Fabrication of 3D Photonic Crystals from Chitosan That Are Responsive to Organic Solvents

Inspired by photonic nanostructures in nature, such as the hair-like chaetae on the body of sea mice, inverse opal photonic crystals films were fabricated with chitosan, a kind of biomacromolecule found in nature. First, monodispersed polystyrene (PS) colloidal crystal templates with different particle sizes were prepared. The inverse opal films (IOFs) were fabricated through in situ cross-linking of the PS templates. The IOFs contain periodically ordered interconnecting pores that endow the films with photonic stop bands and structural colors, which are visible to the naked eye. The IOFs exhibit rapid reversible changes in their structural colors and reflectance peaks in response to alcohols and phenols. Possible mechanisms for the shifts in the IOF’s reflectance peaks are proposed. The changes in the IOFs in response to alcohols and phenols provide a potential way to visually detect these organic solvents

Chemically Responsive Polymer Inverse-Opal Photonic Crystal Films Created by a Self-Assembly Method

The synthesis of poly-2-hydroxyethyl methacrylate inverse-opal hydrogel (IOHG_PHEMA) was realized by capillary-force-induced in situ polymerization in a polystyrene colloidal crystal template. The created IOHG_PHEMA films show brilliant blue-violet color when they are immersed in deionized water and reach swelling equilibrium. The stop band of the IOHG_PHEMA films can be tuned within the entire visible wavelength range by immersing them into different chemical solutions, such as aldehydes, ketones, amides, dimethyl sulfoxide, and alcohols. The extent of the reflective peak shift not only depends on the number of hydrogen band donors but also on the chain length and structure of the chemicals and their concentration. Since the IOHG_PHEMA films have different reflectance spectra and structural colors in response to different compounds of the same series, this provides a potential way to visually detect homologues and other compounds with similar structure and properties. This simple, yet effective, method also has the potential to be used generically to determine approximate concentration of the solution by direct visual observation of the color change

Mechanically and Chemically Robust Sandwich-Structured C@Si@C Nanotube Array Li-Ion Battery Anodes

Stability and high energy densities are essential qualities for emerging battery electrodes. Because of its high specific capacity, silicon has been considered a promising anode candidate. However, the several-fold volume changes during lithiation and delithiation leads to fractures and continuous formation of an unstable solid-electrolyte interphase (SEI) layer, resulting in rapid capacity decay. Here, we present a carbon–silicon–carbon (C@Si@C) nanotube sandwich structure that addresses the mechanical and chemical stability issues commonly associated with Si anodes. The C@Si@C nanotube array exhibits a capacity of ∼2200 mAh g^–1 (∼750 mAh cm^–3), which significantly exceeds that of a commercial graphite anode, and a nearly constant Coulombic efficiency of ∼98% over 60 cycles. In addition, the C@Si@C nanotube array gives much better capacity and structure stability compared to the Si nanotubes without carbon coatings, the ZnO@C@Si@C nanorods, a Si thin film on Ni foam, and C@Si and Si@C nanotubes. <i>In situ</i> SEM during cycling shows that the tubes expand both inward and outward upon lithiation, as well as elongate, and then revert back to their initial size and shape after delithiation, suggesting stability during volume changes. The mechanical modeling indicates the overall plastic strain in a nanotube is much less than in a nanorod, which may significantly reduce low-cycle fatigue. The sandwich-structured nanotube design is quite general, and may serve as a guide for many emerging anode and cathode systems