No abstract

Constructing 2D gold nanorods monolayer films with precise particle assembly is of great importance to fundamental and real applications. However, it is usually difficult to achieve macroscopic size, freestanding feature, high density of particle packing, and precisely controllable particle orientation in monolayer films. In this work, a macroscopic, uniform, freestanding orientational monolayer film is facilely and controllably prepared through precise assembly of asymmetrically modified gold nanorods at water–oil interface. The assembling morphologies can be controlled through regulating the interaction between gold nanorods by varying the amounts and sites of modified molecules. The intriguing tunable assemblies exhibit not only adjustable absorption spectrum in a wide range attributed to different particle coupling, but also optimized photothermal conversion capability under low energy density (0.08 W cm‐2). Together with a commercial thermochromic dye, the patterned assemblies show excellent photothermal anti‐counterfeiting performance by reproducing accurate full images in 20 s that are invisible after laser off in 10 min. The excellent laser writing performance is also demonstrated by writing any information on thermochromic dye‐coated assemblies. With the advantages of being macroscopic, equipment‐free, transferable, scalable and with high photothermal conversion capability, the orientational monolayer films pave the way for on‐demand design of sensing and device applications.

The self-assembled gold nanoparticle (NP) superlattice displays unusual but distinctive features such as high mechanical and free-standing performance, electrical conductivity, and plasmonic properties, which are widely employed in various applications especially in biological diagnostics and optoelectronic devices. For a two-dimensional (2D) superlattice monolayer film composed of a given metal nanostructure, it is rather challenging to tune either its plasmonic properties or its optical properties in a reversible way, and it has not been reported. It is therefore of significant value to construct a free-standing 2D superlattice monolayer film of gold nanoparticles with an intelligent response and desired functions. Herein, we developed an easy and efficient approach to construct a gold nanoparticle superlattice film with a dual-responsive plasmonic switch. In this system, gold nanoparticles were coated by polyaniline (PANI) and then interracially self-assembled into a monolayer film at the air–liquid interface. The PANI shell plays two important roles in the superlattice monolayer film. First, the PANI shell acts as a physical spacer to provide a steric hindrance to counteract the van der Waals (vdW) attraction between densely packed nanoparticles (NPs), resulting in the formation of a superlattice by adjusting the thickness of the PANI shell. Second, the PANI shells provide the superlattice film with multiple stimuli such as electrical potential and pH change, leading to reversible optical and plasmonic responsiveness. The superlattice monolayer film can show a vivid color change from olive green to pink, or from olive green to violet by the change of the corresponding stimuli. Also, the localized surface plasmonic resonance (LSPR) of the superlattice monolayer film can be reversibly modulated by both by changing the local pH and applying an electric potential. Notably, a significant plasmonic shift of 157 nm can be achieved in the superlattice monolayer film when the PANI shell with a thickness of 35 nm and gold nanorods as a core were used. The superlattice monolayer film with dual-responsive plasmonic switches is promising for a range of potential applications in optoelectronic devices, plasmonic and colorimetric sensors, and surface-enhanced Raman scattering (SERS).

We establish the physics and understanding of nonlocal nanoscale wave propagation in carbon nanotubes (CNTs) based on nonlocal elastic stress field theory. This is done by developing an analytical nonlocal nanotube model based on the variational principle for wave propagation in CNTs. Specifically, we successfully derive benchmark governing equations of motion for analyzing wave propagation based on an analytical nonlocal shear deformable model. The physical insights of the analytical nonlocal stress model are presented through examples. Analytical solutions with significant observation of wave propagation have been predicted and the prediction compares favorably with molecular dynamic simulations. Qualitative comparisons with other non-nonlocal approaches, including the strain gradients model, the couple stress model and experiments, justify the stiffness enhancement conclusion as predicted by the new nonlocal stress model. New dispersion and spectrum relations derived using this analytical nonlocal model bring an important focus onto the critical wavenumber: stiffness of CNTs and wave propagation are enhanced below the critical wavenumber, while beyond that a sharp decrease in wave propagation is observed. The physics of nanoscale wave propagation in nanotubes are further illustrated by relating the nanoscale and the phase velocity ratio.