Compelling Alternative Theories for Exclusion Zone Phenomena in Water and Other Liquids

The existence of the exclusion zone (EZ), a layer of water in which plastic microspheres are repelled from hydrophilic surfaces, has now been independently demonstrated by several groups. A better understanding of the mechanisms which generate EZs would help with understanding the possible importance of EZs in biology and in engineering applications such as filtration and microfluidics. Pollack theorizes that EZ water exists in a new phase which has a layered structure. We note several problems with Pollack's proposed structure, some of which were noted in the 1960's when a similar structure was proposed for ``polywater''. We argue that Schurr's diffusiophoresis based theory presents a compelling alternative explanation for the core EZ phenomena, although there remain other findings from Pollack's lab it does not explain. Among other things, Schurr's theory makes predictions about the growth of the EZ with time which have been confirmed by Florea et al.\ and others. In this work we also introduce and explore a novel hypothesis - that some aspects of EZ phenomena may be attributable to repulsive van der Waals forces. Finally, we touch on several possible confounding factors that make experimentation on EZs difficult, such as charged surface groups, dissolved solutes, and adsorbed nanobubbles.