A capillary rise method for studying the effective surface tension of monolayer nanoparticle-covered liquid marbles

The liquid marble covered with a xerogel-derived nanoparticle monolayer is emerging as a simple and ideal physical model for fundamental study. In this work, the effective surface tension, γeff, of this kind of water marble was studied by employing an optimized capillary rise method. This method is distinctive as it can reveal γeff at a specific point rather than the average γeff over the entire marble. γeff at the maximum lateral diameter position was investigated with particle coverage varying from 100% to 10%, showing a quite slow increasing trend from ∼64 to 72 mN m-1. The delay in the evolution of the γeff was attributed to the slow decline in the areal particle density on the side area of the marble. For comparative purposes, the maximum height method was also employed to determine γeff. The results of the two methods supported the position that a liquid marble's γeff depended on very specific conditions including the measurement method and all marble parameters.