Exclusion Zone Phenomena in Water—A Critical Review of Experimental Findings and Theories

Abstract

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. Here we review the experimental evidence for EZ phenomena in water and the major theories that have been proposed. We review experimental results from birefringence, neutron radiography, nuclear magnetic resonance, and other studies. Pollack theorizes that water in the EZ exists has a different structure than bulk water, and that this accounts for the EZ. We present several alternative explanations for EZs and argue that Schurr’s theory based on diffusiophoresis presents a compelling alternative explanation for the core EZ phenomenon. 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. We also touch on several possible confounding factors that make experimentation on EZs difficult, such as charged surface groups, dissolved solutes, and adsorbed nanobubbles.

The Physical Chemistry and Chemical Physics (PCCP) Section of the International Journal of Molecular Sciences in Its Publications: The First 300 Thematic Articles in the First 3 Years

“…Articles [ 1 , 2 , 3 , 4 , 5 , 6 , 7 , 8 , 9 , 10 , 11 , 12 , 13 , 14 , 15 , 16 , 17 , 18 , 19 , 20 , 21 , 22 , 23 , 24 , 25 ] can be attributed to the first of the thematic areas indicated in the PCCP Section, and the distribution of these articles into the above categories is presented in Table 2 . As it can be seen, of the four types of articles established by the magazine’s standards ( Reviews , Originals, Communications , Editorials ), only the first two are presented here.…”

“…These particles are also reviewed in [ 21 ], which provides the latest information on mesoporous silica nanoparticles (MSN), functionalized to target subcellular compartments, with an emphasis on the cytoplasm, mitochondria, and nucleus, which are now widely used as drug carriers due to their unique physical–chemical characteristics. To some extent, this also includes the other two review articles from this thematic area, namely [ 9 , 22 ], the first of which addresses the problem of the existence of the so-called exclusion zones (EZ), namely, a layer of water in which plastic microspheres are repelled from hydrophilic surfaces, the second of which explores the systematization of processes known in the literature for obtaining microparticles of insoluble β-glucans from spent brewer’s yeast and gives an idea of how a by-product of brewing can be converted into potential food items. To the specifics of intermolecular interactions in systems containing surfactants, publications [ 4 , 12 , 18 ] were devoted; intermolecular interactions, in which the formation of hydrogen bonds plays a key role, are discussed to varying degrees in [ 5 , 23 , 25 ].…”

Dynamics of Polymer Membrane Swelling in Aqueous Suspension of Amino-Acids with Different Isotopic Composition; Photoluminescence Spectroscopy Experiments

“…At the same time, it is reckoned that a solid surface can modify an adjacent water layer only within 1–2 nm; this size corresponds to the radius of the so-called dispersion forces, see, for instance, [ 8 ]. The most relevant information on studies of the exclusion zone, including a detailed discussion on the physical mechanisms of formation of this structure, can be found in the review [ 9 ].…”

Another Look at the Water Phases that Exist Under Room Conditions

“…Several alternative explanations for EZ have been presented, in particular, Schurr's theory based on chemotaxis and diffusionophoresis [47]. This theory was strongly supported by Elton et al [48] and Esplandiu et al [49]. Another view of the formation of EZ is associated with swelling in water and partial destruction of Nafion, a solid polymer electrolyte, a popular owner of hydrophilic surfaces [50,51].…”

“…Despite the abundance of experimental evidence for the existence of the near-wall phase of water, a number of researchers stubbornly continue to deny this fact [47][48][49][50][51]. Several alternative explanations for EZ have been presented, in particular, Schurr's theory based on chemotaxis and diffusionophoresis [47].…”