Dielectric spectroscopy studies of low-disorder and low-dimensional materials

In this thesis we employ dielectric spectroscopy (in different implementations) to study the dielectric properties of different materials ranging from completely disordered supercooled liquids to low-disorder solids with only ratcheting reorientational motions, to low-dimensional systems such as thin films or needle-like crystals. The probed material properties include the electrical conductivity, the space-charge processes due to sample heterogeneities, molecular dynamics, hydrogen-bond dynamics, and phase-transition temperature and kinetics. To study materials in thin film form, we implement silicon-based interdigital electrode devices, which we calibrate to obtain their equivalent capacity in vacuum. We also probe two-dimensional samples obtained by intercalating (sandwiching) organic molecules between parallel graphite oxide sheets. We study both organic and hybrid (organic-inorganic) films, and compared the results with the bulk counterpart of the same materials. Rhodamine films are deposited by two different procedures starting from rhodamine 6G chloride: solution-deposited films are ionic and ordered, while vacuum-deposited films consist of a different, neutral species, namely rhodamine19, due to decomposition of rhodamine 6G upon sublimation. Both types of films display variable-range hopping electronic conduction, and a conductivity-induced space-charge relaxation. Solution deposited films display a dipolar relaxation, absent in rhodamine 19 films. We assign the dipolar relaxation to some intramolecular motion involving the charged nitrogen of the Rhodamine and the chlorine counter-ion. We also performed studies on hybrid films of cadmium iodide covalently attached to ethylamine (CdI2EA), deposited by the Langmuir-Blodgett process. Bulk CdI2EA material has a solid-to-solid (structural) phase transition, which in the Langmuir-Blodgett films occurs 5 degrees higher in temperature. The films displayed a dielectric relaxation dynamics absent in the bulk, and which is either due to the existence of molecular motions in the looser structure of the film, or to the motion of teh surfactant covalently attached to CdI2EA for Langmuir-Blodgett film deposition. Another example of low-dimensional material is biclotymol, whose supercooled liquid form crystallizes into a metastable solid phase which consists of one-dimensional needle-like crystallites. The crystallization kinetics of bicotymol is a textbook example of the Avrami law with exponent n = 2 resulting from a temperature independent nucleation rate of the crystallites followed by unidimensional growth. The instability of the supercooled liquid phase may be related to the existence of fast secondary relaxation dynamics. The last two chapters of the thesis focus on ethane derivatives with distinct side groups, namely tetrachloroethane and ethanolamine. The solid phase of tetrachloroethane displays three distinct relaxation processes. We carry out molecular dynamic simulations to identify the three processes: the slowest is a cooperative reorientational dynamics whereby the molecules rotate by passing through an intermediate equivalent state; such collective relaxation is accompanied by a ¿precursor¿ single-molecule relaxation. The third process is a non-cooperative ratcheting motion between the equilibrium orientation and a high-energy orientation. In ethanolamine we observe the existence of a metastable solid phase besides the known stable one. A very prominent relaxation process is observed in both solid phases and in the liquid. The ubiquity of this relaxation indicates that it is related to local fluctuations of the hydrogen-bond network between the molecules. The same relaxation is also present when ethanolamine is sandwiched between graphite oxide sheets, but it is slower and characterized by a broader distribution of relaxation times due to the interaction with the graphite oxide matrix.En esta tesis utilizamos la espectroscopia dieléctrica para estudiar las propiedades dieléctricas de diferentes materiales que van desde líquidos subenfriados completamente desordenados a sólidos de bajo desorden con movimiento de reorientación, hasta sistemas de baja dimensionalidad tales como películas delgadas o cristales casi unidimensionales. Las propiedades estudiadas incluyen la conductividad eléctrica, los procesos de carga espacial debido a las heterogeneidades de la muestra, la dinámica molecular, la dinámica de enlaces por puente de hidrógeno, y la cinética de cristalización. Para el estudio de materiales en forma de película delgada, se han implementado nuevos dispositivos de electrodo interdigital a base de silicio. Muestras bidimensionales han sido obtenidas también por intercalación de moléculas orgánicas entre planos atómicos de óxido de grafito. Estudiamos películas orgánicas e híbridas orgánicas-inorgánicas depositadas mediante procedimientos diferentes, y comparamos los resultados con las fases puras de los mismos materiales. Obtenemos películas ordenadas de rodamina 6G clorada por crecimiento desde solución, y películas amorfas de rodamina 19 por condensación de vapor en vacío. Ambos tipos de películas presentan una conducción electrónica por salto de electrones y una relajación de carga espacial. Las películas de rodamina 6G clorada muestran además una relajación dipolar, que se asigna a movimientos intramoleculares que involucran la carga asociada al nitrógeno de la rodamina 6G y al átomo de cloro. También se han estudiado películas híbridas de ioduro de cadmio covalentemente unido a etilamina (CdI2EA), depositadas mediante el método Langmuir-Blodgett. El material en fase “bulk” presenta una transición estructural, que en la película delgada aparece a una temperatura superior de unos 5 K. Las películas presentan una relajación dinámica ausente en el material puro y que es debida a la existencia de movimientos moleculares en la estructura de la película (menos densa), o bien al movimiento del surfactante que ha sido enlazado químicamente al CdI2EA para lograr la deposición. Otro ejemplo distinto de material de baja dimensionalidad es el biclotymol, para el que el líquido subenfriado cristaliza en una fase sólida que consiste en cristales unidimensionales (en forma de aguja). La cinética de cristalización del bicotymol es un ejemplo perfecto de la ley de Avrami con exponente n = 2, resultante de una tasa de nucleación independiente de la temperatura, seguida por un crecimiento unidimensional. La inestabilidad de la fase líquida subenfriada puede estar relacionada con la existencia de dinámicas moleculares rápidas. Los dos últimos capítulos de la tesis se centran en dos derivados del etano con grupos laterales distintos, a saber, tetracloroetano y etanolamina. La fase sólida del tetracloroetano muestra tres procesos de relajación distintos. Mediante simulaciones moleculares se han podido identificar los tres procesos: el más lento es un proceso cooperativo en el que las moléculas “giran” sobre si mismas pasando por un estado equivalente intermedio; esta relajación colectiva se acompaña de una relajación "precursora", correspondiente al movimiento de una sola molécula. El tercer proceso es una rotación, no cooperativa, entre la orientación de equilibrio y una orientación de alta energía.Postprint (published version

A Brief Introduction of Resource Management Techniques in Cloud Computing Environment

Cloud computing has become a new era technology that has huge potentials in enterprises and markets. By using this technology, Cloud user can access applications and associated data from anywhere. It has many application for example, Companies are able to rent recourses from cloud for storage and other computational purposes so that infrastructure cost can be reduced significantly. For managing large amount of virtual machine request ,the cloud providers require an efficient resource scheduling algorithm. Here in this paper we summarize different recourse management strategies and its impacts in cloud system we try to analyze the resource allocation strategies based on various matrices and it points out that some of the strategies are efficient than others in some aspects. So the usability of each of the methods can varied according to their application area . DOI: 10.17762/ijritcc2321-8169.150612

Confinement study of an SU(4) gauge theory with fermions in multiple representations

We discuss the phase diagnostics used in our finite-temperature study of an SU(4) gauge theory with dynamical fermions in both the fundamental and two-index antisymmetric representations. Beyond the usual Polyakov loop diagnostics of confinement, we employ several Wilson flow phase diagnostics. The first, what we call the "flow anisotropy", is known in the literature: the deconfinement transition introduces anisotropy between the spatial and temporal directions, to which the flow is extremely sensitive. The second, the "long flow time Polyakov loop," is related but novel. While we do not claim to fully understand this diagnostic, we have empirically found it to be useful as an unusually sharp diagnostic of phase.Comment: 7 pages, 6 figures. Presented at Lattice 2017, the 35th International Symposium on Lattice Field Theory, Granada, Spain, 18-24 June 201

Orientational relaxations in solid (1,1,2,2)tetrachloroethane

We employ dielectricspectroscopy and molecular dynamic simulations to investigate the dipolar dynamics in the orientationally disordered solid phase of (1,1,2,2)tetrachloroethane. Three distinct orientational dynamics are observed as separate dielectric loss features, all characterized by a simply activated temperature dependence. The slower process, associated to a glassytransition at 156 ± 1 K, corresponds to a cooperative motion by which each molecule rotates by 180° around the molecular symmetry axis through an intermediate state in which the symmetry axis is oriented roughly orthogonally to the initial and final states. Of the other two dipolar relaxations, the intermediate one is the Johari-Goldstein precursor relaxation of the cooperative dynamics, while the fastest process corresponds to an orientational fluctuation of single molecules into a higher-energy orientation. The Kirkwood correlation factor of the cooperative relaxation is of the order of one tenth, indicating that the molecular dipoles maintain on average a strong antiparallel alignment during their collective motion. These findings show that the combination of dielectricspectroscopy and molecular simulations allows studying in great detail the orientational dynamics in molecular solids.Peer ReviewedPostprint (author's final draft

Water-triggered conduction and polarization effects in a hygroscopic fullerene salt

Impedance spectroscopy is employed to probe the frequency-dependent conductivity and dielectric response of the crystalline C60O24Na24 fulleride, both in its pure form obtained by heating to 473 K and in its bulk-hydrate form stable only below 390 K, of chemical formula C60O24Na24 ·16 H2O. A dielectric loss feature is visible in both the pure material and the hydrate, displaying different strength and activated behavior in different temperature ranges.Peer ReviewedPostprint (published version

Leishmania donovani: Immunostimulatory Cellular Responses of Membrane and Soluble Protein Fractions of Splenic Amastigotes in Cured Patient and Hamsters

Visceral leishmaniasis (VL), caused by the intracellular parasite Leishmania donovani, L. chagasi and L. infantum is characterized by defective cell-mediated immunity (CMI) and is usually fatal if not treated properly. An estimated 350 million people worldwide are at risk of acquiring infection with Leishmania parasites with approximately 500,000 cases of VL being reported each year. In the absence of an efficient and cost-effective antileishmanial drug, development of an appropriate long-lasting vaccine against VL is the need of the day. In VL, the development of a CMI, capable of mounting Th1-type of immune responses, play an important role as it correlate with recovery from and resistance to disease. Resolution of infection results in lifelong immunity against the disease which indicates towards the feasibility of a vaccine against the disease. Most of the vaccination studies in Leishmaniasis have been focused on promastigote- an infective stage of parasite with less exploration of pathogenic amastigote form, due to the cumbersome process of its purified isolation. In the present study, we have isolated and purified splenic amastigotes of L. donovani, following the traditional protocol with slight modification. These were fractionated into five membranous and soluble subfractions each i.e MAF1-5 and SAF1-5 and were subjected for evaluation of their ability to induce cellular responses. Out of five sub-fractions from each of membrane and soluble, only four viz. MAF2, MAF3, SAF2 and SAF3 were observed to stimulate remarkable lymphoproliferative, IFN-γ, IL-12 responses and Nitric Oxide production, in Leishmania-infected cured/exposed patients and hamsters. Results suggest the presence of Th-1 type immunostimulatory molecules in these sub-fractions which may further be exploited for developing a successful subunit vaccine from the less explored pathogenic stage against VL

Solution filtering affects the glassy dynamics of spincoated thin films of poly(4-chlorostyrene)

Abstract. We investigated the impact of sample preparation on the glassy dynamics of thin films of poly(4-chlorostyrene), a polymer whose molecular mobility is particularly sensitive to changes in the specific volume. Samples were obtained by spincoating, the technique most commonly used to prepare thin organic layers, which consists of pouring dilute polymer solutions onto a plate rotating at a high rate. Our experimental results demonstrate that filtering the solutions before spincoating affects the value of the segmental relaxation time of the as-prepared films. Thin polymer layers obtained via filtered solutions show accelerated segmental dynamics upon confinement at the nanoscale level, once below 100nm, while the samples obtained via unfiltered solutions exhibit bulk-like dynamics down to 15-20nm. We analyzed these results by means of the cooperative free volume rate model, considering a larger free volume content in thin films obtained via filtered solutions. The validity of the model predictions was finally verified by measurements of irreversible adsorption, confirming a larger adsorbed amount, corresponding to a higher specific volume, in the case of samples obtained via unfiltered solutions. Our results prove that filtering is a crucial step in the preparation of thin films, and it could be used to switch on and off nanoconfinement effects. Graphical abstract: [Figure not available: see fulltext.].SCOPUS: ar.jinfo:eu-repo/semantics/publishe

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Collective relaxation dynamics and crystallization kinetics of the amorphous Biclotymol antiseptic

We employ dielectric spectroscopy to monitor the relaxation dynamics and crystallization kinetics of the Biclotymol antiseptic in its amorphous phase. The glass transition temperature of the material as determined by dielectric spectroscopy is Tg=290±1K. The primary (a) relaxation dynamics is observed to follow a Vogel-Fulcher-Tammann temperature dependence, with a kinetic fragility index m=86±13, which classifies Biclotymol as a relatively fragile glass former. A secondary relaxation is also observed, corresponding to an intramolecular dynamic process of the non-rigid Biclotymol molecule. The crystallization kinetics, measured at four different temperatures above the glass transition temperature, follows an Avrami behavior with exponent virtually equal to n=2, indicating one-dimensional crystallization into needle-like crystallites, as experimentally observed, with a time-constant nucleation rate. The activation barrier for crystallization is found to be Ea=115±22kJmol(-1