Controlled formation of polyamine crystalline layers on glass surfaces and successive fabrication of hierarchically structured silica thin films

The formation of silica films on the glass plate whose surface was precoated by crystalline linear poly(ethylenimine) (LPEI) in advance was systematically investigated via controlling the surface-specific crystallization of the LPEI on the glass plate. Immersing glass substrates into a hot aqueous solution of LPEI containing additives such as transition metal ions and acidic compounds and retaining them on 30 °C for desired periods resulted in the formation of crystalline LPEI layers on the substrates. Subsequently dipping this LPEI-coated glass into silica source solutions afforded successfully hierarchically structured silica film which coated continuously the surface of the substrates. In this two-step process, we found that the formation of hierarchically structured silica films strongly depended on the LPEI layer formed from the LPEI aqueous solutions containing different additives. The LPEI layer formed by changing the kinds of additives and their concentrations provides the differently structured silica films composed of turbine-like structures flatly lying-on and/or vertically standing-on as well as ribbon network structures on the surface of the substrates. Moreover, we functionalized these silica films by the introduction of hydrophobic alkyl chains or emissive Eu(III) complexes and investigated their wettability and emission properties.     

Direct Polymerization of Polyacrylic Acid on Mica Substrates using ATRP – A Preliminary Study

Summary: Unprecedented direct polymerization of sodium acrylate (NaA) on mica and silica substrates was undertaken using standard ATRP polymerization conditions at room temperature. The resulting thickness of the poly(sodium acrylate) (PNaA) grafted layer was determined using ellipsometry and AFM.     

Stability of polypeptide multilayers as studied by in situ ellipsometry: effects of drying and post-buildup changes in temperature and pH

Polyelectrolyte multilayers (PEM) of poly(L-glutamic acid) (PGA) and poly(L-lysine) (PLL) with an initial layer of polyethyleneimine (PEI) were built on silica and titanium surfaces using the layer-by-layer (LbL) technique. The stability of the film during drying/rewetting, temperature cycles, and pH shifts was studied in situ by means of ellipsometry. The film thickness was found to decrease significantly (approximately 70%) upon drying, but the original film thickness was regained upon rewetting, and the buildup could be continued. The thickness in the dry state was found to be extremely sensitive to ambient humidity, needing several hours to equilibrate. Changes in temperature and pH were also found to influence the multilayer thickness, leading to swelling and deswelling of as much as 8% and 10-20% respectively. The film does not necessarily regain its original thickness as the pH is shifted back, but instead shows clear signs of hysteresis.     

Adsorption studies of polyethers Part II: adsorption onto hydrophilic surfaces

The adsorption of BAB-type triblock copolymers (B=poly(ethylene oxide); A=poly(propylene oxide)) from aqueous solution onto hydrophilic silica particles is described with particular reference to the role of the copolymer composition. The adsorbed amount and the layer thickness were determined by the standard depletion method and photon correlation spectroscopy, respectively. Snowtex-YL silica was used as the adsorbent. The results show an increase in the adsorbed amount with increasing molar masses of both PEO and PPO blocks. The adsorbed layer thickness is found to depend strongly on PEO block mass. Both these parameters (adsorbed amount and hydrodynamic layer thickness) show a maximum as a function of the mole fraction of the PPO block present in the copolymer. The conformation of the adsorbed layer is determined by the surface–copolymer interaction; principally by the interaction of the hydrophilic PEO block with the silica surface. A good qualitative agreement of the experimental results with theoretical predictions and self-consistent mean field calculations has been found.     

Hyperbranching polymerization of aziridine on silica solid substrates leading to a surface of highly dense reactive amine groups

Silica solid substrates such as fused silica, silicon wafers with a natural oxide layer, and glass were treated with aziridine to produce reactive primary amine groups on the top surface. We found that the hydroxyl group on the substrate was able to initiate the ring-opening polymerization of aziridine, resulting in highly branched poly(ethyleneimine) on the surface. In dichloromethane, the thickness of the organic film reached 25 A in 20 h and the absolute density of the primary amine group on the surface was 23 amines/nm(2). Atomic force microscopy shows an embossed morphology after the polymerization in dichloromethane, while use of toluene gives a rather smooth surface. The resulting organic layer shows high thermal and pH stability.     

Formation of Anatase Nanocrystals-Precipitated Silica Coatings on Plastic Substrates by the Sol-Gel Process with Hot Water Treatment

Anatase nanocrystals-precipitated silica coatings were formed on plastic substrates such as poly(ethylene terephtalate) (PET), acrylic resin (AC) and polycarbonate (PC) from silica-titania gel coatings with and without addition of poly(ethylene glycol) (PEG) by hot water treatment. The maximum thickness of the coatings which can be formed without cracking or peeling-off was 100 to 200 nm for PET and PC substrates, whereas it was less than 50 nm for AC substrates. After a hot water treatment at 90°C for 120 min, the size of the anatase nanocrystals increased to be 30 and 50 nm for the coatings obtained with and without PEG, respectively. Anatase nanocrystals were formed throughout the whole of the coatings obtained with PEG and were formed only on the surface of the coatings obtained without PEG. Both coatings obtained with and without PEG were highly transparent. The plastic substrates with coatings obtained without PEG showed good weathering resistance owing to the protective effects of the residual silica under-layer. The coatings obtained with PEG showed higher photocatalytic activities than those obtained without PEG due to smaller size and higher dispersion of anatase nanocrystals in the coatings.     

Synthesis of poly(ethylene glycol) (PEG)-grafted colloidal silica particles with improved stability in aqueous solvents

The known grafting procedures of colloidal silica particles with poly(ethylene glycol) (PEG) lead to grafting layers that detach from the silica surface and dissolve in water within a few days. We present a new grafting procedure of PEG onto silica with a significant improvement of the stability of the grafting layers in aqueous solvents. Moreover, the procedure avoids any dry states or other circumstances leading to strong aggregation of the particles. To achieve the improved water stability, St?ber silica particles are first pre-coated with a silane coupling agent (3-aminopropyl)triethoxysilane (APS) to incorporate active amine groups. The water solubility of the pre-coating layer was minimized using a combination of APS with bis-(trimethoxysilylpropyl)amine (BTMOSPA) or bis-(triethoxysilyl)ethane (BTEOSE). These pre-coated particles were then reacted with N-succinimidyl ester of mono-methoxy poly(ethylene glycol) carboxylic acid to form PEG-grafted silica particles. The particles form stable dispersions in aqueous solutions as well as several organic solvents.     

Ultrathin silica films immobilized on gold supports: fabrication, characterization, and modification

A novel method for covalent attachment of ultrathin silica films (thickness <10 nm) to gold substrates is reported. Silica layers were prepared using spin-coating of sol-gel precursor solutions onto gold substrates that were cleaned and oxidized using UV photo-oxidation in an ozone atmosphere. The gold oxide layer resulting from this process acts as a wetting control and adhesive agent for the ultrathin silica layer. Control of silica layer thickness between approximately 6 and 60 nm through modification of precursor solution composition or by repetitive deposition is demonstrated. Films were characterized using infrared spectroscopy, ellipsometry, atomic force microscopy, and cyclic voltammetry. For the standard deposition parameters developed here, films were determined to be 5.5 +/- 0.75 nm thick, and were stable in aqueous solutions ranging in pH from 2 to 10 for at least 30 min. Films contained nanoscopic defects with radii of 相似文献   

Direct generation of silica nanowire-based thin film on various substrates with tunable surface nanostructure and extreme repellency toward complex liquids

We report our new achievement on the direct generation of linear polyethylenimine@silica hybrid and silica thin films on various substrates, which is composed of 10 nm nanowire silica structure with tunable micro/nano hierarchical surface morphology. We found that a process for the rapid and controlled self-assembly of crystalline template layer of linear polyethylenimine on substrate surface is critical for the formation of ultrathin silica nanowire structure and micro/nano hierarchical morphology, since the template linear polyethylenimine layer directly promotes the hydrolytic condensation of alkoxysilanes. Templated silica mineralization on the self-assembled linear polyethylenimine layer was confirmed by the studies of X-ray photoelectron spectroscopy (XPS) and thin film X-ray diffraction (XRD). The surface of silica nanostructure and hierarchy could be well controlled by simply adjusting the conditions for LPEI assembly, such as the polymer concentrations and substrate surface property. After a simple fluorocarbon modification, the hierarchical silica nanowire thin film demonstrated robust and reliable super-repelling property toward a series of aqueous liquids (such as commercial inkjet (IJ) ink, soy source, milk). Comparative studies clearly confirmed the critical importance of surface hierarchy for enhancing super-repelling property. Moreover, we found that the forcibly formed dirty sports (both wet and dry) from the complexly composed liquids on the super-antiwetting surface could be easily and completely cleaned by simple water drop flow. We expect these tailored nanosurfaces would have the potentials for practical technological applications, such as liquid transferring, self-cleaning, microfluid, and biomedical-related devices.     

Preparation and properties of biocompatible polymer-grafted silica nanoparticle

Grafting of biocompatible polymer onto the surface of silica nanoparticles was achieved by radical graft polymerization of 2-methacryloyloxyethyl phosphorylcholine (MPC), initiated by azo groups previously introduced onto the surface or by a system consisting of Mo(CO)₆ and trichloroacetyl groups on the silica surface. Both of these systems have the ability to initiate graft polymerization of MPC, resulting in the formation of poly(MPC)-grafted silica, but the percentage of poly(MPC) grafting for the latter initiating system was much higher than that of the former. The amount of moisture that could be adsorbed onto the silica surface was found to increase with increasing poly(MPC) grafting. This indicates that grafting of poly(MPC) onto the silica surface markedly increases the hydrophilic nature of the surface. The contact angle of water in composites prepared from poly(vinyl alcohol) and poly(MPC)-grafted silica was found to decrease with increasing poly(MPC)-grafted silica content. When poly(MPC)-grafted silica was added to water containing a small amount of chloroform, it was found to act as stabilizer for droplets of chloroform. In addition, according to tests by the Lee-White method, poly(MPC)-grafted silica shows non-thrombogenic characteristics.     

Highly permeable mesoporous silica membranes synthesized by vapor infiltration of tetraethoxysilane into non-ionic alkyl poly(oxyethylene) surfactant films

Mesoporous silica membranes were prepared on porous alumina substrates by a vapor infiltration of tetraethoxysilane (TEOS) into a non-ionic poly(oxyethylene) (Brij56) surfactant film. Periodic mesostructured silica membranes were formed on both α- and γ-alumina substrates pre-treated with polystyrene. The polystyrene polymer plugged the pores of the alumina substrates and inhibited the deposition of silica in the alumina pores, resulting in the formation of a very thin silica membrane without a silica/alumina composite layer at the interface between mesoporous silica and the alumina substrates. The calcined mesoporous silica membrane showed very high nitrogen permeance (>10⁻⁶ mol m⁻² s⁻¹ Pa⁻¹). The single gas permeation was governed by the Knudsen diffusion mechanism. The durability of the mesoporous silica membrane against moisture in air was improved by a silylation with trimethylethoxysiliane.     

A surface-reactive rod-coil diblock copolymer: nano- and micropatterned polymer brushes.

A diblock copolymer consisting of poly(3-(triethoxysilyl)propylisocyanate) (PIC) and polystyrene(PS) was synthesized by anionic polymerization. A polymeric monolayer of the block copolymer was formed on silica substrates by various grafting techniques such as immersion, casting, or contact-printing. The PIC block adheres covalently to Si substrates in an in-plane fashion due to its extended rodlike conformation and reactivity to the silica. The polystyrene blocks aggregate to form mounds on the surface resulting in a new type of nanopatterned polymer brush. The self-limiting adsorption of the rod coils results in a thickness of about 5 nm regardless of the solution concentration and coating method. This particular property allowed microcontact printing directly onto silicon or glass substrates. The resulting surface morphology consisted of nanoscale domains given by the block copolymer and uniform thickness micropatterns transferred from the stamp within the printed area. This study offers a simple new method to prepare a covalent polymeric monolayer with nano- and micropatterns, which can be performed directly onto various silicon-based substrates.     

The Hofmeister anion effect and the growth of polyelectrolyte multilayers

The influence of a variety of counteranions on the properties of polyelectrolyte multilayers deposited by layer-by-layer technique is studied by using ellipsometry and AFM. We found out that in thin dry multilayers (20-90 nm) ofpoly(4-styrenesulfonate) (PSS) and poly(diallyldimethylammonium) (PDADMA), the thickness follows reasonably well the position of the counteranion in the Hofmeister series. The polyelectrolyte-counteranion interaction is studied by means of viscosity measurements of semidilute solutions of PDADMA in the presence of different anions. The dynamic viscosities follow the Hofmeister series of anions and correlate with the thickness of multilayers. Two parameters describing the interaction of ions with water, the Jones-Dole viscosity B coefficient and the hydration entropy, are used to explain the anion effect on the developing multilayer thickness. Reasonably smooth and monotonic functional dependence is observed between the layer thickness and these two parameters.     

Multilayers of charged polypeptides as studied by in situ ellipsometry and quartz crystal microbalance with dissipation

The buildup of poly(L-glutamic acid) (PGA) and poly(L-lysine) (PLL) multilayers on silica and titanium surfaces, with and without an initial layer of polyethyleneimine (PEI), was investigated and characterized by means of in situ ellipsometry and quartz crystal microbalance with dissipation. A two-regime buildup was found in all systems, where the length of the first slow-growing regime is dependent on the structure of the initial layers. In the second fast-growing regime, the film thickness grows linearly while the mass increases more than linearly (close to exponentially) with the number of deposited layers. The film refractive indices as well as the water contents indicate that the film density changes as the multilayer film builds up. The change in film density was proposed to be due to polypeptides diffusing into the multilayer film as they attach. Furthermore, the use of PEI as the initial layer was found to induce a difference in the thickness increments for PGA and PLL.     

Desorption of bottle-brush polyelectrolytes from silica by addition of linear polyelectrolytes studied by QCM-D and reflectometry

The possibility of exchanging adsorbed layers of PEO(45)MEMA:METAC-X brush polyelectrolytes (with two different charge densities, 10 and 75 mol%, denoted by X), with poly(MAPTAC), a highly charged linear polyelectrolyte, was investigated by quartz crystal microbalance with dissipation and reflectometry. The studies were conducted on a silica substrate at pH 10, conditions under which only electrostatic interactions are effective in the adsorption process. Based on the results, it was concluded that PEO(45)MEMA:METAC-10 forms an inhomogeneous layer at the interface through which poly(MAPTAC) chains can easily diffuse to reach the surface. On the other hand, the PEO(45)MEMA:METAC-75 layer was not affected when exposed to a poly(MAPTAC) solution. We argue that the observed effect for PEO(45)MEMA:METAC-75 is due to the formation of a homogeneous protective brush layer, in combination with the small difference in surface affinity between the bottle-brush polyelectrolyte and poly(MAPTAC), together with the difficulty of displacing highly charged polyelectrolyte chains once they are adsorbed on the oppositely charged surface. We also use the combination of QCM-D and reflectometry data to calculate the water content and layer thickness of the adsorbed layers.     

Swelling behavior of self-assembled monolayers of alkanethiol-terminated poly(ethylene glycol): a neutron reflectometry study

The swelling behavior of alkanethiol-terminated poly(ethylene glycol) with an average molecular weight of 2180 Da (i.e., approximately 45 ethylene glycol, EG, units) in contact with water was investigated by neutron reflectometry as a function of the morphology of the PEG-SH layer. Amorphous films at a low grafting density show significant swelling with an increase of the film thickness from approximately 25 A in the dry state to approximately 70 A in contact with D2O, which corresponds to a total water uptake of approximately 38 mass %. In contrast, quasi-crystalline monolayers exhibit only a small amount of water penetrating into the film (approximately 8 mass %) with a corresponding change of the layer thickness from approximately 110 to approximately 125 A. The water uptake per EG unit corresponds to the literature value of 1.5 for the amorphous layer and to only 0.25 in the case of the quasi-crystalline film.     

Study of film structure and adsorption kinetics of polyelectrolyte multilayer films: effect of pH and polymer concentration

The alternate adsorption of polycation poly(allylamine hydrochloride)(PAH) and the sodium salt of the polymeric dye poly(1-[ p-(3'-carboxy-4'-hydroxyphenylazo)benzenesulfonamido]-1,2-ethandiyl)(PCBS) on quartz crystals coated with silica was studied to understand the structural properties and adsorption kinetics of these films using a combination of quartz crystal microbalance with dissipation monitoring (QCM-D), absorbance, and ellipsometry measurements. In-situ deposition of the polycation PAH on QCM crystals was monitored, followed by rinsing with water and then deposition of the polyanion PCBS. The effects of polymer concentration and pH on film structure, composition and adsorption kinetics were probed. The polymers were adsorbed at neutral pH conditions and at elevated pH conditions where PAH was essentially uncharged to obtain much thicker films. The change in the resonant frequency, Deltaf, of the QCM-D showed a linear decrease with the number of bilayers, a finding consistent with absorbance and ellipsometric thickness measurements which showed linear growth of film thickness. By using the Delta f ratios of PCBS to PAH, the molar ratios of repeat units of PCBS to PAH in the bilayer films as determined by QCM-D were approximately 1:1 at polyelectrolyte concentrations 5-10 mM repeat unit, indicating complete dissociation of the ionic groups. The frequency and dissipation data from the QCM-D experiments were analyzed with the Voigt model to estimate the thickness of the hydrated films which were then compared with thicknesses of dry films measured by ellipsometry. This led to estimates of the water content of the films to be approximately 45 wt %. In addition to the QCM-D, some films were also characterized by a QCM which measures only the first harmonic without dissipation monitoring. For the deposition conditions studied, the deposited mass values measured by the QCM's first harmonic were similar to the results obtained using higher harmonics from QCM-D, indicating that the self-assembled polyelectrolyte films were rigid.     

Temperature sensitivity of capillary-driven flow: application to age monitoring devices

Pervaporation membranes were produced comprising a 4:1 sodium-alginate:poly(vinyl-alcohol) polymer blend selective layer with a plasticizing agent (glycerol). Membranes were supported on a poly(acrylonitrile) mesoporous support layer and non-woven fabric base. Pervaporation separation of ethanol/water mixtures was carefully followed as a function of film thickness and time. It was found, contrary to what might be expected from literature, that these films showed increased selectivity and decreased flux as film thickness was reduced. It is argued that the morphology and structure of the polymer blend changes with thickness and that these structural changes define the efficiency of the separation in these conditions.     

A comparative study of surfactant adsorption on model surfaces using the quartz crystal microbalance and the ellipsometer

The nature of hexaethylene glycol mono-n-tetradecyl ether (C(14)EO(6)) layers adsorbed onto different model surfaces was systematically investigated by means of QCM-D (quartz crystal microbalance-dissipation) and ellipsometry. The amount of non-ionic surfactant adsorbed is determined both at hydrophilic and hydrophobic surfaces. In particular, the substrates employed were hydrophilic silica, hydrophobized silica (using dimethyldichlorosilane), and hydrophobized gold surfaces (using 10-thiodecane and 16-thiohexadecane). It was shown that the frequency shift obtained from the QCM-D experiments results in an overestimation of the adsorbed mass. This is attributed to two different effects, viz. water that is coupled to the adsorbed layer due to hydration of the polar region of the surfactant and second water that for other reasons is trapped within the adsorbed layer. Furthermore, from the ellipsometry data the adsorbed layer thickness is determined. By combining the thickness information and the dissipation parameter (obtained from the QCM-D experiments), we note that the dissipation parameter is insufficient in describing the viscoelastic character of thin surfactant films.     

Assembly of poly(N-isopropylacrylamide)-co-acrylic acid microgel thin films on polyelectrolyte multilayers: Effects of polyelectrolyte layer thickness, surface charge, and microgel solution pH

Temperature- and pH-sensitive poly(N-isopropylacrylamide)?Cco-acrylic acid (pNIPAm-co-AAc) microgels were deposited on glass substrates coated with polyelectrolyte multilayers composed of the polycation poly(allylamine hydrochloride) (PAH) and the polyanion poly(sodium 4-styrenesulfonate) (PSS). The microgel density and structure of the resultant films were investigated as a function of: (1) the number of PAH/PSS layers (layer thickness); (2) the charge on the outer layer of the polyelectrolyte multilayer film; and (3) the pH of microgel deposition solution. The resultant films were studied by differential interference contrast optical microscopy, atomic force microscopy, and scanning electron microscopy. It was found that the coverage of the microgels on the surface was a complex function of the pH of the deposition solution, the charge on the outer layer of the polyelectrolyte thin film and the PAH/PSS layer thickness; although it appears that microgel charge plays the biggest role in determining the resultant surface coverage.