Chiral Structure Formation during Casting of Cellulose Nanocrystalline Films.

A Landau-de Gennes formulation coupled with a mass-transfer equation was used to track the evaporation front and the development of chiral microstructures during the casting of sulfuric acid-hydrolyzed cellulose nanocrystal (CNC) films. These simulations are compared to thin-film casting experiments that used analogous processing parameters and environments. The results show that the initial concentration, chiral strength, surface anchoring, speed of drying, and the influence of initial shear alignment all affect the uniformity of the microstructure and the orientation of the chiral director. In this report, we aim to show that under optimal casting conditions, the lateral size of planar microstructural domains that exhibit uniform selective reflection can be achieved on the order of millimeters.

Dielectric Barrier Discharge Applicator for Heating Carbon Nanotube-Loaded Interfaces and Enhancing 3D-Printed Bond Strength.

Material extrusion (ME) 3D printing is a revolutionary technique for manufacturing thermoplastic parts; however, the printed parts typically suffer from poor interlayer bonding, which causes weak tensile strength in the build direction. Many methods have been proposed to address the mechanical deficiencies of 3D-printed parts, but most fall short of a production-ready solution. Here we report the use of a dielectric barrier discharge (DBD) plasma electrode mounted concentrically around the nozzle of an ME 3D printer for in situ welding of thermoplastic parts. This is the first report of a DBD being used as a non-contact means to induce Joule heating in resistive composite materials. The polymer welding process is accomplished by coupling the DBD with the carbon nanotube-loaded interfaces between the 3D-printed layers. The current passing through the part results in rapid resistive heating of the nanotubes and thermal welding of the interfaces. We show that parts printed with this method have isotropic strength and are equivalent to their injection-molded counterparts.

Orientation Relaxation Dynamics in Cellulose Nanocrystal Dispersions in the Chiral Liquid Crystalline Phase.

A Landau-de Gennes formulation was implemented in dynamic finite element simulations to compare with postshear relaxation experiments that were conducted on cholesteric cellulose nanocrystal (CNC) dispersions. Our study focused on the microstructural reassembly of CNCs in lyotropic dispersions as parameters such as chiral strength and gap confinement were varied. Our simulation results show that homeotropic and/or more complicated three-dimensional helical configurations are possible, depending on the choice of these parameters. We also observed how dynamic banding patterns develop into the hierarchical microstructures that are characterized by an equilibrium pitch length in both the experiments and simulations. This work has immediate relevance for cellulose nanocrystal dispersion processing and provides new insight into fluid phase ordering for tailorable optical properties.

Radio Frequency Heating of Carbon Nanotube Composite Materials.

Here, we give the first-ever report of radio frequency (RF) electromagnetic heating of polymer nanocomposite materials via direct-contact and capacitively coupled electric field applicators. Notably, RF heating allows nanocomposite materials to be resistively heated with electric fields. We highlight our novel RF heating technique for multiwalled carbon nanotube (MWCNT) thermoplastic composites and measure their broadband dielectric properties. We also demonstrate three different electric field applicator configurations and discuss their practical use in an industrial setting. We demonstrate the use of RF heating to cure an automotive-grade epoxy loaded with MWCNTs. Our results show that lap shear joints cured faster with the RF method compared with control samples cured in an oven because of the heat-transfer advantages of directly heating the epoxy composite. Finally, we implement our RF curing technique to assemble an automotive structure by locally curing an epoxy adhesive applied to a truck chassis.

Welding of 3D-printed carbon nanotube-polymer composites by locally induced microwave heating.

Additive manufacturing through material extrusion, often termed three-dimensional (3D) printing, is a burgeoning method for manufacturing thermoplastic components. However, a key obstacle facing 3D-printed plastic parts in engineering applications is the weak weld between successive filament traces, which often leads to delamination and mechanical failure. This is the chief obstacle to the use of thermoplastic additive manufacturing. We report a novel concept for welding 3D-printed thermoplastic interfaces using intense localized heating of carbon nanotubes (CNTs) by microwave irradiation. The microwave heating of the CNT-polymer composites is a function of CNT percolation, as shown through in situ infrared imaging and simulation. We apply CNT-loaded coatings to a 3D printer filament; after printing, microwave irradiation is shown to improve the weld fracture strength by 275%. These remarkable results open up entirely new design spaces for additive manufacturing and also yield new insight into the coupling between dielectric properties and radio frequency field response for nanomaterial networks.

The effect of bending stiffness on scaling laws for the size of colloidal nanosheets.

Using coarse-grained Brownian dynamics simulations, we study the relationship between hydrodynamic radius ([Formula: see text] and the lateral size ([Formula: see text] of dispersed nanosheets. Our simulation results show that the bending modulus of the nanosheets has a significant impact on the exponent of this power-law relationship between the radius of gyration (and thus [Formula: see text] and [Formula: see text] The exponent can vary from 0.17 to 1. This sheds light on the interpretation of dynamic light scattering (DLS) measurements, such that DLS data can capture both nanosheet lateral size and modulus (which is, in turn, affected by nanosheet thickness).