Bicompartmental Phase Transfer Vehicles Based on Colloidal Dimers

Colloidal particles have been used extensively for stabilizing oil–water interfaces in petroleum, food, and cosmetics industries. They have also demonstrated promising potential in the encapsulation and delivery of drugs. Our work is motivated by challenging applications that require protecting and transporting active agents across the water–oil interfaces, such as delivering catalysts to underground oil phase through water flooding for in situ cracking of crude oil. In this Research Article, we successfully design, synthesize, and test a unique type of bicompartmental targeting vehicle that encapsulates catalytic molecules, finds and accumulates at oil–water interface, releases the catalysts toward the oil phase, and performs hydrogenation reaction of unsaturated oil. This vehicle is based on colloidal dimers that possess structural anisotropy between two compartments. We encapsulate active species, such as fluorescent dye and catalytic molecules in one lobe which consists of un-cross-linked polymers, while the other polymeric lobe is highly cross-linked. Although dimers are dispersible in water initially, the un-cross-linked lobe swells significantly upon contact with a trace amount of oil in aqueous phase. The dimers then become amphiphilic, migrate toward, and accumulate at the oil–water interface. As the un-cross-linked lobe swells and eventually dissolves in oil, the encapsulated catalysts are fully released. We also show that hydrogenation of unsaturated oil can be performed subsequently with high conversion efficiency. By further creating the interfacial anisotropy on the dimers, we can reduce the catalyst release time from hundred hours to 30 min. Our work demonstrates a new concept in making colloidal emulsifiers and phase-transfer vehicles that are important for encapsulation and sequential release of small molecules across two different phases

Selecting the Swimming Mechanisms of Colloidal Particles: Bubble Propulsion versus Self-Diffusiophoresis

Bubble propulsion and self-diffusiophoresis are two common mechanisms that can drive autonomous motion of microparticles in hydrogen peroxide. Although microtubular particles, when coated with platinum in their interior concave surfaces, can propel due to the formation and release of bubbles from one end, the convex Janus particles usually do not generate any visible bubble. They move primarily due to the self-diffusiophoresis. Coincidentally, the platinum films on those particles were typically coated by physical evaporation. In this paper, we use a simple chemical deposition method to make platinum–polystyrene Janus dimers. Surprisingly, those particles are propelled by periodic growth and collapse of bubbles on the platinum-coated lobes. We find that both high catalytic activity and rough surface are necessary to change the propulsion mode from self-diffusiophoresis to bubble propulsion. Our Janus dimers, with combined geometric and interfacial anisotropy, also exhibit distinctive motions at the respective stages of bubble growth and collapse, which differ by 5−6 orders of magnitude in time. Our study not only provides insight into the link between self-diffusiophoresis and bubble propulsion but also reveals the intriguing impacts of the combined geometric and interfacial anisotropy on self-propulsion of particles

Electric-Field Assisted Assembly of Colloidal Particles into Ordered Nonclose-Packed Arrays

Nonclose-packed colloidal arrays have many potential applications ranging from plasmonic sensors, light trapping for photovoltaics, to transparent electrodes. However, scalable fabrication of those structures remains a challenge. In this Article, we investigate the robustness of an electric-field assisted approach systematically. A monolayer of nonclose-packed crystalline array is first created under a low-frequency alternating-current electric field in solution. We then apply a sequence of direct-current pulses to fix the particle array onto the substrate so that it remains intact even after both field removal and solvent evaporation. Key process parameters such as the alternating-current field strength, direct-current magnitude, particle concentration, and solvent-evaporation rate that affect both ordering and fixing of colloidal particles have been studied systematically. We find that direct currents with an intermediate magnitude induce electrophoretic motion of particles toward the substrate and facilitate their permanent adhesion on the substrate due to strong van der Waals attraction. A higher current, however, causes lateral aggregation of particles arising from electroosmotic flow of solvent and destroys the periodic ordering between particles. This approach, in principle, can be conveniently adapted into the continuous convective assembly process, thus making the fabrication of nonclose-packed colloidal arrays scalable

Change the Collective Behaviors of Colloidal Motors by Tuning Electrohydrodynamic Flow at the Subparticle Level

As demonstrated in biological systems, breaking the symmetry of surrounding hydrodynamic flow is the key to achieve autonomous locomotion of microscopic objects. In recent years, a variety of synthetic motors have been developed based on different propulsion mechanisms. Most work, however, focuses on the propulsion of individual motors. Here, we study the collective behaviors of colloidal dimers actuated by a perpendicularly applied AC electric field, which controls the electrohydrodynamic flow at subparticle levels. Although these motors experience strong dipolar repulsion from each other and are highly active, surprisingly, they assemble into a family of stable planar clusters with handedness. We show that this type of unusual structure arises from the contractile hydrodynamic flow around small lobes but extensile flow around the large lobes. We further reveal that the collective behavior, assembled structure, and assembly dynamics of these motors all depend on the specific directions of electrohydrodynamic flow surrounding each lobe of the dimers. By fine-tuning the surface charge asymmetry on particles and salt concentration in solution, we demonstrate the ability to control their collective behaviors on demand. This novel type of active assembly via hydrodynamic interactions has the potential to grow monodisperse clusters in a self-limiting fashion. The underlying concept revealed in this work should also apply to other types of active and asymmetric particles

Formation of Colloidal Molecules Induced by Alternating-Current Electric Fields

We report a versatile method for building colloidal molecules from particles that are isotropic in geometry and interfacial properties. When an external alternating-current electric field is applied, the particles experience anisotropic interactions that lead to the formation of colloidal oligomers via different assembly pathways that strikingly resemble chemical reactions of real molecules. We propose a mechanism for the formation of colloidal molecules that agrees well with the experiments. Our method can be used to build colloidal analogues of molecules using spherical particles with isotropic properties, which offers considerable advantages over existing methods. Moreover, our approach does not rely on material-specific properties and thus could have potential applications to a broad range of particles with different chemical properties

Gate Control of the Conduction Mechanism Transition from Tunneling to Thermally Activated Hopping

We explore gate control of electron transport through molecules with different repeat units. In the framework of reduced density matrix theory, the computational results show (i) exponential decay in the tunneling regime and (ii) Arrhenius behavior and similar activation energies in the hopping regime, which are qualitatively consistent with experimental observations. Moreover, the gate enables tuning of the activation energy, indicating that the continuous transition from tunneling to hopping could be experimentally observed. The activation energy–gate voltage characteristics are introduced to investigate different conduction regimes

Time Trends in Epidemiologic Characteristics and Imaging Features of Lung Adenocarcinoma: A Population Study of 21,113 Cases in China

<div><p>Objectives</p><p>This study aims to describe time trends of epidemiologic characteristics and imaging features over 14 years among histologically confirmed lung adenocarcinoma (ADC) in China and to discuss the possible reasons for these changes.</p><p>Materials and Methods</p><p>Data of 21,113 pathologically confirmed lung cancer patients from January 1999 to December 2012 were analyzed retrospectively. Preoperative high-resolution computer tomography (HRCT) images were available and reviewed in 5,439 lung ADC patients since 2005. Time trends of the ADC proportion of lung cancer cases, gender distribution, age at diagnosis, the proportion of early-stage ADC and imaging features were investigated.</p><p>Results</p><p>The proportion of ADC increased during the 14 years (<i>P</i> = 0.000). The ratio of female to male ADC cases was higher than both squamous cell carcinoma (SQCC) and total lung cancer cases (<i>P</i> = 0.000). The median age at diagnosis of ADC patients was younger than that of both SQCC and total lung cancer during the 14 years (<i>P</i> = 0.000). The proportion of age group 45–59 years increased in total lung cancer cases (<i>P</i> = 0.000). When stratified by lung cancer histopathologic subtypes, this trend was also observed in ADC (<i>P</i> = 0.001) and SQCC (<i>P</i> = 0.007). The proportion of early-stage cases of ADC increased from 2008 to 2012 (<i>P</i> < 0.001). The proportion of subsolid nodules (SSN) in ADC increased (<i>P</i> = 0.001) from 2005 to 2012.</p><p>Conclusion</p><p>The data suggests that the proportion of ADC increased from 1999 to 2012 especially in middle-aged, female patients; early-stage ADC and SSN on HRCT images gradually increased, which may have been caused by a change in smoking habits and increased application of HRCT.</p></div

Mapping grazing intensity code

We propose a framework based on machine learning algorithms for livestock spatialization at a fine scale, which in turn generates an annual gridded dataset of grazing intensity (GDGI)</p

The gender distribution of patients with ADC or SQCC or of the total lung cancer patients in CHCAMS from 1999 to 2012.

<p>The gender distribution of patients with ADC or SQCC or of the total lung cancer patients in CHCAMS from 1999 to 2012.</p

Bulk Synthesis of Metal–Organic Hybrid Dimers and Their Propulsion under Electric Fields

Metal–organic hybrid particles have great potential in applications such as colloidal assembly, autonomous microrobots, targeted drug delivery, and colloidal emulsifiers. Existing fabrication methods, however, typically suffer from low throughput, high operation cost, and imprecise property control. Here, we report a facile and bulk synthesis platform that makes a wide range of metal–organic colloidal dimers. Both geometric and interfacial anisotropy on the particles can be tuned independently and conveniently, which represents a key advantage of this method. We further investigate the self-propulsion of platinum-polystyrene dimers under perpendicularly applied electric fields. In 1 × 10^–4 M KCl solution, the dimers exhibit both linear and circular motion with the polystyrene lobes facing toward the moving direction, due to the induced-charge electroosmotic flow surrounding the metal-coated lobes. Surprisingly, in deionized water, the same dimers move in an opposite direction, i.e., the metallic lobes face the forward direction. This is because of the impact of another type of electrokinetic flow: the electrohydrodynamic flow arising from the induced charges on the conducting substrate. The competition between the electrohydrodynamic flow along the substrate and the induced-charge electroosmotic flow along the metallic lobe dictates the propulsion direction of hybrid dimers under electric fields. Our synthetic approach will provide potential opportunities to study the combined impacts of the geometric and interfacial anisotropy on the propulsion, assembly, and other applications of anisotropic particles