Irradiation of polymer films by a CO 2 infrared laser under ambient conditions converts the polymer into porous graphene or laser-induced graphene (LIG). Here, we simulate the formation of LIG from five different commercially available polymers using reactive molecular dynamics. We determined that the molecular structure of the parent polymer has a significant effect on the final graphitic structure. CO is liberated during the initial part of the LIG formation process when the polymer is converted into an amorphous structure, while H 2 is evolved steadily as the amorphous structure is converted to an ordered graphitic structure. The LIG structure has out-of-plane undulations and bends due to a significant number of 5-and 7-member carbon rings present throughout the structure. We find that the simulated molecular structure compares well with recent experimental observations from the literature. We also demonstrate that the yield of LIG is higher in inert conditions, compared to environments with oxygen. Polybenzimidazole-derived LIG has the highest surface area and yield among the five polymers examined. These findings provide knowledge of LIG formation mechanisms that can be leveraged for bulk LIG applications such as sensors, electrocatalysts, microfluidics, and targeted heating for welding polymers.

of their colloidal stability, mechanical strength, high specific surface area, and thermal stability, [2][3][4][5][6] which have been used to produce transparent paper, biodegradable packaging, complex aerogels, and as the reinforcing phase in composites. [2,4,7,8] Despite all of its beneficial properties, cellulose exhibits poor flame resistance and gas barrier properties. [9,10] Improved barrier, mechanical, and flame resistant properties have been reported when montmorillonite clay (MMT) is used as a reinforcing agent in cellulose-based films. [11][12][13] The performance of polymer-clay barrier films is determined primarily by the clay characteristics (e.g., aspect ratio and density) and dispersion properties (i.e., clay exfoliation and orientation). For cellulose/clay composites, different methods to increase the interaction between clay and cellulose have been reported, including TEMPO-oxidation and by adding poly(vinyl alcohol) or chitosan (CH) as a compatibilizer. [14][15][16] Recently, cationic CNF with a quaternary ammonium functionality has been reported. [17] It was shown that the ionic interaction between the cationic CNF and MMT results in better mechanical properties of the composite, but further improvement is limited due to the formation of nanovoids as well as relatively low clay loading. [12,18] Layer-by-layer (LbL) assembly is a nanocoating technique that has been used to construct functional thin films for gas barrier and gas separation coatings, [19,20] energy storage and conversion, [21,22] drug delivery, [23] and adhesives. [24] By alternately depositing oppositely charged polyelectrolytes and/or clay platelets onto a charged substrate, thin films are assembled with high clay concentration and alignment. [25] In the present study, multilayer films consisting of anionic vermiculite (VMT) clay, with a high aspect ratio (≈2000), and cationic cellulose nanofibrils were investigated. This unique combination of highly aligned VMT platelets and cellulose nanofibrils forms a nanobrick wall structure with high transparency, excellent oxygen barrier, and fire resistance (superior to any other cellulose-based film previously reported). A 20 bilayer (BL) CNF/VMT nanocoating, with a thickness of 136 nm, exhibits a low oxygen transmission rate (OTR) of 0.013 cc (m 2 day atm) -1 . With only 2 BL of CNF/VMT, the melting of flexible polyurethane (PU) foam is prevented when exposed to a butane torch flame. These nanocoatings also exhibit high elastic modulus Cellulose nanofibrils (CNF) are abundant in the fiber cell walls of many plants and are considered a nearly inexhaustible resource. With the goal of improving the flame resistance and gas barrier properties of cellulose-based films, cationic CNF are assembled with anionic vermiculite (VMT) clay using the layer-by-layer deposition process. The highly aligned VMT nanoplatelets, together with cellulose nanofibrils, form a nanobrick wall structure that exhibits high optical transparency, flame resistance, super oxygen barrier, and high modulus. A 20 CNF/VMT...

In this report, we investigate the rapid heating ability of laser-induced graphene (LIG) in response to radio frequency (RF) fields. Graphitic structures were produced from various industrially prevalent thermoplastics via laser irradiation of the polymer surface. We find that RF responsive, graphitic structures may be produced from Kapton, polyether imide (PEI), polyether sulfone (PESU), polyether ether ketone (PEEK), and polycarbonate (PC) using a conventional laser cutting machine. The graphitic structures are also electrically conductive in addition to being RF responsive. Exposure of LIG to RF fields resulted in the rapid heating of LIG with remarkable heating rates up to 126 °C/s. Finite-element simulations for these systems show similar heating trends. This heating response may be used in advanced manufacturing as a means to rapidly weld polymer–polymer interfaces, as will be demonstrated in this report. Our technique uses RF fields to induce localized heating in contrast to uniform bulk heating from external sources such as ovens or furnaces. The methods detailed in this paper provide a polymer processing pathway that may be used to generate RF responsive filler in situ. Finally, we aim to show that LIG–polymer composites may function in an industrial setting, with particular application to additive manufacturing and functional coatings.

A thin film coating with tailorable thickness and clay concentration was prepared by solution casting an aqueous slurry containing poly(vinyl alcohol) (PVOH) and montmorillonite (MMT) clay. The anisotropic clay platelets have excellent alignment due to self-orientation during drying, which results in good transparency and oxygen barrier. A 50 wt % clay coating, with a thickness around 4 μm and visible light transmission of 58%, improves the oxygen barrier of a 179 μm poly(ethylene terephthalate) (PET) substrate by more than 3 orders of magnitude. This PVOH/MMT composite thin film also has good thermal stability and mechanical properties. This simple coating procedure could be used for a variety of packaging applications that use plastic film (e.g., food, pharmaceutical, and electronics).

A self-healable gas barrier nanocoating, which is fabricated by alternate deposition of polyethyleneimine (PEI) and polyacrylic acid (PAA) polyelectrolytes, is demonstrated in this study. This multilayer film, with high elastic modulus, high glass transition temperature, and small free volume, has been shown to be a super oxygen gas barrier. An 8-bilayer PEI/PAA multilayer assembly (≈700 nm thick) exhibits an oxygen transmission rate (OTR) undetectable to commercial instrumentation (<0.005 cc (m d atm )). The barrier property of PEI/PAA nanocoating is lost after a moderate amount of stretching due to its rigidity, which is then completely restored after high humidity exposure, therefore achieving a healing efficiency of 100%. The OTR of the multilayer nanocoating remains below the detection limit after ten stretching-healing cycles, which proves this healing process to be highly robust. The high oxygen barrier and self-healing behavior of this polymer multilayer nanocoating makes it ideal for packaging (food, electronics, and pharmaceutical) and gas separation applications.

A dual vapor responsive polymer actuator that can control the bending curvature acts as a fast and reliable environmental detector.

Front Cover: A polyelectrolyte‐based nanocoating exhibits super oxygen barrier and humidity‐responsive self‐healing behavior. An 8‐bilayer polyethylenimine/poly(acrylic acid) thin film improves the oxygen barrier of a thick poly(ethylene terephthalate) substrate by more than 1000×. High humidity (symbolized by the thread in this schematic) completely restores the super oxygen barrier of the damaged/cracked coating in just 10 minutes. This fast and high‐efficiency self‐healing is repeatable for at least 10 damaging–healing cycles. Further details can be found in article number https://doi.org/10.1002/marc.201700064 by Y. Song, K. P. Meyers, J. Gerringer, R. K. Ramakrishnan, M. Humood, S. Qin, A. A. Polycarpou, S. Nazarenko* and J. C. Grunlan*.

It is important to find environmentally friendly replacements for chromate conversion coatings (CCCs) that are effective anticorrosion layers. In this work, high corrosion resistance is demonstrated with ultrathin (and transparent) multilayer coatings deposited on an aluminum alloy. Cationic polyurethane (PU) and anionic vermiculite clay (VMT) multilayer films were deposited from aqueous solutions using layer-by-layer assembly. The combination of relatively hydrophobic polyurethane and highly aligned clay platelets leads to excellent barrier properties for the PU/VMT coating in an aqueous environment. A 30 bilayer PU/VMT coating, with a thickness of only 300 nm, provides 2 orders of magnitude improvement in impedance and imparts corrosion protection for 5 days. Another advantage of this unique coating system is that no surface treatments are required prior to coating due to the strong adhesion of polyelectrolytes to the metal. The work demonstrates the use of novel LbL assembled nanocoatings as a potential replacement for chromate conversion pretreatments.