A method of profile optimization for determining the surface and interfacial tension (IFT) of liquid-fluid systems from the profile of a pendant drop is described. A new, versatile routine for estimating the drop shape parameter is introduced. The factors that affect the available accuracy of the method have been analyzed using theoretical simulations. It was found that the tilt of the drop profiles may lead to large errors in the resultant IFT values if the tilt was not corrected before or during the optimization procedure. This effect could be reduced drastically if a profile were averaged between its two sides and the mean profile were used for optimization. The aspect ratio of a drop image (or profile) can be determined reliably by considering it one of the parameters to be optimized. The dependence of the error in the resultant IFT value on the error in the aspect ratio was found to be highly sensitive to drop shape. The available accuracy of IFT determination using this method depends strongly on the precision of the determination of the drop profiles. After error analysis using theoretical simulations a 95% confidence interval of ca. 0.05 and 0.12% was estimated for this method for the profiles determined with maximum statistical error of 3.5 and 7.0 μm, respectively.

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The reliability of the method described in the preceding paper (B. Song and J. Springer, J. Colloid Interface Sci. 183, in press, 1996) for the determination of surface and interfacial tension (IFT) of liquid-fluid systems from the profile of a pendant drop has been studied experimentally. Influences on the resultant IFT values from factors such as the location of the drop profile and illumination conditions are considered. The reproducibility and accuracy of the measurement method were examined by measuring the time dependence of polyethylene glycol (PEG600)/air and water/air systems and by determining the temperature dependence of the polyethylene glycol (PEG6000)/N2 and LD (low-density) polyethylene/N2 systems. The effect of drop vibrations on the accuracy of the method is discussed.

A new model of molecular scale microcapsule named “super microcapsule” (SMC) obtained from a star copolymer consisting of hydrophilic and hydrophobic blocks was presented. As a first stage, 3 and 4‐arm star polyethylene oxide‐polylactide copolymers (s‐PEO‐PLA) were synthesized by the use of triethanolamine and pentaerythritol and initiating agent, respectively. The block length of PLA and PEO for the copolymers can be controlled by feed and reaction conditions. The molecular weight distributions found to be in the range of 1.3–1.7. The DTA data indicated that the phase separation behavior of s‐PEOPLA copolymers is different from that of linear PEOPLA copolymers with comparable block length. As a evidence of SMC, the shell‐core structure of s‐PEOPLA copolymers in solid state was observed by TEM. The SMC dimensions were estimated to be about 400–1000 Å