RESUMO
Sticky-colored labels are an efficient way to communicate visual information. However, most labels are static. Here, we propose a new category of dynamic sticky labels that change structural colors when stretched. The sticky mechanochromic labels can be pasted on flexible surfaces such as fabric and rubber or even on brittle materials. To enhance their applicability, we demonstrate a simple method for imprinting structural color patterns that are either always visible or reversibly revealed or concealed upon mechanical deformation. The mechanochromic patterns are imprinted with a photomask during the ultraviolet (UV) cross-linking of acrylate-terminated cholesteric liquid crystal oligomers in a single step at room temperature. The photomask locally controls the cross-linking degree and volumetric response of the cholesteric liquid crystal elastomers (CLCEs). A nonuniform thickness change induced by the Poisson's ratio contrast between the pattern and the surrounding background might lead to a color-separation effect. Our sticky multicolor mechanochromic labels may be utilized in stress-strain sensing, building environments, smart clothing, security labels, and decoration.
RESUMO
We report on the preparation of SiO2-based nanoparticles readily available for superhydrophobic applications. In contrast to usual approaches, our process is substrate-free and based on electrostatic adsorption of small SiO2 particles onto large SiO2 cores with the aid of poly(diallyldimethylammonium chloride) followed by calcination and chemical modification with trichlorododecylsilane. The as-prepared nanoparticles are in powder form and exhibit stable superhydrophobic behavior at room temperature because of the unique combination between the hierarchical raspberry-like structure and low surface energy. If properly stored, the nanoparticles retain their functional properties for several months.
RESUMO
A detailed correlation between topographical features and wettability of chemically modified coatings based on silica nanoparticles (SiO2) was performed. In this study, hierarchical structures were prepared by the layer-by-layer (LbL) technique using two different approaches: random roughened surfaces were obtained by exploring stacking defects spontaneously arisen after 15, 30, and 45 assembly cycles of 22 nm SiO2, and a particular structure, commonly known as raspberry-like, was obtained by depositing 22 nm SiO2 over the first deposited 400 nm SiO2. As an intrinsic attribute of the assembly process, the average slope of random roughened surfaces seems to be constant and virtually independent of the number of deposited layers. Additionally, the local slopes are always lower than a critical value (Φcrit) required to stabilize the solid-liquid-air interface; thus, a fully wetted Wenzel state is invariably observed with water contact angles (WCAs) â¼130°. On the other hand, since the local slopes of the raspberry-like structure follow a nearly spherical curvature, small SiO2 can stabilize the solid-liquid-air interface by increasing the local contact angle and avoid the deep penetration of water into the surface asperities, resulting in a WCA â¼167°. The results also suggest that nanoroughness might also play an important role in the pinning effect of the solid-liquid-air contact line, favoring the maintenance of superhydrophobicity of raspberry-like surfaces.