ABSTRACT

I. Introduction 122

II. Experimental and Theoretical Remarks 123

III. Heat Capacity and Other Thermodynamic Properties 124

IV. The Phase Diagram 132

V. Thermal Transitions Detected in Phase Studies 132 A. Melting 132 B. Liquid crystal transitions 141 C. Vaporization 142 D. Decomposition 143 E. Vesicles and liposomes 143

VI. Micellization of Block Copolymer Surfactants 153 A. Effect of other surfactants on block copolymer

micellization 156

VII. Emulsions 157

VIII. The State of Water in Surfactant-Based Systems 159

IX. Lowering of the Melting Point 166

References 172

I. INTRODUCTION Differential scanning calorimetry (DSC) is widely used for studying binary and multicomponent systems containing surfactants. Transition temperatures and enthalpies are often determined and used to draw the limits of existence of the different phases of surfactant-based systems [1-6]. The state of the surfactant molecules in these phases is studied by means of thermal analysis [7,8]. DSC is also a useful technique to obtain information about the phase diagrams of surfactant-based systems and the various microstructures formed in these systems. The properties that can be obtained from DSC for binary systems are the following [6]:

1. Type of phase transition (isothermal or nonisothermal, transformation of one phase into another or a three-phase process)

2. Temperatures of invariant transitions, initial and final temperatures for univariant phase transitions

3. Phase boundaries, extent of heterogeneous regions, coordinates of invariant points for a complete phase diagram consistent with the phase rule

4. Enthalpies of phase transitions; Tamman triangles and enthalpies of threephase processes

5. Specific heats of systems in homogeneous states 6. Heat capacity of systems in heterogeneous states 7. Heat capacity jumps taking place when the number of phases present in the

system changes 8. Three-dimensional diagrams of the dependence of the system heat capacity

on temperature and composition 9. Differential entropy and enthalpy of dissolution of one phase in another

In particular, the enthalpies of invariant processes (melting of pure substances, eutectic and peritectic points, extreme phase transition temperature, etc.) can be measured with great precision.