Electric field‐induced self‐assembly of micro‐ and nanoparticles of various shapes at two‐fluid interfaces
TL;DR: A novel method to assemble spherical micro‐ and nanoparticles into monolayers is proposed and its applicability to particles of various shapes is discussed, and results for particles self‐assembly on air–liquid and liquid–liquid interfaces are presented.
Abstract: Particle lithography which explores the capability of particles to self-assemble offers an attractive means to manufacture nanostructured materials. Although traditional techniques typically lead to the formation of dense crystals, adjustable non-close-packed crystals are crucial in a number of applications. We have recently proposed a novel method to assemble spherical micro- and nanoparticles into monolayers. The technique consists of trapping particles at a liquid-fluid interface and applying an electric field normal to the interface. Particles rearrange themselves under the influence of interfacial and electrostatic forces to form 2-D hexagonal arrays of long-range order and whose lattice constant depends on the electric field strength and frequency. Furthermore, the existence of an electric field-induced capillary force makes the technique applicable to submicron and nanosized particles. Although spherical particles are often used, non-spherical particles can be beneficial in practice. Here, we review the method, discuss its applicability to particles of various shapes, and present results for particles self-assembly on air-liquid and liquid-liquid interfaces. In the case of non-spherical particles, the self-assembly process, while still taking place, is more complex as particles experience a torque which causes them to rotate relative to one another. This leads to a final arrangement displaying either a dominant orientation or no well-defined orientation. We also discuss the possibility of dislodging the particles from the interface by applying a strong electric field such that the Weber number is of order 1 or larger, a phenomenon which can be utilized to clean particles from liquid-fluid surfaces.
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TL;DR: In this article, the authors review recent advances in the field of anisotropic particles at fluid interfaces, by focusing on particles in the micron and submicron range, and discuss capillary adsorption, orientation, migration, and self-assembly, on planar and curved interfaces, and the rheology of particle-laden interfaces.
Abstract: Micro and nanoparticle adsorption to and assembly by capillarity at fluid–fluid interfaces are intriguing aspects of soft matter science with broad potential in the directed assembly of anisotropic media. The importance of the field stems from the ubiquitous presence of multiphase systems, the malleability of fluid interfaces, and the ability to tune the interactions of the particles adsorbed on them. While homogeneous spherical particles at interfaces have been well studied, the behavior of anisotropic particles – whether the anisotropy originates from shape or chemical heterogeneity – has been considered only very recently. We review recent advances in the field of anisotropic particles at fluid interfaces, by focusing on particles in the micron and submicron range. We discuss capillary adsorption, orientation, migration, and self-assembly, on planar and curved interfaces, and the rheology of particle-laden interfaces. Prospects for future work and outstanding challenges are also discussed.
259 citations
TL;DR: In this article, the authors review recent advances in the study of suspensions containing shape anisotropic particles and highlight recent results in three areas: evaporation driven assembly, packing, interfacial behavior and the use of these particles in emulsion stabilization.
Abstract: The recent surge to explore and exploit the effect of particle shape has led to several interesting and unique observations in various diverse fields, ranging from biology to material science. To this end, the development of novel synthesis methods has contributed immensely, and has directed this exciting research on the role of particle shape in colloidal systems and other diverse fields. Furthermore, such investigations have resulted in the development of advanced materials, which are novel and multi-functional. In this article, we review recent advances in the study of suspensions containing shape anisotropic particles. In particular, we investigate those pertaining to rod-like or ellipsoidal particles and highlight recent results in three areas – evaporation driven assembly, packing, interfacial behavior and the use of these particles in emulsion stabilization.
153 citations
TL;DR: This paper reviews basic assembly theory and modeling methods and summarizes progress in using fluidic forces (surface tension, viscous) and external fields (magnetic, electric, light) to aid microscale assembly.
Abstract: Assembly permits the integration of different materials and manufacturing processes to increase system functionality. It is an essential step in the fabrication of useful systems across size scales from buildings to molecules. However, at the microscale, traditional “grasp and release” assembly methods and chemically inspired self-assembly processes are less effective due to scaling effects. Many methods have been developed for improving microscale assembly. Often these methods include fluidic forces or the use a fluidic medium in order to enhance their performance. This paper reviews basic assembly theory and modeling methods. Three basic assembly strategies (tool-directed, process-directed, and part-directed) are proposed for categorizing these methods. It then summarizes progress in using fluidic forces (surface tension, viscous) and external fields (magnetic, electric, light) to aid microscale assembly. Applications of recent advances in both continuous flow and digital microfluidics in microscale assembly are also addressed.
59 citations
TL;DR: The important role of controlling forces of various types in relation to different self-assembly techniques is discussed andSelf-assembly is demonstrated as a complex problem that still needs intensive multi-scaled studies.
Abstract: Self-assembly can happen to particles at all length scales, including atomic, nano-, meso- and macro-particles. Although widely used in nanoresearch, many nano-structures reported in the literature are not self-assembled, posing some fundamental questions. This paper will briefly review this topic, answering the following questions: what is the current status in self-assembling nanoparticles? Why is it so difficult to produce self-assembled structures of nanoparticles? How can we effectively overcome the difficulty? The important role of controlling forces of various types in relation to different self-assembly techniques is discussed. Self-assembly is demonstrated as a complex problem that still needs intensive multi-scaled studies.
53 citations
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TL;DR: In this paper, the authors present an attempt towards a unified picture with special emphasis on certain features of "dry spreading": (a) the final state of a spreading droplet need not be a monomolecular film; (b) the spreading drop is surrounded by a precursor film, where most of the available free energy is spent; and (c) polymer melts may slip on the solid and belong to a separate dynamical class, conceptually related to the spreading of superfluids.
Abstract: The wetting of solids by liquids is connected to physical chemistry (wettability), to statistical physics (pinning of the contact line, wetting transitions, etc.), to long-range forces (van der Waals, double layers), and to fluid dynamics. The present review represents an attempt towards a unified picture with special emphasis on certain features of "dry spreading": (a) the final state of a spreading droplet need not be a monomolecular film; (b) the spreading drop is surrounded by a precursor film, where most of the available free energy is spent; and (c) polymer melts may slip on the solid and belong to a separate dynamical class, conceptually related to the spreading of superfluids.
6,042 citations
TL;DR: In this article, solution phase syntheses and size-selective separation methods to prepare semiconductor and metal nanocrystals, tunable in size from ∼1 to 20 nm and monodisperse to ≤ 5%, are presented.
Abstract: ▪ Abstract Solution phase syntheses and size-selective separation methods to prepare semiconductor and metal nanocrystals, tunable in size from ∼1 to 20 nm and monodisperse to ≤5%, are presented. Preparation of monodisperse samples enables systematic characterization of the structural, electronic, and optical properties of materials as they evolve from molecular to bulk in the nanometer size range. Sample uniformity makes it possible to manipulate nanocrystals into close-packed, glassy, and ordered nanocrystal assemblies (superlattices, colloidal crystals, supercrystals). Rigorous structural characterization is critical to understanding the electronic and optical properties of both nanocrystals and their assemblies. At inter-particle separations 5–100 A, dipole-dipole interactions lead to energy transfer between neighboring nanocrystals, and electronic tunneling between proximal nanocrystals gives rise to dark and photoconductivity. At separations <5 A, exchange interactions cause otherwise insulating ass...
4,116 citations
TL;DR: In this paper, the authors compare the behavior observed in systems containing either particles or surfactant molecules in the areas of adsorption to interfaces, partitioning between phases and solid-stabilised emulsions and foams.
Abstract: Colloidal particles act in many ways like surfactant molecules, particularly if adsorbed to a fluid–fluid interface. Just as the water or oil-liking tendency of a surfactant is quantified in terms of the hydrophile–lipophile balance (HLB) number, so can that of a spherical particle be described in terms of its wettability via contact angle. Important differences exist, however, between the two types of surface-active material, due in part to the fact that particles are strongly held at interfaces. This review attempts to correlate the behaviour observed in systems containing either particles or surfactant molecules in the areas of adsorption to interfaces, partitioning between phases and solid-stabilised emulsions and foams.
3,202 citations
2,821 citations