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Спектральные особенности ЭФ рассматривались только в части его влияния на ЯТ подстилающей поверхности. В работе приводятся примеры спектральной зависимости ^р в ионосфере для разных гелиофизических условий, спектральной зависимости контраста ЯТ гладкой морской поверхности и сред с разными поляризационными свойствами. Спектральная зависимость ^р неплохо согласуется с нашими ранними результатами, полученными для упрощенной модели ионосферы [4]. Особенности спектрального поведения контрастов ЯТ указывают на необходимость дальнейших исследований и, прежде всего, в части пространственно-временных вариаций ЯТ, обусловленных проявлением ЭФ.
Список литературы
1. Мильшин А.А., Гранков А.Г., Шелобанова Н.К. Глобальная модель радиотеплового излучения земной поверхности в L - и Р - участках СВЧ -диапазона // Ш1 научная сессия РНТОРЭС им. А.С.Попова, 20-21 мая 1998. Москва. - С.75-76.
2. Галкин Ю.С., Гранков А.Г., Мильшин А.А., Шма-ленюк А.С. Моделирование ослабления радиоволн лесным пологом в глобальной модели радиоизлучения земной поверхности в L - и Р - диапазонах // Вестник Москов. Гос. ун-та леса - Лесной вестник. - 2007. - Вып.2 (51). - С.90-99.
3. Мильшин А.А., Гранков А.Г., Шелобанова Н.К. Ва-лидация модели глобального крупномасштабного радиоизлучения Земли в дециметровом диапазоне // Современные проблемы дистанционного зондирования земли из космоса. - 2011. - Т.8. - №1. - С.246-254.
4. Мильшин А.А., Гранков А.Г., Шелобанова Н.К. Формирование радиоизлучения почвы в модели глобального крупномасштабного радиотеплового излучения земли в дециметровом диапазоне // Современные проблемы дистанционного зондирования земли из космоса. - 2012. - Т.9. - №3. - С.43-49.
5. Гранков А.Г., Мильшин А.А. О влиянии земной ионосферы на яркостную температуру подстилающей поверхности в дециметровом диапазоне радиоволн при измерениях с искусственного спутника Земли // Радиотехника и электроника. - 1988. - т.33.
- № 7. - С.1345-1351.
6. Гранков А.Г., Шутко А.М. Об использовании диапазона дециметровых волн для исследования акваторий методами СВЧ-радиометрии // Исследование Земли из космоса. - 1986. - № 5. - С.78-89.
7. Le Vine D.M., Abraham S. The Effect of the Ionosphere on Remote Sensing of Sea Surface Salinity From Space: Absorption and Emmision at L Band // IEEE Trans. on Geos. and Rem. Sens. - 2002. - Vol.40.
- №. 4.- P.771-782
8. Meissner T., Wentz F.J. Polarization Rotation and the Third Stokes Parameter: The effects of Spacecraft Attitude and Faraday Rotation // IEEE Trans. on Geos. and Rem. Sens. - 2006. - V.44. - NO.3. - P.506-515.
9. Гранков А.Г., Мильшин А.А., Шелобанова Н.К. Радиоизлучение атмосферы в дециметровом диапазоне волн при спутниковых наблюдениях // Радиофизические методы в дистанционном зондировании сред [Электронный ресурс]: сб. докладов Четвёртой Всероссийской научной школы и конференции. Муром, 30 июня - 3 июля 2009 г. Муром: Изд.-полиграфический центр МИ ВлГУ. 2009. 433 с.: ил. 1 электрон. опт. диск (CD-ROM). - С.107-111.
10. Кравцов Ю.А., Фейзулин З.И., Виноградов А.Г. Прохождение радиоволн через атмосферу Земли. М.: Радио и связь, 1983. - 224 с.
11. Ионосфера Земли. Модель глобального распределения концентрации, температуры и эффективной частоты соударений электронов. ГОСТ 25645.14689. М.: Государственный комитет СССР по управлению качеством продукции и стандартам, 1990. -812 с.
PREPARATION OF FLAT ASYMMETRIC MEMBRANES FROM SOLUTIONS OF PAN AND DMSO
Miteva Milena Pencheva
PhD, Assistant at the Department of Fundamentals of Chemical Technology, University "Prof.D-r. Assen Zlatarov"-
Burgas, Bulgaria Petrov Stoiko Petrov
PhD, Professor and Head of the Department of Fundamentals of Chemical Technology, Dean of the Faculty of
Technical sciences, University "Prof.D-r. Assen Zlatarov"-Burgas, Bulgaria
Todorova Donka Dimitrova
PhD, Assoc.Prof and Head of the Department of Ecology and Environment protection, University "Prof.D -r. Assen
Zlatarov"-Burgas, Bulgaria
ABSTRACT
The possibility to obtain flat asymmetric ultrafiltration (UF) membranes by phase inversion from solutions of polyacrylonitrile (PAN) and dimethylsulfoxide (DMSO) was studied. The physicochemical interactions between the polymer and the solvent were studied by infrared spectroscopy and dynamic viscosity measurements. According to the transport, selective and microscopic characteristics determined, the best properties showed the membrane prepared from 16 mass % PAN/DMSO. Key words: polyacrylonitrile, dimethylsulfoxide, phase inversion, polymer membranes
1. Introduction
Polyacrylonitrile and its copolymers are among the most widely used polymer materials for preparation of ultrafiltration and microfiltration (MF) membranes. The classic
technique used for their synthesis is phase inversion. The development of this method was preceded by systematic research work major part of which were related to the influences of various parameters on the mechanism and the establishment of the
regularities determining membrane morphology [1,p.512, 2,p.231]. It is hard to pre-set and theoretically characterize the resulting membrane structure by taking into account the set of different parameters of the process. In such cases, the relationship is studied individually and it is specific for the particular system. To prepare PAN membranes by the method of phase inversion, solutions of PAN in various solvents and at various ratios are used. Thus, membranes of different technological characteristics and different applications are obtained. The most widely used solvents are dimethylacetamide, N,N - di-methylformamide (DMF), etc. Dimethylsulfoxide is highly polar aprotic solvent having excellent solvent ability for PAN and it is used alone or with additives to prepare mainly hollow fiber membranes [3, p.6]. There are well-known publications reporting for studies on the interactions and peculiarities in DMSO behavior towards organic and inorganic compounds [4,p 7, 5,p.6].
Based on the available literature, it can be stated that the reason is in the type of the interaction between DMSO and the different compounds and their functional groups which affects the membrane formation by phase inversion.
The aim of the present work is to obtain flat asymmetric ultrafiltration membranes by semi-dry phase inversion method from solutions of PAN and DMSO.
2. Experimental
Solutions of PAN and DMSO were used for the experiments. They were prepared from polyacrylonitrile fibers obtained from ternary copolymer with composition: acrylonitrile, methacrylate and 2-acrylamide-2-methylpropane sulfonic acid at ratio 90.6: 8.1: 1, product of "Lukoil Neftochim Burgas" Co and solvent - DMSO, puriss. p.a., ACS reagent, >99.9% (GC), product of „Fluka", Switzerland.
The membranes were formed by laying a film of the polymer solution onto a substrate of two-side calendered polyester matt of grade FO-2403, product of,,Velidon Filter", Germany.
The studies on the transport and selective characteristics of the membranes were carried out with a ultrafiltration laboratory cell SM-165-26 of "Sartorius", England. The calibrant used for their characterization was Albumin fraction V (from bovine serum), Mm=76 000 - product of „Merck", Germany. Selectivity of the different membranes was determined by studying of the resulting filtrate on a UV-VIS spectropho-tometer "UNICAM 8625" at the wavelength (X)=280 nm (for albumin). The membrane structure formed was visualized by scanning electron microscopy by cathode sputtering with microscope JSM-5510, product of "JEOL",Japan.
To prove the physicochemical interactions between the polymer and the solvent, samples of the working solutions were studied by FT-IR spectrophotometer,,TENSOR 27", ''Bruker",Germany. The samples were brought as a capillary layer onto KBr tablets. The spectra were registered under the following conditions: interval studied - 3996^399 cm-1 and resolution - 2.
The rheological properties of the polymer solutions were studied by measuring the dynamic viscosity on a rotational viscosimeter type - REOTEST II -2.1, Germany.
The membranes were prepared by the semi-dry phase inversion method under normal conditions - T=25 oC and atmospheric pressure in precipitation medium - deionized water with the same temperature. Deionized water was used also for their subsequent washing, thermal treatment and characterization.
The thermal treatment was carried out at 80 oC for 10 min with the membranes fixed on a metal frame.
3. Results and discussion
The solvent used DMSO, due to its good solvation properties and specific properties, in this case also determined the structural arrangement in the PAN/DMSO solution. This was expected to affect the conditions of the phase inversion process and to be of certain importance for the formation of the membrane structure. For all phase inversions carried out in present work, the conditions were the same except for the polymer solutions concentrations.
The existence of interaction between the solvent and the polymer was shown by the analyses of the solutions with IR spectroscopy. The spectral data for a solution of PAN/DMSO were compared to these of the pure solvents (Fig.1). Substantial decrease of the intensity of the band at 1026 cm-1,characterizing the O=S group was observed in the PAN/DMSO compared with the spectrum of DMSO. These changes were probably due to coordination interactions with PAN functional groups or other intermolecular interactions [6, p.10].
The degree of these interactions practically affects the viscosity (n) of the system. The structural organization in the solutions is directly connected with their viscosity determined as a result from the influence of the tangential shear stress. The behavior and the rheology of the solutions under mechanical impact (t) were different. It can be seen from the logarithmic dependence shown in Fig.2, that under the same conditions, the flow curve of the 18 mass% PAN/DMSO solution was the highest standing while that of the 15 mass% PAN/DMSO solution - the lowest.
1026
"1500 laao
Waveriurritjer cm-'
Fig. 1. IR spectra of samples: DMSO (A), PAN/DMSO (A1).
The shapes of the three curves indicate for the stability of the polymer solutions where there is no additional supramo-lecular structuring, i.e. they are homogeneous under normal temperatures. Accordingly, the structural organization of 18 mass% PAN/DMSO had the highest viscosity, higher internal friction and smaller rheology. This is due to the differences in the physicochemical behavior of the solvent because of the different amounts of polymer in the solution. The dynamic viscosity measurements and IR spectra showed that the solutions
used were stable and homogeneous which are conditions necessary for the phase inversion to take place and the formation of the membrane structure. The studies showed also that solutions with concentrations in the range from 15 mass% to 18 mass% PAN were the most suitable for formation of UF membranes. Outside this range, the membrane structures did not possess characteristics corresponding to the ultrafiltration scope.
4,5
^ 4 25 jap '
4
3,75 3,5 3,25
• 16%PAN,DMSO
• 18%PAN,DMSO
3
0
0,5
1
1,5
2
2,5
4
3 , 3,5 lg T
Fig. 2. Flow curves of polymer solutions with different concentration of PAN and DMSO.
The membranes obtained were estimated by studying their performance characteristics - permeability (G, l/m2h) and selectivity (9, %). The results obtained for membranes formed from solutions with PAN concentrations 15, 16 and 18 mass% with solvent DMSO. The dependencies of the water permeability (GH2O, l/m2h) on pressure (P, MPa) measured in both directions are presented in Fig.3.
The effects of pressure and concentration can be read from the hysteresis in Fig.3. The highest water permeability was observed for 16 mass% PAN and reached 80 l/m2h at 0.5MPa. The hysteresis area was very small for all the three
membranes and it indicated for their mechanical strength in operation but also for greater densification of the polymer structure.
Considering the results shown in Table 1 on the selectivity (^alb) and permeability (Galb, l/m2h) of the membranes under pressure of 0.3 MPa vs the calibrant albumin, it can be seen that again the membrane prepared from 16 mass% PAN solution showed three times higher selectivity for albumin compared to the other two membranes which showed also very low permeability.
л
a
90 80 70 60 50
p 40
О
.52 30
20 10 0
О
—■— 15%PAN,DMSO
15%PAN,DMSO
—♦— 16%PAN,DMSO
---16%PAN,DMSO
à. 18%PAN,DMSO
—Д— 18%PAN,DMSO
0
0,1
0,2 0,3
P, MPa
0,4
0,5
Fig. 3. Hysteresis curves of membranes prepared from solutions of different concentrations of PAN and DMSO.
Table 1
Permeability and selectivity for water and albumin of membranes prepared from the corresponding solutions
at pressure of 0.3 MPa
Polymer solution GH2O, l/m2h Galb, l/m2h фа1Ь, %
15 mass % PAN/DMSO 5 5 21
16 mass % PAN/DMSO 24 7 76
18 mass % PAN/DMSO 6 4 23
SEM indeed showed that the selective layer surface was substantially densified and took up comparatively deeper into the transport sublayer and the asymmetry of the structure could be clearly distinguished.
Fig. 4. SEM micrographs of a cross section of a membrane formed from solution of 16 mass % PAN/DMSO.
Conclusions 3.
1. The optimal concentration range for preparation of asymmetric membranes was found to be from 15 mass% to 18 mass% PAN/DMSO.
2. It was established that, as a result from the 4. intermolecular interactions between PAN and DMSO,
the best ultrafiltration properties had the membrane prepared from 16 mass% PAN/DMSO.
3. The membrane formed from the solution of 16 mass% 5. PAN/DMSO had low permeability for albumin as a
result from the densification of the surface layer.
References
1. Мулдер M., Введение в мембранную технологию, 6. Москва, Изд. Мир, (1999), с. 512
2. Дубяга В.П., Перепечкин Л.П., Каталевский Е.Е., Полимерные мембраны, Москва,Изд."Хи-мия"(1981), с.231.
Tan L., Liu S., Pan D., Water effect on the gelation behavior of polyacrylonitrile/dimethyl sulfoxide solution, Colloids and Surfaces A: Physicochem. Eng. Aspects, (2009), Vol.340, p. 168-173. Tan L., Pan D., Pan N., Gelation behavior of polyacrylonitrile solution in relation to aging process and gel concentration, Polymer, (2008), Vol.49, p.5676-5682.
Du W., Chen H., Xu H., Pan D., Pan N., Viscoelastic behavior of polyacrylonitrile/dimethyl sulfoxide concentrated solution with water, Journal of Polymer Science Part B: Polymer Physics, (2009), Vol.47, p.1437-1442.
Wu Q.Y., Chen X.N., Wan L.S., Xu Z.K., Polyacrylonitrile and Solvents: Density Functional Theory Study and Two-Dimensional Infrared Correlation Analysis, Journal of Physical Chemistry B, (2012), Vol.116, p.8321-8330.
REQUIREMENTS FOR THE ESTABLISHMENT AND IMPLEMENTATION OF EDUCATIONAL ELECTRONIC EDITIONS
Mukusheva Makhabbat Serikovna
Master degree student, L.N. Gumilyov Eurasian National University, Astana
The 2020 educational system will work in regulatory-legal field of informatization of education defines all regulations and standards of computerization and connectedness; organization of open distance learning; development, testing and replication of digital educational resources and creation of the Kazakh component of the Internet environment; technical and pedagogical support of infrastructure and software of the educational process [1, p.10].
At the present stage of development of educational space one of ways of activating learning activities of students is the use of information technology. Inculcation in the educational process of electronic information and educational resources, such as electronic textbooks and manuals, will contribute of the development of independent, search, research activities of students increase their educational and professional interest.
Consider the requirements that must take into consideration when creating electronic educational editions [2, p. 25].
The process of creating educational electronic editions should provide the production of educational electronic editions that meet the system of psycho-pedagogical, technical and technological, aesthetic and ergonomic requirements.
Educational electronic publications must meet the standard didactic requirements of the traditional educational publications, such as textbooks, and teaching aids.
The requirement for scientific of learning using educational electronic editions means sufficient depth, accuracy and scientific integrity of the training material content, provides educational electronic edition with the latest scientific achievements Learning process with the help of educational electronic editions should be built in accordance with modern scientific knowledge methods: experiment, comparison, observation, abstraction, generalization, concretization, analogy, induction and deduction, analysis and synthesis, simulation method, including mathematics, as well as the method of system analysis.
The requirement of availability, implemented by means of educational electronic editions, is the need to determine the degree of complexity and depth theoretical study of educational material according to age and individual needs of students. Unacceptable congestion and excessive complexity of educational material where acquisition of this material becomes beyond student's strength.
