Microheterogeneous systems of micelles and microemulsions as reaction media of polyesters and polyglycerols: synthesis, physical chemistry approach and theoretical study
Name: VADILSON MALAQUIAS DOS SANTOS
Publication date: 15/06/2023
Examining board:
Name |
Role |
|---|---|
| ADILSON RIBEIRO PRADO | Examinador Externo |
| ELOI ALVES DA SILVA FILHO | Presidente |
| MARTA ALBUQUERQUE MACHADO | Examinador Interno |
| OSMAIR VITAL DE OLIVEIRA | Examinador Externo |
| RICARDO MACHADO KUSTER | Examinador Interno |
Summary: This study investigated the physicochemical effects of polyester and polyglycerol synthesis in heterogeneous and micro-heterogeneous media in monophasic, biphasic, and triphasic liquid/liquid systems. These systems exhibit unique physical and chemical properties that, despite years of study, still have gaps to be elucidated. The study addressed the thermodynamics involved in interfacial and surface phenomena and their impact on the reaction process, including the importance of attractive and repulsive forces for system stability and interactions in the formation of micelles and polymer aggregates. Interfacial tension and temperature were the properties that most influenced the behavior of w/o systems, triphasic mixtures, emulsions, and microemulsions, which were also impacted by interface thickness, surfactants, dissolved salts, alcohols, solvents, and density profiles of the components. The synthesis of polymers using interfacial processes altered the surface tension of the medium and modified the critical micelle concentration (CMC) values of the surfactants, indicating the formation of polymer-micelle associations at concentrations lower than expected from theoretical calculations. Conformational changes in micelle/polymer complexes altered the viscous behavior of the systems and were affected by temperature changes. Polymer/surfactant associations in nonhomogeneous systems also caused changes at the interface, with a shift from spherical to globular or ellipsoidal micelle shapes. All these molecular structures obey unique geometric and topological requirements. Classical methods widely described in the literature for analyzing interfacial properties in the polymer/surfactant interaction process were revisited. The effect of surface tension, CMC, micellar shapes, aggregation numbers, and interfacial phenomena on the macromolecular packaging process in emulsion polycondensation was investigated. As a study model, surfactant/water systems composed of dodecylbenzenesulfonic acid and sodium dodecyl sulfate were employed. Polyesters and polyglycerols were prepared from glycerol, ethylene glycol, diethylene glycol, alcohols, and dicarboxylic acids in surfactant/water systems at temperatures ranging from 70 - 150 . Thermal analysis techniques and DSC indicated the presence of semicrystalline and amorphous regions in the obtained polymers and a glass transition temperature range of 53 to 46, typical of soft matter. The resulting polymers had molecular weights ranging from 1180 to 6800 gmol. Some results showed narrow spherical and ellipsoidal polymer aggregates and the formation of microgels. These systems are suitable for applications in green chemistry. Computational chemistry methods based on Density Functional Theory (DFT) were applied to the structural and electronic analysis of the molecules used in this study. The studies examined the effectiveness of micellar catalysis and proposed methods to improve the surfactant-reagent-catalyst combination. The results obtained indicate new pathways for syntheses in interfacial systems and the search for environmentally and health-friendly materials. This study proposes mechanisms for surfactant/polymer catalysis and the understanding of the hierarchical organization, morphology, and conformation of the studied systems, which are essential for applications in fine chemistry, pharmaceuticals, biodegradable polymers, and catalysis.
