Application of scanning methods to distinguish between entropy and enthalpy driven phase transitions

• Driving forces of phase transitions can be determined using sorption calorimetry.
• Alternative methods to determine the driving forces are QCM-D and DSC.
• Humidity-scanning QCM-D requires only micrograms of sample.
• Hydration-induced transitions to phases with higher curvature are driven by enthalpy.
• Transitions to phases with lower curvature are less common and driven by entropy.

All phase transitions can be divided into enthalpy and entropy driven. The driving forces of phase transitions in aqueous soft matter systems can be resolved by applying scanning methods. In this review three experimental methods — sorption calorimetry, differential scanning calorimetry and humidity scanning quartz crystal microbalance with dissipation monitoring are described. Advantages and disadvantages of the methods are discussed. The driving forces of phase transitions can be directly measured using sorption calorimetry or calculated using van der Waals differential equation using experimental data obtained by other methods. The results of experimental studies show that in surfactant and lipid systems the phase transitions to phases with higher curvature are driven by enthalpy, while phase transitions to phases with lower curvature are driven by entropy.

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