New applications of photothermal techniques for studying interfaces.

Author(s)

Marcos Eduardo Sedra Gugliotti

• Document type: Doctoral Thesis
• Press: São Paulo. , gráficos, ilustrações, tabelas.
• Institution: Universidade de São Paulo (USP). Conjunto das Químicas (IQ e FCF) (CQ/DBDCQ)
• Defense date: 2001-12-06

Examining board members

Mario Jose Politi; Tomaz Catunda; Rosangela Itri; Osvaldo Novais de Oliveira Junior; Frank Herbert Quina

• Advisor: Mario Jose Politi; Mauricio da Silva Baptista
• Field of knowledge: Physical Sciences and Mathematics - Chemistry
• Indexed in: Banco de Dados Bibliográficos da USP-DEDALUS; Biblioteca Digital de Teses e Dissertações - USP
• Location: Universidade de São Paulo. Biblioteca do Conjunto das Químicas; 547.13453; G942n

Abstract

This work presents the development of new instrumentations based on photothermal phenomena to study solid-liquid and liquid-gas interfaces, including in the latter the effect of surfactants. The work is divided into chapters, each one focusing on the development and/or application of a new technique. Chapter I presents an introduction to photothermal phenomena and describes the construction of classical Thermal Lens (TL) instruments in the single and double-beam configurations. Solid-liquid interfaces were studied in chapters II-IV using variations of the classical TL instrumentation. A new photothermal signal was characterized, indicating the formation of an inverted thermal lens at the interface. Z-scan experiments in the reflection configuration were used to determine the change in the refractive index of an interface close to the critical angle, and a similar methodolody was used to measure the thermal diffusivity of opaque samples. In Chapters V-VII, the deformation of liquid surfaces was studied by laser-induced Marangoni effect and the generation of capillary waves. Heat transfer through the liquid-gas interface was monitored by Transverse Photothermal Deflection. In all cases, the influence of surfactants was studied by forming a monolayer on the surface of the liquids. It was observed that a tiny amount of surfactants was able to cease the motion of liquid induced by surface tension gradients and to increase significantly the heat transfer through the interface. The results indicate a correlation between phase transitions of the monolayers and the attenuation of the surface deformation as well as the increase in the heat transfer. Finally, chapter VIII is a collection of other works that derived from the studies related to the instrumentations developed. (AU)