LIQUID STATE PHYSICS

Author: GARCIA TARRES LINO.
Year: 2004.
University: POLITÉCNICA DE CATALUÑA [www.upc.edu].
Place of defense: Sala d'Actes, FIB. Campus Nord, Edifici B6.
Place of preparation: EDIFICI B5 DESPATX 111C Campus NORD.

Summary: The hydration of solutes surfaces apolares in aqueous solution is an issue of great interest in biological systems to intervene in phenomena such as assembling miscelas and membranes and folding of proteins. The computer simulation of systems they can get information directly to the atomic level is hard to come by experimental means. To reduce the computational time of the simulations were conducted by the parallelism of the algorithm that implements the Molecular dynamics simulation using two methodologies. The first is based on the paradigm of âpaso of mensajesâ and second in the use of shared memory. The second method offers higher benefits. It has carried out the molecular dynamics simulation of ions tetrametilamonio (TMA) and tetraetilamonio (TEA) in water. The structural analysis reveals layers of hydration well formed, which has studied the orientation and dynamics of the molecules that comprise and their residence times and numbers of hydration. The molecules are oriented to the timing dipolar almost tangential to the ion. Likewise, have a lower coefficient autodifusión and older times reorientation that pure water; such influence is isotropic. The hydration layer formed around the ion tetraetilamonio presents a substructure in which water molecules are on preferential positions closer to the atom of nitrogen ion. The layer of ion hydration TEA is larger, is further away ion and has residence times greater than the ion TMA. It has proposed a generalization of the Molecular Dynamics Limiting the potential to gain strength average ions poliatómicos, having applied to the particular case of couples ion TMA-Cl and TMATMA. For the pair of ions TMA-Cl, formed two pairs of ions. The so-called âcontact ion pairâ occurs at a separation interiónica of 4.6 Ã and âsolvent separated ion pair â to 7.0 Ã. With regard to the pair of ions TMA-TMA get a pair of contact for a separation between ions 6.4 Ã. All times reorientation obtained for the ion MRI for molecules and their hydration layer are greater when that is associated free state. The effect is the opposite to that seen in the frequencies derived from the autocorrelation functions of the linear and angular velocity, all of which are higher than those in the free ion. The effects estéricos between ion and groups methyl chloride ion TMA produce restrictions on the relative motion between the ions and ion between MRI and hydration layer. Finally there has been a systematic study of the networks of links bridges hydrogen in the layers of hydration. Ions monoatómicos presented a layer of moisture in which water molecules are oriented with the oxygen atom directed toward him. The anions have the opposite direction, the hydrogen atoms of water molecules are those that are closer to the ion. Such guidelines mean that the hydrogen atoms can not form many links hydrogen bridges with other molecules, such as those occurring in pure water. The lifetimes of links hydrogen bridges are generally higher than those obtained for pure water. The ions have an MRI and TEA distribution and dynamics of hydrogen bridges more similar to that of pure water that cations and anions monoatómicos, which may be the result of different orientation and larger sections of hydration.

Author: SIED MOHAMMED EL BACHIR.
Year: 2004.
University: POLITÉCNICA DE CATALUÑA [www.upc.edu].
Place of defense: ETS d'Enginyeria Industrial de Barcelona,.
Place of preparation: EDIFICI B5 PLANTA 1 NORD.

Summary: The wide range of phase transitions in different physical systems have been the subject of intense studies for a large part of the twentieth century. In the vicinity of a transition phase, the physical quantities can vary so either continuously presented sharp differences at the point of transition. The progress made at the theoretical level group intend these phase transitions in the so-called universal classes setting high common features within each class are reflected by the value of critical exponents. These exponents analytically describe the evolution of these physical quantities (such as specific heat) in the vicinity of the transition, and only depend on certain general characteristics such as parameter order or the type of interactions but not in specifics like the magnitude of the latter. Recent research on liquid crystals show that the transition SmA-N belongs to the class universal 3D-XY, although as a result of the coupling between the parameter of order orientacional nemático and parameter order esméctico corresponding to a one-dimensional layered structure is changed the behavior characteristic of the class 3D-XY to the corresponding point tricítico in which the change occurs order of the transition. The first aim of the thesis was to study the order of the transition SmA-N for a series of liquid crystals of the series n-CB and n-OCB. This study was carried out systematically in binary mixtures, as the generation mix is a relatively simple way to vary controladamente coupling between the two order parameters. The second objective was the creation of binary phase diagrams that provide information about the stability and existence of different phases depending on the temperature and composition. In the recent literature there, compared with other materials, very few diagrams of binary phase between liquid crystals, and the few existing presented some incompatibilities thermodynamics. Here, in this second goal we made the thermodynamic analysis of the same people who enabled us to validate thermodynamically phase diagrams, as well as extract information on the thermodynamic properties of excess. Basically have been used as experimental techniques: Calorimetria by power compensation (DSC), Modulation by Calorimetria by temperature compensation (MDSC), X-ray Diffraction (XRD) and Optical Microscopy (MO).

Author: MASIA MARCO.
Year: 2005.
University: POLITÉCNICA DE CATALUÑA [www.upc.edu].
Place of defense: DEPARTAMENTO D'ORGANITZACIÓN DE EMPRESAS.
Place of preparation: EDIFICI B5 DESPATX B5-011 NORD.

Summary: The fundamental argument for this theory is the study of ion solvatación through computer calculations. Three lines of inquiry have been followed: (i) Solvatación and ionic mobility. The main features of the process of exchange between the first and second layer of moisture for Li + ion in water has been found to be independent of the state termodinámico greatly. It has been shown that the mean square displacement of molecules belonging to inert complex is characterized by a long transitional due to the slow rotational relaxation of the complex. The increase in the ion diffusion coefficient due to intecambios in solvatación layer has been calculated for the first time in the case of Li + and Na +. Finally, we have derived laws of probability linking the estereoquímica and speed ionic instant. (Ii) Plasticizers. It proposes a new procedure for the development of areas of strength intramoleculares, which operates successfully in the case of two molecules of interest in the Batterias to Lithium Ion: ethylene carbonate and g-butirolactona. Regarding the solvatación of Li + in the two solvents, the ion is coordinated by 4 molecules through the carbonyl oxygen with small distortions of molecular geometry. The new allocation of vibrational modes made for the two molecules has helped calculate the changes induced by lithium ion, explaining various features of the spectra esperimentales. (Iii) Polarization. It has studied the effectiveness of the most common methods of polarization for Molecular dynamics simulations in dimers ión-molécula, ab initio calculations using as a reference. Rather than focus on the potential energy surface of complete (typical procedure), it seemed only the electrostatic. We have developed new models polarizables water and carbon tetrachloride, which reproduce the behavior of systems carga-molécula. It has been found that in the case of dimers ión-molécula, requires a correction amortiguamento of polarization over short distances. The method of dipoles spot next to the method amortiguamento of Thole reproduces the basic features for successfully cations and anions atomic.