LbL Films Research Articles

Correction to “Effect of Linear Elongation on Carbon Nanotube and Polyelectrolyte Structures in PDMS-Supported Nanocomposite LbL Films”

Correction to “Effect of Linear Elongation on Carbon Nanotube and Polyelectrolyte Structures in PDMS-Supported Nanocomposite LbL Films”

Formation and Properties of Protamine/Pectin LbL-Coatings

The adsorption regularities of protamine sulfate and pectin on the surfaces from solution with different ionic strength were investigated in situ using quartz substrate via the quartz crystal microbalance technique. Both polymers were observed to absorb according to Langmuir's adsorption isotherm. The value of Langmuir adsorption constant (k) is equal to 74,48 and 1,12 sm3/μg for pectin and protamine respectively. Maximum amount of biopolymer (A∞) adsorbed on resonator is 0,87 μg/sm2 for Pect and 0,57 μg/sm2 for PtS. Ultrathin (<100 nm) multilayer (protamine/pectin)8 LbL films were formed and adsorption kinetics of both polyions were studied. The rate constant of protamine and pectin adsorption are (3,9 ± 0,9)·10-2 s-1 and (3,4 ± 0,3)·10-2 s-1 respectively. It was shown, that film thickness increases by 2.5 times with polymers concentration in solution increasing from 0.1 to 3.0 mg/ml.

Improved antifouling properties of polymer membranes using a 'layer-by-layer' mediated method.

Polymeric reverse osmosis membranes were modified with antifouling polymer brushes through a 'layer by layer' (LBL) mediated method. Based on pure physical electrostatic interaction, the attachment of LBL films did not alter separation performance of the membranes. In addition, the incorporation of an LBL film also helped to amplify the number of potential reaction sites on the membrane surfaces for attachment of antifouling polymer brushes, which were then attached to the surface. Attachment of the brushes included two different approaches, grafting to and grafting from. Attenuated total reflectance-Fourier transform infrared spectroscopy (ATR-FTIR), X-ray photoelectron spectroscopy (XPS) and water contact angle measurements showed successful growth of the LBL films and subsequently the polymer brushes. Using this method to modify reverse osmosis membranes, preliminary performance testing showed the antifouling properties of the as-modified membranes were much better than the virgin membrane with no significant loss in water flux and salt rejection.

Hybrid layer-by-layer films based on lanthanide-bridged silicotungstates and poly(ethylenimine)

Hybrid multilayer films composed of poly(ethylenimine) and sandwich-type silicotungstates, K13[Ln(SiW11O39)2] (Ln(SiW11)2), Ln3+=Eu, Tb, Dy, were prepared on glassy carbon electrodes, quartz and glass slides using the electrostatic LbL self-assembly method. The film build up, monitored by electronic spectroscopy, showed a regular stepwise growth indicating a strong interaction between layers. The X-ray photoelectron spectroscopy measurements corroborated the successful fabrication of the hybrid films with the PEI–POMs composition and pointed out that the intrinsic charge compensation from the film components is the major contribution, although there is some extrinsic charge compensation from the counter cations from the POMs and electrolyte. All the LbL films showed W-based reduction processes due to the immobilized POMs; voltammetric responses revealed a kinetic facilitation of the first reduction process in the immobilized Tb(SiW11)2 and Dy(SiW11)2 polyanions relatively to the free POMs and scan rate effect showed that the tungsten reduction process for all POMs is surface-confined. The photoluminescence properties of PEI/Eu(SiW11)2 multilayer films were investigated and showed the characteristic Eu3+ emission pattern.

Effect of Linear Elongation on Carbon Nanotube and Polyelectrolyte Structures in PDMS-Supported Nanocomposite LbL Films

Polyelectrolyte (PE) multilayer (PEM) thin films prepared by layer-by-layer self-assembly on flexible substrates are exposed to elongation in many fields of technology. Upon elongation, these types of films are showing interesting, but not understood, phenomena, such as controlled wetting, stimuli-responsive nanovalves, and lithography-free surface structuring. To investigate the mechanisms causing these interesting phenomena, we employed spectroscopic investigations of supported PEM films that were prepared from polystyrene sulfonate (PSS)-wrapped single-walled carbon nanotubes (SWNTs) or pyrene-labeled PSS (PSS-PY) and polydiallyldiammonium chloride. Our results show that the SWNTs agglomerated upon deposition into the PEM and showed a strong change in orientation upon uniaxial elongation of the PEM. Upon release of elongation, the resulting wrinkling pattern was changing its wavelength upon time, in the case of the SWNT-containing PEM. Fluorescence measurements of the PSS-PY in the PEM showed that the PEs changed their orientation due to constant mechanical force from elongation up to a time scale of 2 days after beginning the elongation. The results prove that elongated and released PEM films, until now considered static structures, possess strong kinetics, which has to be taken into account for their application.

LbL Film with PtNPs as a Sensor of the Dopamine Encapsulated in Liposomes

not Available.

New 2-in-1 Polyelectrolyte Step-by-Step Film Buildup without Solution Alternation: From PEDOT-PSS to Polyelectrolyte Complexes

Although never emphasized and increasingly used in organic electronics, PEDOT-PSS (poly(3,4-ethylenedioxythiophene)-poly(styrene sulfonate)) layer-by-layer (lbl) film construction violates the alternation of polyanion and polycation rule stated as a prerequisit for a step-by-step film buildup. To demonstrate that this alternation is not always necessary, we studied the step-by-step construction of films using a single solution containing polycation/polyanion complexes. We investigated four different systems: PEDOT-PSS, bPEI-PSS (branched poly(ethylene imine)-poly(sodium 4-styrene sulfonate)), PDADMA-PSS (poly(diallyl dimethyl ammonium)-PSS), and PAH-PSS (poly(allylamine hydrochloride)-PSS). The film buildup obtained by spin-coating or dipping-and-drying process was monitored by ellipsometry, UV-vis-NIR spectrophotometry, and quartz-crystal microbalance. The surface morphology of the films was characterized by atomic force microscopy in tapping mode. After an initial transient regime, the different films have a linear buildup with the number of deposition steps. It appears that, when the particles composed of polyanion-polycation complex and complex aggregates in solution are more or less liquid (case of PEDOT-PSS and bPEI-PSS), our method leads to smooth films (roughness on the order of 1-2 nm). On the other hand, when these complexes are more or less solid particles (case of PDADMA-PSS and PAH-PSS), the resulting films are much rougher (typically 10 nm). Polycation/polyanion molar ratios in monomer unit of the liquid, rinsing, and drying steps are key parameters governing the film buildup process with an optimal polycation/polyanion molar ratio leading to the fastest film growth. This new and general lbl method, designated as 2-in-1 method, allows obtaining regular and controlled film buildup with a single liquid containing polyelectrolyte complexes and opens a new route for surface functionalization with polyelectrolytes.

Comparison of Oxygen Reduction Reaction at Silver Nanoparticles and Polycrystalline Silver Electrodes in Alkaline Solution

Adenosine 5′-triphosphate capped silver nanoparticles (ATP-Ag NPs) with diameters of 4.5 ± 1.1 nm were synthesized using a one-pot chemical reduction route. After removal of the ATP capping ligands, the electrochemical activity of these NPs for the oxygen reduction reaction (ORR) in aqueous alkaline solution (0.1 M NaOH) was studied in a single layer-by-layer (1 L LbL) film of NPs and compared with bulk polycrystalline Ag using cyclic voltammetry (CV) and rotating disk electrode (RDE) experiments. For the NPs in the 1 L LbL film, the active area of catalyst available for the ORR was calculated using the charge for the underpotential deposition (UPD) of lead (Pb) on the NPs. RDE data were analyzed to determine the ORR rate constant and the number of electrons (n-value) involved in oxygen reduction. Analysis of Koutecky–Levich (K–L) plots indicates an n-value between 3 and 4 with a higher n-value under some conditions for the NPs than for bare polycrystalline Ag. Possible origins of the variation of n-value...

Dynamics of moisture interaction with polyelectrolyte multilayers containing nanofibrillated cellulose

Abstract Recent findings have shown that it is possible to use the Layer-by-Layer technique to create nanofibrillated cellulose / polyethyleneimine interference films whose colour change with relative humidity. This study uses different optical models to describe spectral ellipsometry measurements data of interference films and how the film properties alter in dry and humid environments. The results indicate that water condensation initially is filling the surface pores within seconds whereas relaxation of the film to adjust to the added water is a slower process that reaches a steady state after »20 min. The maximum swelling ratio of the LbL films is almost independent of the number of layers within the film, but decreases considerably by crosslinking via heat treatment. The films show a distinct birefringence with optical axis perpendicular to the surface. Analysis of the moisture response with different optical models indicates that the films swell uniformly in the thickness direction with no separate water film on top. The results provide important understanding for the design of NFC based LbL films for visual moisture sensors and interactive security paper.

Spectroscopic, morphological and electrochromic characterization of layer-by-layer hybrid films of polyaniline and hexaniobate nanoscrolls

The combination of semiconducting oxides and polyaniline in the nanoscale range may result in hybrid materials having enhanced properties, such as electrochromism and charge capacity. This paper reports the spectroscopic, morphological and electrochromic characterization of hybrid films made up of hexaniobate one-dimensional (1D) nanoscrolls and polyaniline prepared by the layer-by-layer assembly technique (LbL). Secondary electron imaging and backscattered electron imaging techniques performed using a scanning electron microscope showed that polyaniline is adsorbed on the hexaniobate nanoscrolls, which confirms the combination of the components in the nanoscale domain. UV-VIS-NIR electronic spectra of the LbL hybrid films showed the absorption tail in the NIR region, assigned to delocalized polarons of the polyaniline. Resonance Raman spectra in the 1000–1700 cm−1 range indicated that hybrid films present a higher relative intensity of polaron bands at 1337 and 1508 cm−1 than pristine polyaniline in the emeraldine salt form. These results suggest that hexaniobate nanoscrolls induce a secondary doping of polyaniline. The cyclic voltammetry (CV) data for the hybrid film showed a specific capacity of 870 C cm−3. According to CV results, the synergistic effect on charge storage properties of the hybrid material is attributed to the enhanced electroactivity of the hexaniobate component in the LbL film. Spectroelectrochemical experiments showed that the electrochromic efficiencies at 420 nm are ca. −41 and 24 cm2 C−1 as the potential changes from 0.8 to −0.9 V and from −0.9 to −1.8 V, respectively, whereas at 800 nm the efficiencies are ca. −55 and 8 cm2 C−1 for the same potential ranges. The electrochromic efficiencies and multi-colour character of the LbL film of hexaniobate nanoscrolls and polyaniline indicate that this novel hybrid material is an interesting modified electrode for electrochromic devices.

Development of a novel biosensor using cationic antimicrobial Peptide and nickel phthalocyanine ultrathin films for electrochemical detection of dopamine.

The antimicrobial peptide dermaseptin 01 (DS 01), from the skin secretion of Phyllomedusa hypochondrialis frogs, was immobilized in nanostructured layered films in conjunction with nickel tetrasulfonated phthalocyanines (NiTsPc), widely used in electronic devices, using layer-by-layer technique. The films were used as a biosensor to detect the presence of dopamine (DA), a neurotransmitter associated with diseases such as Alzheimer's and Parkinson's, with detection limits in the order of 10−6 mol L−1. The use of DS 01 in LbL film generated selectivity in the detection of DA despite the presence of ascorbic acid found in biological fluids. This work is the first to report that the antimicrobial peptide and NiTsPc LbL film exhibits electroanalytical activity to DA oxidation. The selectivity in the detection of DA is a fundamental aspect for the development of electrochemical sensors with potential applications in the biomedical and pharmaceutical industries.

Dynamically bonded layer-by-layer films for self-regulated insulin release

Layer-by-layer assembled films using reversible/dynamic bonds between the polymer pairs as driving forces are dynamic in nature. They may disintegrate under certain conditions as a result of the breakage of the dynamic bonds. More importantly they disintegrate gradually under conditions of equilibrium control, making them suitable for sustained drug release. Here insulin release from dynamic LbL films was demonstrated as an example. The films were fabricated from a fluorescently-labeled insulin–PVA (PVA: polyvinyl alcohol) conjugate and poly[acrylamide-co-3-(acrylamido)-phenylboronic acid], using a reversible covalent bond, i.e., phenylboronate ester bond, as the driving force. Film fabrication was followed by UV-vis and fluorescence spectroscopy. In all cases linear film growth was observed. The film growth rate increases with decreasing pH and increasing ionic strength of the assembly solutions. Successful integration of insulin into the films was achieved by covalent conjugation of insulin with PVA. When immersed in an aqueous solution, the films disintegrate gradually, thus releasing insulin into the media. Insulin release rate increases with increasing pH and decreasing ionic strength of the media. More importantly, it increases with increasing glucose concentration in the media. The glucose response of the film was attributed to the conversion of PBA (PBA: phenylboronic acid) groups in the film from a neutral form to a negatively charged one as a result of the formation of glucose–PBA complexes, thus increasing the rate of the film disintegration.

LAYER-BY-LAYER SELF-ASSEMBLED FILMS OF ROSE BENGAL

Layer-by-Layer (LBL) self-assembled films of rose bengal (RB) have been fabricated onto quartz substrate by the alternative adsorption of polycation poly (amine hydrochloride) (PAH) and RB. UV–Vis absorption studies reveal the formation of RB dimmer in PAH-RB LbL films. Scanning Electron Micrograph (SEM) picture confirms the aggregation of RB molecules in LbL films. Almost 15 min is required to complete the interaction between RB and PAH molecules in the 1 bilayer LbL film. The dye (RB) was found to come off the film during the subsequent poly cation (PAH) deposition. As an alternative approach RB was anchored to the polycation PAH via physiadsorption and controlling the concentration of the combination of RB and PAH was used as polycation and poly (acrylic acid) (PAA) as polyanion for film deposition. The absorption spectra after each deposition showed that there was no material loss during layer depositions via second method.

Layer-by-layer assembly of titanate nanosheets/poly- (ethylenimine) on PEN films

Alternating layers of TiO 2 nanosheets and poly(ethylenimine) were sequentially dip coated onto a polyethylene naphthalate substrate (PEN) using layer-by-layer assembly. UV–vis spectroscopy shows a linear growth of the PEI/nanosheets bilayer on the PEN substrate. The cross-section microstructure of the LBL film was studied using scanning electron microscopy (SEM). Helium permeability measurement showed that the titania nanosheet/PEI bilayers reduced the permeation rate of He through the coated PEN film.

Electroanalytical Performance of (SiPy+Cl−/CuTsPc)5 LbL Film for Detecting Promethazine Hydrochloride

AbstractA (SiPy+Cl−/CuTsPc)5 layer‐by‐layer film was employed for the electroanalytical determination of promethazine hydrochloride in BR buffer pH 5.0 with peaks at 0.48 and 0.79 V. After optimisation of the square‐wave parameters (f=100 s−1, a=40 mV and ΔEs=2 mV), the peak at 0.79 V was used for quantification and a detection limit of 8.71×10−9 mol L−1 and a quantification limit of 9.31×10−8 were calculated. The applicability of this procedure was tested on commercial formulations of promethazine hydrochloride by observing the stability, specificity, recovery and precision of the procedure in complex samples, without any preliminary treatment.

Collagen containing microcapsules: Smart containers for disease controlled therapy

The protein collagen is the major component of connective tissue and it is involved in many biological functions. Its degradation is at the basis of different pathological processes. The up-regulated expression of matrix metalloproteinases and the down-regulated expression of their inhibitors are the causes for such degradation. The aim of this work was to evaluate the possibility to fabricate collagen based containers for drug encapsulation and release by cellular demand by the action of matrix metalloproteinases. In present work collagen type I based microcapsules were fabricated by means of the layer-by-layer assembly of oppositely charged collagen and poly (stirene sulfonate) onto colloidal particles, followed by removal of the cores to obtain hollow microcapsules. The process of shell growth on planar supports was monitored by quartz crystal microbalance. X-ray reflectivity measurements were carried out at the solid/water interface to study the interaction of matrix metalloproteinase 1 with LbL films of collagen. The morphology of hollow capsules was characterized by scanning electron microscopy, and compared to that of capsules exposed to the matrix metalloproteinase 1. Finally the matrix metalloproteinase 1 mediated permeability of capsules variation was studied by Confocal Laser Scanning Microscopy. The results demonstrated the possibility to fabricate a drug delivery system where the release of the drug is dependent on the biochemistry of the pathological state.

Improved adsorption of choline oxidase on a polyelectrolyte LBL film in the presence of iodide anions

This study describes the effects of F−, Cl−, Br−, and I− anions on the sensitivity of a biosensor assembled via layer-by-layer deposition of poly(diallyldimethylammonium chloride) (PDDA) and choline oxidase (ChO) on the surface of a graphite electrode coated with MnO2. A four-fold increase in sensitivity of the MnO2/PDDAKHal/ChO biosensor was observed when the adsorption of the PDDA layer was carried out from the solution containing I− in a narrow range of concentrations (20–30 mM). According to AFM and SEM data, spatial distribution of the enzyme and gold nanoparticles (AuNPs) on the surface varied with the conditions of PDDA adsorption. A fine-grain film was observed when PDDA was adsorbed from the solution containing Cl−, whereas association of ChO or AuNPs into larger domains took place in the case of I− solution. Absorption spectra of AuNPs adsorbed on a PDDAKI film evidenced aggregate formation as well. A schematic representation of the enzyme layer assembly was proposed for different ionic conditions of the polyelectrolyte pre-adsorption.

Layer-by-layer assembly of a new l-glutamic acid based polymer with PAH: formation of hollow sphere during deposition, dye loading and chiroptical switch

A new polymer with acryl backbone and L-glutamic acid (PAGlu) as the side chain was synthesized and their assembly with cationic poly(allylamine hydrochloride) (PAH) through a layer-by-layer technique was investigated. Although PAGlu dissolved in water showed no particular organized structures, it formed hollow spheres when assembling with PAH. Both SEM and TEM observation for the deposited films confirmed the hollow structure. Furthermore, observation by SEM for each deposition revealed that the hollow structure was formed during the layer-by-layer assembly process. Differently from that of the hollow capsules formed from template nanoparticles, this method provided directly the hollow structure without any template. Moreover, the water-insoluble LbL film with the hollow structure showed a rapid loading and release of dye molecules such as TMPyP (5,10,15,20-tetrakis(4-N-methylpyridyl)porphinetetra(p-toluenesulfonate)). Due to the chiral nature of the PAGlu, the loaded dye molecule showed induced chirality owing to the interaction with the L-glutamic acid moiety. In addition, this dye-loaded film can show a reversible color and chirality change upon alternative exposure to HCl and NH3 gases, realizing a gas sensing chiroptical switch.

Facile and Efficient Approach to Speed up Layer-by-Layer Assembly: Dipping in Agitated Solutions

A facile and efficient approach has been developed to speed up the fabrication of LBL films through sequential dipping in vigorously agitated solutions. By this agitated-dipping (AD) LBL technique, the multilayer films of PAH and PSS were fabricated. The resulting films were explored by UV-vis spectroscopy, X-ray reflectivity, and AFM. Meanwhile, the comparison of the AD and conventional LBL films was made, which demonstrated that AD LBL can decrease dipping time by more than 15 times without reducing film quality remarkably. In addition, to verify the generality of AD LBL, we studied the AD LBL films of PDDA/PSS and PAH/PAA preliminarily as well. AD LBL promotes the efficiency of conventional LBL greatly while preserving its most advantages, such as simplicity, cheapness, precise control, universality in substrates, recycling use of sample solutions, and so on. It would be a promising alternative to build up LBL films rapidly.

Polymeric scaffolds for enhanced stability of melanin incorporated in liposomes

The use of melanin in bioinspired applications is mostly limited by its poor stability in solid films. This problem has been addressed here by incorporating melanin into dipalmitoyl phosphatidyl glycerol (DPPG) liposomes, which were then immobilized onto a solid substrate as an LbL film. Results from steady-state and time-resolved fluorescence indicated an increased stability for melanin incorporated into DPPG liposomes. If not protected by liposomes, melanin looses completely its fluorescence properties in LbL films. The thickness of the liposome-melanin layer obtained from neutron reflectivity data was 4.1 ± 0.2 nm, consistent with the value estimated for the phospholipid bilayer of the liposomes, an evidence of the collapse of most liposomes. On the other hand, the final roughness indicated that some of the liposomes had their structure preserved. In summary, liposomes were proven excellent for encapsulation, thus providing a suitable environment, closer to the physiological conditions without using organic solvents or high pHs.