Fabrication of polyelectrolyte multilayer films comprising nanoblended layers

Polyelectrolyte multilayer thin films were prepared via the alternate deposition of poly(allylamine hydrochloride) (PAH) and a blend of poly(acrylic acid) (PAA) and poly(styrenesulfonate) (PSS). When the pH of the blend solution was 3.5, the presence of PAA in this solution significantly increased the total film thickness. With only 10 wt % PAA in the blend adsorption solution, a large increase in film thickness was observed (92 nm cf. 18 nm). It was also demonstrated that the total amount of PSS adsorbed was enhanced by the presence of PAA in the blend solution, showing that the blend solution composition influenced that of the multilayer films. Thin films prepared with nanoblended layers also showed improved pH stability, because they exhibited reduced film rearrangement upon exposure to acidic conditions (pH = 2.5).     

Protecting peroxidase activity of multilayer enzyme-polyion films using outer catalase layers

Films constructed layer-by-layer on electrodes with architecture {protein/hyaluronic acid (HA)}n containing myoglobin (Mb) or horseradish peroxidase (HRP) were protected against protein damage by H2O2 by using outer catalase layers. Peroxidase activity for substrate oxidation requires activation by H2O2, but {protein/HA}n films without outer catalase layers are damaged slowly and irreversibly by H2O2. The rate and extent of damage were decreased dramatically by adding outer catalase layers to decompose H2O2. Comparative studies suggest that protection results from catalase decomposing a fraction of the H2O2 as it enters the film, rather than by an in-film diffusion barrier. The outer catalase layers controlled the rate of H2O2 entry into inner regions of the film, and they biased the system to favor electrocatalytic peroxide reduction over enzyme damage. Catalase-protected {protein/HA}n films had an increased linear concentration range for H2O2 detection. This approach offers an effective way to protect biosensors from damage by H2O2.     

Fabrication of microfluidic hydrogels using molded gelatin as a sacrificial element

This paper describes a general procedure for the formation of hydrogels that contain microfluidic networks. In this procedure, micromolded meshes of gelatin served as sacrificial materials. Encapsulation of gelatin meshes in a hydrogel and subsequent melting and flushing of the gelatin left behind interconnected channels in the hydrogel. The channels were as narrow as approximately 6 microm, and faithfully replicated the features in the original gelatin mesh. Fifty micrometre wide microfluidic networks in collagen and fibrin readily enabled delivery of macromolecules and particles into the channels and transport of macromolecules from channels into the bulk of the gels. Microfluidic gels were also suitable as scaffolds for cell culture, and could be seeded by human microvascular endothelial cells to form rudimentary endothelial networks for potential use in tissue engineering.     

Structure of ultrathin polyethylene layers in multilayer films

The crystalline structures of “microlayer” and “nanolayer” polyethylene have been examined in coextruded films comprised of alternating layers of high-density polyethylene and polystyrene. Transmission electron microscopy (TEM), small-angle x-ray scattering (SAXS), and wide-angle x-ray scattering (WAXS) reveal that microlayer polyethylene, where the layer thickness is on the order of several microns, crystallizes with the normal unoriented lamellar morphology. In nanolayer films, where the film thickness of tens of nanometers is on the size scale of molecular dimensions, lamellae are oriented with the long axes perpendicular to the extrusion direction in a row-nucleated morphology similar to structures described in the literature. The lamellae are partially twisted about the long axes. The preferred twist angles of ±40° orient the lamellar surfaces normal to the layer surface. The row-nucleated morphology imparts highly anisotropic mechanical properties to the nanolayer polyethylene.     

Facile synthesis of thermo- and pH-responsive biodegradable microgels

A novel and facile strategy has been designed to prepare biodegradable microgels with thermo- and pH-responsive property. The microgels were synthesized by the crosslinking of N-isopropylacrylamide with vinyl groups functionalized poly(L-glutamic acid) (PGA). The resultant microgels exhibited pH-dependent phase transition behaviors in aqueous solutions and underwent abrupt lower critical solution temperature decrease when the pH was reduced below the pK _a of PGA. Dynamic light scattering measurement revealed that the microgels exhibited shrinkage as the temperature increased or the pH decreased.     

Fabrication of hollow spheres of metal oxide using fructose-derived carbonaceous spheres as sacrificial templates

In this report, fructose-derived carbonaceous spheres were utilized as sacrificial templates for the fabrication of metal oxide hollow spheres (MOHSs) by a facile hydrothermal approach. Hollow spheres of a series of crystalline metal oxides (α-Fe₂O₃, Cr₂O₃, Co₃O₄, NiO, and ZnO) have been fabricated, utilizing the metal chloride as the oxide precursors. Heating of an aqueous solution of the metal chloride and fructose to moderate temperature in an autoclave affords a spherical composite consisting of a metal precursor shell sheathing a carbonaceous core. Subsequent removal of the interior carbonaceous cores by thermal treatment through oxidation in air produces free-standing crystalline oxides hollow spheres. The MOHSs were characterized by means of SEM, TEM, XRD, IR spectroscopy, energy dispersive X-ray (EDX) and sorption measurements. The results show convincingly that using fructose as a sacrificial template after application of a hydrothermal synthesis route could be a favourable sacrificial template for the fabrication of various MOHSs.     

pH-responsive copolymer films by surface-catalyzed growth

We have engineered a new class of pH-responsive polymer films on gold surfaces by first developing a controlled, surface-catalyzed polymerization to prepare a copolymer film consistent with poly(methylene-co-ethyl acetate) and subsequently hydrolyzing the ester side chains to varying extents to yield carboxylic acids (denoted as PM-CO2H). When pH is increased, the acid groups become deprotonated or charged, dramatically increasing their water solubility and greatly altering the film properties. The carboxylic acid content within the copolymer film can be adjusted by changing the monomer concentration ratio used in the polymerization process or the length of time for the hydrolysis. We have designed PM-CO2H films to consist predominately (>95%) of polymethylene (PM) so that the film is hydrophobic in the uncharged state and, thereby, exhibits an extremely large pH-induced response in barrier properties once ionized. The effect of polymer composition on pH response was investigated by electrochemical impedance spectroscopy (EIS), reflectance-absorption infrared spectroscopy (RAIRS), and contact angle measurements. At a 1%-4% molar acid content, the copolymer film exhibits a 5 orders of magnitude change in its resistance to ion transport over 2-3 pH units. The pH at which this response begins can be tailored from pH 5 to pH 10 by decreasing the acid content in the film from 4% to 1%.     

Fabrication of photosensitive multilayer films based on polyoxometalate and diazoresin

A novel photosensitive organic-inorganic composite film incorporating polyoxometalate, K7[SiW11O39Co(H3P2O7)] (SiW11CoPP), and diazoresin (DR) has been prepared via layer-by-layer (LBL) self-assembly. Under UV irradiation, followed the decomposition of diazonium in DR, the ionic bonds between the adjacent interfaces of the multilayer film convert to covalent bonds. The LBL multilayers were characterized by UV-vis spectroscopy, X-ray photoelectron spectra (XPS), atomic force microscopy (AFM), FTIR spectrum, cyclic voltammograms (CV), and electron spin resonance (ESR) measurements. UV spectroscopy shows that the deposition process is regular and highly reproducible from layer to layer. XPS spectra confirm the incorporation of DR and SiW(11)CoPP into the films. Atomic force microscopy image indicates that the film surface is uniform and smooth. Solvent etching experiment proves that the film has significant stability towards polar solvent. Electrochemical behavior of the multilayers is investigated.     

Synthesis of polyampholyte microgels from colloidal salts of pectinic acid and their application as pH-responsive emulsifiers

A novel method for obtaining cross-linked microgels of apple pectin has been introduced. This method is based on the Ugi four-component condensation in colloidal suspensions of pectinic acid and amines. Using various processing parameters (the polysaccharide concentration, the type and density of crosslink, and the optimal pH range), particles with controlled colloidal properties have been obtained. Lightly cross-linked polysaccharide chains acquire anionic character due to deprotonation of the carboxyl groups at pH?9–10. Increasing the degree of cross-linking leads to a polyampholyte microgel, which can be protonated in acidic medium or deprotonated in basic medium. Polyampholyte microgels derived from apple pectin have proved to be an effective Pickering emulsifier at low concentrations and pH?2–3, forming stable oil-in-water emulsions. These Pickering emulsions exhibited pH-responsive behavior: raising the solution pH to 10 resulted in immediate demulsification due to the destabilization of microgel network at the oil–water interface.     

Efficient synthesis of sterically stabilized pH-responsive microgels of controllable particle diameter by emulsion polymerization

Emulsion polymerization of 2-vinylpyridine (2VP) in the presence of divinylbenzene (DVB) cross-linker, a cationic surfactant, and a hydrophilic macromonomer, monomethoxy-capped poly(ethylene glycol) methacrylate (PEGMA), at around neutral pH and 60 degrees C afforded near-monodisperse, sterically stabilized latexes at approximately 10% solids. Judicious selection of the synthesis parameters enabled the mean latex diameter to be varied over an unusually wide range for one-shot batch syntheses. Scanning electron microscopy studies confirmed near-monodisperse spherical morphologies, with mean weight-average particle diameters ranging from 370 to 970 nm depending on the initiator, polymeric stabilizer, and surfactant concentrations. Particle sizing studies were also conducted using disk centrifuge photosedimentometry and dynamic light scattering and gave similar data. These lightly cross-linked latexes acquired cationic microgel character at low pH, as expected. The critical pH for this latex-to-microgel transition was around pH 4.1 at 1.0 wt % DVB, which is significantly lower than the pKa of 4.92 estimated for linear P2VP homopolymer by acid titration. 1H NMR and aqueous electrophoresis studies indicated that substantial swelling occurred at low pH due to protonation of the 2VP groups, while dynamic light scattering (DLS) studies indicated volumetric swelling ratios of up to 3 orders of magnitude, depending on the initial latex diameter. Systematic variation of the degree of cross-linking led to a monotonic decrease in the pKa values of the P2VP latexes (as judged by acid titration) and also the critical swelling pH (as judged by visual inspection). This was attributed to the increasingly branched nature of the P2VP chains in their swollen microgel form. Preliminary studies of the kinetics of acid-induced swelling were also conducted using the pH jump method in conjunction with a stopped-flow apparatus. These P2VP latexes swell significantly faster than P2VP latexes described in the literature and the characteristic time scales observed in the present study are much closer to those predicted by the Tanaka equation.     

Synthesis and aqueous solution properties of sterically stabilized pH-responsive polyampholyte microgels

Emulsion copolymerization of poly(methacrylic acid) and poly(2-(diethylamino)ethyl methacrylate) (PMAA/PDEA) yielded pH-responsive polyampholyte microgels of 200-300 nm in diameter. These microgels showed enhanced hydrophilic behavior in aqueous medium at low and high pH, but formed large aggregates of approximately 2500 nm at intermediate pH. To achieve colloidal stability at intermediate pH, a second batch of microgels of identical monomer composition were synthesized, where monomethoxy-capped poly(ethylene glycol)methacrylate (PEGMA) was grafted onto the surface of these particles. Dynamic light-scattering measurements showed that the hydrodynamic radius, Rh, of sterically stabilized microgels was approximately 100 nm at intermediate pH and increased to 120 and 200 nm at pH 2 and 10, respectively. Between pH 4 and 6, these microgels possessed mobility close to zero and a negative second virial coefficient, A2, due to overall charge neutralization near the isoelectric pH. From the Rh, mobility, and A2, cross-linked MAA-DEA microgels with and without PEGMA retained their polyampholytic properties in solution. By varying the composition of MAA and DEA in the microgel, it is possible to vary the isoelectric point of the colloidal particles. These new microgels are being explored for use in the delivery of DNA and proteins.     

Facile fabrication of free-standing colloidal-crystal films by interfacial self-assembly

This paper reports a rapid and facile method of preparing free-standing colloidal crystals from monodisperse charged polystyrene (PS) microspheres. Mixed solvents (ethanol/water) were used as the dispersion medium in the self-assembly process of colloidal crystals. By a simple "floating self-assembly" method, PS microspheres floated on the surface of liquid and self-assembled into large area of three-dimensional (3D) ordered colloidal crystals within 15 min. Then epichlorohydrin was added in as a cross-linking agent to strengthen the colloidal-crystal film. After cross-linking reactions between the microspheres, the obtained colloidal-crystal film was free-standing and could be easily transferred to other substrates. Using tetrabutyl titanate as a titania precursor, 3D porous TiO(2) materials with rodlike skeletal structure were fabricated from the prepared free-standing colloidal crystal. This work provides a facile method to fabricate free-standing colloidal-crystal film, which can be used as an ideal template for the preparation of porous materials.     

Synthesis and characterization of novel pH-responsive microgels based on tertiary amine methacrylates

Emulsion polymerization of 2-(diethylamino)ethyl methacrylate (DEA) in the presence of a bifunctional cross-linker at pH 8-9 afforded novel pH-responsive microgels of 250-700 nm diameter. Both batch and semicontinuous syntheses were explored using thermal and redox initiators. Various strategies were evaluated for achieving colloidal stability, including charge stabilization, surfactant stabilization, and steric stabilization. The latter proved to be the most convenient and effective, and three types of well-defined reactive macromonomers were examined, namely, monomethoxy-capped poly(ethylene glycol) methacrylate (PEGMA), styrene-capped poly[2-(dimethylamino)ethyl methacrylate] (PDMA50-St), and partially quaternized styrene-capped poly[2-(dimethylamino)ethyl methacrylate] (10qPDMA50-St). The resulting microgels were pH-responsive, as expected. Dynamic light scattering and 1H NMR studies confirmed that reversible swelling occurred at low pH due to protonation of the tertiary amine groups on the DEA residues. The critical pH for this latex-to-microgel transition was around pH 6.5-7.0, which corresponds approximately to the known pKa of 7.0-7.3 for linear PDEA homopolymer. The microgel particles were further characterized by electron microscopy and aqueous electrophoresis studies. Their swelling and deswelling kinetics were investigated by turbidimetry. The PDEA-based microgels were compared to poly[2-(diisopropylamino)ethyl methacrylate] (PDPA) microgels prepared with identical macromonomer stabilizers. These PDPA-based microgels had a lower critical swelling pH of around pH 5.0-5.5, which correlates with the lower pKa of PDPA homopolymer. In addition, the kinetics of swelling for the PDPA microgels was somewhat slower than that observed for PDEA microgels; presumably this is related to the greater hydrophobic character of the former particles.     

Enzymatic synthesis of pH-responsive polyaniline colloids by using chitosan as steric stabilizer

Polyaniline colloidal particles were prepared by enzymatic polymerization of aniline using chitosan as steric stabilizer and toluenesulfonic or camphorsulfonic acids as doping agents. Fourier transform infrared and UV-vis spectroscopic studies indicate that enzymatic polymerization of aniline in dispersed media results in the emeraldine salt form of polyaniline. The morphology of the colloids was studied by transmission electron microscopy. Toluenesulfonic acid produced mainly oblong particles whereas rod-like shaped particles were obtained using camphorsulfonic acid. Polyaniline particles with good colloidal stability and size below 200 nm were obtained using 1.0 wt% of chitosan in the reaction media, indicating that this polymer was highly efficient as a steric stabilizer. The content of chitosan attached to the polyaniline colloids was approximately 20 wt% as indicated by elemental analysis. The colloids synthesized either with toluenesulfonic or camphorsulfonic acid showed a strong pH-dependent colloidal stability and underwent rapid flocculation in near neutral or alkaline media. This interesting behavior could be exploited in separation technology applications.     

Fabrication of a gas sensor using pentacene thin films as a detector

Highly sensitive gas sensors for both acidic and basic gases were fabricated based on conducting thin films of polyacene compounds. Gas sensors formed with pentacene thin films deposited on various kinds of substrates were found to exhibit high sensitivity in detecting subppm concentrations of NO₂ or Cl₂ by monitoring the conductivity of the thin film. Improvements in the conductance and duration period for detection were achieved by changing the shape of electrodes and substrate. The sensors with PEN thin films initially doped with iodine could detect ppm concentrations of ammonia gas, since iodine molecules were dedoped upon exposure to ammonia, causing the reduction of the conductivity.     

以Au@Ag双金属纳米棒为核的热响应性核壳复合微凝胶的制备及性能表征

本文采用种子沉淀聚合法将交联的聚(N-异丙基丙烯酰胺)(PNIPAM)包覆在单分散性良好的Au@Ag双金属纳米棒(Au@AgNR)表面,制得以Au@AgNR为核、交联PNIPAM为壳层的Au@AgNR@PNIPAM复合微凝胶。用透射电镜观察到复合微凝胶具有规整的核壳结构,动态激光光散射测试结果证实复合微凝胶存在热响应性。当环境温度从20℃升高到50℃,复合微凝胶中Au@AgNR的纵向局域表面等离子体共振波长从695nm红移到719nm,表明复合微凝胶内的Au@AgNRs的LSPR光学性能可利用温度来进行调节。以该复合微凝胶为SERS分析的基底,检测水溶液中痕量的难以吸附在金属粒子表面的1-萘酚(3×10-5M),结果发现复合微凝胶在发生体积相转变时对1-萘酚具有捕捉效应,因此可通过调节测试温度来达到提高待分析物的SERS的信号强度的目的。     

Fabrication of silver patterns on polyimide films based on solid-phase electrochemical constructive lithography using ion-exchangeable precursor layers

We report a fully additive-based electrochemical approach to the site-selective deposition of silver on a polyimide substrate. Using a cathode coated with ion-doped precursor polyimide layers, patterns of metal masks used as anodes were successfully reproduced at the cathode-precursor interface through electrochemical and ion-exchange reactions, which resulted in the generation of silver patterns on the polyimide films after subsequent annealing and removal from the substrate. Excellent interfacial adhesion was achieved through metal nanostructures consisting of interconnecting silver nanoparticles at the metal-polymer interface, which are electrochemically grown "in" the precursor layer. This approach is a resist- and etch-free process and thus provides an effective methodology toward lower-cost and high-throughput microfabrication.     

Modification of diamond single crystals by chromium ion implantation with sacrificial layers

Single-crystal diamond surfaces were implanted with chromium ions. Ion energies chosen were 120 and 180 keV. Ion doses of 1x10(17) cm(-2) were applied at a substrate temperature of 750 degrees C. Reduced lattice damage could be obtained by deposition of a titanium sacrificial layer with a thickness of 10 and 50 nm before implantation. Depth profiles of the elemental binding states were taken by photoelectron spectroscopy. The effect of the sacrificial layer thickness on diamond lattice damage was investigated by infrared spectroscopy.     

Fabrication and characterization of multilayer films from amphiphilic poly(p-phenylene)s

Over the past two decades, considerable efforts have been devoted to the development of conjugated polymeric materials for electronic applications due to the tunability of their properties through variation of their chemical structure. The LB technique is one of the most effective and precise methods for controlling the organization and thereby the properties of polymer films at the nanoscale for device fabrication. A detailed study was performed on the Langmuir-Schaefer (LS) monolayer and Langmuir-Blodgett-Kuhn (LBK) multilayer formation of newly designed conjugated poly(p-phenylene)s (C(n)PPPOH), incorporated with alkoxy groups with different chain lengths (C(6)H(13)O-, C(12)H(25)O-, and C(18)H(37)O-) and hydroxyl groups on the polymer backbone. The monolayer formed at the air-water interface was characterized using surface pressure-area isotherms, including hysteresis measurements. The films were then transferred to different hydrophilic solid substrates and analyzed using surface plasmon resonance spectroscopy, UV-vis spectroscopy, fluorescence spectroscopy, and AFM measurements. The results showed that the polymer with a short alkoxy chain (C(6)PPPOH) forms uniform monolayers at the air-water interface and can be transferred as multilayer films compared to C(12)PPPOH and C(18)PPPOH. The observed film thicknesses measured by SPR and AFM studies were similar to the theoretical value obtained in the case of C(6)PPPOH, whereas this was not the case with the other two polymers. The present study shows that the polymer C(n)PPPOH with short alkoxy chain can be transferred onto different solid substrates for device fabrication with molecular level control.