Influence of geometries on the assembly of snowman-shaped Janus nanoparticles

The self-assembly of micro/nanoparticles into suprastructures is a promising way to develop reconfigurable materials and to gain insights into the fundamental question of how matter organizes itself. The geometry of particles, especially those deviating from perfectly spherical shapes, is of significant importance in colloidal assembly because it influences the particle "recognition", determines the particle packing, and ultimately dictates the formation of assembled suprastructures. In order to organize particles into desired structures, it is of vital importance to understand the relationship between the shape of the colloidal building blocks and the assembled suprastructures. This fundamental issue is an enduring topic in the assembly of molecular surfactants, but it remained elusive in colloidal assembly. To address this issue, we use snowman-shaped Janus nanoparticles (JNPs) as a model to systematically study the effect of colloidal geometries on their assembled suprastructures. Ten types of JNPs with identical chemical compositions but with different geometries were synthesized. Specifically, the synthesized JNPs differ in their lobe size ratios, phase separation degrees, and overall sizes. We show that by altering these parameters, both finite suprastructures, such as capsules with different curvatures, and nonfinite suprastructures, including free-standing single-layered or double-layered JNPs sheets, can be obtained via self-assembly. All these different types of suprastructures are constituted by highly oriented and hexagonally packed JNPs. These findings demonstrate the significance of geometries in colloidal assembly, such that slightly changing the building block geometries could result in a large variety of very different assembled structures, without altering the chemistry of the particles

Combined experimental and simulation studies of crosslinked polymer brushes under shear

We have studied the effect of crosslinking on the tribological behavior of polymer brushes using a combined experimental and theoretical approach. Tribological and indentation measurements on poly(glycidyl methacrylate) brushes and gels in the presence of dimethylformamide solvent were obtained by means of atomic force microscopy. To complement experiments, we have performed corresponding molecular-dynamics (MD) simulations of a generic bead-spring model in the presence of explicit solvent and crosslinkers. Our study shows that crosslinking leads to an increase in friction between polymer brushes and a counter-surface. The coefficient of friction increases with increasing degree of crosslinking and decreases with increasing length of the crosslinker chains. We find that the brush-forming polymer chains in the outer layer play a significant role in reducing friction at the interface

High-Power and Ultralong-Life Aqueous Zinc-Ion Hybrid Capacitors Based on Pseudocapacitive Charge Storage

© 2019, © 2019, The Author(s). Rechargeable aqueous zinc-ion hybrid capacitors and zinc-ion batteries are promising safe energy storage systems. In this study, amorphous RuO2·H2O for the first time was employed to achieve fast and ultralong-life Zn2+ storage based on a pseudocapacitive storage mechanism. In the RuO2·H2O||Zn zinc-ion hybrid capacitors with Zn(CF3SO3)2 aqueous electrolyte, the RuO2·H2O cathode can reversibly store Zn2+ in a voltage window of 0.4–1.6 V (vs. Zn/Zn2+), delivering a high discharge capacity of 122 mAh g−1. In particular, the zinc-ion hybrid capacitors can be rapidly charged/discharged within 36 s with a very high power density of 16.74 kW kg−1 and a high energy density of 82 Wh kg−1. Besides, the zinc-ion hybrid capacitors demonstrate an ultralong cycle life (over 10,000 charge/discharge cycles). The kinetic analysis elucidates that the ultrafast Zn2+ storage in the RuO2·H2O cathode originates from redox pseudocapacitive reactions. This work could greatly facilitate the development of high-power and safe electrochemical energy storage.[Figure not available: see fulltext.]

Ultrathin, freestanding, stimuli-responsive, porous membranes from polymer hydrogel-brushes

Responsive nanoporous polymeric membranes with tunable morphologies are fabricated by combining self-assembly of particles from liquid interfaces (SALI) and surface-initiated polymerization (SIP).</p

Prior knowledge auxiliary for few-shot pest detection in the wild

One of the main techniques in smart plant protection is pest detection using deep learning technology, which is convenient, cost-effective, and responsive. However, existing deep-learning-based methods can detect only over a dozen common types of bulk agricultural pests in structured environments. Also, such methods generally require large-scale well-labeled pest data sets for their base-class training and novel-class fine-tuning, and these significantly hinder the further promotion of deep convolutional neural network approaches in pest detection for economic crops, forestry, and emergent invasive pests. In this paper, a few-shot pest detection network is introduced to detect rarely collected pest species in natural scenarios. Firstly, a prior-knowledge auxiliary architecture for few-shot pest detection in the wild is presented. Secondly, a hierarchical few-shot pest detection data set has been built in the wild in China over the past few years. Thirdly, a pest ontology relation module is proposed to combine insect taxonomy and inter-image similarity information. Several experiments are presented according to a standard few-shot detection protocol, and the presented model achieves comparable performance to several representative few-shot detection algorithms in terms of both mean average precision (mAP) and mean average recall (mAR). The results show the promising effectiveness of the proposed few-shot detection architecture

Exfoliation of two-dimensional phosphorene sheets with enhanced photocatalytic activity under simulated sunlight

Two-dimensional phosphorene (2D-BP) nanosheets were successfully prepared by an environmental friendly water exfoliation process. The morphology and structure of exfoliated 2D-BP nanosheets were characterized by SEM, AFM, Raman and UV–Vis. The photocatalytic results demonstrated that 2D-BP nanasheets can generate reactive oxygen species of 1O2 and O2− and effectively enhance the photodegradation of dibutyl phthalate pollutants when coexist with water, oxygen, and light

Versatile triblock Janus nanoparticles : synthesis and self-assembly

Multiblock Janus nanoparticles (JNPs) are anisotropic particles composed of different blocks/lobes with distinct physicochemical properties. The ultimate goal is to obtain JNPs that carry two or more contrasting bulk and surface properties on different parts of the same particle. JNPs are promising candidates for various applications, such as building blocks for self-assembly and multifunctional materials. Here, we report the chemical synthesis of a special type of “versatile” triblock JNPs, which contain three lobes with different chemical compositions, whereby “versatile” means that the triblock JNPs can be separately and independently modified on at least two different lobes through different chemical reactions, offering limitless design possibilities. We further prove that specific chemical tailoring determines the way the JNPs interact and self-assemble, such that either normal or reverse micelles are obtained. In particular, the formation of micelles from triblock JNPs constitutes an initial example of the classical concepts extension from triblock polymers to colloids. We regard the triblock JNPs as representatives of a broader class of versatile anisotropic colloids, giving the ability to combine various functionalities on different parts of the same particle, thus enriching the tool box of nanomaterials and broadening their application potential

Growth of nano-/microcolloidal architectures from janus seeds by ATRP

In the natural world, seeds grow into plants, and the seed diversity ensures significant vegetation heterogeneity. Here, we show the growth of colloidal structures from starting seed nanoparticles by controlled radical polymerization, which resembles the natural processes of plant growth from seeds. Specifically, nano-/microsized architectures with a surprising diversity can be “grown” from snowman-type Janus nanoparticle seeds (JNPS) by atom transfer radical polymerization (ATRP) technique. The current approach aims at concentrating ATRP initiators asymmetrically in the bulk of one JNPS lobe. After the initiating of the polymerization, the addition of monomers promotes JNPS growth into asymmetric nano-/microcolloidal architectures. Depending on the types of the JNPS and on the growth conditions, the grown architectures could adopt dish-, basket-, cocoon-, flower-, helmet-, mushroom-, dumpling-, and pumpkin-like geometries. Additionally, the surfaces of these grown architectures could be controlled to have smooth-, island-, and grouped-island-like nanostructures. This method, providing an alternative approach for synthesizing anisotropic colloids with complex geometries and tunable surface morphologies, enriches the variety of colloidal particle synthetic families

Self-assembly of Janus nanoparticles into transformable suprastructures

One of the greatest challenges in colloidal self-assembly is to obtain multiple distinct but transformable suprastructures from the same particles in monophasic solvent. Here, we combined deformable and rigid lobes in snowman-shaped amphiphilic Janus nanoparticles (JNPs). These JNPs exhibited excellent ability to self-assemble into micelles, worms, mini-capsules, giant- and elongated-vesicles. This rich suprastructural diversity was obtained by kinetic manipulation of the self-assembly conditions. The suprastructures consist of four to thousands of highly oriented JNPs with dimensions ranging from 500-nanometer to 30-μm. Moreover, the suprastructures can be transformed into one another or dissembled into individual particles. These features make colloidal assembly highly comparable to that of amphiphilic molecules, however, key differences were discovered