RESUMEN
The prompt visual response is considered to be a highly intuitive tenet among sensors. Therefore, plasmomechanical strain sensors, which exhibit dynamic structural color changes, have recently been developed by using mechanical stimulus-based elastomeric substrates for wearable sensors. However, the reported plasmomechanical strain sensors either lack directional sensitivity or require complex signal processing and device design strategies to ensure anisotropic optical responses. To the best of our knowledge, there have been no reports on utilizing anisotropic mechanical substrates to obtain directional optical responses. Herein, we propose an anisotropic plasmomechanical sensor to distinguish between the applied force direction and the force magnitude. We employ a simple strain-engineered topological elastomer to mechanically transform closely packed metallic nanoparticles (NPs) into anisotropic directional rearrangements depending on the applied force direction. The proposed structure consists of a heterogeneous-modulus elastomer that exhibits a highly direction-dependent Poisson effect owing to the periodically line-patterned local strain redistribution occurring due to the same magnitude of applied external force. Consequently, the reorientation of the self-assembled gold (Au)-NP array manifests dual anisotropy, i.e., force- and polarization-direction-dependent plasmonic coupling. The cost-effectiveness and simple design of our proposed heterogeneous-modulus platform pave the way for numerous optical applications based on dynamic transformation and topological inhomogeneities.
RESUMEN
On-demand photo-steerable amphibious rolling motions are generated by the structural engineering of monolithic soft locomotors. Photo-morphogenesis of azobenzene-functionalized liquid crystal polymer networks (azo-LCNs) is designed from spiral ribbon to helicoid helices, employing a 270° super-twisted nematic molecular geometry with aspect ratio variations of azo-LCN strips. Unlike the intermittent and biased rolling of spiral ribbon azo-LCNs with center-of-mass shifting, the axial torsional torque of helicoid azo-LCNs enables continuous and straight rolling at high rotation rates (≈720 rpm). Furthermore, center-tapered helicoid structures with wide edges are introduced for effectively accelerating photo-motilities while maintaining directional controllability. Irrespective of surface conditions, the photo-induced rotational torque of center-tapered helicoid azo-LCNs can be transferred to interacting surfaces, as manifested by steep slope climbing and paddle-like swimming multimodal motilities. Finally, the authors demonstrate continuous curvilinear guidance of soft locomotors, bypassing obstacles and reaching desired destinations through real-time on-demand photo-steering.
RESUMEN
Programmable 3D shape morphing of hot-drawn polymeric sheets has been demonstrated using photothermal local shrinkage of patterned hinges. However, the hinge designs have been limited to simple linear hinges used to generate in-plane local folding or global curvature. Herein, we report an unprecedented design strategy to realize localized curvature engineering in 3D structures employing radial hinges and stress-releasing facets on 2D polymeric sheets. The shape and height of the 3D structures are readily controlled by varying the number of radial patterns. Moreover, they are numerically predictable by finite elemental modeling simulation with consideration of the spatio-temporal stress distribution, as well as of stress competition effects. Localized curvature engineering provides programming capabilities for various designs including soft-turtle-shell, sea-shell shapes, and saddle architectures with the desired chirality. The results of local curvilinear actuation with quantifiable stress implies options to advance the applicability of self-folded architectures embodying coexisting curved and linear geometric surfaces.
RESUMEN
We herein propose a multiwalled carbon nanotube (MWCNT) doping method into liquid crystal (LC) alignment polyimides (PIs) with low resistivity for resolving both issues of voltage holding and image sticking in low-frequency-driven fringe-field switching (FFS) LC modes using negative dielectric LCs (n-LCs). By utilizing strong ion trapping ability of MWCNTs, the FFS n-LC cell aligned by low resistivity PIs with 0.05 wt% MWCNT doping exhibited an excellent voltage holding ratio of 99% under an extremely low operation frequency of 0.5 Hz and approximately 23.6 times better surface discharging property than that aligned by high resistivity PIs.
RESUMEN
We derived a new analytic physical model for describing the temperature-dependent dielectric permittivities εe(T) and εo(T) in anisotropic mesophase molecules of nematic liquid crystals (NLCs). These temperature-dependent dielectric properties of NLCs could be explained by a six-parameter dielectric permittivity model, where the analytic dielectric permittivity curves of εe(T), εo(T), and Δε(T) from the model using the six parameters ε*, Aε, Bε, (Δε)o, λε, and T* showed excellent agreement with experimental data. The six-parameter dielectric permittivity model was compared to the conventional four-parameter refractive index model. To systematically investigate the temperature-dependent properties of the refractive indices (ne(T) and no(T)) and dielectric permittivities according to the molecular structure of the NLCs, four similar types of fluorinated phenyl bicyclohexane NLCs were selected. Using the presented models, the temperature-dependent behaviour of these four fluorinated NLCs was discussed, according to the molecular length of the alkyl chains and the positions of the fluorine substituents. In particular, two fitting equations for the temperature-dependent properties of threshold voltage and splay elastic LC constant could also be developed using the physical coefficients extracted from the six-parameter dielectric permittivity model, and these equations coincided well with experimental results.
RESUMEN
We propose a highly oriented photochromic dye film for an ultraviolet (UV)-sensing layer, where spirooxazine (SO) derivatives are aligned with the liquid crystalline UV-curable reactive mesogens (RM) using a guest-host effect. For effective electrical UV sensing with a simple metal-insulator-metal structure, our results show that the UV-induced switchable dipole moment amount of the SO derivatives is high; however, their tilting orientation should be controlled. Compared to the dielectric layer with the nearly planar SO dye orientation, the photochromic dielectric layer with the moderately tilted dye orientation shows more than seven times higher the UV-induced capacitance variation.
RESUMEN
We analyzed a transient blinking phenomenon in a fringe-field switching liquid crystal (LC) mode that occurred at the moment of frame change even in the optimized DC offset condition for minimum image flicker. Based on the positional dynamic behaviors of LCs by using a high-speed camera, we found that the transient blink is highly related to the asymmetric responses of the splay-bend transitions caused by the flexoelectric (FE) effect. To remove the transient blink, the elastic property adjustment of LCs was an effective solution because the FE switching dynamics between the splay-enhanced and bend-enhanced deformations are highly dependent on the elastic constants of LCs, which is the cause of momentary brightness drop.
