Ultrasonic Effect on the Growth of Crystals from Aqueous Electrolyte Solutions on Polymer Substrates: The Role of Isotopic Composition of Liquid

Abstract

The peculiarities of the crystal formation from supersaturated aqueous solutions of CuSO₄ on polymer substrates were studied using X-ray diffractometry. During the crystal formation, the test solutions were irradiated with one or two counter-propagating ultrasonic beams. Test solutions were prepared using natural deionized water with a deuterium content of 157 ± 1 ppm. The other liquid used was deuterium-depleted water with a deuterium content of 3 ppm. It was shown that irradiation with one/two ultrasonic beams resulted in drastic changes in the structure of the crystal deposit formed on the polymer substrate in the case when natural deionized water was chosen for preparing the supersaturated solution of CuSO₄.

Keywords: X-ray diffractometry; aqueous electrolyte solution; crystallization; deionized water; polymer membrane; ultrasonic beam.

Figure 1

Oscillogram of electrical pulses supplied to a piezoelectric transducer.

Figure 2

Diffraction patterns of CuSO₄ crystals deposited on a polymer substrate from DDW-solution (CuSO₄ × 5H₂O, black curve) and NW-solution (CuSO₄ × 3H₂O, red curve) in the absence of ultrasonic treatment. A set of crystallographic indices (h,k,l) for some of the highest peaks is given; the indices highlighted in red refer to the trihydrate, whereas the indices highlighted in black refer to the pentahydrate.

Figure 3

Diffraction patterns of CuSO₄ crystal hydrates grown on a polymer substrate from NW- solution under irradiation with a single ultrasonic beam at a pulse voltage on the piezoelectric element of U₀ = 60 V (black curve), under irradiation with two counter-propagating ultrasonic beams at a pulse voltage on the piezoelectric elements of U₀ = 60 V (red curve), and in the absence of irradiation (blue curve). Black ovals mark reflexes related to the structure of CuSO₄ × 5H₂O pentahydrate included in the trihydrate matrix as a result of ultrasonic treatment.

Figure 4

X-ray diffraction patterns of CuSO₄ crystal hydrates deposited on the Nafion substrate from NW-solution under irradiation with a single ultrasonic beam at a pulsed voltage on the piezoelectric element of U₀ = 60 V (black curve) and U₀ = 6 V (red curve), as well as deposited on the Nafion substrate from the DDW-solution at a pulsed voltage of U₀ = 60 V (blue curve). Panel (a) shows the reflexes in a range of 15–35°. Panel (b) shows the reflexes in a range of 30.5–34°.

Figure 5

CuSO₄ crystal hydrate formed on the Nafion substrate from NW-solution under the irradiation with one ultrasonic beam at a pulse voltage of U₀ = 6 V. Panels (a,b): the formation of the deposit continues, since the solution has not completely evaporated. Panel (c): the end of the formation of the deposit; water is absent in the cuvette. It is seen that the deposit is formed predominantly near the piezoelectric transducer.

Figure 6

The dependences of pH vs. deuterium content of water; the parameter of these dependences is the soaking time τ. Explanations are in the text.

Figure 7

Locally stable configurations of a model fragment of the Nafion polymer matrix with folded (left), unfolded (right), and partially unfolded and hydrated side polymer chains in the presence of 35 water molecules (bottom).