Donor-Acceptor Viologens with Through-Space Conjugation for Enhanced Visible-Light-Driven Photocatalysis.

A series of novel donor-acceptor (D-A) type viologens with through-space conjugation (TSC) are synthesized. The synergistic effect of D-A conjugation and TSC endow these compounds with a narrower energy gap, excellent redox properties, strong absorption in the visible range (up to 450 nm), and high efficiency of intramolecular charge transfer (ICT). These compounds also exhibit a long-lived charge separation state and stable radical formation.

Concurrent stiffening and softening in hydrogels under dehydration.

Hydrogels are an extraordinary soft matter system that serve as a laboratory for a rich plethora of multiphysical phenomena and find applications that range from biocompatible sensors to soft robots. Here, we report a peculiar experimental observation suggesting concurrent stiffening and softening in hydrogels during the dehydration process. Theories based on Flory's work fail to capture the scaling of mechanical behavior with water content, observed in our experiments.

Antifouling Bilayer Graphene Slit Membrane for Desalination of Nanoplastic-Infested Seawater: A Molecular Dynamics Simulation Study.

It has been shown that the nanoplastic particles present in graphene membranes have a high tendency to cause fouling in them due to the high affinity between graphene and nanoplastic molecules. This poses a significant challenge for the use of graphene membranes for desalination. In this paper, we introduce a double-layer graphene slit membrane as a viable solution to significantly reduce fouling caused by the presence of nanoplastic particles in graphene membranes.

On the Performance of Vertically Aligned Graphene Array Membranes for Desalination.

In this paper, we perform molecular dynamics simulations to investigate the performance of multilayer graphene slit membranes. Graphene slit membranes at a critical slit size have been found to be promising desalination membranes. In this contribution, it is shown that multilayer slit membranes have the potential to provide significantly better permeability while retaining outstanding salt rejection.

A Ternary Seismic Metamaterial for Low Frequency Vibration Attenuation.

Structural vibration induced by low frequency elastic waves presents a great threat to infrastructure such as buildings, bridges, and nuclear structures. In order to reduce the damage of low frequency structural vibration, researchers proposed the structure of seismic metamaterial, which can be used to block the propagation of low frequency elastic wave by adjusting the frequency range of elastic wave propagation. In this study, based on the concept of phononic crystal, a ternary seismic metamaterial is proposed to attenuate low frequency vibration by generating band gaps.

Fabrication of patterned magnetic hydrogels by ion transfer printing.

Magnetic hydrogels have found a myriad of applications in bioengineering and soft robotics. As the function of magnetic hydrogels is affected by the distribution of magnetic nanoparticles, it is imperative to propose a strategy for fabricating patterned magnetic hydrogels. However, previous strategies can only achieve very simple distribution by using external magnetic fields to guide the chain-like assembly of nanoparticles.

Theoretical and Numerical Analysis of Mechanical Behaviors of a Metamaterial-Based Shape Memory Polymer Stent.

Shape memory polymers (SMPs) have gained much attention in biomedical fields due to their good biocompatibility and biodegradability. Researches have validated the feasibility of shape memory polymer stent in treatment of vascular blockage. Nevertheless, the actual application of SMP stents is still in infancy.

A Temperature-Dependent Model of Shape Memory Alloys Considering Tensile-Compressive Asymmetry and the Ratcheting Effect.

Tensile-compressive asymmetry and the ratcheting effect are two significant characteristics of shape memory alloys (SMAs) during uniaxial cyclic tests, thus having received substantial attention in research. In this study, by redefining the internal variables in SMAs by considering the cyclic accumulation of residual martensite, we propose a constitutive model for SMAs to simultaneously reflect tensile-compressive asymmetry and the cyclic ratcheting effect under multiple cyclic tests. This constitutive model is temperature dependent and can be used to reasonably capture the typical features of SMAs during tensile-compressive cyclic tests, which include the pseudo-elasticity at higher temperatures as well as the shape-memory effect at lower temperatures.

Study on Large Deformation Behavior of Polyacrylamide Hydrogel Using Dissipative Particle Dynamics.

Meso-scale models for hydrogels are crucial to bridge the conformation change of polymer chains in micro-scale to the bulk deformation of hydrogel in macro-scale. In this study, we construct coarse-grain bead-spring models for polyacrylamide (PAAm) hydrogel and investigate the large deformation and fracture behavior by using Dissipative Particle Dynamics (DPD) to simulate the crosslinking process. The crosslinking simulations show that sufficiently large diffusion length of polymer beads is necessary for the formation of effective polymer.

Nanopumping of water via rotation of graphene nanoribbons.

In this paper, we perform molecular dynamics simulations to propose a novel bio-inspired nanopumping mechanism that is achieved through the rotation of graphene nanoribbons. Due to the rotation and interaction with water, the graphene nanoribbons undergo morphological transformation. It is shown that with appropriate geometrical and spatial parameters, the resulting morphology is twisted ribbon, which is efficient in pumping of water through a channel.

Side Chains and the Insufficient Lubrication of Water in Polyacrylamide Hydrogel-A New Insight.

Existing theories cannot predict the mechanical property changes of polyacrylamide hydrogels with different water content because of the absence of side chains. In this study, polyacrylamide hydrogels are prepared and tested to investigate the side chain effect on their mechanical properties. First, the comparison between the effective chain density and total chain density provides proof of the large amount of side chains in the polymer network of PAAm hydrogel.

The Marriage of Carborane with Chalcogen Atoms: Nonconjugation, σ-π Conjugation, and Intramolecular Charge Transfer.

A series of chalcogen-containing carborane derivatives were synthesized through a one-pot reaction. The nonconjugated six-membered ring of carborane-fused disulfide () can be electrochemically reduced to a dithiolate derivative. The five-membered ring of carborane-fused chalcogenophenes (-) showed aromaticity and considerable σ-π conjugation.

Phase Transition Effects on Mechanical Properties of NIPA Hydrogel.

Due to its excellent temperature sensitivity, the Poly(-isopropylacrylamide) (NIPA) hydrogel has attracted great interest for a wide variety of applications in tissue engineering and regenerative medicine. NIPA hydrogel undergoes an abrupt volume phase transition at a lower critical solution temperature (LCST) of 30⁻35 °C. However, the mechanical behaviors of NIPA hydrogel induced by phase transition are still not well understood.

Thermal Conductivity of Polyacrylamide Hydrogels at the Nanoscale.

A polymer network can imbibe copious amounts of water and swell, and the resulting state is known as a hydrogel. In many potential applications of hydrogels, such as stretchable conductors, ionic cables, and neuroprostheses, the thermal conductivities of hydrogels should be understood clearly. In the present work, we build molecular dynamics (MD) models of random cross-linked polyacrylamide hydrogels with different water volume fractions through a reaction method.

Effects of temperature on the fracture and fatigue damage of temperature sensitive hydrogels.

As an excellent model material for fundamental studies on temperature-sensitive hydrogels, poly(-isopropylacrylamide) (NIPA) hydrogel has been applied in drug delivery, tissue engineering, and soft robotics. However, the lack of study on fracture and fatigue hinders further development of hydrogels for applications where cyclic loading-unloading is unavoidable. In this study, the fracture and fatigue damage of the NIPA hydrogel were studied for the first time by pure shear tests at different temperatures.

Effects of CNT size on the desalination performance of an outer-wall CNT slit membrane.

We investigate the effect of varying carbon nanotube (CNT) size on the desalination performance through slit confinements formed by horizontally aligned CNTs stacked on top of one another. By increasing the CNT size, the results obtained from this study indicate a corresponding increase in the water flow rate, accompanied by a slight reduction in salt rejection performance. However, due to the increase in the membrane area with CNT size, the permeability performance is observed to reduce as the CNT size increases.

Spontaneous rolling-up and assembly of graphene designed by using defects.

The inverse Stone-Wales defect is a typical defect in graphene, which causes local bumps and local deformation in graphene sheets. Our molecular dynamics simulations show that the spontaneous rolling up of graphene sheets can be induced by orderly distributed inverse Stone-Wales defect bumps, when defective graphene is cut into small strips. This spontaneous process is mainly dominated by the defect density and tailored graphene size.

Pattern Switching in Soft Cellular Structures and Hydrogel-Elastomer Composite Materials under Compression.

It is well known that elastic instabilities induce pattern transformations when a soft cellular structure is compressed beyond critical limits. The nonlinear phenomena of pattern transformations make them a prime candidate for controlling macroscopic or microscopic deformation and auxetic properties of the material. In this present work, the novel mechanical properties of soft cellular structures and related hydrogel⁻elastomer composites are examined through experimental investigation and numerical simulations.

Defects Mediated Corrosion in Graphene Coating Layer.

Mixed results were reported on the anticorrosion of graphene-coated metal surfaces-while graphene serves as an effective short-term barrier against corrosion and oxidation due to its low permeability to gases, the galvanic cell between graphene and the metal substrate facilitates extensive corrosion in the long run. Defects in the graphene layer provide pathways for the permeation of oxidizing species. We study the role of defects in graphene in the anticorrosion using first-principles theoretical modeling.

Tension-compression asymmetry in the binding affinity of membrane-anchored receptors and ligands.

Cell adhesion plays a crucial role in many biological processes of cells, e.g., immune responses, tissue morphogenesis, and stem cell differentiation.

Torsional Detwinning Domino in Nanotwinned One-Dimensional Nanostructures.

How to maintain sustained deformation in one-dimensional nanostructures without localized failure is an important question for many applications of nanotechnology. Here we report a phenomenon of torsional detwinning domino that leads to giant rotational deformation without localized failure in nanotwinned one-dimensional metallic nanostructures. This mechanism is demonstrated in nanotwinned Cu nanorods via molecular dynamics simulations, where coherent twin boundaries are transformed into twist boundaries and then dissolved one by one, resulting in practically unlimited rotational deformation.

Nano-optomechanical actuator and pull-back instability.

This paper studies the nonlinear behavior of a nano-optomechanical actuator, consisting of a free-standing arc in a ring resonator that is coupled to a bus waveguide through evanescent waves. The arc deflects when a control light of a fixed wavelength and optical power is pumped into the bus waveguide, while the amount of deflection is monitored by measuring the transmission spectrum of a broadband probe light. This nanoactuator achieves a maximal deflection of 43.

Comparing the effects of dispersed Stone-Thrower-Wales defects and double vacancies on the thermal conductivity of graphene nanoribbons.

Classical molecular dynamics with the AIREBO potential is used to investigate and compare the thermal conductivity of both zigzag and armchair graphene nanoribbons possessing various densities of Stone-Thrower-Wales (STW) and double vacancy defects, within a temperature range of 100-600 K. Our results indicate that the presence of both kinds of defects can decrease the thermal conductivity by more than 80% as defect densities are increased to 10% coverage, with the decrease at high defect densities being significantly higher in zigzag compared with armchair nanoribbons. Variations of thermal conductivity in armchair nanoribbons were similar for both kinds of defects, whereas double vacancies in the zigzag nanoribbons led to more significant decreases in thermal conductivity than STW defects.

pH-Sensitive Hydrogel for Micro-Fluidic Valve.

The deformation behavior of a pH-sensitive hydrogel micro-fluidic valve system is investigated using inhomogeneous gel deformation theory, in which the fluid-structure interaction (FSI) of the gel solid and fluid flow in the pipe is considered. We use a finite element method with a well adopted hydrogel constitutive equation, which is coded in commercial software, ABAQUS, to simulate the hydrogel valve swelling deformation, while FLUENT is adopted to model the fluid flow in the pipe of the hydrogel valve system. The study demonstrates that FSI significantly affects the gel swelling deformed shapes, fluid flow pressure and velocity patterns.