Georgian Scientists/ . 7 N 4, 2025 429 Georgian Scientists Vol. 7 Issue 4, 2025 https://doi.org/10.52340/gs.2025.07.04.23 Some issues in membrane pore size research 1George Bibileishvili, 2Liana Ebanoidze, 3Nana Gogesashvili, 4Liana Kuparadze, 5Tinatin Butkhuzi, 6Ia Gogiberidze 1Academic Doctor of Chemical and Biological Engineering - e-mail 75bibileishvili@mail.com ORCID https://orcid.org/0009-0003-7712-2436 Engineering Institute of Membrane Technologies Georgian Technical University Abstract The paper presents a comparative analysis of the pore sizes membranes obtained by the bubble point method and scanning probe microscopy. The dependence of the membranes filtration characteristics on its pores size has been revealed. It has been established that the membrane pore sizes by the bubble point method, somewhat correspond to the pore sizes obtained by scanning probe microscopy. Keywords: Microfiltration, Membrane, Pore size, Specific efficiency The basic filtration characteristics of micro- and ultrafiltration membranes can be assessed by pore size, porosity, and specific efficiency of the membranes. Membrane pore size can be studied by direct methods such as electron microscopy, scanning probe microscopy, and by indirect methods such as the bubble point method [1-2]. The aim of the work was to determine the size of membrane pores the bubble point method and to perform a comparative analysis of the pore sizes obtained during the study with a scanning probe microscope. The determination of membrane pore size was performed on a laboratory device MTSI- BP-3 developed and created at the Membrane Technology Engineering Institute, which provides the study of disc-type micro- and ultrafiltration membranes of four different sizes (Diameters 10, 16, 26, 34 mm). Its main parts were manufactured using a ULTIMAKER 2 3D printer and calibrated in accordance with five foreign-made membrane standards, whose pore sizes and corresponding pressure ratings are shown in Table 1. Table 1. Pressure at the moment of first bubble formation and membrane pore size Membrane Pressure at the moment of bubble formation, P, bar Membrane pore size, m M1 0.06 5.00 M2 0.25 1.20 M3 0.65 0.45 M4 1.48 0.20 M5 2.95 0.10 Georgian Scientists/ . 7 N 4, 2025 430 The working principle of the device is based on the method of creating a bubble point based on the capillary effect, according to which the pores of the membrane are equivalent to capillaries and the liquid is retained in the pores by capillary forces. The pore size of the membrane is calculated by the formula: = 0.81/ where The diameter of the membrane pore ( m) which has the shape of a capillary; Pressure (bar) at which the first bubble forms. Deionized water was chosen as the standard solution, and air was chosen as the gas [3-7]. The study of the membrane surface structure was carried out on a CERTUS STANDARD V scanning probe microscope, the 2D and 3D images of which visually show the structure and dimensions of the membrane pores. Scanning was performed in non-contact mode, with an NSG20 type cantilever (probe radius of curvature is 10 nm) [8-10]. Turbidity of natural water before and after filtration was determined on a turbidimeter TURB 555, in formazin units. [11-13]. The specific productivity of the membrane obtained by phase inversion was determined using the MTSI-JM-5 laboratory device [14-17]. The results obtained from the experimental study are presented in Table 2. Table 2. Pressure at the moment of first bubble formation, membrane pore size, water turbidity, and membrane specific productivity Membrane Pressure at the moment of bubble formation, P, bar Membrane pore size, m Turbidity of natural water, FTU Specific productivity of the membrane J, l/m2h Before filtering After filtration M1 3.0 4.500 1.90 0.03 5200 M2 3.5 3.850 1.90 0.03 4000 M3 4.0 3.370 1.90 0.03 3400 M4 4.5 3.000 1.90 0.03 3100 M5 5.0 2.700 1.03 0.03 2800 M6 5.5 2.450 1.91 0.03 2710 M7 6.0 2.250 1.87 0.03 2530 M8 6.5 2.070 1.89 0.02 2370 M9 7.0 1.920 1.90 0.02 2215 M10 7.5 1.800 1.89 0.02 2065 M11 8.0 1.680 1.90 0.01 1920 M12 8.5 1.580 1.91 0.01 1780 M13 9.0 1.500 1.90 0.01 1645 M14 9.5 1.420 1.90 0.01 1515 M15 10.0 1.350 1.90 0.01 1390 M16 10.5 1.280 1.90 0.01 1270 M17 11.0 1.220 1.90 0.01 1155 M18 11.5 1.170 1.90 0.01 1045 M19 12.0 1.120 1.90 0.01 940 M20 12.5 1.080 1.90 0.01 840 Georgian Scientists/ . 7 N 4, 2025 431 M21 13.0 1.030 1.90 0.01 745 M22 13.5 1.000 1.90 0.01 720 M23 14.0 0.960 1.90 0.01 700 M24 14.5 0.930 1.90 0.01 680 M25 15.0 0.900 1.90 0.01 660 M26 15.5 0.870 1.90 0.01 645 M27 16.0 0.840 1.90 0.01 630 M28 16.5 0.820 1.90 0.01 620 M29 17.0 0.790 1.90 0.01 610 M30 35.5 0.380 1.90 0.01 490 M31 36.0 0.375 1.90 0.01 480 M32 36.5 0.369 1.90 0.01 475 M33 37.0 0.364 1.90 0.01 470 M34 37.5 0.360 1.90 0.01 465 M35 38.0 0.355 1.90 0.01 460 M36 38.5 0.350 1.90 0.01 450 M37 39.0 0.346 1.90 0.01 445 M38 39.5 0.341 1.90 0.01 435 M39 40.0 0.337 1.90 0.01 430 M40 41.5 0.324 1.90 0.01 420 M41 42.0 0.320 1.90 0.01 415 M42 42.5 0.316 1.90 0.01 410 M43 43.0 0.312 1.90 0.01 405 M44 43.5 0.310 1.90 0.01 400 The dependence of the specific productivity of the membrane on its pore size was revealed in the study using the bubble point formation method. From the data presented in Table 2, it can be seen that the M1 membrane has the maximum specific productivity membrane (5200 l/m2h) and the largest pore size (4.500 m), for which the lowest indicator minimum pressure for bubble formation is 3.0 bar. The results obtained from the scanning probe microscopy study are presented in Table 3 and Figure 3.a.,b.,c. The results show that the geometric parameters (average length, width, and depth of the 2D image of the membrane) of the smallest membrane pore size were determined. Table 3. Geometric parameters (the average length, width and depth of the 2D image) of the smallest membrane pore, m Membrane Geometric parameters (the average length, width and depth of the 2D image) of the smallest membrane pore, m length width depth M1 4.4384 4.7937 0.036628 M28 0.82777 0.24944 0.017666 M43 0.32818 0.27646 0.10132 Georgian Scientists/ . 7 N 4, 2025 432 Figure 3. a. M1 2D Photomicrograph of the membrane surface Figure 3. b. M8 Photomicrograph of the membrane surface Figure 3. c. M12 Photomicrograph of the membrane surface As a result of a comparative analysis of the filtration characteristics of membranes obtained from various polymers, it was established that the membrane pore size determined by the bubble point generation method is in some agreement with the pore size values obtained by scanning probe microscopy. Therefore, based on the filtration characteristics and the results of the analysis of the filtered water, the membranes manufactured at the institute can be used in water microfiltration. Georgian Scientists/ . 7 N 4, 2025 433 References 1. F. Anis, R. Hashaikeh, N. Hilal. Microfiltration Membrane Processes: A Review of Research Trends over the Past Decade. Journal of Water Process Engineering, V.32, 2019. pp.100941; 2. R. Shoshaa, M. Y. Ashfaq, M. A. 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ISSN: 1512-0287. https://doi.org/10.36073/1512-0287. 1 , 2 , 3 , 4 , 5 , 6 1 , - e-mail 75bibileishvili@mail.com ORCID https://orcid.org/0009-0003-7712-2436 . . , . : , , ,