Assembly Of Multilayer Films Research Articles

A general objective-orientated automatic optimization of multi-layer thermochromic smart glazes

VO2-based thermochromic smart glazes have attracted much attention for energy-saving buildings. Their practical applications need high visible luminous transmittance (Tlum) and high solar light modulation efficiency (ΔTsol). High Tlum and ΔTsol are difficult to be realized by a single-layer VO2 film, and constructing multi-layer film assemblies has been a widely adopted way to increase Tlum and ΔTsol. Tlum and ΔTsol of a multi-layer film assembly are multi-dimensional functions of the complex dielectric permittivity and the thickness of each layer, respectively. The current research reported a computer automatic searching of the total minimum of an evaluation function that together takes the cool-state Tlum, hot-state Tlum, and ΔTsol into account. It can be used to optimize a multi-layer assembly composed of any components according to the given objectives and weights for Tlum and ΔTsol. Different multi-layer film systems consisting of SiO2, TiO2, and VO2 layers were optimized. The best film system was proposed to be TiO2/VO2/TiO2/s, and the effects of objectives and weights on Tlum and ΔTsol were also checked. The physical reason that leads to high Tlum and ΔTsol was analyzed based on the optimized reflectance and transmittance spectra. The RGB tristimulus of the optimized multi-layer system can also be obtained from the transmittance spectra. The program can also realize an automatic optimization with some variables being constrained, and the composite layers are also involved under the basis of the Bruggeman effective media theory. The results showed that a satisfied objective-orientated optimization can be realized for a thermochromic layer system; this should be meaningful for the design and preparation of the multi-layer film assemblies according to the different user's demands.

Facile fabrication of thermoplastic starch/poly (lactic acid) multilayer films with superior gas and moisture barrier properties

Multilayer films comprised of thermoplastic starch (TPS) and poly (lactic acid) (PLA) were fabricated via a reactive extrusion, compression molding, and dip coating processes. Maleic anhydride (MA) modification of TPS was employed to improve the interfacial adhesion between TPS and PLA layers of the film. The level and effect of TPS modification were evaluated using Fourier transform infrared spectroscopy (FTIR), proton nuclear magnetic resonance (H NMR), titration, and thermogravimetric analysis (TGA). Nanoclays were incorporated in the TPS and maleated TPS (MTPS) matrices to further enhance the physico-mechanical properties of the multilayer films. The optimized multilayer film fabricated in this study, which was the nanoclays-filled maleated thermoplastic starch and PLA multilayer film (MTPS-3C/PLA) displayed good transparency and tensile properties, and excellent moisture and oxygen barrier properties. This multilayer film assembly provided 1300% improvement in moisture barrier compared to TPS films, and 3300% improvement in oxygen barrier properties as compared to PLA films adjusted for thickness. Moreover, these multilayer films are composed of compostable, food-grade, inexpensive, and bio-based ingredients and as such they are expected to be compostable with great cost structure and environmentally friendly.

Robust multiphase and multilayer starch/polymer (TPS/PBAT) film with simultaneous oxygen/moisture barrier properties

The demands for bioplastics that provide good barrier properties against moisture and oxygen while simultaneously displaying good physical properties without compromising their biodegradability is ever-increasing. In this work, a multiphase and multilayer film assembly composed of thermoplastic starch (TPS) and its maleated counterpart (MTPS) with poly(butylene adipate-co-terephthalate) (PBAT) was constructed as a suitable barrier film with excellent mechanical properties. The bioplastic film assemblies were fabricated through reactive extrusion, compression molding, and dip-coating process. The incorporation of PBAT co-blend with TPS in the core layer enhanced the multilayer film's interfacial bond. The MTPS/PBAT film assembly provided 86.8% and 74.3% improvement in moisture barrier and oxygen barrier as compared to the baseline TPS and PBAT films, respectively. Overall, the multiphase and multilayer film assembly displayed good mechanical properties in conjuncture with excellent barrier properties indicating their potential as a biodegradable and cost effective alternative to conventional plastics used in the packaging industry.

(Invited) 2D MXenes As Building Blocks for Assembly of High-Performance Electrodes for Electrochemical Energy Storage

Two-dimensional (2D) transition metal carbides/nitrides (MXenes) have shown promise for a range of applications due to their unique physical and chemical properties. The high electrical conductivity, 2D and layered structure, and rich surface chemistry of MXenes have sparked great interest in their properties as electrode materials for energy storage devices. MXenes are particularly of high interest because they can store charge in the bulk of the electrode through ultrafast intercalation of ions and fast and reversible redox reactions. To date, about 30 different MXenes with a general formula of Mn+1XnTx (M is a transition metal, X is carbon and/or nitrogen, n=1,2, and 3, and Tx represents different functional groups present at their surface) are synthesized by selective etching of the A layer atoms (i.e. Al) from MAX phases (e. g. Ti2AlC), a large group of layered ternary carbides and nitrides.1 However, similar to other 2D materials, the applications of MXenes in batteries and supercapacitors is dependent on their assembly into electrode structures with high electrical and ionic conductivities. The main focus of this talk is our group’s recent research on the assembly of MXene flakes into electrode structures with high energy and power densities. We have found that the electrochemical properties of MXene electrodes are highly dependent on the size of MXene flakes used in their fabrications.2,3 Controlling the flake size in the electrode structures leads to significant improvements in their specific capacitance and rate capability. Furthermore, our recent studies on the assembly of multilayer MXenes films and particles using electrostatic assembly methods will be discussed. The electrodes fabricated by these methods show superior chemical and electrochemical stabilities as well as energy storage capability.4 Finally, our work on 3D assembly of MXenes through a versatile 3D printing process will be presented. References (1) Anasori, B.; Lukatskaya, M. R.; Gogotsi, Y. 2D Metal Carbides and Nitrides (MXenes) for Energy Storage. Nat. Rev. Mater. 2017, 2 (2), 16098. https://doi.org/10.1038/natrevmats.2016.98. (2) Kayali, E.; VahidMohammadi, A.; Orangi, J.; Beidaghi, M. Controlling the Dimensions of 2D MXenes for Ultrahigh-Rate Pseudocapacitive Energy Storage. ACS Appl. Mater. Interfaces 2018, 10 (31), 25949–25954. https://doi.org/10.1021/acsami.8b07397. (3) VahidMohammadi, A.; Moncada, J.; Chen, H.; Kayali, E.; Orangi, J.; A. Carrero, C.; Beidaghi, M. Thick and Freestanding MXene/PANI Pseudocapacitive Electrodes with Ultrahigh Specific Capacitance. J. Mater. Chem. A 2018, 6 (44), 22123–22133. https://doi.org/10.1039/C8TA05807E. (4) VahidMohammadi, A.; Mojtabavi, M.; Caffrey, N. M.; Wanunu, M.; Beidaghi, M. Assembling 2D MXenes into Highly Stable Pseudocapacitive Electrodes with High Power and Energy Densities. Adv. Mater. 2019, 31 (8), 1806931. https://doi.org/10.1002/adma.201806931.

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.

Spontaneous Biomacromolecule Absorption and Long-Term Release by Graphene Oxide.

Biomacromolecule loading is the popular research in the biomedical field. To control the loading amount and releasing profile, various materials and fabrication techniques were developed. In this study, layer-by-layer assembly of multilayer films between collagen (Col) and graphene oxide (GO) was used to control the release of the loading molecule. By mixing GO into the system, ovalbumin (OVA) can be spontaneously adsorbed onto the GO sheet (denoted as GO/OVA) via the hydrophobic interaction. Two kinds of multilayer films (Col/GO/OVA and Col/GO/OVA) were fabricated. The thickness growth curve, quantitative of each layer adsorption, film morphology, stability, cell viability, and OVA release from multilayer films were investigated. The result has shown excellent film stability, macromolecule loading, and sustained release because of GO ability.

Polymeric ionic liquid based on magnetic materials fabricated through layer-by-layer assembly as adsorbents for extraction of pesticides

In this study, layer-by-layer assembly of polyelectrolyte multilayer films on magnetic silica provided a convenient and controllable way to prepare polymeric ionic liquid-based magnetic adsorbents. The resulting particles were characterized by Fourier transform infrared spectroscopy, X-ray diffraction, transmission electron microscopy, and magnetic measurements. The data showed that the magnetic particles had more homogeneous spherical shapes with higher saturation magnetization when compared to those obtained by free radical polymerization method. This facilitated the convenient collection of magnetic particles, with higher extraction repeatability. The extraction performance of the multilayer polymeric ionic liquid-based adsorbents was evaluated by magnetic solid-phase extraction of four pesticides including quinalphos, fenthion, phoxim, and chlorpropham. The data suggested that the extraction efficiency depended on the number of layers in the film. The parameters affecting the extraction efficiency were optimized, and good linearity ranging from 2 to 250μgL−1 was obtained with correlation coefficients of 0.9994–0.9998. Moreover, the proposed method presented low limit of detection (0.5μgL−1, S/N=3) and limit of quantification (1.5μgL−1, S/N=10), and good repeatability expressed by the relative standard deviation (2.0%–4.6%, n=5). The extraction recoveries of four pesticides were found to range from 58.9% to 85.8%. The reliability of the proposed method was demonstrated by analyzing environmental water samples, and the results revealed satisfactory spiked recovery, relative standard deviation, and selectivity.

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.

Subdiffraction-Resolution Optical Measurements of Molecular Transport in Thin Polymer Films.

The measurement of molecular transport within polymer films yields information about the internal structural organization of the films and is useful in applications such as the design of polymeric capsules for drug delivery. Layer-by-layer assembly of polyelectrolyte multilayer films has been widely used in such applications where the multilayer structure often exhibits anisotropic transport resulting in different diffusivities in the lateral (parallel to the film) and transverse (normal to the film) directions. Although lateral transport can be probed using techniques such as fluorescence recovery after photobleaching (FRAP), it cannot be applied to probing transverse diffusivity in polymer films smaller than the diffraction limit of light. Here we present a technique to probe the transport of molecules tagged with fluorphores in polymer films thinner than the optical diffraction limit using the modulation of fluorescence emission depending on the distance of the tagged molecules from a metal surface. We have used this technique to probe the diffusion of proteins biotin and bovine serum albumin (BSA) in polyelectrolyte multilayer films. We also studied the interdiffusion of chains in multilayer films using this technique. We observed a 3 order of magnitude increase in interdiffusion as a function of the ionic strength of the medium. This technique, along with FRAP, will be useful in studying anisotropic transport in polymer films, even those thinner than the diffraction limit, because the signal in this technique arises only from transverse and not lateral transport. Finally, this technique is also applicable to studying the diffusion of chromophore-labeled species within a polymer film. We demonstrate this aspect by measuring the transverse diffusion of methylene blue in the PAH-PAA multilayer system.

Rapid and efficient sprayed multilayer films for controlled drug delivery

ABSTRACTThe speed and scalability of film fabrication can dictate the translation of technologies from the laboratory scale to industrial level mass production. Spray‐assisted layer‐by‐layer (LbL) film assembly enables the rapid coating of geometrically complex and porous substrates with functional polyelectrolyte multilayers. Unfortunately, the encapsulation efficiency can be as low as one percent, making this technique prohibitively costly with even modestly priced materials. Herein, we used containment chambers to separately capture the aerosolized solutions for each step in the spray‐LbL process and analyzed the effect of recycling on multilayer film assembly. With potential biomedical applications, we studied the controlled release films of (Poly 2/heparin/lysozyme/heparin)n films and tracked the distribution of lysozyme after film assembly. In a “Conventional” Spray‐LbL protocol, only 6% of the aerosolized lysozyme is incorporated into the film. By collecting and returning the expended solutions to their respective reservoirs (Recycle Spray‐LbL), we increased this efficiency to 15%. We also tuned the final distribution of lysozyme by adjusting the spray times (Optimized Spray‐LbL), which minimized the amount of lysozyme lost to non‐specific adsorption and reduced the fraction of lysozyme lost to the wash step from 30% and 75% (Conventional and Recycle Spray‐LbL, respectively) to 13%. Despite the changes in film assembly parameters, each film demonstrated similar controlled release properties. With the inherent limitations of time and cost facing Dip and Conventional Spray‐LbL technologies, respectively, the implementation of recycling to the latter demonstrates improvements in efficiency and time that may make it more attractive for the manufacture of biomedical coatings. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016, 133, 43563.

Layer-by-layer assembly of versatile nanoarchitectures with diverse dimensionality: a new perspective for rational construction of multilayer assemblies.

Over the past few decades, layer-by-layer (LbL) assembly of multilayer thin films has garnered considerable interest on account of its ability to modulate nanometer control over film thickness and its extensive choice of usable materials for coating planar and particulate substrates, thus allowing for the fabrication of responsive and functional thin films for their potential applications in a myriad of fields. Herein, we provide elaborate information on the current developments of LbL assembly techniques including different properties, molecular interactions, and assembly methods associated with this promising bottom-up strategy. In particular, we highlight the principle for rational design and fabrication of a large variety of multilayer thin film systems including multi-dimensional capsules or spatially hierarchical nanostructures based on the LbL assembly technique. Moreover, we discuss how to judiciously choose the building block pairs when exerting the LbL assembly buildup which enables the engineering of multilayer thin films with tailor-made physicochemical properties. Furthermore, versatile applications of the diverse LbL-assembled nanomaterials are itemized and elucidated in light of specific technological fields. Finally, we provide a brief perspective and potential future challenges of the LbL assembly technology. It is anticipated that our current review could provide a wealth of guided information on the LbL assembly technique and furnish firm grounds for rational design of LbL assembled multilayer assemblies toward tangible applications.

On-chip highly sensitive saliva glucose sensing using multilayer films composed of single-walled carbon nanotubes, gold nanoparticles, and glucose oxidase

It is very important for human health to rapidly and accurately detect glucose levels in biological environments, especially for diabetes mellitus. We proposed a simple, highly sensitive, accurate, convenient, low-cost, and disposable glucose biosensor on a single chip. A working (sensor) electrode, a counter electrode, and a reference electrode are integrated on a single chip through micro-fabrication. The working electrode is functionalized through a layer-by-layer (LBL) assembly of single-walled carbon nanotubes (SWNTs) and multilayer films composed of chitosan (CS), gold nanoparticles (GNp), and glucose oxidase (GOx) to obtain high sensitivity and accuracy. The glucose sensor has following features: (1) direct electron transfer between GOx and the electrode surface; (2) on-a-chip; (3) glucose detection down to 0.1mg/dL (5.6μM); (4) good sensing linearity over 0.017–0.81mM; (5) high sensitivity (61.4μA/mM-cm2) with a small reactive area (8mm2); (6) fast response; (7) high reproducibility and repeatability; (8) reliable and accurate saliva glucose detection. Thus, this disposable biosensor will be an alternative for real time tracking of glucose levels from body fluids, e.g. saliva, in a noninvasive, pain-free, accurate, and continuous way. In addition to being used as a disposable glucose biosensor, it also provides a suitable platform for on-chip electrochemical sensing for other chemical agents and biomolecules.

Layer-by-layer assembly of luminescent multilayer thin films by MMT, anionic chromophores and magnetic CoAl-LDHs nanosheets

In this report, luminescent multilayer thin films (MTFs) based on oppositely-charged montmorillonite (MMT) and transition metal-bearing layered double hydroxides (LDHs) nanosheets were fabricated via a layer-by-layer assembly method. Oppositely-charged inorganic nanosheets can be expected to assemble an electronic microenvironment (EME), and transition metal-bearing LDHs nanosheets can offer an additional magnetic field (MF) for the chromophores at the same time. Surprisingly, the luminescent lifetimes of MTFs with EME and MF are significantly prolonged compared with that of the pristine chromophores, even much longer than those of MTFs without oppositely-charged and magnetic architecture. Therefore, it is highly expected that the EME and MF formed by oppositely-charged and transition metal-bearing inorganic nanosheets have remarkable influence on enhancing the luminescent lifetimes of chromophores, which suggest a new potential way to manipulate, control and develop the novel light-emitting materials and optical devices at molecular level.

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.

Programmed Degradation of DNA Multilayer Films

The design and assembly of DNA multilayer films with programmable degradation properties are reported. The nanostructured DNA films are assembled through the layer-by-layer (LbL) assembly technique and can be programmed to degrade by subsequently introducing DNA strands of specific sequences. The strands preferentially hybridize to the building blocks that stabilize the film structure, causing the film to rearrange and degrade. The rate of degradation is influenced by both the availability and accessibility of the complementary DNA binding sites within the film, as well as the degree of crosslinking within the film. Similar results are obtained for DNA multilayer films assembled on planar and particle supports. This approach offers an avenue to tailor degradability features into DNA-based materials that may find application in the biosciences, in areas such as biosensing and drug delivery.

Just spray it--LbL assembly enters a new age.

Over the past two decades the Layer-by-Layer (LbL) assembly of multilayer thin films has witnessed an explosive growth. However, this has so far not been translated into numerous industrial applications mainly owing to the time-consuming multistep assembly procedure which was originally based on dipping of a substrate into a solution. More recently the use of spray-based approaches, both for planar films as well as for the construction of polymeric particles, has emerged. Here we highlight these recent advances that have the potential to move the LbL field forward.

Biocatalytic Polymer Coatings: On‐Demand Drug Synthesis and Localized Therapeutic Effect under Dynamic Cell Culture Conditions

Biocatalytic surface coatings are prepared herein for localized synthesis of drugs and their on-demand, site-specific delivery to adhering cells. This novel approach is based on the incorporation of an enzyme into multilayered polymer coatings to accomplish enzyme-prodrug therapy (EPT). The build-up of enzyme-containing multilayered coatings is characterized and correlations are drawn between the multilayer film assembly conditions and the enzymatic activity of the resulting coatings. Therapeutic effect elicited by the substrate mediated EPT (SMEPT) strategy is investigated using a prodrug for an anticancer agent, SN-38. The performance of biocatalytic coatings under flow conditions is investigated and it is demonstrated that EPT allows synthesizing the drugs on-demand, at the time desired and in a controllable amount to suit particular applications. Finally, using cells cultured in sequentially connected flow chambers, it is demonstrated that SMEPT affords a site-specific drug delivery, that is, exerts a higher therapeutic effect in cells adhering directly to the biocatalytic coatings than in the cells cultured "downstream". Taken together, these data illustrate biomedical opportunities made possible by engineering tools of EPT into multilayered polymer coatings and present a novel, highly versatile tool for surface mediated drug delivery.

Layer-by-layer assembly of multilayer films for controlled drug release

Drug efficacy has been improved using various methods that enhance targeting, decrease toxicity, and facilitate timely and sustained drug release. To achieve these properties, various drug loading and release platforms have been developed. Layer-by-layer (LbL) self-assembly is widely used to generate controlled and sustained drug release LbL multilayer films because it allows desired functions and structures to be obtained through a simple procedure. In this review article, we highlight controlled drug release from LbL self-assembling films with diverse release kinetics, particularly with regard to mechanisms of drug release.

ChemInform Abstract: Layer‐by‐Layer Assembly of Microcapsules and Their Biomedical Applications

AbstractReview: 306 refs.

Redox-Induced Conformational Change in Mercaptoalkanoic Acid Multilayer Films

We discuss the assembly, structure, and stability of multilayer molecular films formed from multiple mercaptoalkanoic acid monolayers ligated via carboxyl and thiol interactions with divalent copper ions. Using dual-polarization interferometry to study the assembly of multilayer films in real time, we observe a clear linear relationship between the number of layers within a film and the overall average film thickness. Unexpectedly, however, we find a restructuring of the lower monolayer upon association of the Cu(2+) ions to form the Cu carboxylate surface. In particular, the thickness of the lower monolayer was found to decrease significantly, accompanied by an increase in the film density. The conformation of the monolayer subsequently recovered to that observed originally following the reduction of the Cu ion to Cu(+) upon chemisorption of the adlayer. Comparable restructuring was also observed in molecular dynamics simulations of a bilayer film assembled on a gold surface. Our combined experimental and theoretical study suggests that the observed restructuring is a result of charge-charge interactions between adjacent Cu ions that exist in the +2 oxidation state in the copper carboxylate surface and in the +1 oxidation state following chemisorption of the adlayer.