Photochemical Design for Diverse Controllable Patterns in Self-Wrinkling Films.

Harnessing the spontaneous surface instability of pliable substances to create intricate, well-ordered, and on-demand controlled surface patterns holds great potential for advancing applications in optical, electrical, and biological processes. However, the current limitations stem from challenges in modulating multidirectional stress fields and diverse boundary environments. Herein, this work proposes a universal strategy to achieve arbitrarily controllable wrinkle patterns via the spatiotemporal photochemical boundaries. Utilizing constraints and inductive effects of the photochemical boundaries, the multiple coupling relationship is accomplished among the light fields, stress fields, and morphology of wrinkles in photosensitive polyurethane (PSPU) film. Moreover, employing sequential light-irradiation with photomask enables the attainment of a diverse array of controllable patterns, ranging from highly ordered 2D patterns to periodic or intricate designs. The fundamental mechanics of underlying buckling and the formation of surface features are comprehensively elucidated through theoretical stimulation and finite element analysis. The results reveal the evolution laws of wrinkles under photochemical boundaries and represent a new effective toolkit for fabricating intricate and captivating patterns in single-layer films.

Dynamic Optical Encryption Fueled via Tunable Mechanical Composite Micrograting Systems.

Optical grating devices based on micro/nanostructured functional surfaces are widely employed to precisely manipulate light propagation, which is significant for information technologies, optical data storage, and light sensors. However, the parameters of rigid periodic structures are difficult to tune after manufacturing, which seriously limits their capacity for in situ light manipulation. Here, a novel anti-eavesdropping, anti-damage, and anti-tamper dynamic optical encryption strategy are reported via tunable mechanical composite wrinkle micrograting encryption systems (MCWGES). By mechanically composing multiple in-situ tunable ordered wrinkle gratings, the dynamic keys with large space capacity are generated to obtain encrypted diffraction patterns, which can provide a higher level of security for the encrypted systems. Furthermore, a multiple grating cone diffraction model is proposed to reveal the dynamic optical encryption principle of MCWGES. Optical encryption communication using dynamic keys has the effect of preventing eavesdropping, damage, and tampering. This dynamic encryption method based on optical manipulation of wrinkle grating demonstrates the potential applications of micro/nanostructured functional surfaces in the field of information security.

Deformation-Induced Photoprogrammable Pattern of Polyurethane Elastomers Based on Poisson Effect.

Elastomers with high aspect ratio surface patterns are a promising class of materials for designing soft machines in the future. Here, a facile method for fabricating surface patterns on polyurethane elastomer by subtly utilizing the Poisson effect and gradient photocrosslinking is demonstrated. By applying uniaxial tensile strains, the aspect ratio of the surface patterns can be optionally manipulated. At prestretched state, the pattern on the polyurethane elastomer can be readily constructed through compressive stress, resulting from the gradient photocrosslinking via selective photodimerization of an anthracene-functionalized polyurethane elastomer (referred to as ANPU). The macromolecular aggregation structures during stretching deformation significantly contribute to the fabrication of high aspect ratio surface patterns. The insightful finite element analysis well demonstrates that the magnitude and distribution of internal stress in the ANPU elastomer can be regulated by selectively gradient crosslinking, leading to polymer chains migrate from the exposed region to the unexposed region, thereby generating a diverse array of surface patterns. Additionally, the periodic surface patterns exhibit tunable structural color according to the different stretching states and are fully reversible over multiple cycles, opening up avenues for diverse applications such as smart displays, stretchable strain sensors, and anticounterfeiting devices.

Dynamic metal patterns of wrinkles based on photosensitive layers.

Regulating metal surfaces with micro-/nanoscale structures is of great significance for both material science and potential applications. However, the intrinsic properties of metals, such as fixed isotropic moduli and inflexible structures, in a sense present major limitations in developing next-generation smart patterned surfaces. In this work, a facile and general patterning strategy is proposed to endow insensitive metal surfaces with controllable spontaneous topologies and dynamic performance by exquisitely introducing an essential photosensitive interlayer. The arresting anthracene-containing photocrosslinking interlayer can selectively predetermine the anisotropic property of compliant bilayers without damaging metals' homogeneous properties, and realize a changeable stiff/soft layer. Furthermore, the mechanical transition mechanism of the self-adaptive wrinkling modes in metal-based trilayer systems is revealed to pave the pathway for regulating functional wrinkled metal surfaces. This photodriven metal patterning strategy can promote the development of brand-new methods for tuning the instability of multilayered materials, and be potentially applied in smart optical devices with dynamic reflectance, including light gratings and "magic" mirrors.

Rotational temperature of nitrogen glow discharge obtained by optical emission spectroscopy.

Measurements of rotational temperature as low as several hundred Kelvin have been measured using optical emission spectroscopy (OES) in nitrogen direct current (DC) glow discharge. The strongest band of the first negative system of nitrogen was chosen to deduce the rotational temperature at four different positions in nitrogen DC glow discharge, the back of cathode; cathode sheath; positive column; and anode glow. In positive column the rotational temperature increased apparently with the increasing discharge voltage from 500 to 1000 V when the pressure was 10 Pa. But with pressure of 20 Pa the rotational temperature in positive column increased slightly with the increase of discharge voltage. On the contrary, the rotational temperature in cathode sheath took reverse tendencies when the discharge voltage varies from 500 to 1000 V. As regard the anode glow, the rotational temperature at 10 Pa decreased with the increase of discharge voltage, but that at pressure of 20 Pa increased. We attribute the different tendencies of the rotational temperature to the different discharge statues at different pressures. When the discharge voltage varies from 500 to 1100 V, the discharge with pressure of 10 Pa is normal glow and that with 20 Pa is abnormal glow.

[Measurement of rotational temperature in N2 DC glow discharge by optical emission spectroscopy].

Measurements of rotational temperature as low as several hundred Kelvin have been achieved using optical emission spectroscopy (OES) in nitrogen DC glow discharge. The strongest band of the first negative system of nitrogen molecule ion was chosen to determine the rotational temperature of nitrogen DC glow discharge at 4 different positions in the discharge area: back of the cathode; cathode sheath; positive column and anode glow region. In positive column the rotational temperature of N2+ increases apparently with the increasing discharge voltage from 500-1,100 V when the pressure is 10 Pa. However at pressure of 20 Pa the rotational temperature in positive column increases slightly with the increase of discharge voltage. On the contrary, the rotational temperature in cathode sheath takes reverse tendency when the discharge voltage varies from 500-1,100 V. As regard the anode glow region, the rotational temperature at 10 Pa decreases with the increase of discharge voltage, but that at the 20 Pa increases. We attribute the different changing tendencies of the rotational temperature to the different discharge status at different pressure. When the discharge voltage varies from 500 to 1,100 V, the discharge at pressure of 10 Pa is normal glow and that at 20 Pa is abnormal glow.