ABSTRACT
I. Introduction 60
II. The Behavior of Water Near Surfaces 60
III. State of Water 61
IV. Methodology 63
V. Information Obtained via the Exothermic Scanning Mode 67 A. Structural transitions 67 B. Percolation transitions 69
VI. Information Obtained via the Endothermic Scanning Mode 76 A. Ethoxylated alcohols 76 B. Ethoxylated siloxanes 77 C. Sucrose esters 77 D. Phosphatidylcholine 80
VII. Results and Discussion 80 A. Variation of water peak temperatures with water content 80 B. Full hydration of the surfactant 83 C. Free water 87 D. Nonfreezable water 89 E. Evaluation of the thickness of the bound water layer 93 F. Alcohol interaction with other constituents 94
G. Exothermic peaks 98 H. The problem of phase separation 107
VIII. Conclusion 113
References 114
I. INTRODUCTION The purpose of this review is to examine several methodological aspects concerning the use of subzero temperature differential scanning calorimetry (hereafter designated as SZT-DSC), for the study of surfactant-water interactions and to highlight some recent results related to (mostly) nonionic microemulsions. In contrast to the common view that there need not be any a priori relation between properties of hydration measured at low temperatures and those measured at room temperature [1], we shall try to show that if the water-surfactant interaction is defined in terms of a perturbation to the freezing (or melting) of water at about 0°C, then the thermal behavior of microemulsions at ambient temperature is directly related to that at subzero temperatures. It should be stressed that SZT-DSC allows us only a dim glance into the microstructure of microemulsions and an even dimmer glance into its details. Yet the combination of SZT-DSC data and the results of spectroscopic measurements may deepen our understanding of these problems, as will be shown in this review.
