Fabricating microscale helical structures from small molecules remains challenging due to the disfavoured torsion energy of twisted architectures and elusory chirality control at different ...hierarchical levels of assemblies. Here we report a combined solution-interface-directed assembly strategy for the formation of hierarchically self-assembled helical microtoroids with micrometre-scale lengths. A drop-evaporation assembly protocol on a solid substrate from pre-assembled intermediate colloids of enantiomeric binaphthalene bisurea compounds leads to microtoroids with preferred helicity, which depends on the molecular chirality of the starting enantiomers. Collective variable-temperature spectroscopic analyses, electron microscopy characterizations and theoretical simulations reveal a mechanism that simultaneously induces aggregation and cyclization to impart a favourable handedness to the final microtoroidal structures. We then use monodispersed luminescent helical toroids as chiral light-harvesting antenna and show excellent Förster resonance energy transfer ability to a co-hosted chiral acceptor dye, leading to unique circularly polarized luminescence. Our results shed light on the potential of the combined solution-interface-directed self-assembly approach in directing hierarchical chirality control and may advance the prospect of chiral superstructures at a higher length scale.
Forming robust associative interactions has been an effective strategy for the design of tough hydrogels. However, the role of associative interactions in the dynamics of hydrogels still remains ...elusive. Here, we report a series of poly(acrylamide-co-methacrylic acid) hydrogels with moderate water contents and excellent mechanical properties that are facilely synthesized by free-radical copolymerization. The mechanical properties of these hydrogels vary with the feeding molar fraction of acrylamide (f am). The gels with f am of 0.2–0.35 exhibit high toughness and good stability in water, which is related to the dense hydrogen bonds and relatively high segment rigidity of the matrix. Dynamic modulus spectra extended by time-temperature superposition and relaxation measurements indicate that the gels undergo glassy-to-rubbery transition with decreased frequency, and the robust hydrogen bonds, whose density is 1–3 times that of entanglements, retard chain disentanglement and contribute to the plateau modulus of the gels at low frequencies. The activation energy for the dissociation of the robust hydrogen bonds is ∼46 kJ mol–1. Furthermore, a decrease in water content results in the shift of dynamic modulus spectra to low frequencies and an increase in transition temperature due to the reduced segment relaxation. To further examine the structure of gel networks, the tensile behaviors of the gels are analyzed using a viscoelastic model. It is found that each partial chain includes 20–30 Kuhn segments, which are stretched after the fracture of intrachain hydrogen bonds to release the hidden length, dissipate energy, and thus toughen the gels. This understanding of the dynamics of the network at different timescales and the contribution of associative interactions to the mechanical properties should be informative for the design of other tough hydrogels.
In situ growing transition metals on N‐doped carbon by atomic doping produces a class of promising alternatives to replace Pt‐based catalysts for redox reactions, yet still suffer from unsatisfactory ...activity and durability in acidic and basic media. Herein, a simple synthetic strategy to fabricate an MnO modifying Co‐Nx/C catalyst with high activity and robust durability is presented. The interphase engineering well controls the Co and N species in the carbon matrix, affording the material with more pyridine N and graphite N; the interaction between Co‐Nx and MnO phase is also well discussed. Accordingly, the obtained Co‐Nx/C‐MnO catalyst exhibits excellent electrocatalytic properties towards oxygen reduction reaction, achieving a half‐wave potential of 0.87 and 0.66 V versus reversible hydrogen electrode in 0.1 m KOH and 0.1 m HClO4 solutions, as well as excellent durability with only −16.9 and −12.2 mV shift after 1000 cycles, respectively. This study provides insights into the design of noble‐metal‐free electrocatalysts from the perspective of active sites and catalyst carriers.
A simple two‐step solid‐phase method is illustrated to obtain the Co‐Nx/C‐MnO catalyst rich of active Co‐Nx moieties. It is unravelled that the Co dopant tunes the intrinsic valence state of Mn meanwhile the synergistic Mn‐Co‐Nx center attenuates the affinity of adsorbed species, thus facilitating oxygen reduction reaction (ORR) kinetics. Particularly, the acidic ORR stability of this catalyst is greatly enhanced by promoting the dissociation of intermediate OOH* and suppressing the H2O2 generation. This study provides a new idea for the design of high active and durable ORR catalysts for clean energy conversion.
Abstract
Many creatures have the ability to traverse challenging environments by using their active muscles with anisotropic structures as the motors in a highly coordinated fashion. However, most ...artificial robots require multiple independently activated actuators to achieve similar purposes. Here we report a hydrogel-based, biomimetic soft robot capable of multimodal locomotion fueled and steered by light irradiation. A muscle-like poly(
N
-isopropylacrylamide) nanocomposite hydrogel is prepared by electrical orientation of nanosheets and subsequent gelation. Patterned anisotropic hydrogels are fabricated by multi-step electrical orientation and photolithographic polymerization, affording programmed deformations. Under light irradiation, the gold-nanoparticle-incorporated hydrogels undergo concurrent fast isochoric deformation and rapid increase in friction against a hydrophobic substrate. Versatile motion gaits including crawling, walking, and turning with controllable directions are realized in the soft robots by dynamic synergy of localized shape-changing and friction manipulation under spatiotemporal light stimuli. The principle and strategy should merit designing of continuum soft robots with biomimetic mechanisms.
This letter presents the design, fabrication, and testing of a diaphragm-based, all-silica fiber tip pressure sensor. A piece of 1.2-μm-thick silica diaphragm was thermally bonded to the end face of ...an etched fiber with an outer diameter (OD) of 125 μm to form a Fabry-Perot (FP) interferometer. The diameter of the etched FP cavity is 105 μm, enabling the sensing area to be large, and thus, a static pressure sensitivity of 12.4 nm/kPa (85.3 nm/psi) is accomplished without the need for any post polishing or etching. The sensor also shows a low-temperature cross sensitivity during tests, owing to its all-silica structure. It is suitable for extensive production, and it has a great potential to work in applications, where miniature size and high sensitivity are essential such as medical applications.
Abstract Chirality is a fundamental property in nature and is widely observed at hierarchical scales from subatomic, molecular, supramolecular to macroscopic and even galaxy. However, the ...transmission of chirality across different length scales and the expression of homochiral nano/microstructures remain challenging. Herein, we report the formation of macroscopic homochiral helicoids with ten micrometers from enantiomeric pyromellitic diimide-based molecular triangle (PMDI-Δ) and achiral pyrene via a screw dislocation-driven co-self-assembly. Chiral transfer and expression from molecular and supramolecular levels, to the macroscopic helicoids, is continuous and follows the molecular chirality of PMDI-Δ. Furthermore, the screw dislocation and chirality transfer lead to a unidirectional curvature of the helicoids, which exhibit excellent circularly polarized luminescence with large | g lum | values up to 0.05. Our results demonstrate the formation of a homochiral macroscopic organic helicoid and function emergence from small molecules via screw dislocations, which deepens our understanding of chiral transfer and expression across different length scales.
•Differing from other interference-based image encryption schemes, two retrieved phase-only masks are considered as two main keys to enhance the security level.•The annoying silhouette problem ...existed in the interference-based image encryption approaches can be effectively avoided.•Two main keys are directly related to original pain images, and the cryptosystem has high resistance against the potential attacks.•Additional parameters such as the conditions of the logistic map, wavelength, and axial distance can further enhance the security of the cryptosystem.
A novel double-image encryption approach has been proposed based on optical interference and logistic map. Initially, original images are rearranged into two scrambled components with the use of the random sequence engendered based on the logistic map with the given conditions such as initial value and bifurcate parameter. One component is used as the input image of the framework of double random phase encoding and encrypted into the ciphertext. Another is decomposed into two phase masks, which are placed into the input plane and transform plane of double random phase encoding, respectively. To strength the nonlinearity of the cryptosystem, these phase masks considered as the main secret keys are further encoded by the aid of two random sequences. Because these keys are produced in the encryption process and directly related to original images, the proposed scheme has high resistance against the potential attacks such as chosen plaintext attack. Meanwhile, the parameters such as wavelength, axial distance, and conditions of the logistic map are considered as additional keys, which can enhance the security level further. Most importantly, the annoying silhouette problem existed in the interference-based encryption methods can be avoided effectively. A set of numerical simulations are presented to demonstrate the validity and feasibility of the proposed technique.
Bioethanol from lignocellulosic biomass is a promising and sustainable strategy to meet the energy demand and to be carbon neutral. Nevertheless, the damage of lignocellulose-derived inhibitors to ...microorganisms is still the main bottleneck. Developing robust strains is critical for lignocellulosic ethanol production. An evolved strain with a stronger tolerance to formate and acetate was obtained after adaptive laboratory evolution (ALE) in the formate. Transcriptional analysis was conducted to reveal the possible resistance mechanisms to weak acids, and
coding for formate dehydrogenase was selected as the target to verify whether it was related to resistance enhancement in
F3. Engineered
FA with
overexpression exhibited boosted tolerance to both formate and acetate, but the resistance mechanism to formate and acetate was different. When formate exists, it breaks down by formate dehydrogenase into carbon dioxide (CO
) to relieve its inhibition. When there was acetate without formate, FDH1 converted CO
from glucose fermentation to formate and ATP and enhanced cell viability. Together,
overexpression alone can improve the tolerance to both formate and acetate with a higher cell viability and ATP, which provides a novel strategy for robustness strain construction to produce lignocellulosic ethanol.
Abstract
In situ growing transition metals on N‐doped carbon by atomic doping produces a class of promising alternatives to replace Pt‐based catalysts for redox reactions, yet still suffer from ...unsatisfactory activity and durability in acidic and basic media. Herein, a simple synthetic strategy to fabricate an MnO modifying Co‐N
x
/C catalyst with high activity and robust durability is presented. The interphase engineering well controls the Co and N species in the carbon matrix, affording the material with more pyridine N and graphite N; the interaction between Co‐N
x
and MnO phase is also well discussed. Accordingly, the obtained Co‐N
x
/C‐MnO catalyst exhibits excellent electrocatalytic properties towards oxygen reduction reaction, achieving a half‐wave potential of 0.87 and 0.66 V versus reversible hydrogen electrode in 0.1
m
KOH and 0.1
m
HClO
4
solutions, as well as excellent durability with only −16.9 and −12.2 mV shift after 1000 cycles, respectively. This study provides insights into the design of noble‐metal‐free electrocatalysts from the perspective of active sites and catalyst carriers.
A Jaya algorithm was recently proposed for solving effectively both constrained and unconstrained optimization problems. In this article, the Jaya algorithm is further extended for solving the ...optimization-based damage identification problem. In the current optimization problem, the vector of design variables represents the damage extent of elements discretized by the finite element model, and a hybrid objective function is proposed by combining two different objective functions to determine the sites and extent of damage. The first one is based on the multiple damage location assurance criterion and the second one is based on modal flexibility change. The robustness and efficiency of the proposed damage detection method are verified through three specific structures. The obtained results indicate that even under relatively high noise level, the proposed method not only successfully detects and quantifies damage in engineering structures, but also shows better efficiency in terms of computational cost.
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