Layer-by-layer formation of oligoelectrolyte multilayers: a combined experimental and computational study

For the first time, the combination of experimental preparation and results of fully atomistic simulations of an oligoelectrolyte multilayer (OEM) made of poly(diallyl dimethyl ammonium chloride)/poly(styrene sulfonate sodium salt) (PDADMAC/PSS) is presented. The layer-by-layer growth was carried out by dipping silica substrates in oligoelectrolyte solutions and was modeled by means of atomistic molecular dynamics simulations with a protocol that mimics the experimental procedure up to the assembly of four layers. Measurements of OEM thickness, surface roughness and amount of adsorbed oligoelectrolyte chains obtained from both approaches are compared. A good agreement between simulated and experimental results was found, with some deviations due to intrinsic limitations of both methods. However, the combination of information extracted from simulations to support the analysis of experimental data can overcome such restrictions and improve the interpretation of experimental results. On the other hand, processes dominated by slower kinetics, like the destabilization of adsorbed layers upon equilibration with the surrounding environment, are out of reach for the simulation modeling approach, but they can be investigated by monitoring in situ the oligoelectrolyte adsorption during the assembly process. This demonstrates how the synergistic use of simulation and experiments improves the knowledge of OEM properties down to the molecular scale

Deposition of Supercoiled DNA on Mica for Scanning Force Microscopy Imaging

The deposition of DNA molecules on mica is driven and controlled by the ionic densities around DNA and close to the surface of the substrate. Dramatic improvements in the efficiency and reproducibility of DNA depositions were due to the introduction of divalent cations in the deposition solutions. The ionic distributions on DNA and on mica determine the mobility of adsorbed DNA molecules, thus letting them assume thermodynamically equilibrated conformations, or alternatively trapping them in non-equilibrated conformations upon adsorption. With these prerequisites, mica does not seem like an inert substrate for DNA deposition for microscopy, and its properties greatly affect the efficiency of DNA deposition and the appearance of the molecules on the substrate. In our laboratory, we have some preliminary evidence that mica could also participate in DNA damage, most likely through its heavy metal impurities

The properties and the effect of operating parameters on nickel plating (review)

The energy required in an electroplating process and the material costs are important considerations in product manufacturing. The most important plating criteria, however, are quality and the uniformity of the deposited metals. The nickel plating process is used extensively for decorative, engineering, and electroforming purposes. Because of the appearance and other properties of the electrodeposited material, nickel deposition can be varied, over a wide range, by controlling the composition and the operating parameters of the plating solution. Decorative applications account for about 80% of the nickel consumed in plating; 20% is consumed for engineering and electroforming purposes. Autocatalytic (electroless) nickel plating processes are commercially important but are outside the scope of this review. In this review, the basic facts of nickel electroplating processes, thickness test and methods, are discussed. The properties of nickel and the different effects of the operating parameters on nickel plating, together with the simulation and design tools, are also reviewed. Simulation tools can help to obtain better plating results. Non-destructive techniques to evaluate the coatings on a microstructural and the technical evaluation with TEM, SEM, XRD and other techniques were also reviewed

Cross-linked polyvinyl alcohol films as alkaline battery separators

Cross-linking methods were investigated to determine their effect on the performance of polyvinyl alcohol (PVA) films as alkaline battery separators. The following types of cross-linked PVA films are discussed: (1) PVA-dialdehyde blends post-treated with an acid or acid periodate solution (two-step method) and (2) PVA-dialdehyde blends cross-linked during film formation (drying) by using a reagent with both aldehyde and acid functionality (one-step method). Laboratory samples of each cross-linked type of film were prepared and evaluated in standard separator screening tests. The pilot-plant batches of films were prepared and compared to measure differences due to the cross-linking method. The pilot-plant materials were then tested in nickel oxide - zinc cells to compare the two methods with respect to performance characteristics and cycle life. Cell test results are compared with those from tests with Celgard

DEVELOPING NANOPORE ELECTROMECHANICAL SENSORS WITH TRANSVERSE ELECTRODES FOR THE STUDY OF NANOPARTICLES/BIOMOLECULES

This study concerns development of a technology of utilizing metallic nanowires for a sensing element in nanofluidic single molecular (nanoparticle) sensors formed in plastic substrates to detect the translocation of single molecules through the nanochannel. We aimed to develop nanofluidic single molecular sensors in plastic substrates due to their scalability towards high through and low cost manufacturing for point-of-care applications. Despite significant research efforts recently on the technologies and applications of nanowires, using individual nanowires as electric sensing element in nanofluidic bioanalytic devices has not been realized yet. This dissertation work tackles several technical challenges involved in this development, which include reduction of nanowire agglomerates in the deposition of individual nanowires on a substrate, large scale alignment/assembly of metallic nanowires, placement of single nanowires on microelectrodes, characterization of electrical conductance of single nanowire, bonding of a cover plate to a substrate with patterned microelectrodes and nanowire electrodes. Overcoming the abovementioned challenges, we finally demonstrated a nanofluidic sensor with an in-plane nanowire electrode in poly(methyl methacrylate) substrates for sensing single biomolecules. In the first part of this study, we developed the processes for separation and large-scale assembly of individual NiFeCo nanowires grown using an electrodeposition process inside a porous alumina template. A method to fabricate microelectrode patterns on plastic substrates using flexible stencil masks was developed. We studied electrical and magnetic properties of new composite core-shell nanowires by measuring the electrical transport through individual nanowires. The core-shell nanowires were composed of a mechanically stable FeNiCo core and an ultrathin shell of a highly conductive Au gold (FeNiCo-Au nanowires). In the second part of this study, we simulated the effects of the nanopore geometry on the current drop signal of the translocation through a nanopore via finite element method using COMSOL. Using the above techniques, we developed for the fabrication and alignment of the microelectrodes and nanowires, we studied the optimum conditions to integrate the transverse nanoelectrode with the nanochannel on plastic substrates. The main challenge was to find the conditions to embed the micro-/nanoelectrodes into the nanochannel substrate as well as the nanochannel cover sheet

Fabrication of highly ordered multilayer thin films and its applications

A new method is introduced to build up organic/organic multilayer films composed of cationic poly(allylamine hydrochloride) (PAH) and negatively charged poly(sodium 4-styrenesulfonate) (PSS) by using the spinning process. The adsorption process is governed by both the viscous force induced by fast solvent elimination and the electrostatic interaction between oppositely charged species. On the other hand, the centrifugal and air shear forces applied by the spinning process significantly enhance the desorption of weakly bound polyelectrolyte chains and also induce the planarization of the adsorbed polyelectrolyte layer. The film thickness per bilayer adsorbed by the conventional dipping process and the spinning process was found to be about 4 å and 24 å, respectively. The surface of the multilayer films prepared with the spinning process is quite homogeneous and smooth. Electroluminescence (EL) devices composed of alternating poly(p-phenylene vinylene) (PPV) and polyanions films show higher quantum efficiency when prepared by the spin self-assembly (SA) method.This work was financially supported by the National Research Laboratory Program (Grant M1-0104-00-0191) and funded in part by the Ministry of Education through the Brain Korea 21 Program at Seoul National University

Processing and Functionality Improvements of Layer-By-Layer Assembled Multilayer Super Gas Barrier Nanocoatings

High oxygen barrier materials are becoming increasingly important for food packaging, pressurized systems, and flexible electronics protection. The widely used traditional aluminized plastics and inorganic gas barrier coatings (SiOx and AlxOy) exhibit low transparency and/or flexibility. Layer-by-layer assembly (LbL) provides a costeffective and environmental-friendly alternative, with lower oxygen permeability and greater transparency. This dissertation focuses on improvements of the coating process and development of new functionalities. Four studies are discussed in detail on this topic and two future research directions are also introduced. Layer-by-layer assembled multilayer nanocoatings have been shown to provide excellent oxygen barrier to poly(ethylene terephthalate) (PET) film, which is commonly used for encapsulation and packaging. Polymer-clay (polyethylenimine (PEI)/vermiculite (VMT)) and all-polymer ((PEI)/poly(acrylic acid) (PAA)) multilayer systems are shown to be equally beneficial as barrier coatings for polyolefin substrates (e.g., polyethylene and polypropylene), which suffer from a high oxygen transmission rate. A 30 bilayer PEI/VMT nanocoating reduces the OTR of biaxially oriented polypropylene (BOPP) by more than 160X, rivaling most inorganic coatings. WVTR is simultaneously reduced by 43%. In addition to VMT, montmorillonite (MMT) clay has been widely used to prepare gas barrier nanocoatings. In an effort to produce high oxygen barrier with fewer deposition steps, pH of the MMT aqueous suspension was reduced. In a PEI/PAA/PEI/MMT iii quadlayer system, the reduced pH of MMT causes the preceding PEI layer to be more charged, which results in more clay deposited. A compromise between high polyelectrolyte diffusion (high pH) and high clay deposition (low pH) was found at pH 6, where the best oxygen barrier is obtained. A 179 μm thick PET substrate, coated with just three quadlayers (44 nm thick), exhibits an undetectable oxygen transmission rate (< 0.005 cm3/(m2 day atm)). In another attempt to achieve better oxygen barrier of the PEI/MMT bilayer (BL) system, a “salty clay” strategy was carried out, where an “indifferent” electrolyte (NaCl) was introduced into the MMT suspension. NaCl alters the ionic strength of the clay suspension and subsequently changes the rheological behavior of clay platelets. As a result, a multilayer film with a more tortuous path and better clay coverage (and alignment) is produced. Lower OTR is achieved as a result of this structural engineering. An 8 BL PEI/MMT film, assembled with a clay suspension containing 5 mM NaCl, exhibits an order of magnitude reduction in OTR relative to its no-salt counterpart. The ability to self-repair after damaging (e.g., cracking) and restore original properties is highly desired for polymers and composites. The PEI/PAA nanocoating has the ability to self-heal after being cracked by stretching. Cracks in the film lead to loss of oxygen barrier. High humidity is employed as an external healing stimulus to repair these cracks. The OTR of a PEI/PAA multilayer nanocoating remains below detection after 10 stretching-healing cycles, which shows this healing process to be highly robust

LOADING AND COATING WATER SOLUBLE POLY(ETHYLENE OXIDE) SUBSTRATES UNDER ETHANOL USING THE LAYER- BY-LAYER TECHNIQUE

ABSTRACTA poly(ethylene oxide) (PEO) and poly(acrylic acid) (PAA) layer-by-layer (LBL) coating was self-assembled on a PEO substrate under non-aqueous conditions using ethanol. After lysine, ferricyanide, and Prussian blue (PB) had been loaded into the PEO granules, the resulting PEO polymer gel was dried to obtain strips that could be dip-coated onto silica wafers to obtain planar base coats with a bilayer thickness of 115 Aoat pH = 6 and 350 Aoat pH = 2. Further analysis revealed that upon coating, retention in the PEO core was \u3e 95% for PB, ~80% for ferricyanide, and ~73% for lysine. A dissolution test of PB loaded on coated and uncoated PEO strips showed that the former remained intact under an aqueous solution of pH ≤ 6.5 for at least 20 minutes whereas the latter dissolved within 3 minutes. These hydrogen-bonded ethPEO/PAA LBL films degrade atpH\u3e4.4 under aqueous conditions