。ＨＴＤＩＯＯ单层ＬＢ膜具有有序结构；而在多层ＬＢ膜中，ＨＴＤＩＯＯ分子则聚集在一起形成了一定的畴结构。     

In-situ investigations on the SILAR-growth of ZnS films as studied by tapping mode atomic force microscopy

Tapping mode atomic force microscopy (TM-AFM) has been successfully used for in-situ imaging of the deposition of ZnS films with the successive ionic layer adsorption and reaction (SILAR) method. The films were deposited in-situ using the commercial TM-AFM liquid cell as a flow-through reactor. The potential of TM-AFM has been used to study the growth of ZnS on different substrates up to 50 SILAR cycles. Reactants and rinsing water were alternately exchanged in the cell by a computer controlled valve system. In comparison to earlier work performed with the conventional AFM operated in contact mode, imaging artefacts introduced by lateral shear forces can be largely eliminated with TM-AFM. On glass the roughness is observed to decrease initially until typical island formation takes place at a larger number of deposition cycles. On mica island formation can be observed right from the beginning of the process and the roughness increases with increasing number of deposition cycles.