Anand Yethiraj

Bio: Anand Yethiraj is an academic researcher from St. John's University. The author has contributed to research in topics: Phase transition & Liquid crystal. The author has an hindex of 22, co-authored 72 publications receiving 2381 citations. Previous affiliations of Anand Yethiraj include University of British Columbia & Fundamental Research on Matter Institute for Atomic and Molecular Physics.

Nature of an electric-field-induced colloidal martensitic transition.

Abstract: We study the properties of a solid-solid close-packed to body-centered tetragonal transition in a colloidal suspension via fluorescence confocal laser scanning microscopy, in three dimensions and in real space. This structural transformation is driven by a subtle competition between gravitational and electric dipolar field energy, the latter being systematically varied via an external electric field. The transition threshold depends on the local depth in the colloidal sediment. Structures with order intermediate between close-packed and body-centered tetragonal were observed, with these intermediate structures also being stable and long lived. This is essentially a colloidal analogue of an ‘‘atomiclevel’’ interfacial structure. We find qualitative agreement with theory (based purely on energetics). Quantitative differences can be attributed to the importance of entropic effects.

Dynamics, crystallization and structures in colloid spin coating

Abstract: Spin coating is an out-of-equilibrium technique for producing polymer films and colloidal crystals quickly and reproducibly. In this review, we present an overview of theoretical and experimental studies of the spin coating of colloidal suspensions. The dynamics of the spin coating process is discussed first, and we present insights from both theory and experiment. A key difference between spin coating with polymer solutions and with monodisperse colloidal suspensions is the emergence of long range (centimeter scale) orientational correlations in the latter. We discuss experiments in different physical regimes that shed light on the many unusual partially ordered structures that have long-range orientational order, but no long-range translational order. The nature of these structures can be tailored by adding electric or magnetic fields during the spin coating procedure. These partially ordered structures can be considered as model systems for studying the fundamentals of poorly crystalline and defect-rich solids, and they can also serve as templates for patterned and/or porous optical and magnetic materials.

Electric field driven self-assembly of ionic microgels

Abstract: We study, using fluorescent confocal laser scanning microscopy, the directed self-assembly of cross-linked ionic microgels under the influence of an applied alternating electric field at different effective packing fractions ϕeff in real space. We present a detailed description of the contribution of the electric field to the soft interparticle potential, and its influence on the phase diagram as a function of ϕeff and field strength E at a constant frequency of 100 kHz. In our previous work [Mohanty et al., Soft Matter, 2012, 8, 10819], we demonstrated the existence of field-induced structural transitions both at low and high ϕeff. In this work, we revisit the phase behavior at low and intermediate ϕeff with a focus on both structure and dynamics. We demonstrate the existence of various field induced transitions such as an isotropic fluid to string phase to body centered tetragonal (BCT) crystal phase at low concentrations and a reversible field-induced crystal (face centered cubic, FCC) to crystal (BCT) transition at intermediate concentrations. We also investigate the kinetics of the crystal–crystal transition and demonstrate that this occurs through an intermediate melting process. These results are discussed in the light of previous studies of dipolar hard and charged colloids.

Multiple Path-Dependent Routes for Phase-Transition Kinetics in Thermoresponsive and Field-Responsive Ultrasoft Colloids

Abstract: The nature of solid-solid phase transformations has been a long-standing question spanning the fields of metallurgy and condensed-matter physics, with applications from metallic alloys and ceramics to modern shape-memory materials. In spite of the importance of solid-to-solid transformations in many areas of materials science and condensed-matter physics and the numerous experimental and theoretical studies, a deep understanding of the microstructural changes and the underlying kinetic mechanisms is still missing. In this work, we establish a versatile model system composed of micron-scale ionic microgel colloids, where we not only probe the single-particle kinetics in real space and real time but also tune the phase transition in a multiple-parameter space. In the presence of an imposed electric field, a face-centered cubic (FCC) crystal transforms diffusively into a body-centered tetragonal (BCT) crystal via nucleation and growth. In the reverse direction, however, the BCT phase transforms cooperatively into a long-lived metastable body-centered orthorhombic phase, which only relaxes back to the equilibrium FCC when annealed at higher temperatures. The kinetics is thus either diffusive or martensitic depending on the path, and we believe that these two path-dependent transitions provide the first real-space, particle-level insights of diffusive and martensitic transformations, respectively, in a single system.

An NMR study of macromolecular aggregation in a model polymer-surfactant solution.

Abstract: A model complex-forming nonionic polymer–anionic surfactant system in aqueous solution has been studied at different surfactant concentrations. Using pulsed-field-gradient diffusion NMR spectroscopy, we obtain the self-diffusion coefficients of poly(ethylene glycol) (PEO) and sodium dodecyl sulfate (SDS) simultaneously and as a function of SDS concentration. In addition, we obtain NMR relaxation rates and chemical shifts as a function of SDS concentration. Within the context of a simple model, our experimental results yield the onset of aggregation of SDS on PEO chains (CAC=3.5 mM), a crossover concentration (C2=60 mM) which signals a sharp change in relaxation behavior, as well as an increase in free surfactant concentration and a critical concentration (Cm=145 mM) which signals a distinct change in diffusion behavior and a crossover to a solution containing free micelles. Cm also marks the concentration above which obstruction effects are definitely important. In addition, we obtain the concentration of...

疟原虫var基因转换速率变化导致抗原变异[英]／Paul H, Robert P, Christodoulou Z, et al//Proc Natl Acad Sci U S A

Abstract: 抗原变异可使得多种致病微生物易于逃避宿主免疫应答。表达在感染红细胞表面的恶性疟原虫红细胞表面蛋白1（PfPMP1）与感染红细胞、内皮细胞、树突状细胞以及胎盘的单个或多个受体作用，在黏附及免疫逃避中起关键的作用。每个单倍体基因组var基因家族编码约60种成员，通过启动转录不同的var基因变异体为抗原变异提供了分子基础。

Anisotropy of building blocks and their assembly into complex structures

Abstract: A revolution in novel nanoparticles and colloidal building blocks has been enabled by recent breakthroughs in particle synthesis These new particles are poised to become the ‘atoms’ and ‘molecules’ of tomorrow’s materials if they can be successfully assembled into useful structures Here, we discuss the recent progress made in the synthesis of nanocrystals and colloidal particles and draw analogies between these new particulate building blocks and better-studied molecules and supramolecular objects We argue for a conceptual framework for these new building blocks based on anisotropy attributes and discuss the prognosis for future progress in exploiting anisotropy for materials design and assembly

Directed self-assembly of a colloidal kagome lattice

Abstract: A challenging goal in materials chemistry and physics is spontaneously to form intended superstructures from designed building blocks. In fields such as crystal engineering and the design of porous materials, this typically involves building blocks of organic molecules, sometimes operating together with metallic ions or clusters. The translation of such ideas to nanoparticles and colloidal-sized building blocks would potentially open doors to new materials and new properties, but the pathways to achieve this goal are still undetermined. Here we show how colloidal spheres can be induced to self-assemble into a complex predetermined colloidal crystal-in this case a colloidal kagome lattice-through decoration of their surfaces with a simple pattern of hydrophobic domains. The building blocks are simple micrometre-sized spheres with interactions (electrostatic repulsion in the middle, hydrophobic attraction at the poles, which we call 'triblock Janus') that are also simple, but the self-assembly of the spheres into an open kagome structure contrasts with previously known close-packed periodic arrangements of spheres. This open network is of interest for several theoretical reasons. With a view to possible enhanced functionality, the resulting lattice structure possesses two families of pores, one that is hydrophobic on the rims of the pores and another that is hydrophilic. This strategy of 'convergent' self-assembly from easily fabricated colloidal building blocks encodes the target supracolloidal architecture, not in localized attractive spots but instead in large redundantly attractive regions, and can be extended to form other supracolloidal networks.

Equilibrium cluster formation in concentrated protein solutions and colloids

Abstract: Controlling interparticle interactions, aggregation and cluster formation is of central importance in a number of areas, ranging from cluster formation in various disease processes to protein crystallography and the production of photonic crystals. Recent developments in the description of the interaction of colloidal particles with short-range attractive potentials have led to interesting findings including metastable liquid-liquid phase separation and the formation of dynamically arrested states (such as the existence of attractive and repulsive glasses, and transient gels). The emerging glass paradigm has been successfully applied to complex soft-matter systems, such as colloid-polymer systems and concentrated protein solutions. However, intriguing problems like the frequent occurrence of cluster phases remain. Here we report small-angle scattering and confocal microscopy investigations of two model systems: protein solutions and colloid-polymer mixtures. We demonstrate that in both systems, a combination of short-range attraction and long-range repulsion results in the formation of small equilibrium clusters. We discuss the relevance of this finding for nucleation processes during protein crystallization, protein or DNA self-assembly and the previously observed formation of cluster and gel phases in colloidal suspensions.