UV-cross-linkable multilayer microcapsules made of weak polyelectrolytes

Microcapsules composed of weak polyelectrolytes modified with UV-responsive benzophenone (BP) groups were fabricated by the layer-by-layer (LbL) technique. Being exposed to UV lights, capsules shrunk in the time course of minutes at irradiation intensity of 5 mW/cm(2). The shrinkage adjusted the capsule permeability, providing a novel way to encapsulate fluorescence-labeled dextran molecules without heating. Cross-linking within the capsule shells based on hydrogen abstraction via excited benzophenone units by UV showed a reliable and swift approach to tighten and stabilize the capsule shell without losing the pH-responsive properties of the weak polyelectrolyte multilayers.     

Molecular dynamics simulations of multilayer films of polyelectrolytes and nanoparticles

We performed molecular dynamics simulations of multilayer assemblies of flexible polyelectrolytes and nanoparticles. The film was constructed by sequential adsorption of oppositely charged polymers and nanoparticles in layer-by-layer fashion from dilute solutions. We have studied multilayer films assembled from oppositely charged polyelectrolytes, oppositely charged nanoparticles, and mixed films containing both nanoparticles and polyelectrolytes. For all studied systems, the multilayer assembly proceeds through surface overcharging after completion of each deposition step. There is almost linear growth in the surface coverage and film thickness. The multilayer films assembled from nanoparticles show better layer stratification but at the same time have higher film roughness than those assembled from flexible polyelectrolytes.     

Electrodeposition of layered manganese oxide nanocomposites intercalated with strong and weak polyelectrolytes

Multilayered manganese oxide nanocomposites intercalated with strong (poly(diallyldimethylammonium) chloride, PDDA) and weak (poly(allylamine hydrochloride), PAH) polyelectrolytes can be produced on polycrystalline platinum electrode in a thin film form by a simple, one-step electrochemical route. The process involves a potentiostatic oxidation of aqueous Mn2+ ions at around +1.0 V (vs Ag/AgCl) in the presence of polyelectrolytes. Fully charged PDDA polycations are accommodated tightly in the interlayer space by electrostatic interaction with negative charges on the manganese oxide layers, leading to an interlayer distance of 0.97 nm. The layered film prepared with PAH has a larger polymer content (PAH/Mn molar ratio of 0.98) than that (PDDA/Mn molar ratio of 0.43) made with PDDA because of the smaller charging degree of PAH, exhibiting a larger interlayer distance (1.19 nm). The interlayer PAH contains neutral (-NH2) and positively charged (-NH3(+)) amine groups, and the -NH3(+) groups are associated with Cl- (to generate -NH3(+) Cl- ion pairs) as well as the negatively charged manganese oxide layers. Both polyelectrolytes once incorporated were not ion exchanged with small cations in solution. The layered structure of PDDA/MnO(x) was collapsed during the reduction process in a KCl electrolyte solution, accompanying an expansion of the interlayer as a result of incorporation of K+ ions for charge neutrality. On the contrary, the layered PAH/MnO(x) film showed a good electrochemical response due to the redox reaction of Mn3+/Mn4+ couple with no change in the structure. X-ray photoelectron spectroscopy revealed that, in this case, excess negative charges generated on the manganese oxide layers upon reduction can be balanced by the protons being released from the -NH3(+) Cl- sites in the interlayer PAH; the Cl- anions becoming unnecessary are inevitably excluded from the interlayer, and vice versa upon oxidation.     

Fabrication of composite films containing zirconia and cationic polyelectrolytes

Composite films were prepared by electrophoretic deposition of poly(ethylenimine) or poly(allylamine hydrochloride) combined with cathodic precipitation of zirconia. Films of up to several micrometers thick were obtained on Ni, Pt, stainless-steel, graphite, and carbon-felt substrates. When the concentration of polyelectrolytes in solutions and the deposition time were varied, the amount of the deposited material and its composition can be varied. The electrochemical intercalation of yttria-stabilized zirconia particles into the composite films has been demonstrated. Obtained results pave the way for the electrodeposition of other polymer-ceramic composites. The deposits were studied by thermogravimetric analysis, X-ray diffraction analysis, scanning electron microscopy, and atomic force microscopy. The mechanisms of deposition are discussed.     

Assembly of ultrathin polymer multilayer films by click chemistry

Layer-by-layer (LbL) assembly is a versatile and robust technique for fabricating tailored thin films of diverse composition. Herein we report a new method of covalent coupling, click chemistry, to facilitate the LbL assembly of thin films. Linear film growth was observed using both UV-vis and FTIR spectroscopy, and film thicknesses were determined by ellipsometry and atomic force microscopy. The assembled films are shown to be stable in a wide pH range. This technique offers the potential to enable the synthesis of new types of stable and responsive LbL films from a variety of polymers.     

Assembly of multilayer films incorporating a viral protein cage architecture

Protein cage architectures such as viral capsids, heat shock proteins, ferritins, and DNA-binding proteins are nanoscale modular subunits that can be used to expand the structural and functional range of composite materials. Here, layer-by-layer (LbL) assembly was used to incorporate cowpea chlorotic mottle virus (CCMV) into multilayer films. Three types of multilayer films were prepared. In the first type, ionic interactions were employed to assemble CCMV into triple layers. In the second type, complementary biological interactions (streptavidin/biotin) were used for this purpose. In a third variation of LbL assembly, complementary biological interactions were employed to produce nanotextured films that exhibit in-plane order over a micron scale without the need to adsorb onto a prepatterned template.     

Reduction of 2,3,5-triphenyl-2H-tetrazolium chloride in the presence of polyelectrolytes containing 4-styrenesulfonate moieties

The redox behavior of 2,3,5-triphenyl-2H-tetrazolium chloride (TTC) in the presence of different polyelectrolytes such as poly(sodium 4-styrenesulfonate) (PSS), poly(sodium 4-styrenesulfonate-co-sodium maleate) at two different comonomer compositions (P(SS(1)-co-MA(1)) and P(SS(3)-co-MA(1))), poly(sodium acrylate-co-sodium maleate) (P(AA(1)-co-MA(1))), and poly(sodium acrylate) (PAA) is studied. Due to aromatic-aromatic interactions, the polyelectrolytes containing benzene sulfonate groups produce a decrease on the reduction rate of TTC in the presence of ascorbic acid (ASC) and a shift of the anodic and cathodic peaks to higher negative potentials for the electrochemical reaction of TTC. As an important conclusion, these effects are a function of the linear aromatic density of the polyelectrolytes.     

Control of composition in the multilayer films fabricated from mixed solutions containing two dendrimers

A series of multilayer films were fabricated alternately from poly(4-vinylpyridine) solution and mixed solutions of two carboxyl-terminated dendrimers. UV-Vis absorption spectroscopy was applied to study the composition of the multilayer films. In contrast to mixed solutions of linear polymers, the total amount of dendrimers in multilayer film is independent of the ratio of dendrimers in mixed solution, which is possibly due to the globular conformation of the dendrimer. Furthermore, the ratio of two dendrimers in films is linearly dependent on the ratio of the two dendrimers in solutions, which facilitates control of the composition in multilayer films.     

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.     

Water distribution in multilayers of weak polyelectrolytes

The water localization in thin polyelectrolyte multilayers assembled from poly(acrylic acid) and poly(allylamine hydrochloride) was investigated with neutron reflectivity in an atmosphere of controlled humidity and with bulk water. Water was found to be distributed asymmetrically within the multilayer and to localize preferentially at the polymer surface. The diffusion of water into the multilayer did not completely penetrate to the substrate, but instead there appeared to be an exclusion zone near the Si substrate. These results help to explain previous observations of anomalous water transport kinetics in weak polyelectrolyte systems.     

Study of nonlinear optical properties of multilayer Langmuir-Blodgett films containing bacteriorhodopsin

Multilayer oriented Langmuir-Blodgett films of bacteriorhodopsin were prepared and their nonlinear optical properties, including second harmonic generation and photoresponse at a two phase-modulated beams mixing, were investigated. The nonlinear component of refractive index of the films was measured.     

Self-similar extrapolation from weak to strong coupling

The problem is addressed of defining the values of functions, whose variables tend to infinity, from the knowledge of these functions at asymptotically small variables close to zero. For this purpose, the extrapolation by means of different types of self-similar approximants is employed. Two new variants of such an extrapolation are suggested. The methods are illustrated by several examples of systems typical of chemical physics, statistical physics, and quantum physics. The developed methods make it possible to find good approximations for the strong-coupling limits from the knowledge of the weak-coupling expansions.     

Bragg-type polarization gratings formed in thick polymer films containing azobenzene and tolane moieties

Holographic gratings were formed in thick polymer films containing azobenzene and diphenylacetylene (tolane) moieties in the Bragg regime. Amorphous polymers containing various contents of the azobenzene moiety with photosensitivity and the tolane moiety with large birefringence in the side chain were synthesized, and optically transparent thick polymer films were prepared. The films were irradiated with a linearly polarized beam from an Ar+ laser (488 nm), and the transmittance of a He-Ne laser beam (633 nm) through a pair of crossed polarizers, with the film between them, was measured to estimate a photoinduced birefringence (deltan). The value of deltan increased with an increase in the tolane moiety content in the polymer films. When two linearly polarized beams at 488 nm were interfered in the film, a diffraction beam was observed, and the maximum diffraction efficiency (eta) increased with the tolane moiety content. In the film containing 70 mol% of the tolane moiety, the highest eta of 99% was achieved, and angular selectivity due to Bragg diffraction was clearly observed. We consider the cooperative molecular motion of the tolane moieties to be induced by the photoinduced change in alignment of the azobenzene moieties even if the polymers show no liquid-crystalline phase. When two orthogonal circularly polarized beams were allowed to interfere in the film, a Bragg-type polarization grating was formed. It was found that the value of eta reached 90% within 920 ms.     

Direct surface force measurements of polyelectrolyte multilayer films containing nanocrystalline cellulose

Polyelectrolyte multilayer films containing nanocrystalline cellulose (NCC) and poly(allylamine hydrochloride) (PAH) make up a new class of nanostructured composite with applications ranging from coatings to biomedical devices. Moreover, these materials are amenable to surface force studies using colloid-probe atomic force microscopy (CP-AFM). For electrostatically assembled films with either NCC or PAH as the outermost layer, surface morphology was investigated by AFM and wettability was examined by contact angle measurements. By varying the surrounding ionic strength and pH, the relative contributions from electrostatic, van der Waals, steric, and polymer bridging interactions were evaluated. The ionic cross-linking in these films rendered them stable under all solution conditions studied although swelling at low pH and high ionic strength was inferred. The underlying polymer layer in the multilayered film was found to dictate the dominant surface forces when polymer migration and chain extension were facilitated. The precontact normal forces between a silica probe and an NCC-capped multilayer film were monotonically repulsive at pH values where the material surfaces were similarly and fully charged. In contrast, at pH 3.5, the anionic surfaces were weakly charged but the underlying layer of cationic PAH was fully charged and attractive forces dominated due to polymer bridging from extended PAH chains. The interaction with an anionic carboxylic acid probe showed similar behavior to the silica probe; however, for a cationic amine probe with an anionic NCC-capped film, electrostatic double-layer attraction at low pH, and electrostatic double-layer repulsion at high pH, were observed. Finally, the effect of the capping layer was studied with an anionic probe, which indicated that NCC-capped films exhibited purely repulsive forces which were larger in magnitude than the combination of electrostatic double-layer attraction and steric repulsion, measured for PAH-capped films. Wherever possible, DLVO theory was used to fit the measured surface forces and apparent surface potentials and surface charge densities were calculated.     

Percolation conductivity in Langmuir-Blodgett multilayer films containing a long-chain TTF derivative

The room-temperature DC in-plane electrical conductivity of multilayer Langmuir-Blodgett films of the long-chain tetrathiafulvalene (TTF) derivative octadecanoyl-TTF (ODTTF), mixed with either octadecanoic acid (OA) or pentacosa-10,12-diynoic acid (PA) and doped with iodine, has been measured with a standard two-probe technique. The conductivity was found to depend strongly on the proportion of fatty acid contained in the film, and this behaviour has been compared with that predicted by classical, two-site, two-dimensional (2D) and three-dimensional percolation theory. A percolation threshold corresponding to an ODTTF content of approximately 50% was observed in both cases, in agreement with the value obtained from the 2D model. For films diluted with OA, however, the conductivity transition was smeared out, suggesting a contribution by charge transport perpendicular to the plane of the substrate. Optical microscope studies of these multilayer films have provided further evidence of a two-phase structure.     

The electroactive multilayer films of polyelectrolytes and Prussian blue nanoparticles and their application for H2O2 sensors

Prussian blue (PB) nanoparticles were immobilized in polyelectrolyte (PE) multilayers of various compositions and thickness. Films containing nanoparticles and poly(allylamine hydrochloride) (PAH) were formed using the layer-by-layer adsorption method. A layer of branched poly(ethyleneimine) (PEI) was used to anchor the multilayer structure at the surface of a gold electrode. The films exhibited electroactive properties, increasing with the number of deposited PB layers. The properties of PEI/(PB/PAH) _n multilayers were then compared with the ones containing additionally the conductive polymer poly(3,4-ethylenedioxythiophene)–poly(styrenesulfonate) (PEDOT:PSS). We found that the addition of the conductive, water-soluble polymer enhances the electroactive properties of the multilayer films. It also increased sensitivity of the multilayer-covered electrodes for electrochemical detection of hydrogen peroxide.     

含双噻唑自组装膜的制备及磁性能研究

以2,2′-二氨基-4,4′-联噻唑(DABT)和苯酚为原料合成了新型的偶氮化合物2,2′-对苯酚偶氮基-4,4′-联噻唑(BTDP),将其与聚二甲基二烯丙基氯化铵(PDDA)在聚乙烯(PE)膜上进行层层自组装,并与过渡金属离子进行了配位.UV-Vis和FT-IR表征发现这种膜可以均匀的进行组装,且能较好的与金属离子配位.多功能材料物理特性测量系统(physical property measurement system,PPMS)测定配合物的磁性能,测试结果表明,与两者溶液直接混合后沉淀配合物的磁性相比,在PE膜上形成的自组装膜配合物的磁性能有较大幅度的提高.     

Amperometric uric acid sensors based on polyelectrolyte multilayer films

Uricase (UOx) and polyelectrolyte were used for preparation of a permselective multilayer film and enzyme multilayer films on a platinum (Pt) electrode, allowing the detection of uric acid amperometrically. The polyelectrolyte multilayer (PEM) film composed of poly(allylamine) (PAA) and poly(vinyl sulfate) (PVS) were prepared via layer-by-layer assembly on the electrode, functioning as H₂O₂-selective film. After deposition of the permselective film (PAA/PVS)₂PAA, UOx and PAA were deposited via layer-by-layer sequential deposition up to 10 UOx layers to prepare amperometric sensors for uric acid. Current response to uric acid was recorded at +0.6 V vs. Ag/AgCl to detect H₂O₂ produced from the enzyme reaction. The response current increased with increasing the number of UOx layers. Even in the presence of ascorbic acid, uric acid can be detected over the concentration range 10⁻⁶-10⁻³ M. The response current and deposited amount of UOx were affected by deposition bath pH and the addition of salt. The deposition of PAA/UOx film prepared in 2 mg ml⁻¹ solution (pH 11) of PAA with NaCl (8 mg ml⁻¹) and 0.1 mg ml⁻¹ solution (pH 8.5) of UOx with borate (100 mM) resulted in an electrode which shows the largest response to uric acid. The response of the sensor to uric acid was decreased by 40% from the original activity after 30 days.     

Rapid gel-like latex film formation through controlled ionic coacervation of latex polymer particles containing strong cationic and protonated weak acid functionalities

We introduce a controlled ionic coacervation (CIC) process that rapidly forms uniform, gel-like latex films with significant mechanical integrity without loss of water from the film. This process uses latex particles that contain both strong cationic charges and weak protonated acid groups. An increase in pH ionizes the weak acid and triggers the rapid setting of the latex films. The necessary increase in pH can be achieved by coating the latex onto an alkaline surface (such as concrete) or by controlled release of a fugitive acid (such as carbon dioxide). We explore the effect of latex composition and concentration on this process. We show that the CIC process does not require a water-soluble polymer to obtain the rapid-set film properties. Our proposed mechanism for CIC process is consistent with models for rapid, irreversible, particle-particle aggregation.