Layer-by-layer Films Research Articles

The effect of surfactants in the silsesquioxane solution for LbL films assembly

The interaction of surfactants and hydrophobic polymers in solution has attracted substantial interest due to the broad application in industry. In this study, the interactions of the nonionic surfactant polyethylene glycol-p-(1,1,3,3 tetramethylbutyl)-phenyl ether (Triton X) and anionic surfactant sodium dodecyl sulfate (SDS) with a cationic polymer 3-chloride-n-propylpyridinium silsesquioxane (SiPy+Cl−) and their effects on the layer-by-layer (LbL) film assembly with nickel tetrasulfonated phthalocyanine (NiTsPc) have been analyzed by surface tension, viscosity, and Brewster angle microscopy. As Triton X and SDS surfactants are inserted in the solution containing the polycation SiPy+Cl−, they are immediately incorporated in the hydrophobic nanodomains present in the silsesquioxane skeleton. The association between polyelectrolytes and oppositely charged surfactants starts at very low surfactant concentrations far below the critical micelle concentration, named critical aggregation concentration (cac), which was determined for both surfactants in the presence of SiPy+Cl− (cac Triton X = 2.4 × 10−6 and SDS = 8.2 × 10−7 mol L−1). The coexistence of mixed and pure micelles containing only Triton X and SDS also occurs in higher surfactant concentrations. The implication of these aggregates adsorption on the surface was analyzed in thin films by using the LbL technique. Multilayered films were obtained in presence of surfactants, (T-SiPy/NiTsPc) n or (S-SiPy/NiTsPc) n to compare with LbL films in absence of surfactant (SiPy/NiTsPc) n , and these films were characterized by UV–Vis, FTIR, and Raman spectroscopies to analyze the molecular interactions and to investigate the presence of specific interactions between the polyelectrolytes. The formation of LbL film in the architectures (T-SiPy/NiTsPc) n or (S-SiPy/NiTsPc) n is more efficient in relation to (SiPy/NiTsPc) n LbL films since the presence of the surfactants causes a greater amount of material to be deposited on each bilayer formed. The results of UV–Vis indicate that the film in the presence of SDS has a higher amount of material added to each bilayer. The electrochemical studies of (S-SiPy/NiTsPc)3 film show that the charge transfer resistance is lower than the one observed for the other architectures. Thus, the characteristic hopping electron effect of LbL film may be responsible for lower capacitance and lower resistance of the films. When the surfactant SDS is present, a higher oxidation peak current of dopamine is seen.

Concentration-dependent dye aggregation in the LbL-assembly of fluorescein isothicyanate labeled poly(allylamine hydrochloride) and poly(acrylic acid) on cotton fabrics

In this work, we prepared layer-by-layer (LbL) assembled films of fluorescein isothicyanate labeled poly(allylamine hydrochloride) (PAH-FITC) and poly(acrylic acid) (PAA) on cotton fabrics, and researched the influence of the PAH-FITC concentration on the FTIC aggregation. With the LbL assembly, the ratio of FITC dimers to monomers in films approached a constant that was decided by the deposition situation of PAH-FITC on cotton. The concentration increase of the PAH-FITC solution induced more FTIC dyes to deposit on fabrics, thus generating a higher degree of H-aggregation. Interestingly, as the PAH-FITC concentration decreased, a high content of FITC dimers was obtained in LbL-assembled films as well. The possible reason is the excessive PAA in LbL films made the counter PAH-FITC chains coil overlap, increasing the aggregation degree. Additionally, the H-aggregates with weak fluorescence were effectively inhibited in PAH-FITC films, which were prepared by a multi-immersion in the PAH-FITC solution. This work shows the concentration-dependent dye aggregation in LbL-assembly, providing a new strategy for the applications of dye molecules on fabrics.

Organic-inorganic hybrid layer-by-layer electrostatic self-assembled film of cationic dye Methylene Blue and a clay mineral: Spectroscopic and Atomic Force microscopic investigations

The metachromic cationic dye Methylene Blue (MB) belongs to the thiazine class of organic dye. This dye cation can interact electrostatically with inorganic clay mineral Montmorillonite (MMT) to form organic-inorganic hybrid layer-by-layer (LbL) self-assembled film onto a poly(allylamine hydrochloride) coated quartz substrate. The degree of dye aggregations in LbL films was found to depend on concentrations of both MMT clay and MB in LbL self-assembled films as evidenced by UV–vis absorption spectroscopic technique. The adsorption of dye molecules to the LbL films was found to a two-step exponential process: first step was very fast and the later process had a much delay period. Also the assembling behavior and organizations of MB molecules in the host clay matrix in LbL films significantly depend on pH of dye solution from which LbL film was fabricated. For MMT/MB mixed solution the π-π* transition of absorption bands of MB shifted to lower wavelength due to the formation of large number of H-aggregates in their mixed aqueous solution. Fourier Transform infrared (in ATR mode) spectroscopic method was employed to explore the electrostatic interaction between clay MMT and MB in LbL films. Atomic Force microscopic image of hybrid LbL films revealed the surface morphology and roughness profile of the organic-inorganic hybrid molecular assemblies onto the solid substrate.

Linear and Star Poly(ionic liquid) Assemblies: Surface Monolayers and Multilayers.

The surface morphology and organization of poly(ionic liquid)s (PILs), poly[1-(4-vinylbenzyl)-3-butylimidazolium bis(trifluoromethylsulfonyl)imide] are explored in conjunction with their molecular architecture, adsorption conditions, and postassembly treatments. The formation of stable PIL Langmuir and Langmuir-Blodgett (LB) monolayers at the air-water and air-solid interfaces is demonstrated. The hydrophobic bis(trifluoromethylsulfonyl)imide (Tf2N-) is shown to be a critical agent governing the assembly morphology, as observed in the reversible condensation of LB monolayers into dense nanodroplets. The PIL is then incorporated as an unconventional polyelectrolyte component in the layer-by-layer (LbL) films of hydrophobic character. We demonstrate that the interplay of capillary forces, macromolecular mobility, and structural relaxation of the polymer chains influence the dewetting mechanisms in the PIL multilayers, thereby enabling access to a diverse set of highly textured, porous, and interconnected network morphologies for PIL LbL films that would otherwise be absent in conventional LbL films. Their compartmentalized internal structure is relevant to molecular separation membranes, ultrathin hydrophobic coatings, targeted cargo delivery, and highly conductive films.

Layer-by-Layer Self-Assembly of Pd Films and Their Catalytic Properties toward Nitroarenes Hydrogenation

Metal–organic films onto the solid surface have been successfully assembled through Layer-by-Layer (LbL) deposition methods. The organic ligand isonicotinic acid (3-pyridylmethylene) hydrazide containing pyridine groups was chosen to act as a useful building unit, and K2PdCl4 was used as the precursor for the films preparation. UV–vis spectra, transmission electron microscopy (TEM), atomic force microscopy (AFM), and inductively coupled plasma optical emission spectrometry (ICP-OES) were applied to understand the growth process of the resulting LbL multilayers. The LbL films with 10 layers (denoted as (Pd-ligand)10) were further applied as catalysts for the hydrogenation of nitroarenes. It is worth mentioning that our films catalyst is convenient to recycle and possesses good reusability.

Gas‐sensor fabrication by a layer‐by‐layer technique using polydiacetylene

ABSTRACTIn order to increase the sensitivity of a polydiacetylene (PDA) sensor, PDA, and poly(sodium 4‐styrene‐sulfonate) (PSS) were alternately stacked to form a layer‐by‐layer (LBL) film on the quartz. In this study, N‐(2‐aminoethyl)pentacosa‐10,12‐diynamide (AEPCDA) was used as a constituent of the PDA and n‐butylamine was used as a target compound. The formed‐film sensor showed higher sensitivity than the vesicle solution. There was a large difference in sensitivity depending on the method used to form the LBL film. Unlike the vesicle solution state, the formed‐film sensor exhibited excellent reversibility in the color change caused by heat. The LBL film formed worked very well as a sensor that detects the actual gas, n‐butyl amine, showing its potential for practical applications. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017, 134, 44997.

Inkjet-based multilayered growth factor-releasing nanofilms for enhancing proliferation of mesenchymal stem cells in vitro

We report the preparation and characterization of inkjet-based basic fibroblast growth factor (bFGF)-containing nanofilms on a flexible PET substrate. bFGF and heparin (HEP) were assembled by inkjet-based layer-by-layer (LbL) assembly driven by electrostatic interactions. The bFGF/HEP nano-assembly surface coatings were formed via alternating printing adsorption of positively charged bFGF and negatively charged HEP; the process was monitored by UV–vis spectroscopy and quartz crystal microbalance. The bFGF release profile could be controlled by altering the number of layers of printed LbL films. Mesenchymal stem cells, which are capable of extended proliferation in vitro, require a continuous supply of bFGF for proliferation. However, enhancing mesenchymal stem cell proliferation by continuous supplying bFGF is difficult, even with medium replacement, because of the instability of bFGF. Here, we established a novel system for releasing bioactive bFGF from a modified surface by using an inkjet-based nanofilm fabrication method.

Cell Guidance on Nanostructured Metal Based Surfaces.

Metal surface nanostructuring to guide cell behavior is an attractive strategy to improve parts of medical implants, lab-on-a-chip, soft robotics, self-assembled microdevices, and bionic devices. Here, we discus important parameters, relevant trends, and specific examples of metal surface nanostructuring to guide cell behavior on metal-based hybrid surfaces. Surface nanostructuring allows precise control of cell morphology, adhesion, internal organization, and function. Pre-organized metal nanostructuring and dynamic stimuli-responsive surfaces are used to study various cell behaviors. For cells dynamics control, the oscillating stimuli-responsive layer-by-layer (LbL) polyelectrolyte assemblies are discussed to control drug delivery, coating thickness, and stiffness. LbL films can be switched "on demand" to change their thickness, stiffness, and permeability in the dynamic real-time processes. Potential applications of metal-based hybrids in biotechnology and selected examples are discussed.

Layer-by-layer assembled polyelectrolyte-decorated graphene multilayer film for hydrogen gas barrier application

Abstract A facile approach for the fabrication of chemically-modified reduced graphene oxide (RGO) based multilayer films was developed for gas barrier applications. Polyethyleneimine (PEI) and poly(sodium 4-styrenesulfonate) (PSS) were utilized as surface modifiers to yield water-dispersible RGO with opposite charges. Altering the deposition pH of PEI-RGO layer resulted in different phase morphology and bonding of the multilayer films. PEI-RGO and PSS-RGO were assembled into multilayer films via a layer-by-layer (LbL) assembly method through electrostatic and hydrogen bonding interactions, respectively. The LBL assembly of polymer-decorated RGO based multilayer films were characterized by various characterization techniques. Hydrogen gas transmission rate (H2GTR) of the hydrogen bonding interaction based LbL film with 24 bilayers was 5.8 cc/m2·d·atm; and H2GTR value was 46.2 cc/m2·d·atm for the corresponding LbL film based on electrostatic interactions. Hydrogen bonding interaction based multilayer films exhibited very low H2GTR values compared to electrostatic interaction based multilayer and bare polyethylene terephthalate films.

Redox Properties of Polyvinylamine-g-TEMPO in Multilayer Films with Sodium Poly(styrenesulfonate).

Layer-by-layer (LbL) assemblies of polyvinylamine with grafted TEMPO moieties (PVAm-T) with sodium polystyrenesulfonate (PSS) were prepared on gold-sulfonate surfaces, and the redox properties were measured by cyclic voltammetry. LbL compositions were probed by quartz crystal microbalance (wet) and ellipsometric (dry) film measurements. Approximately 30% of the TEMPO moieties in the LbL assemblies were redox-active when the total TEMPO coverage was varied up to 6 μmol/m2, by either varying the TEMPO content in PVAm-T or by varying the number of LbL bilayers. Three non-redox-active PVAm/PSS blocking bilayers were required to prevent the electrode from oxidizing PVAm-T in the exterior LbL layer. This suggests significant intermixing between the layers in the LbL film. In addition to contributing to the small but growing body of work on redox polymers based on grafted TEMPO, this work serves as a reference point for understanding the redox properties of colloidal PVAm-T-laccase complexes in future work.

Properties improvement of poly(o-methoxyaniline) based supercapacitors: experimental and theoretical behaviour study of self-doping effect

Conducting polymers (CP) are very versatile materials with important properties due to their unique structure, including redox behaviour upon electrochemical polarization. Supercapacitors are among the devices in which CP show a promising performance due to their large specific capacitance. However, the major drawback of these materials is their low durability, which is an inbuilt process caused by ion intercalation, a side effect of the redox process. A viable strategy to increase CP stability is, therefore, the inhibition of the ion intercalation/de-intercalation process. Several strategies have been proposed to minimize this effect, among them self-doping. Self-doping makes the redox process mass-transport independent, decreasing the response time and increasing durability. With this purpose, this work have described the synthesis of layer-by-layer films (LBL) of poly(o-methoxyaniline)/poly(3-thiopheneacetic acid) (POMA/PTAA) and contributes to understand how the redox process leads to premature aging, and how self-doping minimizes this problem. The main techniques of characterisation used were electrochemical impedance spectroscopy (EIS) experiments and density functional theory (DFT) calculations. EIS provides important information about the electrochemical behaviour, while DFT calculations allowed to characterize, at the molecular level, the changes in the material structure. The association of both techniques helped to understand how self-doping improves the POMA properties. DFT calculations showed that in the layer-by-layer (LBL) films, the twisting of the polymer chain due to the oxidation is 12% less while the chain shortening is 5% compared with films prepared POMA by casting. The EIS data showed the effect of these molecular changes in the structure; the swelling of the LBL films is 50% less than cast ones. These observations are important because the PTAA layer acts beyond a charge-compensator, working as a backbone structure that mechanically stabilize the POMA layer, leading to an increase in the durability, and improving the electrochemical properties.

Graphene-based LbL deposited films: further study of electrical and gas sensing properties

Graphene-surfactant composite materials obtained by the ultrasonic exfoliation of graphite powder in the presence of ionic surfactants (either CTAB or SDS) were utilised to construct thin films using layer-by-layer (LbL) electrostatic deposition technique. A series of graphene-based thin films were made by alternating layers of either graphene-SDS with polycations (PEI or PAH) or graphene-CTAB with polyanions (PSS). Also, graphene-phthalocyanine composite films were produced by alternating layers of graphene-CTAB with tetrasulfonated nickel phthalocyanine. Graphene-surfactant LbL films exhibited good electric conductivity (about 0.1 S/cm) of semiconductor type with a band gap of about 20 meV. Judging from UV-vis spectra measurements, graphene-phthalocyanine LbL films appeared to form joint π-electron system. Gas sensing testing of such composite films combining high conductivity of graphene with the gas sensing abilities of phthalocyanines showed substantial changes (up to 10%) in electrical conductivity upon exposure to electro-active gases such as HCl and NH 3 .

Cyclodextrin-containing layer-by-layer films and microcapsules: Synthesis and applications

This article reviews the synthesis and applications of cyclodextrin (CD)-containing layer-by-layer (LbL) films and microcapsules. CD-containing LbL films and microcapsules have been synthesized through the electrostatic interactions between charged CDs and polyelectrolytes or the formation of host–guest complexes. In the former strategy, sulfonated and carboxylated CDs are often combined with oppositely charged polyelectrolytes. In contrast, in the latter strategy, CD-bearing polymers and guest-modified polymers are used as components of LbL assembly. Typical guest molecules include adamantane, ferrocene, and azobenzene derivatives. Electrochemical biosensors have been constructed by coating the surface of electrodes with CD-containing LbL films. In addition, CD-containing LbL assemblies are used as scaffolds for constructing drug delivery systems, in which hydrophobic, poorly soluble drugs are loaded on the film through host–guest complexation.

DNA multilayer film for loading and release of DNA oligomer

The Layer-by-Layer (LbL) method using polyelectrolytes is a typical strategy for preparing functional polymeric multi-layered films. Besides the electrostatic force between positively and negatively charged polyelectrolytes, the hybridization force between complementary DNA strands can be also used for building the DNA LbL films. Herein, we report the thermal responsible DNA LbL film that is designed to release specific DNA oligomers (10 bases) at an elevated temperature. Because the temperature and the ionic strength (IS) of the medium affect the hydrogen bonds in the double stranded DNA, the structural stability of the film against temperature and IS was investigated. The loading and release of the releasable oligomers were repeatedly performed on the DNA LbL film.

A nanostructured cell-free photosynthetic biocomposite via molecularly controlled layer-by-layer assembly

Thylakoids, on which complete sets of photosynthetic membrane proteins are contained, behave as soft nanoparticles of a few tens nm sizes. Thus, we separated the thylakoid extracts from spinach chloroplasts and densely organized them in a film with either insulating polyethyleneimine (PEI) or conducting polyaniline (PANI) by molecularly controlled layer-by-layer (LBL) assembly. The resulting nanostructured composite films demonstrated photoelectrochemical activities with thylakoids whose stabilities were significantly improved on the charge balanced LBL multilayers compared to one on a randomly deposited film or in solution. The thylakoid LBL films continuously generated photochemical electrons for longer than 130h with the 2,6-dichlorophenolindophenol (DCPIP) mediated photosynthetic energy conversion cycle while photoactivities of thylakoid moiety slowly decreased in the open circuit potential measurements throughout which the photosynthetic redox cycles were incomplete. As the photofunctional groups of the thylakoid films originated from a biotic system and the photofuctional thylakoids were exceptionally well preserved on the charge-balanced artificial structures, the developed thylakoid LBL film have shown inherent biocompatibility upon PC12 neural cell attachment and differentiation tests, which are essential qualities for emerging human-friendly electronic applications such as disposable electronics, artificial retina, and implantable neural interfacing meditronics as well as cell-free photosynthetic production.

Adsorption and interlayer diffusion controlled growth and unique surface patterned growth of polyelectrolyte multilayers

In this work, extremely high molecular weight (Mw) poly(allylamine hydrochloride) (PAH, 900K g/mol) and poly(acrylic acid) (PAA, 225 K g/mol) were selected to amplify the difference in the growth of multilayers in comparison with low Mw PAA (15K g/mol) and PAH (15K g/mol). By varying the pH conditions, the PAH/PAA multilayers were fabricated via the layer-by-layer (LbL) assembly in both linear and exponential growth regimes. In the linear growth regime with interlayer diffusion suppressed, high Mw polyelectrolytes with low charge density could slow down the adsorption step, leading to the decrease of thickness compared to low Mw polyelectrolytes when the deposition time was limited. However, the effect of Mw could be reversed by increasing the deposition time, for the adsorption of low Mw polyelectrolyte reached equilibrium, while the adsorption of high Mw polyelectrolyte continued. The larger coil size of high Mw polyelectrolyte could enable the surpassing of multilayer thickness compared with low Mw polyelectrolyte. In the exponential growth regime, besides the slow adsorption, the application of high Mw polyelectrolytes further suppressed the interlayer diffusion, leading to the decrease of multilayer thickness regardless of deposition time. We further studied the effects of deposition time, Mw of polyelectrolytes, and the number of bilayers on the surface morphology in the exponential growth regime. Surface roughness significantly increased with the application of high Mw PAA and the increase in deposition time. For the first time, the unique LbL film growth patterns of islet, ring and cantaloupe skin-like structures that consecutively formed on the surface of polyelectrolyte multilayers were reported by tuning the above parameters.

Layer-by-layer assembly and thermal sensitivity of poly(3,4-ethylenedioxythiophene) nanofilms

ABSTRACTThe functional nanofilms of poly(3,4-ethylenedioxythiophene) – poly(styrenesulfonate) (PEDOT:PSS) anionic complex were prepared on the transparent substrates by layer-by-layer (LBL) assembly with N-cetylpyridinium bromide (CPB) as cationic surfactant. It has studied dependence of films thickness on the number of bilayers of PEDOT:PSS/CPB and on initial concentration of PEDOT:PSS in colloid solution. The LBL films of PEDOT:PSS/CPB demonstrate the thermal sensitivity of optical absorption in visible and near IR range of spectrum which promises their application in sensor devices.

SPECTROSCOPIC CHARACTERIZATION OF NIAGARA BLUE DYE IN THE RESTRICTED GEOMETRY OF LAYER-BY-LAYER SELF-ASSEMBLED FILMS

Multilayer films can be precisely engineered on solid substrate via layer-by-layer (LbL) self-assemble technique using negatively charged organic dye and positively charged polyelectrolytes or surfactants. This communication first time reports the successful incorporation of an anionic dye Niagara blue (NB) in Polyallylamine hydrochloride (PAH) by electrostatic sequential alternative LbL adsorption. The photo-physical characteristics of LbL films are investigated by varying different parameters such as number of deposited layer, dipping time in dye solution, pH of PAH solution, concentration of the dye, etc. In addition, the interaction of NB with double tail surfactant Didodecyl dimethyl ammonium bromide (DDAB) at different concentrations is also studied in the light of UV–Vis absorption spectroscopy. Spectroscopic analysis reveals that NB has been successfully anchored to PAH or DDAB through electrostatic self-assembled technique and forms molecular aggregates. The formation of aggregates is further confirmed by atomic force microscopic (AFM) study.

Fabrication and characterization of graphene-based hybrid nanocomposite: assessment of antibacterial potential and biomedical application

The present investigation deals with synthesis of graphene oxide (GO) and fabrication of GO-based hybrid nanocomposites (Ncs). Synthesized GO and Ncs were primarily confirmed by UV visible and Fourier transform infrared (FT-IR) spectroscopy. Fabricated Ncs showed potential antimicrobial activity against Gram-positive and Gram-negative bacterial strains. Surface morphology, Elemental analysis, and FTIR imaging analysis were carried out to confirm Ncs formation. The Ncs were impregnated into the pullulan polymeric layer-by-layer (LbL) ultrathin film by using novel spin-coating approach. Mechanical properties were determined using Brookfield texture analyzer, and percentage moisture content confirmed the physicochemical stability of LbL film.

Unraveling the importance of controlled architecture in bimetallic multilayer electrode toward efficient electrocatalyst

Even though traditional electrode fabrication methods such as simple mixing process have been used in various energy storage and conversion devices due to its handiness, these methods could not fully utilize and maximize the intrinsic properties of each active material. With the limited control over the internal structure of the electrode, it also often poses a significant challenge to elucidate the structure-property relationship between components within the electrode. Taking advantages of versatile layer-by-layer (LbL) assembly which can tailor nano-architecture of hybrid electrodes, here we report electrocatalytic thin films for methanol oxidation by adjusting the assembly sequence of LbL films composed of the Au and Pd nanoparticles (NPs) and graphene oxide (GO) nanosheets. In case of co-assembled bimetallic LbL structure of (GO/Au/GO/Pd)n where respective Au and Pd NPs are supported with GO nanosheets, the electrocatalytic activity is significantly higher than that of respective monometallic LbL electrode (i.e. (GO/Au)n and (GO/Pd)n). To further investigate the architecture effect on the electrochemical behavior, Au and Pd NPs are assembled with GO in a different relative position of hybrid multilayer electrodes. It is proved that the electrocatalytic activity can be highly tunable by the position of metal NPs in the LbL structure, suggesting the structural dependence of charge and mass transfer between the electrolyte and the electrode, which is otherwise impossible to investigate in a simple conventional electrode fabrication method. Because of the highly tunable properties of LbL assembled electrodes coupled with electrocatalytic NPs, we anticipate that the general concept presented here will offer new insights in the nanoscale control over the architecture of the electrode toward development of novel electroactive catalysts.