Polyelectrolyte Multilayer Thin Films Research Articles

Conformation-dependent thermoelectric power factor of multilayer nanocomposites

Polyelectrolyte multilayer thin films, assembled by sequentially depositing bilayer (BL) of poly(allyamine hydrochloride) (PAH) and double-walled carbon nanotubes (DWNT) stabilized in polyacrylic acid (PAA) using the layer-by-layer assembly technique, are studied in an effort to establish the relationships between the conformational changes and thermoelectric performances. Controlling the charge density of weak polyelectrolytes with assembly pH conditions gives rise to a different physical, structural, and mechanical properties. The 7.5PAH/3.5(DWNT-PAA) films exhibit an exponentially-grown thickness behavior due to in-and-out diffusion of the partially charged polyelectrolytes with coiled polymeric conformation, which results in randomly distributed nanotubes within the multilayers. Films made with the same sequences, but with extended polymeric conformation due to high charge density along the polymer chain (PAH at pH 6 and PAA at pH 6.5), show the linear growth behavior with a uniformly oriented nanotube structure and relatively higher elastic modulus. The precise control of the polymeric conformation upon charge density at the nanoscale level significantly affects the thermoelectric performances. A 14 BL 6PAH/6.5(DWNT-PAA) film exhibits an electrical conductivity of 417 S cm−1 and Seebeck coefficient of 85 μV K−1. This translates to a power factor of 301 μW m−1 K−2, which is 75 times higher than the same films made at pH 7.5/3.5.

Simplifying Molecular Transport in Polyelectrolyte Multilayer Thin Films

AbstractThe matrix properties of polyelectrolyte multilayer thin films (PEM) are critical in making them a viable candidate for various biomedical applications. The location and ability of molecules to diffuse through the PEM architecture determines their encapsulation and release capabilities in a given matrix for various biomedical applications. The main aim of this review article is to provide a complete understanding of molecular transport on the surface as well as across the bulk of the PEM matrix. Different physiochemical strategies to promote or suppress the diffusivity of various molecules inside the PEM are mentioned in brief. A set of guiding principles is uncovered for getting a complete picture of loading and release of molecules across the PEM structure, which can play a key role in designing a desirable PEM assembly and have important implications for designing multicomponent, targeted and controlled drug‐delivery vehicles. Understanding the molecular diffusivity in PEM stack at the nano and micro scales will help to design superior host materials for biomedical engineering applications.

Fabrication, characterization and application of polymer based nanomaterials in the removal of pollutants from industrial effluents

In this research, multilayer nano thin films fabricated using poly (allyl amine hydrochloride) (PAH), TiO 2 and poly (styrene sulphonate sodium salt) (PSS), on silica template by Layer-by-Layer (L-b-L) technique and its potential application for the photo degradation of textile and oil refinery wastewater under solar irradiation has been reported. TiO 2 nanoparticles of size less than 5 nm were synthesized using modified sol–gel method and the characterization of the particles are performed using Dynamic Light Scattering (DLS), Scanning Electron Microscopy (SEM), X-ray Diffraction (XRD), Fourier Transform Infra-red Spectroscopy (FTIR). The L-b-L assembly was carried out at pH 2.5 and the development of the thin layers was investigated using UV/Vis spectrophotometer at an absorbance of 230 nm. The morphological characterization of the fabricated film was analyzed using Atomic Force Microscopy (AFM). A comparative study has been carried out using textile and oil refinery effluents for the photo degradation of TiO 2 /PSS/PAH thin films and suspension form of TiO 2 by varying the process parameters such as number of bilayers, polymer concentration and solar irradiation time. The TiO 2 /Polyelectrolyte multilayer thin films performed extremely well in the reduction of Chemical Oxygen Demand (COD) and Total Organic Carbon (TOC) to the standards. The five-bilayer film considerably reduced the TOC and COD to 85% and 87%, respectively. In TiO 2 suspension form, a reduction in TOC and COD was observed to be 70% and 73.5%, respectively. This study illustrates that immobilized nanoparticles could effectively remove pollutants from wastewater and the process seems to be attractive in the environmental applications. • In this research Novel nanomaterial’s are fabricated using polymers and nanoparticles. • Fabricated Nano thin films are applied in effluent treatment applications. • Glass slide was used template for the preparation of nano thin films by Layer-by-Layer (L-b-L). • The potential application of thin films for the photo degradation of textile and oil refinery wastewater under solar irradiation has been reported.

Study on the Effect of Poly(Styrene 4-Sulfonic Acid-co-Maleic Acid) Toward Metallization and Plasmonic Tuning of Silver Nanoparticle Thin Films

Thin films with tunable optical properties from yellow to metallic were prepared from a monolayer coating of silver nanoparticles (AgNP) onto a polyelectrolyte multilayer (PEM) thin film. The AgNP were synthesized using various concentrations of stabilizing polyelectrolytes leading to a competitive adsorption concept in which AgNP compete with excess polyelectrolytes to coat the cationic PEM top layer. The AgNP were synthesized by chemical reduction of Ag salts using poly(styrene 4-sulfonic acid-co-maleic acid) (PSS-co-MA) as stabilizing agent to produce nanoparticles coated with both a strong acid (sulfonic) and a weak acid (carboxylic) moiety. Although all the nanoparticle solutions displayed a characteristic bright yellow due to the localized surface plasmon band around 420 nm, the monolayer films of nanoparticles obtained after dipping displayed striking different optical properties. When using a high PSS-co-MA content in the solution, a pale-yellow film was obtained which color shifted to orange and metallic when the capping concentration was decreased from 0.25 to 0.001 mM. The optical properties of the AgNP film could be further changed by galvanic replacement of the Ag with gold ions to produce a gold monolayer. These results are interesting to produce surface with tunable catalytic properties, tunable optical properties, or to be used as primer for the metallization of polymeric surfaces.

Surface modification of polyethylene naphthalate substrates by ultraviolet light-irradiation and assembling multilayers and their application in electroless deposition: The chemical and physical properties of the stratified structure

Electroless metal deposition on polymer surface is useful for fabricating metallic patterns. The surfaces of polyethylene naphthalate (PEN) substrates were modified by ultraviolet (UV) light -irradiation and layer-by-layer assembly of polyelectrolyte multilayer thin films, and then nickel and copper films were electrolessly deposited on the substrate surfaces to form the stratified structure, PEN-substrate/multilayer/metal-film. The chemical and physical properties of the modified layer in the substrate surfaces were studied by X-ray photoelectron spectroscopy, nanoindentation test, and measuring contact angle. The properties of the UV-irradiated surface layer depended on the condition of surface modification and affected the adhesion of the deposited metal film. Adhesive nickel films were deposited on the UV (254 nm)-irradiated PEN substrates that have thin modified layers compatible with the multilayers. In contrast, no adhesive nickel films were deposited on the substrate surfaces having thicker and fragile modified layers. These contrasting results are originated from the oxygenation and crosslinking of the polymer chains in the substrate surface layers, and reactive species formed by the UV irradiation induce the oxygenation and crosslinking. The properties of the modified substrate-surface play an important role for depositing adhesive metal films.

Polyelectrolyte multilayer microchamber-arrays for in-situ cargo release: Low frequency vs. medical frequency range ultrasound

An implantable ultrasound triggered controlled release micro-chamber (MC) array based on polylactic acid (PLA) sealed polyelectrolyte multilayers (PEM) is presented. In this work Rhodamine B (RhB) nano-precipitates are loaded as model cargo and sealed water tight within micro-air bubbles. Cargo release at low frequency (LFUS (37 kHz)) and high frequency ultrasound (HFUS (2 MHz, medical range)) is compared. The release speed and mechanism varies significantly between both ultrasound frequencies, allowing for a 60 times faster MC opening at HFUS. LFUS MC opening is based on material fatigue combined with thermo-acoustic effects while strong thermo-acoustic effects are responsible for MC opening at HFUS. The slower MC opening at LFUS allows for controlling the release amount and enables multiple release pulses compared to HFUS. Not PLA coated and no air bubble entrapping PEM thin films are in case of HFUS destroyed, while no interaction is determined at LFUS.

Temperature controlled loading and release of curcumin in polyelectrolyte multilayers thin films

The temperature triggered loading and release of hydrophobic model drug (1,7-bis[4-hydroxy-3-methoxyphenyl]-1,6-heptadiene-3,5-dione) (curcumin) from polyelectrolyte multilayer (PEM) thin films was demonstrated. Thin films built from the layer-by-layer (LbL) deposition of poly(diallyldimethylammonium chloride) (PDADMAC) and poly(4-styrene sulfonate) (PSS) were dipped in curcumin and studied as patches that could be used in temperature controlled drug delivery applications. Three different solvents (methanol, ethanol and isopropanol) were mixed with different fractions of water (from 60:40% to 95:5% aqueous:organic solvent) and fixed amount of curcumin (100 ppm). The loading of curcumin in the PEM increased when the polarity of the solvent mixture was increased or when the temperature was decreased. Interestingly, curcumin could spontaneously be released in warm water and as an example, curcumin was loaded PEM film at 5 °C and release at 37 °C thus demonstrating the body temperature triggered release of a hydrophobic model drug. Using this method a new type of transdermal patch for the release of hydrophobic drugs from PEM membrane would be possible.

Micro-Patterned Polystyrene Sheets as Templates for Interlinked 3D Polyelectrolyte Multilayer Microstructures

Polystyrene (PS) is currently mainly used as a sacrificial template during pattern release upon microcontact printing or for self-assembled flat free-standing films. We hereby present a method for creating 3D microstructured free-standing self-assembled polyelectrolyte multilayer (PEM) thin films. The approach presented utilizes a sacrificial microstructured PS template which can be coated with PEM thin films, whereby dissolution of the PS facilitates a free-standing 3D microstructured PEM film. The PS templating approach allows for omitting hot embossing on silicon masters, since PS templates can be prepared by drop casting on silicon masters. The prepared PEM film offers, if gold nanoparticles are incorporated, stimuli-responsive properties like light-induced chamber opening.

Surface modification of PEN and PET substrates by plasma treatment and layer-by-layer assembly of polyelectrolyte multilayer thin films and their application in electroless deposition

Surface modification of PEN and PET substrates by plasma-treatment and LbL assembly of polyelectrolyte multilayers and subsequent electroless nickel deposition.

Patterned Microstructure Fabrication: Polyelectrolyte Complexes vs Polyelectrolyte Multilayers.

Polyelectrolyte complexes (PEC) are formed by mixing the solutions of oppositely charged polyelectrolytes, which were hitherto deemed “impossible” to process, since they are infusible and brittle when dry. Here, we describe the process of fabricating free-standing micro-patterned PEC films containing array of hollow or filled microchambers by one-step casting with small applied pressure and a PDMS mould. These structures are compared with polyelectrolyte multilayers (PEM) thin films having array of hollow microchambers produced from a layer-by-layer self-assembly of the same polyelectrolytes on the same PDMS moulds. PEM microchambers “cap” and “wall” thickness depend on the number of PEM bilayers, while the “cap” and “wall” of the PEC microchambers can be tuned by varying the applied pressure and the type of patterned mould. The proposed PEC production process omits layering approaches currently employed for PEMs, reducing the production time from ~2 days down to 2 hours. The error-free structured PEC area was found to be significantly larger compared to the currently-employed microcontact printing for PEMs. The sensitivity of PEC chambers towards aqueous environments was found to be higher compared to those composed of PEM.

Highly Conductive Graphene and Polyelectrolyte Multilayer Thin Films Produced From Aqueous Suspension.

Rapid, large-scale exfoliation of graphene in water has expanded its potential for use outside niche applications. This work focuses on utilizing aqueous graphene dispersions to form thin films using layer-by-layer processing, which is an effective method to produce large-area coatings from water-based solutions of polyelectrolytes. When layered with polyethyleneimine, graphene flakes stabilized with cholate are shown to be capable of producing films thinner than 100 nm. High surface coverage of graphene flakes results in electrical conductivity up to 5500 S m-1 . With the relative ease of processing, the safe, cost effective nature of the ingredients, and the scalability of the deposition method, this system should be industrially attractive for producing thin conductive films for a variety of electronic and antistatic applications.

Improved pH Sensing of Curcumin Loaded Polyelectrolyte Multilayers Thin Films

Improved pH Sensing of Curcumin Loaded Polyelectrolyte Multilayers Thin Films

Stimuli-responsive weak polyelectrolyte multilayer films: A thin film platform for self triggered multi-drug delivery.

Polyelectrolyte multilayer (PEM) thin film composed of weak polyelectrolytes was designed by layer-by-layer (LbL) assembly of poly(allylamine hydrochloride) (PAH) and poly(methacrylic acid) (PMA) for multi-drug delivery applications. Environmental stimuli such as pH and ionic strength showed significant influence in changing the film morphology from pore-free smooth structure to porous structure and favored triggered release of loaded molecules. The film was successfully loaded with bovine serum albumin (BSA) and ciprofloxacin hydrochloride (CH) by modulating the porous polymeric network of the film. Release studies showed that the amount of release could be easily controlled by changing the environmental conditions such as pH and ionic strength. Sustained release of loaded molecules was observed up to 8h. The fabricated films were found to be biocompatible with epithelial cells during in-vitro cell culture studies. PEM film reported here not only has the potential to be used as self-responding thin film platform for transdermal drug delivery, but also has the potential for further development in antimicrobial or anti-inflammatory coatings on implants and drug-releasing coatings for stents.

Microcontact printing of polyelectrolyte multilayer thin films: Glass–viscous flow transition based effects and hydration methods

Abstract Micro and nano-patterned surfaces are important for many applications ranging from antibiofouling over tissue engineering to electronics. Often the incorporation of functional entities is of interest. Polymer coatings especially polyelectrolyte multilayer (PEM) films and patterns are materials offering a large variety of tuning and engineering. The PEM pattern printing quality bases not only on the surface force balance but also in the way the PEM is softened, which can be done by printing the PEM in water, using an ultrasound humidifier or by exposing the film to (hot) water vapor. In this publication it is shown, that cold water vapor from an ultrasound humidifier or direct printing in water is superior to steam evaporation onto PEM thin films as humidification method. In addition the capillary pressure of the patterns within the stamp and the glass–viscous flow transition point of the PEM thin film are the significant parameters for PEM printing. This is because the PEM can surpass the glass–viscous flow transition point due to the shear forces and be sucked into the stamp microwells (or holes) preventing a structure replication. Under high temperatures and in aqueous conditions, the PEM can be expelled from the microwells due to the osmotic pressure produced by the counter ions of PEM in glass–viscous flow state and dissolving polyelectrolyte if a PEM with counter ion based charge balance is used.

Modification of PEN and PET film surfaces by plasma treatment and layer-by-layer assembly of polyelectrolyte multilayer thin films

The surfaces of polyethylene naphthalate and polyethylene terephthalate films were modified by plasma treatment, layer-by-layer (LbL) assembly of polyelectrolyte multilayer thin films and subsequent deposition of SiO2 particles. Plasma treatment rendered the film surfaces hydrophilic and led to the formation of fibrillar patterns. The plasma-treated film surfaces were compatible with multilayers acquired via LbL assembly, and the outer adsorbed polyelectrolyte layer determined the charge of the multilayer surfaces. Negatively charged SiO2 particles were adsorbed to the positively charged surface of the multilayers. This process is potentially applicable to surface modifications of polymer materials by charged compounds.

Electrocatalytic amplification of nanoparticle collisions at electrodes modified with polyelectrolyte multilayer films.

We report electrochemical catalytic amplification of individual collisions between ∼57 nm diameter Pt nanoparticles (Pt NPs) and 12.5 μm diameter Au ultramicroelectrodes modified with passivating, electrostatically assembled polyelectrolyte multilayer (PEM) films prepared by the layer-by-layer deposition method. Two key findings are reported. First, despite the thicknesses of the insulating PEM films, which range up to 5 nm, electrons are able to tunnel from the Pt NPs to the electrode resulting in electrocatalytic N2H4 oxidation at the PEM film-solution interface. These single-particle measurements are in accord with prior reports showing that the electrochemical activity of passive PEM films can be reactivated by adsorption of metallic NPs. Second, it is possible to control the frequency of the collisions by manipulating the net electrostatic charge present on the outer surface of the PEM thin film. These results, which demonstrate that chemistry can be used to control electrocatalytic amplification, set the stage for future sensing applications.

Micro-contact printing of PEM thin films: effect of line tension and surface energies

A theory and method for calculating printing resolution limits for microcontact printing of a condensed polyelectrolyte multilayer thin film, based on surface energies and line tension is presented.

Improved loading of hydrophobic molecules in polyelectrolyte multilayers thin films by surfactants surface modification

Improved loading of hydrophobic molecules in polyelectrolyte multilayers thin films by surfactants surface modification

Charge-dependent transport switching of single molecular ions in a weak polyelectrolyte multilayer.

The tunable nature of weak polyelectrolyte multilayers makes them ideal candidates for drug loading and delivery, water filtration, and separations, yet the lateral transport of charged molecules in these systems remains largely unexplored at the single molecule level. We report the direct measurement of the charge-dependent, pH-tunable, multimodal interaction of single charged molecules with a weak polyelectrolyte multilayer thin film, a 10 bilayer film of poly(acrylic acid) and poly(allylamine hydrochloride) PAA/PAH. Using fluorescence microscopy and single-molecule tracking, two modes of interaction were detected: (1) adsorption, characterized by the molecule remaining immobilized in a subresolution region and (2) diffusion trajectories characteristic of hopping (D ∼ 10–9 cm2/s). Radius of gyration evolution analysis and comparison with simulated trajectories confirmed the coexistence of the two transport modes in the same single molecule trajectories. A mechanistic explanation for the probe and condition mediated dynamics is proposed based on a combination of electrostatics and a reversible, pH-induced alteration of the nanoscopic structure of the film. Our results are in good agreement with ensemble studies conducted on similar films, confirm a previously-unobserved hopping mechanism for charged molecules in polyelectrolyte multilayers, and demonstrate that single molecule spectroscopy can offer mechanistic insight into the role of electrostatics and nanoscale tunability of transport in weak polyelectrolyte multilayers.

Low-temperature thermal reduction of graphene oxide nanobrick walls: unique combination of high gas barrier and low resistivity in fully organic polyelectrolyte multilayer thin films.

Layer-by-layer assembly from aqueous solutions was used to construct multilayer thin films (<200 nm) comprising polyethylenimine and graphene oxide. Low-temperature (175 °C) thermal reduction of these films improved gas barrier properties (e.g., lower permeability than SiOx), even under high humidity conditions, and enhanced their electrical conductivity to 1750 S/m. The flexible nature of the aforementioned thin films, along with their excellent combination of transport properties, make them ideal candidates for use in a broad range of electronics and packaging applications.