Reversible Conductive Inkjet Printing of Healable and Recyclable Electrodes on Cardboard and Paper

Stabilization of Apolar Nanoparticle Dispersions by Molecular Additives

We study the effect of additives on the colloidal stability of alkanethiol-coated gold nanoparticles. Cyclic amines and sulfides of different sizes were added to dispersions in decane at additive concentrations below 128 mM. Small-angle X-ray scattering (SAXS) indicated that tetrahydrothiophene reduced the agglomeration temperature, Tagglo, by up to 29 °C, a considerable increase in colloidal stability. Amines had a much weaker stabilizing effect of up to 2.5 °C. We found an unexpected maximum of stabilization for low additive concentrations, where Tagglo increased at concentrations above 64 mM. Molecular dynamics simulations were used to correlate these observations with the ligand shell structure. They excluded the physisorption of additives as a stabilization mechanism and suggested that sulfides replace hexadecanethiol on the AuNP surfaces by chemisorption. This hinders ligand ordering, thereby reducing Tagglo, which explains the stabilizing effect. Clustering of chemisorbed additive molecules at high concentration restabilized the ligand ordered state, explaining the detrimental effect of higher additive concentrations. The predictions of the simulations were confirmed by using thermogravimetric analyses and SAXS measurements of washed samples that indicated that the structure of the ligand shell itself, not the presence of physisorbed additives, changes Tagglo. Finally, we calculated potentials of mean force, which show that larger sulfide-based additives have a weaker affinity for the gold surface than smaller ones due to stronger steric hindrance. This explains why smaller cyclic sulfides were the most efficient stabilizers.

Mechanically Robust, Inkjet-Printable Polymer Nanocomposites with Hybrid Gold Nanoparticles and Metal-like Conductivity

Hybrid core-shell nanoparticles with metal cores and conductive polymer shells yield materials that are sinter-free and highly conductive but mechanically weak. Conventional composites of such nanoparticles are electrically insulating. Here, we introduce microscale phase-separated nanocomposites of hybrid gold-PEDOT:PPS particles in insulating poly(vinyl alcohol) (PVA). They combine electrical conductivities of up to 2.1 × 105 S/m at 10 vol % PVA with increased mechanical adhesion on polyethylene terephthalate and glass substrates. We studied the effects of the PVA molecular weight, hydrolyzation degree, and volume fraction. Composites with 10 vol % highly hydrolyzed PVA at a MW of 89-98 kDa had the highest conductivities and stabilities; highly hydrolyzed PVA even increased the conductivity of the hybrid particle layers. We propose the formation of hydrogen bonds between PVA and PEDOT:PSS that lead to demixing and the formation of stable, structured composites. Finally, we demonstrated the inkjet-printability of inks containing PVA in water with viscosities of 1.6-2.0 Pa s at 50.1 s-1 and prepared bending-resistant electrical leads.

Ti3 C2 TX MXene Ink Direct Writing Flexible Sensors for Disposable Paper Toys

Flexible electronics have gained great attention in recent years owing to their promising applications in biomedicine, sustainable energy, human-machine interaction, and toys for children. Paper mainly produced from cellulose fibers is attractive substrate for flexible electronics because it is biodegradable, foldable, tailorable, and light-weight. Inspired by daily handwriting, the rapid prototyping of sensing devices with arbitrary patterns can be achieved by directly drawing conductive inks on flat or curved paper surfaces; this provides huge freedom for children to design and integrate "do-it-yourself (DIY)" electronic toys. Herein, viscous and additive-free ink made from Ti3 C2 TX MXene sediment is employed to prepare disposable paper electronics through a simple ball pen drawing. The as-drawn paper sensors possess hierarchical microstructures with interweaving nanosheets, nanoflakes, and nanoparticles, therefore exhibiting superior mechanosensing performances to those based on single/fewer-layer MXene nanosheets. As proof-of-concept applications, several popular children's games are implemented by the MXene-based paper sensors, including "You say, I guess," "Emotional expression," "Rock-Paper-Scissors," "Arm wrestling," "Throwing game," "Carrot squat," and "Grab the cup," as well as a DIY smart whisker for a cartoon mouse. Moreover, MXene-based paper sensors are safe and disposable, free from producing any e-waste and hazard to the environment.

Flexible biomimetic materials with excellent photothermal performance and superhydrophobicity

Although thousands of superhydrophobic composites have been reported, it is still a challenge to develop eco-friendly superhydrophobic materials by a simple and low-cost strategy. Here, a paper-based superhydrophobic material was prepared by carbon fiber powders and polydimethylsiloxane through a facile spraying method. This obtained material has excellent liquid resistance and self-cleaning properties, whose contact angle reaches 155°. In addition, it possesses excellent photothermal conversion characteristics with a stable surface temperature of 73.4 °C and good water evaporation performance with an evaporation rate up to 1.08 kg/(m2·h) under one solar intensity (100 mW/cm2). Also, it has outstanding self-deicing performance, whose deicing time is 120 s earlier than that of the untreated surface under one solar intensity. An adaptability test shows this strategy of functional coatings can also be applied to other fiber substrates (coating paper, kraft paper, non-woven fabric, paulownia veneer, etc.). Overall, this superhydrophobic material has a promising application prospect in many fields such as waterproof packaging, deicing materials, water evaporation materials, etc.

Large-Scale Synthesis of Hybrid Conductive Polymer-Gold Nanoparticles Using "Sacrificial" Weakly Binding Ligands for Printing Electronics

We describe the gram-scale synthesis of hybrid gold nanoparticles with a shell of conductive polymers. A large-scale synthesis of hexadecyltrimethylammonium bromide (CTAB)-capped gold nanoparticles (AuNP@CTAB) was followed by ligand exchange with conductive polymers based on thiophene in a 10 L reactor equipped with a jacket to ensure a constant temperature of 40 °C and a mechanical stirrer. Slow and controlled reduction of the gold precursors and the presence of small amounts of silver nitrate are revealed to be the critical synthesis variables to obtain particles with a sufficiently narrow size distribution. Batches of approximately 10 g of faceted AuNP@CTAB with tunable average particle sizes from 54 to 85 nm were obtained per batch. Ligand exchange with poly(3,4-ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS) in the same reactor then yielded hybrid Au@PEDOT:PSS nanoparticles. They were used to formulate sinter-free inks for the inkjet printing of conductive structures without the need for a sintering step.