Formation of Water-Free Cavity in the Process of Nafion Swelling in a Cell of Limited Volume; Effect of Polymer Fibers Unwinding

Abstract

When Nafion swells in water, colloidal particles are repelled from the polymer surface; this effect is called the formation exclusion zone (EZ), and the EZ size amounts to several hundred microns. However, still no one has investigated the EZ formation in a cell whose dimension is close to the EZ size. It was also shown that, upon swelling in water, Nafion fibers “unwind” into the water bulk. In the case of a cell of limited volume, unwound fibers abut against the cell windows, and water is completely pushed out from the region between the polymer and the cell window, resulting in a cavity appearance. The temporal dynamics of the collapse of this cavity was studied depending on the cell size. It is shown that the cavity formation occurs due to long-range forces between polymer strands. It turned out that this scenario depends on the isotopic composition of the water, ionic additives and water pretreatment. The role of nanobubbles in the formation and collapse of the cavity were analyzed. The results obtained allowed us to conclude that the EZ formation is precisely due to the unwinding of polymer fibers into the liquid bulk.

Long-Term Effect of Low-Frequency Electromagnetic Irradiation in Water and Isotonic Aqueous Solutions as Studied by Photoluminescence from Polymer Membrane

“…Indeed, the structure of the channels in the bulk of polymer is similar (conditionally) to the lipid bilayer of the cell membrane, while the external structure of the polymer fibers is similar to the glycocalyx (extracellular matrix, see [ 15 ]). This analogy was developed on a qualitative level in our recent work [ 16 ]; Within the approach based on this analogy a number of features revealing at swelling of polymer membranes in water and aqueous salt solutions have been explained. Therefore, there is a natural interest in investigating the specific interaction of Nafion with deionized water and various isotonic solutions, which were subjected to the low-frequency electromagnetic irradiation.…”

“…As shown in [ 16 ], a number of effects associated with the swelling of the Nafion membrane in water and aqueous solutions of salts (in [ 16 ], aqueous solutions of NaCl were studied in a wide range of concentrations) are due to the presence of a nanobubble phase in water and aqueous solutions of electrolytes (for more details see Section 4 below). Furthermore, it was found in [ 16 ] that the swelling kinetics of the Nafion membrane has a long-term relaxation effect. Namely, effective shaking of a liquid sample (deionized water) leads to a change in the kinetics of membrane swelling, and this effect has a significant relaxation time (about a day).…”

Another Look at the Water Phases that Exist Under Room Conditions

“…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]. When this polymer swells, its fibers partially untwist and go out into bulk water.…”

“…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].…”

“…When this polymer swells, its fibers partially untwist and go out into bulk water. Such elongated strands can also form a rigid, parallel palisade that can repel colloidal microparticles; this, according to the authors of [51], creates the effect of an exclusion zone near Nafion. Analysis of alternative opinions is beyond the scope of this work.…”