Differential scanning calorimetry supercooled water

Differential scanning calorimetry measurements have shown a marked cooling/heat-ing cycle hysteresis and that water entrapped in AOT-reversed micelles is only partially freezable. Moreover, the freezable fraction displays strong supercooling behavior as an effect of the very small size of the aqueous micellar core. The nonfreezable water fraction has been recognized as the water located at the water/surfactant interface engaged in solvation of the surfactant head groups [97,98]. 

Differential Scanning Calorimetry. Differential scanning calorimetry (DSC) is a technique with the potential to determine the relative amounts of free and emulsified water. The freezing, or more correctly, the supercooling behavior of emulsified water is very different from that of free water, so the amount of free versus emulsified water in a sample can be characterized. This parameter is important in the characterization of produced fluids and interface emulsions in which water might exist simultaneously as both continuous and emulsified phases. 

Figure 30. Freezing behavior of an emulsion characterized by differential scanning calorimetry. The free water will freeze at approximately 273 K. Emulsified water will supercool and freeze at lower temperatures, depending upon size distribution. The smallest droplets freeze last because of the smaller volume, and so fewer nucleation sites are available for ice crystal formation and water freezing. The different freezing behavior of free versus emulsified water gives this technique the potential to quantify the relative proportions of these two types of water. (Reproduced with permission from reference 114.

Figure 10.9. DSC heating and cooling curves (5°C/min) of cholesteryl myristate in the bulk and in colloidal dispersion (5% CM, 2% PVA PCS z-average 172 nm, PDI 0.09). With kind permission from Springer Science + Business Media Fharm. Res. Supercooled smectic nanoparticles A potential novel carrier system for poorly water soluble drugs, 21, (2004), 1834-1843, J Kuntsche et al. Abbreviations DSC differential scanning calorimetry, PVA polyvinyl alcohol, PCS Photon correlation spectroscopy, PDI Polydispersity index.

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