Consecutively spin-assembled layered nanoarchitectures of poly(sodium 4-styrene sulfonate) and poly(allylamine hydrochloride)

The recently established spin-coating electrostatic self-assembly (SCESA) technique has been shown to facilitate not only the rapid fabrication of polyelectrolyte multilayer assemblies, but also allow each layer to be easily controlled on a monomolecular scale by minimizing the film thickness across a substrate surface. In this paper, the influence of polyelectrolyte concentration on the amount and thickness of spin-deposited polymer films has been examined for a multilayer system of poly(allyamine hydrochloride) (PAH) and poly(sodium 4-styrenesulfonate) (PSS), when the washing steps employed for removing weakly bound polyelectrolytes on a resultant film on a substrate are excluded from the standard fabrication procedure of the SCESA method. The thickness of the spin-deposited PAH/PSS bilayer increased linearly for the PSS concentrations in the range from 1 to 10 mM with PAH constant at 1 mM, which demonstrates the uniform deposition of each layer material onto the thin film. The thickness of PAH/PSS bilayers increased from 1.43 ± 0.06 to 3.37 ± 0.08 nm as the PSS concentration increased from 1 to 10 mM, while the PAH concentration was kept constant at 1 mM. The multilayer films were found to be stable in a good solvent (H₂O) for at least 30 h, without any noticeable loss of the adsorbed layer component of the polyelectrolyte. This improvement to the SCESA method (exclusion of washing steps) provides a convenient way to create multilayer heterostructures with the thickness of each layer being easily adjusted.     

Enhanced accumulation and visible light-assisted degradation of azo dyes in poly(allylamine hydrochloride)-modified mesoporous silica spheres

A new route for the economic and efficient treatment of azo dye pollutants is reported, in which surface-modified organic-inorganic hybrid mesoporous silica (MS) spheres were chosen as microreactors for the accumulation and subsequent photodegradation of pollutants in defined regions. The surface-modified silica materials were prepared by anchoring the polycationic species such as poly(allylamine hydrochloride) on MS spheres via a simple wet impregnation method. The as-synthesized spheres with well-defined porous structures exhibited 15 times of accumulating capacity for orange II and Congo red compared to that of the pure MS spheres. Diffuse reflectance UV-vis spectroscopy and confocal laser scanning microscopy demonstrated that the accumulated orange II and CR in defined MS spheres were rapidly degraded in the presence of Fenton reagent under visible radiation. Kinetics analysis in recycling degradation showed that the as-synthesized materials might be utilized as environment-friendly preconcentrators/microreactors for the remediation of dye wastewater.     

Fracture toughness of exponential layer-by-layer polyurethane/poly(acrylic acid) nanocomposite films

This paper characterizes the fracture toughness of layer-by-layer (LBL) manufactured thin films with elastic polyurethane, a tough polymer, and poly(acrylic acid) as a stiffening agent. A single-edge-notch tension (SENT) specimen is used to study mode I crack propagation as a function of applied loading. Experimental results for the full-field time histories of the strain maps in the fracturing film have been analyzed to obtain R-curve parameters for the nanocomposite. In particular, by using the strain maps, details of the traction law are measured. A validated finite strain phenomenological visco-plastic constitutive model is used to characterize the nanocomposite film while a discrete cohesive zone model (DCZM) is implemented to model the fracture behavior. The LBL manufactured nanocomposite is found to display a higher fracture toughness than the unstiffened base polymer.     

Dynamic scale theory for characterizing surface morphology of layer-by-layer films of poly(o-methoxyaniline)

The dynamic scale theory and fractal concepts are employed in the characterization of surface morphological properties of layer-by-layer (LBL) films from poly(o-methoxyaniline) (POMA) alternated with poly(vinyl sulfonic acid) (PVS). The fractal dimensions are found to depend on the procedures to fabricate the POMA/PVS multilayers, particularly with regard to the drying procedures. LBL films obtained via drying in ambient air show a more homogeneous surface, compared to films dried under vacuum or a flow of nitrogen, due to a uniform rearrangement of polymer molecules during solvent evaporation.     

Thermal stability of poly(o-methoxyaniline) layer-by-layer films investigated by neutron reflectivity and UV-VIS spectroscopy

Neutron reflectivity measurements were used to investigate the thermal stability of layer-by-layer (LBL) films of poly(o-methoxyaniline) (POMA), which was probed by increasing the temperature up to 80 degrees C of a D2O solution in contact with the LBL films. The study was made possible by adsorbing POMA layers on a PEI/(PSS/PAH)5/PSS LBL film template, leading to less rough POMA layers in comparison with the POMA/poly(vinylsulfonic acid sodium salt) (PVS) LBL films adsorbed directly on glass and silicon substrates. While the latter yielded almost fringeless neutron reflectivity curves due to the large roughness, the fitting of the data for POMA films adsorbed onto the template film and UV-vis measurements indicated that the topmost layer is affected for films heated in solution up to 80 degrees C. This is essentially the same thermal stability of LBL films from the template films made with conventional polyelectrolytes. A decrease in thickness of approximately 10 A was inferred when the solution temperature increased from 25 degrees C to 80 degrees C, which was maintained when the sample was cooled back to 25 degrees C. This decrease, observed for solutions of pH 3 and pH 8, is consistent with thermally-stimulated desorption and was corroborated by UV-VIS absorption experiments. The unexpected stability of the POMA layer at pH 8 is attributed to the layer-by-layer structure of the films that allows POMA to remain doped, in its salt emeraldine form, even at high pH.     

Study of polarization and relaxation phenomena of polyblend films of poly(vinyl chloride) and poly(methyl methacrylate)

Thermally stimulated discharge current (TSDC) studies were carried out on pure poly(methyl methacrylate), poly(vinyl chloride) and polyblends (of various weight ratios, 100:0, 90:10, 80:20 and 70:30) as a function of polarizing fields at constant temperature, to study the polarization and relaxation phenomena in them. For PVC and different blends a peak around 140–180 °C and for PMMA two peaks at around 95 and 165 °C were observed. No regular variation in peak position for PMMA and blends was observed. The various TSDC parameters i.e. activation energy, charge released and relaxation times were calculated. In the blend samples it is suggested that the chains are so entangled that in the total polarization the dipolar contribution is less and the observed polarization seems to be mainly due to the formation of induced dipoles and an increase in free volume and mobility of charge carriers due to a plasticization effect.     

Crosslinking poly(allylamine) fibers electrospun from basic and acidic solutions

Mechanically robust, non-toxic polymer fiber mats are promising materials for a range of biomedical applications; however, further research into enhancing polymer selection is needed. In this study, poly(allylamine) (PAH), an amine-containing polyelectrolyte, was successfully electrospun from aqueous solutions into continuous, cylindrical fibers with a mean diameter of 150 ± 41 nm. A one-step crosslinking method using glutaraldehyde provides insight into the chemical and morphological changes that result from altering the molar ratio of amine to aldehyde groups, whereas a two-step crosslinking method yielded chemically and mechanically robust mats. These results indicate PAH fibrous mats synthesized from aqueous solutions could potentially be applied in biomedical applications.     

Preparation of nanoporous polyimide thin films via layer-by-layer self-assembly of cowpea mosaic virus and poly(amic acid)

Low dielectric (low-κ) materials are of key importance for the performance of microchips. In this study, we show that nanosized cowpea mosaic virus (CPMV) particles can be assembled with poly(amic acid) (PAA) in aqueous solutions via the layer-by-layer technique. Then, upon thermal treatment CPMV particles are removed and PAA is converted into polyimide in one step, resulting in a porous low-κ polyimide film. The multilayer self-assembly process was monitored by quartz crystal microbalance and UV-Vis spectroscopy. Imidization and the removal of the CPMV template was confirmed by Fourier transform infrared spectroscopy and atomic force microscopy respectively. The dielectric constant of the nanoporous polyimide film thus prepared was 2.32 compared to 3.40 for the corresponding neat polyimide. This work affords a facile approach to fabrication of low-κ polyimide ultrathin films with tunable thickness and dielectric constant.     

Crack-growth phenomena in fatigued poly(methylmethacrylate)

The conditions under which crack-growth occurs from a natural crack induced in one side of a tensile specimen of poly(methylmethacryiate), when subject to a cyclic tensile load, at 20±3° C and 166 c/min, have been examined. The fracture surface can show three distinct regions, viz. a fissured rough growth area, a smooth growth area in which crack profiles extend across the width of the specimen, and a final area where catastrophic rupture has occurred. Under the conditions used, the fatigue life is mainly determined by the rate of growth of the crack through the rough-growth region. The number of cycles to failure has been determined for various values of the maximum bulk stress applied per cycle and of the initial crack length. The results appear to be consistent with a relationship put forward by Thomas, based on a tearing energy concept, which successfully predicts the dynamic cut-growth behaviour of certain natural and synthetic (SBR) gum rubbers. The conditions for the onset of catastrophic failure appear to be in accord with the Griffith criterion for brittle fracture.     

Photoinduced charge transfer through films containing poly(hexylthiophene), phthalocyanine, and porphyrin-fullerene layers

Efficient photoinduced interlayer electron transfer from a phthalocyanine derivative, ZnPH4, to porphyrin cation of a porphyrin-fullerene donor-acceptor dyad was demonstrated by using time-resolved photovoltage technique. Multicomponent thin films with desired layer arrangements were constructed by the Langmuir-Blodgett and spin-coating methods in order to study charge transfer in solid state. As a contradiction to the photovoltage experiments, the dyad monolayer in the film structure did not enhance the current amplitude in electrochemical photocurrent measurements. This is associated with a weak electronic interaction between fullerene and aqueous electrolyte, reducing the photocurrent generation. The use of poly(3-hexylthiophene) as a hole conducting layer was shown to improve photocurrent yield of the device by forming efficient heterojunction together with the ZnPH4 layer.     

Myoglobin-loaded layer-by-layer films containing SiO(2) nanoparticles studied using electrochemistry

In the present work, a new kind of protein-loaded layer-by-layer (LbL) film based on nanoparticles was fabricated on electrodes. First, oppositely charged SiO(2) nanoparticles and poly(diallyldimethylammonium) (PDDA) were alternately adsorbed on solid surfaces, forming {PDDA/SiO(2)}(n) LbL films. In the next step, the films were immersed in myoglobin (Mb) solution at pH 5.0 to load Mb, forming {PDDA/SiO(2)}(n)-Mb films. The loading behavior of {PDDA/SiO(2)}(n) films toward Mb was investigated by monitoring the cyclic voltammetric responses of the Mb heme Fe(III)/Fe(II) redox couple, and comparing them with those of {PDDA/PSS}(n) films, where PSS stands for poly(styrenesulfonate). Scanning electron microscopy (SEM) and electroactive probe tests demonstrated that the porosity of {PDDA/SiO(2)}(n) films assembled with 'hard' and rigid SiO(2) nanoparticles was much better than that of {PDDA/PSS}(n) films fabricated with just 'soft' polyelectrolytes, which led to the better electrochemical and electrocatalytic responses for the {PDDA/SiO(2)}(n)-Mb films. A series of comparative experiments showed that the main driving force for Mb to diffuse into the films was most probably electrostatic interaction between positively charged Mb and negatively charged SiO(2) components of the films, while the major force in stabilizing Mb in the {PDDA/SiO(2)}(n)-Mb films in blank buffers was more likely hydrophobic interaction.     

Electrosyntheses of free-standing poly (dibenzofuran) films

High quality free-standing poly (dibenzofuran) (PDBF) films with conductivity of 10⁰ S cm^− 1 were synthesized electrochemically by direct anodic oxidation of dibenzofuran in mixed electrolytes of boron trifluoride diethyl etherate (BFEE) containing 30% trifluoroacetic acid (TFA) (by volume). The structure analysis of PDBF was performed using UV–vis and FTIR spectroscopy. To the best of our knowledge, this is the first report on the electrodeposition of free-standing PDBF films.     

Biocompatibility and biodegradation of poly(hydroxybutyrate)/poly(ethylene glycol) blend films

Using chloroform as co-solvent, a series of poly(3-hydroxybutyrate) (PHB) and polyethylene glycol (PEG) blend materials with different ratio ranging from 80 : 20 (wt %) to 20 : 80 (wt %) were prepared by solution blend. The blood-compatibility was evaluated by means of platelet clotting time test and exploring its morphological changes. The results showed that PEG played an important role in resisting platelet adhesion. With the increased addition of PEG, the clotting times became longer and the number of platelet adhesion decreased apparently. All platelets were in discrete state, no pseudopodium had been found and no collective phenomenon had been happened. The cell-compatibility was evaluated via Chinese Hamster Lung (CHL) fibroblast cultivation in vitro. The cells cultured on the matrix spread and proliferated well. With the increase of PEG content in the blend films, the number of live cells became more and more. These results indicated that PHB exhibited satisfying cell-compatibility and the addition of PEG also could improve the cell-compatibility of PHB. The biodegradation experiment indicated that the degradation of PHB/PEG was accelerated by enzyme in vitro and the blending of PEG was favorable to degradation.     

Local thermal-mechanical analysis of ultrathin interfacially mixed poly(ethylene oxide)/poly(acrylic acid) layer-by-layer electrolyte assemblies

Ion conductivities of layer-by-layer (LBL) assemblies of solid thin film polyelectrolyte systems involving poly(ethylene oxide) (PEO) and poly(acrylic acid) (PAA) were found to be a strong function of the number of bilayer stacks, n, with conductivities approaching 10^− 7 S/cm for n < 10, compared to 10^− 9 S/cm for n ≥ 10 and 10^− 10 S/cm for bulk PEO. Increased ion conductivity for low LBL stack numbers (n < 10) originated to part from an effective suppression of the PEO crystallization via PEO/PAA blending, which could be inferred from local glass transition temperature measurements involving shear modulation force microscopy. Another phenomenon responsible for high conductivity in thin films was found in the in-plane phase heterogeneity of PEO and PAA. Increased ion conductivity for larger LBL stacks (n ≥ 10) were attributed to low concentration autoblending caused by PEO-PAA hydrogen bonding, and an average layer thickness of noticeably less than 100 nm. The effect of interfacial constraints was evident in the degree of intermixing, addressed by a thin film extended Fox blend analysis, in the glass and melting transitions of PEO and PAA pure film components. While the glass transition value of PAA decreased by 55% to 46 °C for an 8 nm film, the melting transition for PEO decreased by 15% to 64 °C caused by surface tension effects.     

Fabrication of a stable superhydrophobic film constructed by poly(vinylpyrrolidone)/poly(urushiol)-CuS through layer-by-layer assembly

This article describes a simple stepwise layer-by-layer assembly method to fabricate a stable superhydrophobic film based on urushiol. First, by means of the chelation between Cu(II) and the phenolic hydroxyl group in urushiol (U), urushiol–Cu nanoparticles (U–Cu) were obtained. Then, by the method of layer-by-layer assembly, a hydrophobic film with microstructure was prepared via hydrogen-bonding and coordination between U–Cu and PVP. After introducing S²⁻ into the film, a novel micro- and nanoscale hierarchical superhydrophobic film with a water contact angle of 152° was finally obtained. Due to the unique performances of urushiol, it is believed that the as-prepared surface can be used in the fabrication of chemical engineering materials at broad range.     

Immobilization of ibuprofen-containing nanospheres in layer-by-layer films

Liposomes have been applied to many fields as nanocarriers, especially in drug delivery as active molecules may be entrapped either in their aqueous interior or onto the hydrophobic surface. In this paper we describe the fabrication of layer-by-layer (LbL) films made with liposomes incorporating the anti-inflammatory ibuprofen. The liposomes were made with dipalmitoyl phosphatidyl choline (DPPC), dipalmitoyl phosphatidyl glycerol (DPPG) and palmitoyl oleoyl phosphatidyl glycerol (POPG). LbL films were assembled via alternate adsorption of the polyamidoamine dendrimer (PAMAM), generation 4, and liposomes containing ibuprofen. According to dynamic light scattering measurements, the incorporation of ibuprofen caused DPPC and DPPG liposomes to become more stable, with a decrease in diameter from 140 to 74 nm and 132 to 63 nm, respectively. In contrast, liposomes from POPG became less stable, with an increase in size from 110 to 160 nm after ibuprofen incorporation. These results were confirmed by atomic force microscopy images of LbL films, which showed a large tendency to rupture for POPG liposomes. Film growth was monitored using nanogravimetry and UV-Vis spectroscopy, indicating that growth stops after 10 bilayers. The release of ibuprofen obtained with fluorescence measurements was slower for the liposomes, with decay times of 9.2 and 8.5 h for DPPG and POPG liposomes, respectively, than for the free drug with a decay time of 5.2 h. Ibuprofen could also be released from the LbL films made with DPPG and POPG liposomes, which is promising for further uses in patches.     

Preparation and characterization of poly(amide-imide) multilayer films

Multilayer films of poly(amide-imide)s were prepared as follows: (1) monolayers of long alkyl amine salts of poly(amide-amic acid) were prepared at the air- water interface; (2) these monolayers were deposited on an appropriate plate by the Langmuir-Blodgett method; (3) the multilayers of poly(amide-amic acid) salts on the solid support were treated with acetic anhydride to afford poly(amide-imide) multilayer films. The monolayer thickness of the poly(amide-imide) multilayer films were 0.43–0.55 nm.     

Supramolecular architectures in layer-by-layer films of single-walled carbon nanotubes,chitosan and cobalt (II) phthalocyanine

The building of supramolecular structures in nanostructured films has been exploited for a number of applications, with the film properties being controlled at the molecular level. In this study, we report on the layer-by-layer (LbL) films combining cobalt (II) tetrasulfonated phthalocyanine (CoTsPc), chitosan (Chit) and single-walled carbon nanotubes (SWCNTs) in two architectures, {Chit/CoTsPc}_n and {Chit-SWCNTs/CoTsPc}_n (n = 1–10). The physicochemical properties of the films were evaluated and the multilayer formation was monitored with microgravimetry measurements using a quartz microbalance crystal and an electrochemical technique. According to atomic force microscopy (AFM) results, the incorporation of SWCNTs caused the films to be thicker, with a thickness ca. 3 fold that of a 2-bilayer LbL film with no SWCNTs. Cyclic voltammetry revealed a quasi-reversible, one electron process with E_1/2 at −0.65 V (vs SCE) and an irreversible oxidation process at 0.80 V in a physiological medium for both systems, which can be attributed to [CoTsPc(I)]⁵⁻/[CoTsPc(II)]⁴⁻ and CoTsPc(II) to CoTsPc(III), respectively. The {Chit-SWCNTs/CoTsPc}₅ multilayer film exhibited an increased faradaic current, probably associated with the supramolecular charge transfer interaction between cobalt phthalocyanine and SWCNTs. The results demonstrate that an intimate contact at the supramolecular level between functional SWCNTs immobilized into biocompatible chitosan polymer and CoTsPc improves the electron flow from CoTsPc redox sites to the electrode surface.     

The electrical conductivity of poly(divinylbenzene) films

Conductivity measurements reported previously for thin films of poly(divinylbenzene) have been interpreted in terms of a quantum mechanical tunneling conductivity mechanism. Quantum mechanical tunneling of carriers through thin spots (5–45 Å) in films having dielectric thickness of a few hundred Å is more consistent with the reported current-voltage-temperature characteristics than the previously suggested Richardson-Schottky mechanism.