Determination of activity coefficients via microdroplet evaporation experiments

Exploring the complexity of aerosol particle properties and processes using single particle techniques

“…If measurements are made of the size of an evaporating droplet consisting of a binary mixture into a gas phase in which one of the components (typically the component with the higher vapour pressure and often water) has a finite, constant concentration, the activity coefficients of the two components in solution can be obtained. 55,218,219 For example, to study the evaporation of a SVOC from an aqueous droplet, the water partial pressure (RH) must be maintained at a constant value. Then, the change in size with time reflects the evaporation of the organic component and the associated loss of water, such that the composition of the droplet does not change with time.…”

Binary activity coefficients from microdroplet evaporation

“…A typical intensity vs. time spectrum obtained from a glycerol droplet evaporating in 17.4% ethanol saturated air is shown in Figure 2. In previous studies, such spectra obtained from evaporating droplets have been visually matched with theoretical spectra to obtain size and/or refractive index vs. time information (Richardson et al, 1986;Taflin et al, 1988;Ray et al, 1989Allen et al, 1990). The visual matching is only accurate for situations in which the refractive index of the droplet and the functional form of the size variation with time are known.…”

“…Recently, Allen et al (1990) have shown that measurements on a binary solution microdroplet evaporating in a vapor-free atmosphere inside an electrodynamic balance can be used to determine activity coefficients of two relatively nonvolatile components. They have used weight change and scattered intensity data to determine the droplet size and composition, and interpreted the results using quasi-steady-state mass flux relations.…”

Determination of Thermodynamic Parameters from Evaporation of Binary Microdroplets of Volatile Constituents

“…Other methods are based on data obtained from evaporating and growing binary microdroplets and determination of droplet size and composition as functions of time from light scattering data. For example, Allen et al (6) have estimated activity coefficients of both components from evaporation rates of single microdroplets of two relatively nonvolatile components in vapor-free atmospheres. They interpreted droplet mass loss and angular light scattering data along with optical resonances observed in intensity versus time spectra to resolve droplet size and composition.…”