Possibility to Alter Dynamics of Luminescence from Surface of Polymer Membrane with Ultrasonic Waves

Abstract

The temporal dynamics of luminescence from the surface of Nafion polymer membranes have been studied. In fact, the polymer membrane was soaked in liquids with different contents of deuterium. The test liquids were ordinary (natural) water (deuterium content equal to 157 ppm) and deuterium-depleted water (deuterium content is equal to 3 ppm). Simultaneously with the excitation of luminescence, the Nafion plate was irradiated with ultrasonic pulses, having a duration of 1 μs. The ultrasonic waves were generated with different repetition rates and amplitudes, and irradiated the surface of Nafion in the geometry of grazing or normal incidence. Luminescence regimes were studied when the membrane was irradiated with one ultrasonic wave (one piezoelectric transducer) or two counter-propagating waves (two piezoelectric transducers). It turned out that ultrasonic waves, which fall normal to the membrane interface, do not affect the dynamics of luminescence. At the same time, in the case of ultrasonic irradiation in the grazing incidence geometry, sharp jumps in the luminescence intensity occur, and the behavior of these jumps substantially depends on the mode of irradiation: one or two piezoelectric transducers. This allows for control of the dynamics of luminescence from the polymer surface. In accordance with this model, the possibility of altering the luminescence dynamics is due to the effect of unwinding the polymer fibers from the surface toward the liquid bulk upon soaking. It is important that such unwinding does not occur in deuterium-depleted water, which was confirmed in a direct experiment with dynamic light scattering from polydisperse aqueous suspensions of Nafion nanometer-sized particles; these suspensions were prepared in ordinary water and deuterium-depleted water. Thus, ultrasonic irradiation affects the dynamics of luminescence only when Nafion is swollen in ordinary water; in the case of deuterium-depleted water this effect is missed.

Adsorption of Methylene Blue on the Surface of Polymer Membrane; Dependence on the Isotopic Composition of Liquid Matrix

“…Thus, the study of the interaction between the Nafion polymer membrane and MB is interesting not only from the viewpoint of studying the possibility of increasing the durability of the polymer membrane in the fuel cell, but also in the context of biophysical applications. Indeed, as was previously shown in our works, devoted to the study of Nafion membrane swelling in aqueous media with different deuterium contents [ 18 , 19 , 20 ], when swelling in natural water (the deuterium content in this liquid is 157 ppm, see [ 21 ]), the polymeric fibers unwind toward the water bulk. These fibers do not completely tear off the polymer substrate, forming a flexible brush-type structure, and the size of this structure in the bulk of water amounts to 300 microns [ 19 ].…”

“…Indeed, as was previously shown in our works, devoted to the study of Nafion membrane swelling in aqueous media with different deuterium contents [ 18 , 19 , 20 ], when swelling in natural water (the deuterium content in this liquid is 157 ppm, see [ 21 ]), the polymeric fibers unwind toward the water bulk. These fibers do not completely tear off the polymer substrate, forming a flexible brush-type structure, and the size of this structure in the bulk of water amounts to 300 microns [ 19 ]. At the same time, when the membrane is soaked in deuterium-depleted water (DDW; the deuterium content is 3 ppm), the effect of unwinding is absent.…”

“…As was concluded in works [ 18 , 19 , 20 ], a polymer membrane containing through channels inside its matrix and decorated with unwound polymer fibers is similar to a cell membrane. Indeed, the cell membrane also contains through channels inside the lipid bilayer, and is surrounded from the outside by the polysaccharide fibers (glycocalyx, or extracellular matrix, ECM); see [ 22 ].…”

“…Thus, in the case of a flat membrane surface, the adsorption of water followed by desorption can apparently be described analytically, providing that the constants A , B , and C ( t ) are known to us. However, in the case of polymer fibers unwound into the bulk of liquid, the adsorption dynamics can no longer be described within the framework of such a simple model, as the electrically charged surface of the adsorbent is not flat, and the length of unwound (also charged) polymer fibers reaches 300 microns (see [ 19 ]), i.e., it substantially exceeds the value of R D . In this case, the problem of the distribution of the electric field strength E becomes very difficult, especially bearing in mind the nonstationary character of this problem.…”

Effects of Low-Frequency Randomly Polarized Electromagnetic Radiation, as Revealed upon Swelling of Polymer Membrane in Water with Different Isotopic Compositions

“…As was obtained in our recent work [ 18 ], if photoluminescence is excited from the surface of polymer membrane together with simultaneous irradiation of the membrane with one or two counter-propagating ultrasonic waves, directed across the unwound fibers, the random jumps in the luminescence intensity arise in the case of swelling in natural deionized (DI) water. However, if Nafion swells in DDW, there are no random jumps in the luminescence intensity.…”