Self-assembly of multilayer films containing gold nanoparticles via hydrogen bonding

Polymer/Au nanoparticle multilayer ultrathin films are fabricated via hydrogen-bonding interaction by a layer-by-layer technique. The Au nanoparticles surface-modified with pyridine groups of poly(4-vinylpyridine) (PVP) are prepared in dimethyl formamide (DMF). Transmission electron microscopy (TEM) image shows that uniform nanoparticles are dispersed in the PVP chains. Poly(3-thiophene acetic acid) (PTAA) and poly(acrylic acid) (PAA) are utilized to form hydrogen bonds with PVP, respectively. Considering the pH-sensitive dissociation behavior of PTAA and PAA, we investigate the release behavior of the Au-containing multilayers at different pH values in this work. UV-vis spectroscopy and atomic force microscopy (AFM) are employed to monitor the buildup and the release of the multilayers. The results indicate that in the films assembled with gold nanoparticles, the polymers are difficult to be removed from the substrate. The interaction between the gold particles and the neighboring PVP chains is responsible for the phenomenon. Gold particles act as physical cross-link points in the multilayers. Due to the additional interaction caused by the gold nanoparticles in the films except the hydrogen-bonding interaction between PTAA (or PAA) and PVP, the stability of the Au-containing multilayer film is ensured even though the changes in pH values may result in the break of the hydrogen bonds.     

Chemical patterning of ultrathin polymer films by direct-write multiphoton lithography

We applied 2-photon laser ablation to write subdiffraction nanoscale chemical patterns into ultrathin polymer films under ambient conditions. Poly(ethylene glycol) methacrylate brush layers were prepared on quartz substrates via surface-initiated atom-transfer radical polymerization and ablated to expose the underlying substrate using the nonlinear 2-photon absorbance of a frequency-doubled Ti:sapphire femtosecond laser. Single-shot ablation thresholds of polymer films were ~1.5 times smaller than that of a quartz substrate, which allowed patterning of nanoscale features without damage to the underlying substrate. At a 1/e(2) laser spot diameter of 0.86 μm, the features of exposed substrate approached ~80 nm, well below the diffraction limit for 400 nm light. Ablated features were chemically distinct and amenable to chemical modification.     

Thin liquid films containing micelles or nanoparticles

The stratification/microstructure formation inside suspended thin liquid films containing micelles or other nanoparticles is reviewed with the aim of clarifying some key issues and suggesting unresolved questions requiring further investigation. New experiments reveal that the micellar layer thinning phenomenon is a reversible process in films formed from non-ionic micellar solutions. The important factors contributing to the correlation between the ordered microstructure formation that leads to a high structural stabilization force in a single free suspended film and the stability of macrodispersions (such as foams and emulsions and particle suspensions) are also discussed.     

Surface engineering the cellular microenvironment via patterning and gradients

Cell organization, proliferation, and differentiation are impacted by diverse cues present in the cellular microenvironment. As a result, the surface of a material plays an important role in cellular function. Synthetic surfaces may be augmented by physical as well as chemical means. In particular, patterning and interfacial gradients may be utilized to mitigate the cellular response. Patterning is advantageous as it affords control over a range of feature sizes from several nanometers to millimeters. Gradients exist in vivo, for instance in stem cell niches, and the ability to create interfacial gradients in vitro can provide valuable insights into the influence of a series of minute surface changes on a single sample. This review focuses on fabrication methods for generating micro‐ and nanoscale surface patterns as well as interfacial gradients, the impact of these surface modifications on the cellular response, and the advantages and challenges of these surfaces in in vitro applications. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys., 2013     

Preparation of antibacterial polyimide films containing silver nanoparticles

Polyimide/silver composite films were successfully prepared by in situ polymerization. A precursor, AgNO₃ was used as the source of the silver nanoparticles. The structure and morphology of resulting films were characterized by FTIR spectroscopy, X-ray diffraction (XRD) and scanning electron microscopy (SEM). Consequently, the silver nanoparticles were well dispersed in polyimide matrix. Meanwhile, thermal properties from thermal gravimetric analyses (TGA) and mechanical properties from tensile test which confirmed composites were kept good performance as compared to pure polyimide. In addition, the antimicrobial activity of polyimide/silver composite films against three different bacteria, B. subtilis, S. aureus, and E. coil, illustrated excellent activity. This composite is potential useful as antimicrobial material with good thermal performance in a wide variety of biomedical and general use applications.     

Molecular imprinting in ultrathin titania gel films via surface sol-gel process

Recent progresses of molecular imprinting in metal oxide matrices were summarized. Application of the surface sol-gel process to mixtures of organic carboxylic acids and titanium alkoxide provides ultrathin layers of titania gel (10-20 nm thick), in which molecule-sized cavities are kept intact upon removal of the organic templates. The imprinted cavity reflects the structural and functional features of the template molecule, and the enantioselective imprinting of dipeptide isomers is observed. Robustness and flexibility of the ultrathin titania layer is demonstrated by the formation of interconnected titania hollow structures. Possible practical applications and unsolved problems of this technique are discussed.     

Simultaneous patterning of nanoparticles and polymers using an evaporation driven flow in a vapor permeable template

Nanoparticles and polymers have great potential for lowering cost and increasing functionality of printed sensors and electronics. However, creation of practical devices requires that many of these materials be patterned on a single substrate, and many current patterning processes can only handle a single material at a time, necessitating alignment of serial processing steps. Higher throughput and lower cost can be achieved by patterning multiple materials simultaneously. To this end, the microfluidic molding process is adapted to pattern various nanoparticle and polymer inks simultaneously, in a completely additive manner, with three-dimensional control and high relative positional accuracy between the different materials. A differential template distortion observed in channels containing different inks is analyzed and found to result from pressure force in the template due to flow of a highly viscous and highly concentrated ink in small channels. The resulting optimization between patterning speed and dimensional fidelity is discussed.     

Zinc oxide nanoparticles incorporated in ultrathin layer silicate films and their photocatalytic properties

This study has been conducted to determine whether the nanosized semiconductor crystals qualify as photocatalysts also in that case when they are self-assembled to form ultrathin films in the thickness range of 10–500 nm. For this purpose, multilayer films of Zn(OH)₂ and ZnO nanoparticles were prepared by the layer-by-layer self-assembly method on glass surface. A transparent layer silicate, synthetic hectorite was used as sticking material. The quality of multilayer formation has been investigated in detail by absorption spectrophotometry, XRD and atomic force microscopy (AFM). Evidence was found for the uniform deposition of the different components. The increment of nanofilm thickness was constant and independent from the number of layers deposited previously. Photocatalytic measurements were made with model organic materials β-naphtol and industrial kerosene in a home-made loop-type batch reactor. Decomposition has been continously monitored by UV spectrometry. Significant photodegradation of the organic molecules were only found in the presence of the nanofilms.     

Hybrid organic-inorganic coatings and films containing conducting polyaniline nanoparticles

Hybrid organic-inorganic coatings and free-standing films made from [3-(glycidyloxy)propyl]trimethoxysilane, amino-terminated poly(oxypropylene) (Jeffamine D-230), colloidal polyaniline nanoparticles and, in some cases, colloidal nanosilica were prepared and characterized. HCl or 4-methylbenzene-1-sulfonic acid were used as catalysts for the sol-gel process and pH tuning, water-propan-2-ol mixture as a solvent. Electrical and mechanical properties and surface morphology of films were studied. The coatings were blue and non-conducting, or green and conducting, depending on preparation conditions. They have a smoother surface than in-situ polymerized polyaniline films.     

Photomagnetic hybrid ultrathin films

Two novel types of photomagnetic hybrid ultrathin film (film A and B) of metal cyanides have been fabricated by means of the modified Langmuir–Blodgett method using a smectite clay mineral. Film A is composed of an amphiphilic azobenzene cation, a montmorillonite, and Prussian Blue in which photocontrol in the magnetization was realized by the photoisomerization of azobenzene chromophore. The observed photomagnetic efficiency was large (ca. 11%) due to the well-organized structure of the ultrathin film. Film B is composed of a quaternary ammonium salt, a montmorillonite, and Co–Fe Prussian Blue in which the photoinduced magnetization caused by the electron transfer exhibited an anisotropic response with regards to the direction of the applied magnetic field. This phenomenon is ascribed to the unique structure of Co–Fe Prussian Blue formed onto the clay layer. Contribution to special issue “Magnetic field effects in Electrochemistry”     

Reactive μCP on ultrathin block copolymer films: Localized chemistry for micro- and nano-scale biomolecular patterning

Three different, complementary soft lithographic approaches for the fabrication of chemical patterns on ultrathin polystyrene-block-poly(tert-butyl acrylate) (PS₆₉₀-b-PtBA₁₂₁₀) films are discussed. Central to the methodology is the previously introduced reactive PS₆₉₀-b-PtBA₁₂₁₀ platform that allows one to covalently graft (bio)molecules via robust amide linkages in high densities on flat, as well as on structured, surfaces. As shown in this paper, the combination of the polymer-based platform and reactive microcontact printing (μCP) patterning approaches allows one to obtain patterns of (bio)molecules with (sub)micrometer feature sizes. The μCP approaches comprise: (A) the direct transfer of functional (bio)molecules from an oxidized elastomeric stamp to hydrolyzed and N-hydroxysuccinimide (NHS) activated PS₆₉₀-b-PtBA₁₂₁₀; (B) the transfer of a passivating poly(ethylene glycol) layer to hydrolyzed and NHS-activated PS₆₉₀-b-PtBA₁₂₁₀ followed by wet chemical grafting of functional moieties; (C) the local hydrolysis of the PtBA skin layer with trifluoroacetic acid (TFA), followed by NHS activation and wet chemical derivatization. The applicability and the versatility of the combination of the polymer thin film-based platform and soft lithographic methodologies for patterning biologically relevant molecules is demonstrated for polyamidoamine (PAMAM) dendrimers, different proteins, as well as probe DNA. The successful hybridization of target DNA and the immobilization of fibronectin in micropatterns show that ultrahigh density patterns for micro- and nano-arrays, as well as for studies of cell-surface interactions, can be conveniently fabricated based on these approaches and platforms.     

Incorporation into paper of cellulose triacetate films containing semiconductor nanoparticles

CdSe/ZnS quantum dots (QDs) were embedded in films of cellulose triacetate (CTA) to give clear films with the broad absorbance and well-defined, size-tunable fluorescence characteristic of QDs. The relative quantum yields of the QDs in polymer were compared to that of the initial QDs dispersed in toluene. Alkaline hydrolysis of the film surfaces to regenerated cellulose rendered the previously hydrophobic CTA film surfaces hydrophilic and compatible with aqueous papermaking. Films containing combinations of different sized QDs gave more complex emission patterns. Small pieces of fluorescent films were added to pulp slurries and incorporated into laboratory paper sheets through hydrogen bonding between the regenerated cellulose film surfaces and cellulosic pulp fibers. The film system (cellulose ester bulk/cellulose surface) can be used to incorporate hydrophobic particles or molecules compatible with solutions of cellulosic polymers into paper products at both high and low loadings. QDs in paper may prove useful for security applications, such as sheets with unique optical signatures.     

Structure and properties of biodegradable carboxymethyl cellulose films containing silver nanoparticles

Silver nanoparticles stabilized in a solution of sodium carboxymethyl cellulose with a degree of substitution of 0.85 and a degree of polymerization of 600 have been synthesized. The structuring; physical, chemical, and mechanical properties; and antimicrobial activities of films prepared from sodium carboxymethyl cellulose solutions containing silver nanoparticles have been studied. The shapes, quantities, and sizes of the silver nanoparticles occurring in the sodium carboxymethyl cellulose films were determined with the use of transmission electron microscopy, atomic force microscopy, and UV spectroscopy. It was found that an increase in the concentration of silver nitrate in sodium carboxymethyl cellulose solutions, as well as photoirradiation of the films, leads to the changes in the sizes and shapes of silver nanoparticles. The shapes, sizes, and quantities of silver nanoparticles determine their biological activity. An increase in the quantity of 5- to 25-nm silver nanoparticles was found to enhance the microbicidal activities of the carboxymethyl cellulose films.     

Polydiacetylene nanowires in ultrathin films

In this paper the results of studies carried out on thin films of new poly[bis(carbazol-9-ylmethyl)diacetylene]s (PCDAs) are reported. The preparation of the films has required clever synthesis to make processable the conjugated polymers without degrading their optoelectronic properties. To this end, the parent poly(diacetylene), (polyDCHD), has been modified by introducing long alkyl or acyl chains in the 3 and 6 positions of the carbazole rings. Electronic absorption spectra and linear and nonlinear optical characterization of three types of PCDAs are reported and compared.     

Diffusion in ultrathin liquid films

Inhomogeneous molecular diffusion in layered structures of thin liquid films deposited on solid surfaces is observed via wide field single molecule microscopy. The fluorescence dyes Rhodamine 6G and Oregon Green 514 are used to probe the diffusion in tetrakis(2-ethylhexoxy)-silane and polydimethylsiloxane. A broad distribution of diffusion constants is observed which can be attributed to diffusion within distinct layers of the liquid. Comparison with computer simulations shows that diffusion is normal but depends strongly on the distance of the molecules from the solid surface. Diffusion within layers is faster than between the layers and additional temperature activation is necessary to speed up interlayer diffusion.     

pH-sensitive bipolar ion-permselective ultrathin films

pH-Sensitive bipolar ion-permselective films of polyelectrolyte multilayers were prepared by layer-by-layer (LbL) assembly and photo-cross-linking of benzophenone-modified poly(acrylic acid) (PAA-BP) and poly(allylamine hydrochloride) (PAH-BP). The multilayer structure and ionizable group composition was finely tuned by changing the pH of the dipping solution. This structure and composition was in turn "preserved" by photo-cross-linking, forming highly stable membrane films. Since PAA-BP and PAH-BP are weak polyelectrolytes, it is possible to control the number of unbound, un-ionized -COOH or -NH2 groups in the multilayer by changing the pH. Moreover, the pH of the deposited film also plays an important role in determining selective latter permselectivity. For example, PAA-BP/PAH-BP multilayers deposited from two pH conditions, pH = 3 (PAA-BP) and pH = 6 (PAH-BP), showed pH-switchable permselectivity for both cationic (pH = 10) and anionic (pH = 3) probe molecules in a single film. The system offers advantages in film stability and introducing reversible selective ion permeability over previous multilayer film and cross-linking methods.     

Surface chemistry of ultrathin films of histidine on gold as probed by high-resolution synchrotron photoemission

Procedures for the vacuum deposition of thin histidine films on polycrystalline Au(111) and their characterization with high-resolution synchrotron-radiation-based photoelectron spectroscopy are reported. The chemical form of histidine (anionic vs zwitterionic) and the nature of its interactions with the substrate (strong ionic-covalent vs weak van der Waals bonding) in mono- and multilayer films are analyzed. It is shown that water adsorption on a pre-prepared histidine film at 100 K results in protonation of histidine molecules and partial formation of hydroxyl anions. These chemical effects are carefully differentiated from spectral changes associated with radiation damage of the histidine films.     

Enhanced visible photoluminescence in ultrathin poly(3-hexylthiophene) films by incorporation of Au nanoparticles

Incorporation of non-luminescent dodecanethiolate-protected gold clusters into regioregular poly(3-hexylthiophene) films results in a 6-fold increase in the visible photoluminescence (PL) of the polymer, which arises predominantly from NP-induced structural changes in the composite films.