PHYSICS OF COLLOIDS

Author: VALLE DELGADO JUAN JOSÉ.
Year: 2003.
University: GRANADA [www.ugr.es].
Place of defense: FACULTAD DE CIENCIAS.
Place of preparation: FACULTAD DE CIENCIAS.

Summary: Since the Astrophysics (whose object of study are the stars, galaxies and constellations) to the Particle Physics and High Energy (where electrons, protons, neutrons and elementary particles also are the target of investigations), the physics can be divided into very different fields. One of those areas is the Colloidal Physics, responsible for the study of particles that are midway between the microscopic and the macroscopic world, with sizes ranging from a few nanometers and several microns. The dispersions of these particles in a medium are called colloids. In the case where the means of dispersion is a liquid (usually water) speaks of colloidal dispersion or dissolution. Paints, lacquers, aerosols, food dispersions (mayonnaise, butter, ice cream, milk, etc..), Inks, biological fluids such as blood, pharmaceuticals and cosmetics are just some examples of colloidal dispersion. The study of the interactions between colloidal particles and analysis of the dependence of these interactions with the characteristics of the particles (size, type, density surface loading) and environmental conditions (temperature, pH, the presence of salt and / or other particulates, implementation of an external field -gravitatorio, electric or magnetic, etc.). are some of the main objectives of Physics Colloidal. These interactions can be repulsive, keeping colloidal particles as individual entities in the dissolution (then said that the dispersion coloidas is stable), or can be attractive, favoring the aggregation of these particles (spoken then of instability of the colloidal dispersion ). The study of the phenomena of aggregation or colloidal stability is not only important for enhancing and improving our intellectual baggage (from the standpoint of basic science), but also because there are many practical applications of these phenomena: coating surfaces, purification of sewage, oil extraction, separation of minerals, sedimentation, adsorption on surfaces are a few examples among many others. There are different types of interactions between surfaces or colloidal particles: repulsion of electric double layer, van der Waals forces estéricas forces hydrophobic forces hydration, and so on. This paper has as its primary objective the study of interactions between systems hidrófilos very different nature (latex anfótero, silíce, proteins), paying particular attention to possible hydration forces present in them. These forces are repulsive interactions short-range (less than 3 or 4 nm) falling exponentially with the distance of separation between surfaces. Traditionally associated with the formation of a layer of water heavily linked to the area or the presence of highly hydrated ions around them. Thus, through techniques sipersión light has been studied colloidal stability of a latex anfótero introducing identical groups surface (Carboxilos and aminos) to the protein. This látexo could be used as a model system to better understand the stability and behavior of proteins at different conditions d epH and concentrations of salt. The impressive results achieved, particularly with regard to stability in certain environmental conditions of dissolution, leading to a broad discussion of the interactions that may exist between these particles. But without a doubt, the best way to study the interactions is midiéndolas directly. The invention and development in recent years sophisticated devices capable of measuring the forces of interaction between two surfaces has provoked an enormous revolution in physics Colloid and Interface. This paper describes some of these devices (Característi 8 cas, come afd tajas, constraints, etc..), With particular emphasis on the fundamentals of atomic force microscope (AFM) and the technique for measurement probe colloidal interactions surface geometry known. This device, and this technique have yielded experimental results shown in this paper: interaction between surfaces in aqueous medium silica, between surfaces depoliestireno and between layers of protein. In all cases he examines the effect of pH and the concentration of salt in the environment, as well as the type of salt used. Especially interesting is the interaction between layers of protein. The big impact it may have on various fields of science, industry and technology knowledge of the interactions between proteins make this point, without a doubt, one of the most interesting d this work. Thus, two different proteins have been studied: bovine serum albumin or BSA and apoferritina. In the case d BSA has also analyzed the effect of different substrates of adsorption (silica and polystyrene). The striking thing about the results obtained with proteins has been the extent of a further push to high concentrations of salt when the pH of the medium is superior to point isoeléctrio of proteins. This push has been associated with hydration forces by the very presence of hydrated ions on the surface protein. It also discusses the important implications of these interactions on the stability of these biomolecules in biological systems and their possible application, for example, in stabilizing inmunodiagnóstico test. The last chapter of this work is reserved for an analysis on the origin of the forces of hydration. Various theories have emerged in the last thirty years are contrasted with experimental results of interaction between silicon surfaces, leading to some interesting conclusions. We can end this summary highlighting the utility of AFM as tools for measuring interactions between biological molecules (proteins). The enormous potential and the continued development of this device portend a very promising future as both the AFM to scientific research in fields such as Surface Science, Materials Engineering, Biology, Medicine, etc..

Author: BARBOSA FERNÁNDEZ SILVIA.
Year: 2004.
University: SANTIAGO DE COMPOSTELA [www.usc.es].
Place of defense: FACULTAD DE FÍSICA.
Place of preparation: FACULTAD DE FÍSICA.

Summary: Doctoral Thesis This has been done in the Laboratory of Physics of Colloids and Polymers Group of Complex Systems, Department of Physics of Condensed Matter at the University of Santiago de Compostela. The results obtained in this thesis can be divided into two distinct parts: The first part is a continuation of the line of investigation launched a few years ago by our research group. This line began with the thermodynamic study of the formation of aggregates of substances anfifílicas with aplícaciones pharmaceutical, and then move on to study the interaction of natural polymer molecules anfifílicas: drugs and surfactants, some of whose results are presented in the memory of Thesis. The interaction between protínas globular and substances anfifílicas has been objero of estuio for over fifty years. These interactions lead to the formation of complexes between the protein molecules and those of substance anfifílica. The importaf) ment of this kind of research has its origins in the action of many agents antímicrobianos depends on their ability to interact with proteins. The affinity of them by the agent, and thus their power therapy, is relacionaado with interactions hidrófilas-hidrófobas in the molecule, and this character is primarily responsible for their interactions with proteins. Moreover, the physical demands to be a drug store, as well as dose-dependent in vivo administration of their característícas aggregation. For its pharmacological action is eficarz once administered should interact with biomolecules. Thus, many drugs, particularly those with anesthetic effects, reassuring, antidepressants or antibiotics, exert their action via interactions with membrans biological weapons. However, these compounds are to be transported to their place of action and, normally, that function is carried out by blood plasma proteins, primarily seroalbúmina human. Therefore, we need a knowledge of the interactions between proteins for blood plasma and drugs structure anfifílica to determine the optimal dose administration of these compounds, which will enable them to exercise their therapeutic action. Thus, in the first, which corresponds to Chapter 3 of memory, we carried out a survey and thermodynamic characterization of the complex formed by the human protein seroalbúmina (HSA) and the synthetic penicillins nature anfifílica cloxacillin and dicloxacilina. They have used the following experimental techniques: densimetría, speed of sound, surface tension, calorimetry and static and dynamic scattering of light. On the other hand, a condíción necessary for any drug to be absorbed by a cell membrane is their solubility. There are a large number of pharmaceutical compounds whose solubility in water is invalid or does not reach the concentrations required for its therapeutic effect. A mechanism that provides a promising future as medío solubilizador and transport of drugs are insoluble or slightly soluble block copolymers. Thus, the second part of the memory is centered a new line of research that we have recently begun in collaboration with groups investígación the powers of Chemistry and Pharmacy Manchester: characterization of block copolymers as transportation systems and release of drugs and the study of mechanisms of control of its molecular structure by the presence of additives in the system. The copolymers we are analyzed non-ionic block copolymer for 8 mados po a76 r uníón through liaison type ether (COC) from their blocks, and belonging to the family of polioxiranos. Such copolymers presented character anfifílico because, in them, combine blocks hidrófilos and block hidrófobos. The sequential polymerization oxide etilieno with other oxides alquíleno leads to the formation of a broad range of block copolymers with different hidrofobicidades and structures. These copolymers, to be formed by blocks hidrófilos and hidrófobos, associate in solution, forming aggregates micelares. Therefore, in disolucíón aqueous these aggregates can act as a support to facilitate the transport of substances and solubilisation Pharmaceutical insoluble, or very little soluble through adsorption or solubilisation micelar. This second part, which corresponds to Chapter 4 of memory, begins with the study termodinámíco of copolymer diblque P94E316 where EyP are blques wool of oxieti! Eno hydrophobic of oxipropileno respectively subscripts and their average lengths. This copolymer has been parciamente characterized previously, and the interest of our study lies on the one hand, to complete its characterization through a análisís thermodynamic its association process, and secondly, to provide familiarization with the comporamiento such compounds. Due to the need to find new block copolymers whose properties are best for the solubilization and transporting drugs, in Chapter 4 also presents the characterization of hydrophobic block copolymer tribloque with units consisting of ether fenilglicidilo (G) E65G7E65. SE hopes that this blque G is more hydrophobic that studied so far and to submit a glass transition temperature (above this temperature the core micelar were maintains mobile) within the temperature range of interest for the solubilization of drugs is say, around 37Â ° C. In addition, the study of such copolymers with blques G introduced extra interest to be a new compound from which no referncas in literature. The experimental techniques used in this part were aemás from those used in previous investment tube and rheology.

Author: ESPÍN MILLA MANUEL JESÚS.
Year: 2004.
University: GRANADA [www.ugr.es].
Place of defense: FACULTAD DE CIENCIAS.
Place of preparation: FACULTAD DE CIENCIAS.

Summary: This research work incorporates the study of the properties electrorreológicas (ER) of colloidal suspensions. The application of electric fields (of the order kV / mm) on non-conductive dispersions causes an abrupt change (a significant increase in viscosity and the emergence of an effort threshold) in the rheological behavior of these systems: the so-called ER effect. The origin of this phenomenon lies in the changes that the electric field induced in the structure of the suspensions, a liquid initial configuration cuasi-sólida end. This structural transition not only affects the mechanical properties of ER fluids but also their optical and electrical properties are also studied in this work. The system under consideration of this work consisted of particles of red cells (iron oxide) in silicone oil. The choice of these materials are of bió mainly to the fact that although the solid phase is a semiconductor material, has a significantly higher electrical conductivity than the other solids used in the preparation of ER fluids. This fact is especially relevant because the samples will be subjected to electric fields of high magnitude. The thesis is divided into two main blocs. On the one hand, deals with the study of ER properties under the action of alternating electric fields. Rheological properties were determined as a function of the electric field strength and the volume fraction of solids. The analysis of the effort threshold induced expressing samples showed that the physical mechanism responsible for this response is the interfacial polarization of the sample. For this reason, a study was conducted of the dielectric behavior of the suspensions depending on the scattering medium and the concentration of particles. This relaxation process depends solely on the electrical properties of the solid phases and lúqida, which were also identified. In particular, special attention was given to obtaining the conductivity of solid samples of hematite. Finally, we applied a model of microstructure, forming chains of particles between electrodes, in order to justify the experimental results obtained. The second part of the thesis is devoted to the study of the rheological properties, electro-ópticas and structural suspensions under the action of continuous electric fields. First, it proceeded in a manner similar to the previous case, namely the identification of curves effort shear viscosity and in steady state. It was noted that, again demonstrating dispersion behavior plastic fluidificante although, in this case, the effort threshold analysis indicated that the forces originating power of this phenomenon depends linearly with the field thus demonstrating that in the case of continuous electric fields, ER response is not due solely to the interfacial polarization of the suspensions, but other (s) processes are involved. To better understand this behavior was analyzed by optical absorbance measures, the action of the electric field on suspensions of hematite at rest. The experimental results showed that the optical properties of the samples ER is a complex function of the electric field strength and the concentration of particles. The analysis of these results showed that there is an electric field that separates two critical behaviors electro-opticos different, and consequently, two different structural processes. Lastly, he also discussed the transition from the initial state of rest and steady flow conditions, ie properties relógicas very small deformations. It was found that the electric field strength (and the volume fraction) No 8 only af 849 ectan the plastic behavior of the suspensions (flow conditions), but also to elastic behavior and viscoplástico small shears. To understand the rheological behavior of the suspensions under the action of continuous electric fields was conducted a structural analysis of the same. In quiescence, small-scale electric fields led to the formation of strings between the electrodes, thereby showing that the phenomenon of polarization interfacial prevails under these experimental conditions. However, for high electric fields, are phenomena of dissociation and injection load which dominate and lead to the formation of layers of aggregate particles on the electrodes. It has conducted a detailed analysis of the preponderance of one of these two processes depending on the conductivity of the particles and magnitude of the electric field applied. It has also evaluated the effect of an electric field simultaneously and effort on the suspensions Check applying a shear effort not only leads to a breakdown of the aggregate particles between electrodes, but induced the formation of more complex structures: annular structures particle. Finally, this research also discusses briefly the electric current in the ER fluids and the effect of activadores-contaminantes the response ER.

Author: López León Teresa.
Year: 2006.
University: GRANADA [www.ugr.es].
Place of defense: FACULTAD DE CIENCIAS (UNIVERSIDAD DE GRANADA).
Place of preparation: FACULTAD DE CIENCIAS (UNIVERSIDAD DE GRANADA).

Summary: This thesis explores phenomena of specificity or ionic effects Hofmeister in colloidal systems. Despite being universal phenomena, the origin of the effects Hofmeister is a subject of debate and one of the challenges currently facing the Físico-Química. In order to investigate the microscopic mechanisms that underlie these phenomena are analyzed first as the effects Hofmeister alter colloidal stability, mobility electroforética and kinetic processes of aggregation systems simple type hard sphere. In a second part were analyzed more complex systems, specifically particles termosensibles based PNIPAM. In this case Hofmeister effects were studied in phase transitions both in volume and electrokinetic, colloidal stability and cononsolvencia (in the presence of solvents mixed ethanol / water) microgeles of PNIPAM. In addition was designed and synthesized a novel system whose properties make it suitable for investigating the mechanisms responsible

Author: PIÑEIRO REDONDO YOLANDA.
Year: 2006.
University: SANTIAGO DE COMPOSTELA [www.usc.es].
Place of defense: FACULTAD DE FÍSICA.
Place of preparation: FACULTAD DE FÍSICA.

Summary: In this paper, has developed a numerical model of gel physical level mesoscópico with an aggregation process that follows the pattern of gelatin (aggregation of three different channels at one point). Based on a Monte Carlo method of dynamic network, a system of condensed phase chains autoexcluyentes with interaction and associative (ISAW), discusses the properties of sol-gel transition, through dynamic simulation cycles that follow a sequence of successive decrease heat. The continued registration of the information configuracional allows access for each temperature at magnitudes of topological and physical interest: the number of nodes in the network (the equivalent of triple helices of gelatine), the number of segments internodales (variable that determines the value of steady elastic modulus), the distribution of nodal degree (allowing time to assess the heat of the transiciónde phase homogeneous to heterogeneous), the nodal grade average (also related to the rigidity of the network), the size of pores gel ( by analyzing the distance euclidea average). Also given qeu the algorithm is implemented local jumps very local, we can studiar the dynamics of the system by analyzing: magnitudes of transportation (mean square displacement of masses inside), which records a regime change in the distribution of normal anomalous; optical properties, through the static structure factor (there is the appearance of excess low dispersion angle consistent with the gelatin in gel phase) and dynamic (who plays the apriciónde a potential decline in the sol-gel transition with features similar to those observed in the pilot area for gelatine), and dielectric properties through the normal mode of relaxation for polymers tipo-A (who gets to reproduce the fall of dielectric jump in the transition sol-geld and the geltaiana low frequencies and the possible abolition of how to conditions gel strengths). The algorithm jumps local implemented, allows relaxation configuracional of non-associated links and also of the links involved in the node (triple helix character mesoscópico), more partial. Besides depending on the intensity of interaction imposed on the links node, this is more or less reversible, bringing the network generated relaxes entálpica and entropy. By varying the relative intensity of the nodes are obtained networks character more or less reversible.