Emergent Soft Lithographic Tools for the Fabrication of Functional Polymeric Microstructures

Polymeric microstructures (PMs) are useful to a broad range of technologies applicable to, for example, sensing, energy storage, and soft robotics. Due to the diverse application space of PMs, many techniques (e. g., photolithography, 3D printing, micromilling, etc.) have been developed to fabricate these structures. Stemming from their generality and unique capabilities, the tools encompassed by soft lithography (e. g., replica molding, microcontact printing, etc.), which use soft elastomeric materials as masters in the fabrication of PMs, are particularly relevant. By taking advantage of the characteristics of elastomeric masters, particularly their mechanical and chemical properties, soft lithography has enabled the use of non-planar substrates and relatively inexpensive equipment in the generation of many types of PMs, redefining existing communities and creating new ones. Traditionally, these elastomeric masters have been produced from relief patterns fabricated using photolithography; however, recent efforts have led to the emergence of new methods that make use of masters that are self-forming, dynamic in their geometric and chemical properties, 3D in architecture, and/or sacrificial (i. e., easily removed/released using phase changes). These “next generation” soft lithographic masters include self-assembled liquid droplets, microscale balloons, templates derived from natural materials, and hierarchically microstructured surfaces. The new methods of fabrication supported by these unique masters enable access to numerous varieties of PMs (e. g., those with hierarchical microstructures, overhanging features, and 3D architectures) that would not be possible following established methods of soft lithography. This review explores these emergent soft lithographic methods, addressing their operational principles and the application space they can impact.     

Direct Structuring of a Biomimetic Anti‐Reflective,Self‐Cleaning Surface for Light Harvesting in Organic Solar Cells

A one‐step method to fabricate a biomimetic dual‐scale hierarchical structure for a transparent anti‐reflective, self‐cleaning layer for organic solar cells is reported. Template‐mediated UV replica molding is used to directly create a multi‐functional surface with an acrylate‐functionalized perfluoropolyether without complicated processing steps. The surface exhibits superhydrophobic properties and self‐cleaning characteristics. In addition, the surface leads to an enhancement of photovoltaic power conversion efficiency by ≈10% as a result of reflection suppression and transmittance enhancement. The method can easily be applied to large area substrates (22 cm × 24 cm) in a cost‐effective manner. Furthermore, the solar cell can withstand harsh outdoor conditions for a long time, without a notable change in the device performance, owing to robust surface layer and non‐fouling properties.

     

Adsorption and diffusion of argon confined in ordered and disordered microporous carbons

We use a combination of grand canonical Monte Carlo and microcanonical molecular dynamics simulations to study the adsorption and diffusion of argon at 77 K and 120 K confined in previously generated models of a disordered bituminous coal-based carbon, BPL, and an ordered carbon replica of Faujasite zeolite (C-FAU). Both materials exhibit a maximum in the diffusion coefficient as well as anomalous (sub-diffusive) behavior in the mean-squared displacements at short times at some relative pressures. In BPL, the anomalous diffusion occurs at low relative pressures, due to the trapping of argon atoms in small pores. In C-FAU, the anomalous diffusion occurs at high relative pressures, due to competitive diffusion of atoms traveling through windows and constrictions which interconnect the pores. All diffusion eventually tends to Fickian diffusion at longer times.     

Bioinspired preparation of regular dual‐level micropillars on polypropylene surfaces with robust hydrophobicity inspired by green bristlegrass leaves

The fine microstructure on the natural green bristlegrass leaf of Setaria viridis (L.) Beauv, which exhibits a contact angle (CA) of 155°±2° and a rolling angle (RA) of 79°±2°, is carefully observed. Based on the understanding of the underlying mechanisms for superhydrophobicity and moderate surface adhesion, an efficient replica molding strategy is proposed for mimicking the microstructures on green bristlegrass leaf surface to polypropylene (PP) surfaces. The bioinspired PP replica with dual‐level micropillars are molded by using the unitized template of steel Meshes A and B. Interestingly, the PP replica inherits both hydrophobicity and adhesion of the natural leaf. Furthermore, the PP replica can stabilize its hydrophobic state under a 980 Pa external pressure, which is attributed to the composite Cassie‐Wenzel mixed wetting state on the microstructured interface. The CA comparatively goes down and RA increases, resulting in superhydrophobic surface with moderate adhesion on the bioinspired surface. Hence, the microstructures and hydrophobicity are successfully replicated to the PP surface by only using the low cost, available and reliable steel meshes in the bioinspired replica molding process.     

Hierarchical parallelization of divide-and-conquer density functional tight-binding molecular dynamics and metadynamics simulations

Massively parallel divide-and-conquer density functional tight-binding (DC-DFTB) molecular dynamics and metadynamics simulations are efficient approaches for describing various chemical reactions and dynamic processes of large complex systems via quantum mechanics. In this study, DC-DFTB simulations were combined with multi-replica techniques. Specifically, multiple walkers metadynamics, replica exchange molecular dynamics, and parallel tempering metadynamics methods were implemented hierarchically into the in-house Dcdftbmd program. Test simulations in an aqueous phase of the internal rotation of formamide and conformational changes of dialanine showed that the newly developed extensions increase the sampling efficiency and the exploration capabilities in DC-DFTB configuration space.     

Reactive Bond-Order Simulations Using Both Spatial and Temporal Approaches to Parallelism

We describe two different approaches to exploiting parallel computing architecture that have been used successfully for reactive molecular simulation using bond-order potentials. These potentials are based on the Tersoff bond-order formalism, and allow accurate treatement of covalent bonding reactions in the framework of a classical potential. They include both Brenner's reactive empirical bond order (REBO) potential and our adaptive intermolecular version of this potential (AIREBO). Traditional spatial and atom-based parallel decompositioon techniques have been employed in the RMD-CE program developed for parallel molecular dynamics simulations with a variety of reactive potentials. Key features of this implementation, including the object-oriented approach and novel algorithms for the integrator and neighbor lists, are discussed. The resulting code provides efficient scaling down to system sizes of 400 atoms per processor, and has been applied successfully to systems of as many as half a million atoms. For smaller systems, the parallel replica dynamics algorithm has been successfully applied to take advantage of parallelism in the time domain for rare-event systems. This approach takes advantage of the independence of different parts of a dynamics trajectory, and provides excellent parallel efficiencies for systems as small as tens of atoms, where other parallel simulation techniques are not applicable. This technique has been used to model the pyrolysis of hexadecane on the microsecond timescale, at more realistic temperatures than are achievable with other simulation methods.     

Walking freely in the energy and temperature space by the modified replica exchange molecular dynamics method

Replica Exchange Molecular Dynamics (REMD) method is a powerful sampling tool in molecular simulations. Recently, we made a modification to the standard REMD method. It places some inactive replicas at different temperatures as well as the active replicas. The method completely decouples the number of the active replicas and the number of the temperature levels. In this article, we make a further modification to our previous method. It uses the inactive replicas in a different way. The inactive replicas first sample in their own knowledge‐based energy databases and then participate in the replica exchange operations in the REMD simulation. In fact, this method is a hybrid between the standard REMD method and the simulated tempering method. Using different active replicas, one can freely control the calculation quantity and the convergence speed of the simulation. To illustrate the performance of the method, we apply it to some small models. The distribution functions of the replicas in the energy space and temperature space show that the modified REMD method in this work can let the replicas walk freely in both of the two spaces. With the same number of the active replicas, the free energy surface in the simulation converges faster than the standard REMD. © 2016 Wiley Periodicals, Inc.     

Fabrication of biomimetic superhydrophobic surfaces by a simple flame treatment method

A simple flame treatment method was explored to construct micro/nanostructures on a surface and then fabricate a biomimetic superhydrophobic surface at a relatively low cost. SiO₂‐containing polydimethylsiloxane (PDMS) was used as a substrate. The PDMS replicas with various micropatterned surfaces were fabricated using grass leaf, sand paper, and PET sheet with parallel groove geometry as templates via PDMS replica molding. The PDMS replica surfaces with micron structures and the surface of a flat PDMS sheet as a control sample were further treated by flame. The fabricated surfaces were characterized by scanning electron microscopy and water contact angle measurements. The effect of surface microstructures on the transparency of PDMS was also investigated. The studies indicate that the fine nanoscale structures can be produced on the surfaces of PDMS replicas and a flat PDMS sheet by a flame treatment method, and that the hierarchical surface roughness can be adjusted and controlled by varying the flame treatment time. The flame‐treated surfaces of PDMS replicas and a flat PDMS sheet possess superhydrophobicity and an ultra‐low sliding angle reaching a limiting value of 1°, and the anisotropic wettability of the PDMS replica surface with oriented microgroove structures can be greatly suppressed via flame treatment. The visible light transmittance of the flame‐treated flat PDMS surface decreases with prolonged flame treatment times. Copyright © 2016 John Wiley & Sons, Ltd.     

Transparent Electronic Skin Device Based on Microstructured Silver Nanowire Electrode

Transparent, flexible electronic skin holds a wide range of applications in robotics, humanmachine interfaces, artificial intelligence, prosthetics, and health monitoring. Silver nanowire are mechanically flexible and robust, which exhibit great potential in transparent and electricconducting thin film. Herein, we report on a silver-nanowire spray-coating and electrodemicrostructure replicating strategy to construct a transparent, flexible, and sensitive electronic skin device. The electronic skin device shows highly sensitive piezo-capacitance response to pressure. It is found that micropatterning the surface of dielectric layer polyurethane elastomer by replicating from microstructures of natural-existing surfaces such as lotus leaf, silk, and frosted glass can greatly enhance the piezo-capacitance performance of the device. The microstructured pressure sensors based on silver nanowire exhibit good transparency, excellent flexibility, wide pressure detection range (0-150 kPa), and high sensitivity (1.28 kPa^-1).     

副本交换分子动力学

副本交换分子动力学(REMD)是一种广泛应用于蛋白质功能性构象变化模拟及相应自由能计算的增强型采样算法。由于REMD理论严格且采样效率高,近年来备受关注,尤其是针对传统REMD方法的发展和优化,显著提高了REMD的采样效率,拓展了其应用范围。但是各种REMD新型方法的最佳适用范围也存在较大区别,使得如何选用合适的REMD方法成为实际应用的难题和挑战。因此,有必要对各种REMD方法及其应用进行阐述,深入比较各方法的优缺点及其实际应用体系。本综述从REMD的原理出发,回顾了近年来各类REMD方法的变形策略,以助于对REMD方法的理解、应用和继续改进。