Vinay Raman

Bio: Vinay Raman is an academic researcher from Saudi Aramco. The author has contributed to research in topics: Nanoparticle & Nanostructure. The author has an hindex of 5, co-authored 9 publications receiving 178 citations. Previous affiliations of Vinay Raman include Indian Institute of Technology Madras & Massachusetts Institute of Technology.

Long-Range Ordering of Symmetric Block Copolymer Domains by Chaining of Superparamagnetic Nanoparticles in External Magnetic Fields

Abstract: A new method to achieve long-range orientational order in symmetric diblock copolymer nanodomains through the alignment and chaining of superparamagnetic nanoparticles in a magnetic field is investigated computationally and theoretically. The effects of nanoparticle size, volume fraction, and magnetization strength are explored using the hybrid particle field (HPF) technique for particles that selectively segregate into one domain of a symmetric diblock copolymer assembly. A critical selectivity of the particles for one nanodomain is observed, above which strong alignment results and below which comparatively disordered structures are formed. The 2D simulations reveal that, for a given nanoparticle volume fraction, only a nanoparticle size commensurate with the block copolymer domain spacing yields well-aligned nanostructures. Nanoparticles significantly larger than the domain spacing break the symmetry of the lamellar phase and result in poor alignment, while high defect densities are observed for smalle...

Mapping Local Cavitation Events in High Intensity Ultrasound Fields

Abstract: Linear acoustic pressure field is obtained by solving the homogenous Helmholtz equation using FEMLAB package (COMSOL Multi-physics 3.2b). The pressure field is used to calculate the collapse pressure of the transient cavitation bubbles by using the cavity cluster approach (1). The regions where the local pressure exceeds the Blake threshold are potential regions of transient cavitation events (2). These are potential sites for active cavitational events that are characterized by experimentally observed chemical and mechanical effects. The ultrasound intensity distribution is calculated from the pressure field distribution. This provides a prediction across the geometry of active cavitation zones which are crucial for the optimization of sonochemical reactors. The results obtained are in disagreement with those previously published (1, 2). This disagreement arises from the incorrect use by others of the out-of-plane wave number, kz, resulting in exponential decay solutions instead of the correct sinusoidal ones.

Particle grinding by high-intensity ultrasound: Kinetic modeling and identification of breakage mechanisms

Abstract: High-intensity ultrasound, is sought as a means to break particles. A horn-type ultrasonic transducer is used to apply HIU into a suspension of alumina particles causing breakage to occur. The rate of particle breakage is monitored continuously via in-line laser-based particle chord length measurement. Kapur function analysis is used to arrive at the grinding kinetics under variations of ultrasonic power, particle loading, temperature of the suspension and particle size. The first Kapur function increases monotonically with increase in input ultrasonic power. Increasing temperature also increases the first Kapur function but an optimum in the range investigated (10–50°C) is observed near 25°C. An exponential relation is found for the variation of first Kapur function with particle size, this being unique to ultrasound-mediated particle breakage. The breakage mechanism is attributed mainly to particle abrasion. Different breakage mechanisms are observed at different temperatures. © 2010 American Institute of Chemical Engineers AIChE J, 2011

Magnetic Field Induced Morphological Transitions in Block Copolymer/Superparamagnetic Nanoparticle Composites

Abstract: This two-dimensional computational study investigates the effect of external magnetic fields on thin film nanocomposites comprised of superparamagnetic nanoparticles dispersed within block copolymer melts, which display a variety of morphological transitions based on the field orientation, nanoparticle loading, and selectivity of the nanoparticles for the blocks. In-plane magnetic fields lead to chaining of the nanoparticles; when selective for the minority block in a hexagonal block copolymer nanostructure, this chaining results in the formation of stripe phases oriented parallel to the magnetic field. When selective for the majority block of the hexagonal structure, nanoparticle chains of sufficient persistence length drive the orientation of the hexagonal morphology with the ⟨100⟩ direction oriented parallel to the magnetic field. Out-of-plane magnetic fields induce repulsive dipolar interactions between the nanoparticles that annihilate the defects in the hexagonal morphology of the block copolymer wh...

Directed self-assembly of block copolymers: a tutorial review of strategies for enabling nanotechnology with soft matter

Abstract: Self-assembly of soft materials is broadly considered an attractive means of generating nanoscale structures and patterns over large areas. However, the spontaneous formation of equilibrium nanostructures in response to temperature and concentration changes, for example, must be guided to yield the long-range order and orientation required for utility in a given scenario. In this review we examine directed self-assembly (DSA) of block copolymers (BCPs) as canonical examples of nanostructured soft matter systems which are additionally compelling for creating functional materials and devices. We survey well established and newly emerging DSA methods from a tutorial perspective. Special emphasis is given to exploring underlying physical phenomena, identifying prototypical BCPs that are compatible with different DSA techniques, describing experimental methods and highlighting the attractive functional properties of block copolymers overall. Finally we offer a brief perspective on some unresolved issues and future opportunities in this field.

Theory and simulation studies of effective interactions, phase behavior and morphology in polymer nanocomposites

Abstract: Polymer nanocomposites are a class of materials that consist of a polymer matrix filled with inorganic/organic nanoscale additives that enhance the inherent macroscopic (mechanical, optical and electronic) properties of the polymer matrix. Over the past few decades such materials have received tremendous attention from experimentalists, theoreticians, and computational scientists. These studies have revealed that the macroscopic properties of polymer nanocomposites depend strongly on the (microscopic) morphology of the constituent nanoscale additives in the polymer matrix. As a consequence, intense research efforts have been directed to understand the relationships between interactions, morphology, and the phase behavior of polymer nanocomposites. Theory and simulations have proven to be useful tools in this regard due to their ability to link molecular level features of the polymer and nanoparticle additives to the resulting morphology within the composite. In this article we review recent theory and simulation studies, presenting briefly the methodological developments underlying PRISM theories, density functional theory, self-consistent field theory approaches, and atomistic and coarse-grained molecular simulations. We first discuss the studies on polymer nanocomposites with bare or un-functionalized nanoparticles as additives, followed by a review of recent work on composites containing polymer grafted or functionalized nanoparticles as additives. We conclude each section with a brief outlook on some potential future directions.