Studies physical-statistical and computational models of network solutions simple mixture of amphiphilic single-tailed and double-tailed.

Author(s)

Cláudio Saburo Shida

• Document type: Doctoral Thesis
• Press: São Paulo.
• Institution: Universidade de São Paulo (USP). Instituto de Física (IF/SBI)
• Defense date: 1998-05-22

Examining board members

Vera Bohomoletz Henriques; Carlos Eugenio Imbassahy Carneiro; Eloi da Silva Feitosa; Wagner Figueiredo; Amando Siuiti Ito

• Advisor: Vera Bohomoletz Henriques

Abstract

We present a detailed study of the equilibrium properties of square lattice models for solutions of simple molecules, and of single and double tail amphiphiles, at constant concentration. In order to study these models we have developed simulation algorithms and computer programs based on the Monte Carlo method. Ergodicity and detailed balance conditions are discussed. We show that thermal equilibration, and calculations of time correlation functions and of specific heat are a delicate question in model amphiphilic systems. For the simple mixture lattice solution, thermodynamic averages for different equilibrium properties of the system were obtained for the whole Concentration x Temperature phase diagram. The equivalent properties for the amphiphilic systems were measured and compared. Specific heat as a function of temperature presents a broad maximum which does not exist in the case of simple solutions, and can be associated with the micelar phase. We have constructed, for the single tail model, the Concentration x Temperature phase diagram, for low concentrations, in which we identify a hydrated solid, a micelar and a homogeneous phase, using criteria from experimental and theoretical studies. The model phase diagram presents good qualitative agreement with experimental results. Finally, we present evidence that both models, detergent and model phospholipid solutions systems, studied present the same forms for the aggregated structures for either detergent or lipids models are not different and, besides that, they present the same phases in the corresponding temperature region. (AU)