Bart Stevens

Completely Organic Multilayer Thin Film with Thermoelectric Power Factor Rivaling Inorganic Tellurides

Composed exclusively of organic components, polyaniline (PANi), graphene, and double-walled nanotubes (DWNTs) are alternately deposited from aqueous solutions using a layer-by-layer assembly. The 40 quadlayer thin film (470 nm thick) exhibits electrical conductivity of 1.08 × 10(5) S m(-1) and a Seebeck coefficient of 130 μV K(-1) , producing a thermoelectric power factor of 1825 μW m(-1) K(-2) .

Polymer–Graphene Oxide Quadlayer Thin-Film Assemblies with Improved Gas Barrier

Layer-by-layer assembly was used to create quadlayers (QLs) of chitosan (CH), poly(acrylic acid) (PAA), CH, and graphene oxide (GO). Electron microscopy confirmed GO coverage over the film and a highly ordered nanobrick wall structure. By varying pH deviation between CH and PAA, a thick and interdiffused polymer matrix was created because of the altered chain conformation. A 5 CH (pH 5.5)/PAA (pH 3)/CH (pH 5.5)/GO QL assembly (48 nm) exhibits very low oxygen permeability (3.9 × 10(-20) cm(3) cm cm(-2) Pa(-1) s(-1)) that matches SiOx barrier coatings. In an effort to maintain barrier performance under high humidity, GO was thermally reduced to increase hydrophobicity of the film. This reduction step increased H2/CO2 selectivity of a 5 QL film from 5 to 215, exceeding Robesons upper bound limit. This unique water-based multilayer nanocoating is very promising for a variety of gas purification and packaging applications.

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.

Nanobrick wall multilayer thin films grown faster and stronger using electrophoretic deposition

In an effort to speed up the layer-by-layer (LbL) deposition technique, electrophoretic deposition (EPD) is employed with weak polyelectrolytes and clay nanoplatelets. The introduction of an electric field results in nearly an order of magnitude increase in thickness relative to conventional LbL deposition for a given number of deposited layers. A higher clay concentration also results with the EPD-LbL process, which produces higher modulus and strength with fewer deposited layers. A 20 quadlayer (QL) assembly of linear polyethyleneimine (LPEI)/poly(acrylic acid)/LPEI/clay has an elastic modulus of 45 GPa, tensile strength of 70 MPa, and thickness of 4.4 μm. Traditional LbL requires 40 QL to achieve the same thickness, with lower modulus and strength. This study reveals how these films grow and maintain a highly ordered nanobrick wall structure that is commonly associated with LbL deposition. Fewer layers required to achieve improved properties will open up many new opportunities for this multifunctional thin film deposition technique.

Ultrastrong, Chemically Resistant Reduced Graphene Oxide-based Multilayer Thin Films with Damage Detection Capability.

Multilayer thin films of graphene oxide (GO) and poly(vinylamine) (PVAm) were deposited via layer-by-layer assembly. Poly(vinylamine) pH was used to tailor film thickness and GO layer spacing. Graphene oxide concentration in the films was controlled through simple pH adjustment. Thermal reduction of the PVAm/GO multilayer thin films rendered them electrically conductive, which could be further tailored with PVAm pH. These reduced films also exhibited exceptionally high elastic modulus of 30 GPa and hardness of 1.8 GPa, which are among the highest of any graphene-filled polymer composite values ever reported. Cross-linking of these films with glutaraldehyde improved their chemical resistance, allowing them to survive strongly acidic or salty solutions. Additionally, scratches in the films can be instantaneously detected by a simple electrical resistance measurement. These films are promising for a variety of packaging and electronic applications.

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.