Newsletter - 2004/10 - Ausgabe 07
Importance of Baseline Determination for Contact Angle Measurements:
When determining the contact angle of a liquid drop on a solid surface, many factors can influence the outcome of the result. Poor lighting, improper drop deposition, and poor fit routines are but a few. All of these can be properly controlled with proper training, automated syringes, and high quality/mathematically sound software. The most important variable in determining an accurate contact angle is most often the placement of the drop baseline. The DSA software has the capability to determine an automatic baseline, taking much of the variability from the measurement.
Equilibrium isotherms of ionic surfactants on fluid interfaces: Determination of the adsorption and the covered area fraction; role of the salt and the type of the hydrophobic phase
We present a simple thermodynamic method for determination of the adsorption (amount per unit area) of ionic surfactant on a fluid interface. The adsorption is obtained from a polynomial fit of the equilibrium interfacial tension, measured in the presence of arbitrary (and fixed) concentration of inorganic electrolyte, vs. the logarithm of the mean ionic activity. We performed measurements with sodium dodecyl sulfate (SDS) on air/ water and oil/ water boundaries, at different salt concentrations. On oil/ water interfaces the adsorption is always lower than that on air/ water surface; addition of inert electrolyte increases the adsorption.