On the effective surface tension of powder-derived liquid marbles

Effective surface tension (γeff) is a fundamental property of liquid marbles, i.e., particle-covered drops in an air environment. Recently, studies of monolayer nanoparticle-covered (mNPc) liquid marbles produced with a sol-gel film have significantly updated previous understandings regarding γeff. Examining the derived explanations with the most common powder-derived liquid marbles should be meaningful. Here, the maximum height and pendant drop methods were employed for γeff measurements of liquid marbles produced with a polytetrafluoroethylene powder. Following the methodology proposed in mNPc liquid marble studies, the measurement processes were addressed in detail with the uncertainties in parameter identification as the main concerns, and the results were analyzed by highlighting the effective surface tension's equivalence nature and liquid marbles' surface solidity. By combining the present findings and conclusions related to both mNPc and powder liquid marbles, the key issues in measuring and understanding liquid marble γeff were summarized.