  Surface tension and contact angle measurements are fundamental
characterization techniques relevant to thermal and fluidic applications. Drop
shape analysis techniques for the measurement of interfacial tension are
powerful, versatile and flexible. Here we develop a Spline-based Interface
Modeling and Optimization (SIMO) tool for estimating the surface tension and
the contact angle from the profiles of sessile and pendant drops of various
sizes. The employed strategy models the profile using a vector parametrized
cubic spline which is then evolved to the eventual equilibrium shape using a
novel thermodynamic free-energy minimization-based iterative algorithm. We
perform experiments to show that in comparison, the typical fitting-based
techniques are very sensitive to errors due to image acquisition, digitization
and edge detection, and do not predict the correct surface tension and the
contact angle values. We mimic these errors in theoretical drop profiles by
applying the Gaussian noise and the smoothing filters. We then demonstrate that
our optimization algorithm can even drive such inaccurate digitized profiles to
the minimum energy equilibrium shape for the precise estimation of the surface
tension and the contact angle values. We compare our scheme with software tools
available in public domain to characterize the accuracy and the precision of
SIMO.
