The self-assembly of colloidal particles into larger structures is of interest both scientifically and technologically. The range of possible structures that may be formed by isotropically-interacting spherical particles is narrow, encompassing only a few possibilities. To overcome this limitation, one can introduce one or more forms of anisotropy to the particles to guide their self-assembly.In this work, we study the fabrication and behavior of polymeric microparticles that are chemically- and shape-anisotropic. Single-component, rod-shaped particles are fabricated by stop-flow lithography (SFL) using either hydrophobic and hydrophilic materials. SFL is also used to fabricateJanus particles that incorporate both chemistries within a single particle. The dynamical behavior and self-assembly of these rods are investigated using fluorescence and confocal microscopy over a rangeof different aspect ratios and environmental conditions. We also developed image processing algorithms to enable the quantitative analysis of these data, adapting standard particle identification and tracking techniques to the analysis of rod-shaped colloids.Finally, we demonstrated the fabrication of colloidal particles with branched and more complex morphologies, and briefly studied the self-assembly of these "patchy" particles.
Anisotropic Particle Assemblies: Synthesis, Assembly, Modeling, and Applications covers the synthesis, assembly, modeling, and applications of various types of anisotropic particles. Topics such as chemical synthesis and scalable fabrication of colloidal molecules, molecular mimetic self-assembly, directed assembly under external fields, theoretical and numerical multi-scale modeling, anisotropic materials with novel interfacial properties, and the applications of these topics in renewable energy, intelligent micro-machines, and biomedical fields are discussed in depth. Contributors to this book are internationally known experts who have been actively studying each of these subfields for many years.This book is an invaluable reference for researchers and chemical engineers who are working at the intersection of physics, chemistry, chemical engineering, and materials science and engineering. It educates students, trains the next generation of researchers, and stimulates continuous development in this rapidly emerging area for new materials and innovative technologies. Provides comprehensive coverage on new developments in anisotropic particles Features chapters written by emerging and leading experts in each of the subfields Contains information that will appeal to a broad spectrum of professionals, including but not limited to chemical engineers, chemists, physicists, and materials scientists and engineers Serves as both a reference book for researchers and a textbook for graduate students
Colloidal self-assembly promises to be an elegant and efficient route to the bottom-up fabrication of 3-dimensional structures. Programming hierarchical schemes for colloid self-assembly has the potential to widen structural diversity and mimic biological complexity. However, it remains a grand challenge to bridge hierarchies of multiple length- and time-scales associated with the structure and dynamics along complex self-assembly pathways. This thesis employs a variety of computational techniques to address this challenge in silico, programming colloidal self-assembly for structural hierarchy in close connection with contemporary experimental research. In a series of studies, the self-assembly of designer charge-stabilised colloidal magnetic particles into a number of supracolloidal polyhedra for size-selected clusters is demonstrated. The design space supports self-assembled polyhedra of very different morphologies, namely tubular and hollow spheroidal structures, for which the dominant pathways for self-assembly are elucidated, revealing two distinct mechanisms. Here, it is found that for a staged assembly pathway the structure, which derives the strongest energetic stability from the first stage and the weakest from the second stage, is most kinetically accessible. Stemming from these findings, a generic design principle exploiting a hierarchy of interaction strengths is introduced. This design principle is subsequently employed to demonstrate the hierarchical self-assembly of triblock patchy colloidal particles into a variety of colloidal crystals. Furthermore, this design framework exhibits a novel bottom-up route to the fabrication of cubic diamond colloidal crystals, which until recently, have remained elusive.
Self-assembly of Nano- and Micro-structured Materials Using Colloidal Engineering, Volume 12, covers the recent breakthroughs in the design and manufacture of functional colloids at the micro- and nanoscale level. In addition, it provides analyses on how these functionalities can be exploited to develop self-assembly pathways towards nano- and micro-structured materials. As we seek increasingly complex functions for colloidal superstructures, in silico design will play a critical role in guiding experimental fabrication by reducing the element of trial-and-error that would otherwise be involved. In addition to novel experimental approaches, recent developments in computational modelling are also presented, along with an overview of the arsenal of designing tools that are available to the modern materials scientist. Focuses on promoting feedback between experiment, theory and computation in this cross-disciplinary research area Shows how colloid science plays a crucial role in the bottom-up fabrication of nanostructured materials Presents recent developments in computational modelling
Named after the two-faced roman god, Janus particles have gained much attention due to their potential in a variety of applications, including drug delivery. This is the first book devoted to Janus particles and covers their methods of synthesis, how these particles self-assemble, and their possible uses. By following the line of synthesis, self-assembly and applications, the book not only covers the fundamental and applied aspects, but it goes beyond a simple summary and offers a logistic way of selecting the proper synthetic route for Janus particles for certain applications. Written by pioneering experts in the field, the book introduces the Janus concept to those new to the topic and highlights the most recent research progress on the topic for those active in the field and catalyze new ideas.
A diverse set of functional materials can be fabricated using dispersions of colloids and nanoparticles. If the dispersion is responsive to an external field, like dielectric and charged particles in an electric field or paramagnetic particles in a magnetic field, the field can be used to facilitate self-assembly and control particle transport. One promising feature of field-responsive materials is the ability to drive them out of equilibrium by varying the external field in time. Without the constraints of equilibrium thermodynamics, out-of-equilibrium dispersions display a rich array of self-assembled states with useful material and transport properties. To leverage their unique behaviors in real applications, a predictive, theoretical framework is needed to guide experimental design. In this thesis, I carry out a systematic investigation of the self-assembly and dynamics of colloidal dispersions in time-varying external fields using computer simulations, equilibrium and nonequilibrium thermodynamics, and electro-/magnetokinetic theory. I first develop efficient computational models for simulating suspensions of polarizable colloids in external fields. The simulations are accurate enough to quantitatively reproduce experiments but fast enough to reach the large length and time scales relevant for self-assembly. I use this simulation method to construct the complete equilibrium phase diagram for polarizable particles in steady external fields and find that many-bodied, mutual polarization has a remarkably strong influence on the nature of the self-assembled states. Correctly accounting for mutual polarization enables a thermodynamic theory to compute the phase diagram that agrees well with simulations and experiments. Though the equilibrium structures are crystalline, in practice, dispersions typically arrest in kinetically-trapped, disordered or defective metastable states due to strong interparticle forces. This is a key difficulty preventing scalable fabrication of colloidal crystals. I show that cyclically toggling the external field on and off over time leads to growth of colloidal crystals at significantly faster rates and with many fewer defects than for assembly in a steady field. The toggling protocol stabilizes phases that are only metastable in steady fields, including complex, transmutable crystal structures. I use nonequilibrium thermodynamics to predict the out-of-equilibrium states in terms of the toggle parameters. I also investigate the transport properties of dispersions of paramagnetic particles in rotating magnetic fields. Like toggled fields, rotating fields also drive dispersions out of equilibrium, and their dynamics can be tuned with the rotation frequency. I find that the rotating field greatly increases particle self-diffusivity compared to steady fields. The diffusivity attains a maximum value several times larger than the Stokes- Einstein diffusivity at intermediate rotation frequencies. I develop a simple phenomenological model for magnetophoresis through porous media in rotating fields that predicts enhanced mobility over steady fields, consistent with experiments. Lastly, I study the nonlinear dynamics of polarizable colloids in electrolytes and report a new mode of electrokinetic transport. Above a critical external field strength, an instabilty occurs and particles spontaneously rotate about an axis orthogonal to the field, a phenomenon called Quincke rotation. If the particle is also charged, its electrophoretic motion couples to Quincke rotation and propels the particle orthogonally to the driving field, an electrohydrodynamic analogue to the Magnus effect. Typically, motion orthogonal to a field requires anisotropy in particle shape, dielectric properties, or boundaries. Here, the electrohydrodynamic Magnus (EHM) effect occurs for bulk, isotropic spheres, with the Quincke rotation instability providing broken symmetry driving orthogonal motion. In alternating-current (AC) fields, electrophoresis is suppressed, but the Magnus velocity persists over many cycles. The Magnus motion is decoupled from the field and acts as a self-propulsion, so I propose the EHM effect in AC fields as a mechanism for generating a new type of active matter. The EHM "swimmers" behave as active Brownian particles, and their long-time dynamics are diffusive, with a field-dependent effective diffusivity that is orders of magnitude larger than the Stokes-Einstein diffusivity. I also develop a continuum electrokinetic theory to describe the electrohydrodynamic Magnus effect that is in good agreement with my simulations.
This concise book covers fundamental principles of colloidal self-assembly and overviews of basic and applied research in this field, with abundant illustrations and photographs. Experimental and computer simulation methods to study the colloidal self-assembly are demonstrated. Complementary videos "Visual Guide to Study Colloidal Self-Assembly" on the research procedures and assembly processes are available via SpringerLink to support learning. The book explains basic elements of mechanics and electromagnetism required to study the colloidal self-assembly, so that graduate students of chemistry and engineering courses can learn the contents on their own. It reviews important research topics, including the authors' works on the colloidal self-assembly of more than 30 years’ work. The principal topics include: (1) crystallization of colloidal dispersions, with the emphasis on the role of surface charges, (2) fabrication of large and high-quality colloidal crystals by applying controlled growth methods, (3) association and crystallization by depletion attraction in the presence of polymers, (4) clustering of colloidal particles, especially those in oppositely charged systems, and (5) two-dimensional colloidal crystals. Furthermore, it covers (6) applications of colloidal crystals, ranging from cosmetics to sensing materials. We also describe space experiments on colloidal self-assembly in the International Space Station. This book will interest graduate school students in colloid and polymer science, pharmaceutics, soft matter physics, material sciences, and chemical engineering courses. It will also be a useful guide for individuals in academia and industry undertaking research in this field.
Anisotropic colloids differ from isotropic particles as they may combine a non-spherical shape with a heterogeneous composition or surface chemistry. These versatile colloids have moved into the focus of various research groups in the fields of chemistry and physics. Hence, preparation pathways for novel model systems and their characterization are challenging aspects in fundamental research and material science. In the first part of this work, the author describes the synthesis and characterization of two colloidal systems with dumbbell-shaped core-shell morphology. The core consists of poly(methyl methacrylate) and poly(styrene). As a special feature, the attached shell layer promotes the change of the particle size and the aspect ratio by simply changing the ionic strength or temperature. Depolarized dynamic light scattering (DDLS) was used to investigate how these stimuli affect the translational and the rotational diffusion in the highly diluted state. The hydrodynamics of the particles could be well described with stick-boundary conditions by using analytical expressions for a double sphere, prolate ellipsoid and cylinder or the shell model, respectively. Electron and scanning force microscopy were applied to image the particle morphology in real space. The second part is devoted to the hydrodynamics of monodisperse, submicron-sized colloidal clusters, which consist of one to four spherical building blocks. The author demonstrates that the shell model is an excellent tool to identify the rotational relaxations which are accessible by DDLS.
Materials Nanoarchitectonics: From Integrated Molecular Systems to Advanced Devices provides the latest information on the design and molecular manipulation of self-organized hierarchically structured systems using tailor-made nanoscale materials as structural and functional units. The book is organized into three main sections that focus on molecular design of building blocks and hybrid materials, formation of nanostructures, and applications and devices. Bringing together emerging materials, synthetic aspects, nanostructure strategies, and applications, the book aims to support further progress, by offering different perspectives and a strong interdisciplinary approach to this rapidly growing area of innovation. This is an extremely valuable resource for researchers, advanced students, and scientists in industry, with an interest in nanoarchitectonics, nanostructures, and nanomaterials, or across the areas of nanotechnology, chemistry, surface science, polymer science, electrical engineering, physics, chemical engineering, and materials science. Offers a nanoarchitectonic perspective on emerging fields, such as metal-organic frameworks, porous polymer materials, or biomimetic nanostructures Discusses different approaches to utilizing "soft chemistry" as a source for hierarchically organized materials Offers an interdisciplinary approach to the design and construction of integrated chemical nano systems Discusses novel approaches towards the creation of complex multiscale architectures
