Nghiên cứu biến tính bề mặt màng lọc : Đề tài NCKH. QT.08.28

ĐẠI IIO( Q l ()( ỊO I I A N O I - 2(109 HẠI HỌC' Ql ( ' plasma treated sample, membrane weight reduced quickly due to ablation effect occurred soon Fig 1: SI 'M images of PAN membrane surface (left) and cross-section (right) nm X 300 nm membrane area Fig gives A I’M images of PAN UF membrane surfaces before and after plasma treatments 50 100 150 200 250 300 350 Jlas111 a treatment time (s) Fig 2: Membrane weight loss ratio after plasma treatments M em brane surface topology The topology of membrane surface was characterized by atomic force spectroscopy (SPA-400 SPA-400 Seiko Instrument Inc.) Silicon antilever with tetrahedral lip was used lo scan le membrane surfaces and produc producc the images The tapping tappinu, I'll mode was selected to siudy ihe polymeric mcmbn at room tempi; rut ure rite sciinniim had boon done at 2.5 II/ for 300 5X4 The pictures indicate that the roughness of membrane surface increases after plasma treatments The roughness of Ar plasma treated membrane surface is higher than that of He plasma treated one meanwhile the roughness of (>, plasma treated surface is the lowest These results could be due to the physical etching effect of Ar plasma is stronger than that of He plasma In the case of plasma treatment, the strongest physical etching effect causes the largest weight loss ratio of the sample meanwhile the highest ablation effect leads to the lowest roughness of’ sample surface The results also indicate that when the plasma treatment time increasing, the ablation effect OÍ Ar and He plasmas also increases, which makes the weight loss ratio increased anti the sample surface roughness decreased For o plasma Ilie extended plasma treatment time leads to the damage of the sample surface because the lonutT physical etching and ablation effects occurred simultaneous!V plasma treated (Ira in) o , plasma treated (3 mill) Ar plasma treated Ar plasma treated (3 mill) He plasma treated (1 min)(1mill) He plasma treated (3 min) Fig 3: Al'M images of untreated and plasma treated membrane surfaces M em brane hydrophilizalion In th is experiment, the water contact angles f me in brane surfaces were measured using oniprneier equipped with video capturing /stem Figure shows the changes in the :>ntaci angles of membrane surfaces treated by ilium and oxygen plasmas, which is carried 111 at the power input of 10 \v and the gas flow lie of 18 seem vviili the different treatment IIÌCS Ii can be seen that live contact angles of 1Cmb rune surfaces reduce after plasma treatments This is due to the increase of membrane surface roughness and the introducing of functional groups into membrane surfaces then With the short treatment time of less than 30 sec, the contact angles of Ot and He plasma treated surfaces were almost similar, but the final contact angles of the surface treated with oxygen plasma decreased significantly when the plasma treatment lime increase further These results come from (lie fuel thill the liydrophilicily depends mainly on the 385 functional groups incorporated on the modified membrane surface's; the hydrophiiicily of oxygen plasma treated membrane surfaces must be higher than iltai of helium plasma treated ones, and the higher roughness as well as the larger amount of hydrophilic groups will be formed with the longer oxygen plasma treatment time For helium plasma treated surfaces, although the oxy,j;en-conLiinin!’ groups could he formed by the post-oxidation when exposure of the surface in air after plasma treatments, the contact angles is still lower because of the smaller amount of oxygen containing groups incorporated on the surface in comparison with thilt of the oxygen plasma treated ones o , plasm a H e plasm a 20 40 60 80 00 120 100 200 300 400 500 600 He plasma treatment time (sec) Treatment time (sec) Fig 4\ Contact angles of plasma Heated membrane surfaces Figure shows the permeability of plasma treated membranes, the results indicated that the permeability of oxygen plasma treated PAN membranes increases more significantly in comparison with that of helium plasma treated ones under the same of other plasma treatment conditions In fact, the increase of membrane surface hydrophilicity plays an important role for ihe enhancement of membrane permeability, In addition, the enlargement of membrane skin pore size and the increase of skin pore density due to plasma treatment may also contribute considerably for the increase of permeability of plasma treated membranes 100 500 ■ - J= 0 E a - 300 m A He plasma ■ O; plasma • i 200 c S ' 80 Jj — 60 ■9 40 A - A ft) B - eu 100 l, ± i 10 20 a 30 40 20 ▲ 50 A 60 Treatment time (s) 70 20 40 60 80 , 10 12 lie plasma treatment time (sec) Vrmeabiliiv of plasma treated membranes 177(1997) IV - < ON< 'I I Sl( )NS l’lasma treatments of ultra fillralion einbiaiK- siirlacc using non-polymer-forming asmas such as oxygen and inert gas plasmas ad 10 the formation of higher hydrophilic icmbianes, whose surface roughness increased id ihe oxygen-containing groups could be >rmcd ami incorporated on membrane surface tie r p lasm a tre a tm e n ts The increase of lembrane surface hydrophilicity results in the nprovement of membrane permeability And, nder the same of other plasma treatment Dnditions, oxygen plasma treated membranes Live a higher hydrophilicity and thus a higher ermcability in comparison with that of the inert as plasma treated ones Rl IT.RI'.NCT.S N Iiumaki, S Tasaka, and H Kawai J Polym Sci.: Part A: Polym Chem., 33, 2001 (1995) c M Chan, M Ko, and H Hiraoka Surf Sci Reports, 24, (1996) S D Lee, M Sannadi, 1' Denes, and J L Shohci Plasma and Polymers, Vol 2, No 3, M Stiohcl, S Corn, c s Lyons, and G A Korba J I’olym Sci.: Polym Chem Fdit., 23 125 (1995) i: M Liston, L Martinu and M R Wertheimer Plasma Surface Modification of Polymer, lũls: M Strobel, c s Lyons and K I,- Miual, VSP(I994) z Q Hua, R Sitaru, F Denes, and R A Young Plasmas and Polymers, Vol 2, No 3, 199(1997) I Gancarz, Ci Pozniak, A Bryjak Eur Polym J-, 36, 1563(2000) N Inagaki, s Tasaka, and H Kawai J App Polyrn Sci., Appl Polym Symp., 46 399(1990) Gancar/, Cl Pozniak, M Bryjak Eur Polym J„ 35, 1419- 1428(1999) 10 P w Kramer, Y s Yeh, II Yasuda J Membr Sci., 46 - 28 (1989) 11 K R Kull, M L Steen, E R Fisher J Membr Sci., 246, 203 -2 (2005) 12 11 Yasuda Plasma Polymerization, Academic Press, Inc., New York (1985) C O M P O S IT E M E M B R A N E S F A B R IC A T E D B Y P L A S M A P O L Y M E R IZ A T IO N O F O R G A N IC C O M P O U N D S Dung Thi Tran Shinsuke M o r i K i m Ba Viet Le \ and Masaaki S u zuki2 Dept Chem Tech Faculty o f Chemistry, Hanoi University o f Science, VNU, Vietnam ‘ Dept Chem Eng Faculty of Engineering, Tokyo Institute of Technology, Japan ABSTRACT Composite membranes fabricated by plasma polymerization using some organic compounds as monomers to form a plasma polymer top-layer deposited onto a porous substrate membrane surface The characterization of the composite membranes was investigated in terms of membrane morphology, membrane surface functionality, membrane separation efficiency and so on The experimental results indicated that Ihe plasma deposited polymer properties and thus the composite membrane characteristics depend highly on the plasma polymerization conditions The thickness of plasma deposited polymer top-layer is proportional with plasma polymerization time then membrane skin pore size reduces gradually The cross-linking degree of plasma deposited polymer is affected much by the effective plasma energy transferred to monomer molecules, which involves the monomer flow rate and plasma power input applied during plasma polymerization The experimental results also showed that the membrane separation efficiency depends not only on the plasma polymerization conditions but also on the nature of monomer and substrate using for the preparation of plasma polymerized composite membranes KEYWORDS plasma polymerization; deposit layer; composite membrane; separation efficiency; Intro d u ctio n Plasma modification is one of the useful methods for modification of polymer surfaces This method can be distinguished into plasma treatment and plasma polymerization depending on the type of gas using for plasma modification processes In the field of separation membranes, plasma modification can improve membrane surfaces hydrophilicity by plasma treatment using non-polymer-forming gases, and can be used for preparation of composite membranes by plasma polymerization using organic compounds [1-4] The possibility of plasma technique to modify substrate surfaces without affecting of the bulk properties of the base materials is an advantageous for development of surface-modified separation membranes [5-9] Plasma polymerization to deposit a barrier film directly from gaseous phase monomer onto micro-porous substrates is one of the effective methods employed for preparation of composite membranes, especially membranes for gas separation, pervaporation, nanofiltration and reverse osmosis [10-13], Plasma polymerization can produce a very thin skin layer and these plasma deposited films have a high cross-linked degree with good adhesion properties and pinhole free uniformity structure over the substrate surface In addition, many organic compounds and various porous substrates can be used for plasma polymerization [14 -17] During plasma polymerization, monomer molecules are subjected to fragmentation by transferred plasma energy The excited fragments then recombined and condensed onto a porous substrate surface, building up a polymeric deposited to form the top-layer for composite membranes The characterization of these membranes depends highly on the plasma polymerization parameters such as monomer flow rate, plasma discharge power, plasma polymerization time, plasma deposition pressure and etc In this work, the composite reverse osmosis membranes were prepared by plasma polymerization of acrylic acid and allylamine monomers to form a plasma polymer top-layer deposited onto polyacrylonilrile and polyimide microporous membrane surfaces The characterization of the composite membranes prepared at the different plasma conditions were investigated and compared in terms of membrane morphology, surface functionality, separation efficiency and so on Experim ental 2.1 Materials The substrates used as sublayer for the deposition of plasma polymer top-layer are polyacrylonitrile (PAN) ultrafiltration (UF) and polyimide (PI) microfiltration (MF) membranes The monomers used for plasma polymerization include acrylic acid (AA) and allylamine (AAM), which were purchased from Wako Industrial Chemicals Co (Japan) and used without further purification 2.2 Plasma reactor The plasma polymerization system consists of a tubular type reactor (diameter of 30 mm and length of 400 mm) with two external electrodes (10 mm wide and 100 mm apart) connected with a cold trap and a rotary vacuum pump, a monomer reservoir connected with a mass flow m eter and a metering valve, a radio frequency generator of 13.56 MHz with a matching network 2.3 Membrane characteristics The morphology of membranes was characterized by scanning electron microscopy (SEM, Hitachi S-800) To prevent the surface charging, a thin film (5 nm) of Pt was sputtered onto the surface and cross-section of samples by ion sputter (Hitachi, E-1030) prior to imaging The functionality of membrane surfaces was analyzed by FTIR-ATR spectra using Jeol- SPX 200 spectroscopy with one hundred scans were taken at a resolution of c m '1 The separation property of membranes was determined through the desalination experiments carried out in a membrane cell (Osmonic, USA) using 3000 ppm sodium chloride feed solution at a pressure driving force of 3.5 MPa R esults and D iscussion 3.1 S E M s t u d i e s on the substrate surface but also on the skin pore wall of substrates Therefore, after the certain time of plasma polymerization, the number of substrate skin pores could be completely covered and closed by the plasma deposited polymer 3.2 FTIR spectra The qualitative information about the functionality of composite membrane surfaces prepared by the deposition of AA and AAM plasma polymerized layer onto substrates can be obtained by FTIR-ATR spectra The results demonstrate the appearance of the new functional groups on membrane surfaces after plasma polymerization For acrylic acid plasma polymerization, the spectra show the presence of c - o (v = 1250, 1150, 1000, 920 cm ') and c = o (v = 1720 cm'1) For plasma polymerized allylamine, the spectra show the presence of NH and NH^ (v = 3250 cm'1), CsN (v = 2200 cm '1), C=N and c = (v = 1650 cm'1) The presence of oxygen in allylamine plasma polymer is not surprised because the plasma polymers are known to rapidly react with atmospheric oxygen and continue to so during storage in air [17] 3.3 Separation efficiency In this experiment, the separation efficiency of PAN-based and Pl-based composite membranes with the top-layer formed from AA and AAM plasma deposited polymers was investigated The results show that the salt rejection increases and the water flux decreases when a plasma polymerization time increasing This is due to the increase of the plasma deposited layer thickness and the decrease of the membrane skin pore size during plasma polymerization For the PAN-based composite membranes, the membrane separation factors could be reached a critical value after minutes of plasma polymerization and the further deposition of plasma polymer just causes the decline of the water flux only meanwhile the membrane selectivity is almost not changed And, the results also indicate that the composite membranes with AAM plasma polymerized top-layer could have a better separation efficiency by the higher selectivity and larger water flux in comparison with that of the membranes with AA plasma polymerized top-layer under the same of plasma polymerization conditions The comparison about the separation efficiency of Pl-based and PAN-based composite membranes with AAM plasma polymerized top-layer indicates that the separation efficiency of the PAN-based composite membranes can get a critical value earlier than that of the Pi-based composite ones And, with the sam e of the salt rejection value, the water flux of the Pl-based composite membranes is higher than this of the PAN-based composite membranes although the plasma deposited top-layer of the PAN-based composite membrane must be thinner than that of the Pl-based composite one This could be due to the larger mass resistance itself of the PAN sublayer in comparison with that of the PI sublayer Next the influence of the plasma polymerization conditions on the separation efficiency of composite m em branes was investigated The obtained results pointed out that the salt rejection increases and starts to reduce meanwhile the water flux decreases and then increases when monomer flow rate increasing It is well known that the plasma energy transferred to monomer molecules will be reduced when monomer flow rate increasing That means, at the fixed plasma power input and plasma polymerization time there is an optimum range of monomer flow rate in which the plasma deposited polymer layer has a higher cross-linking degree in comparison with that of the layer formed at the lower or excess monomer flow rales In addition, at the fixed monomer flow rate, the salt rejection increased and the water flux reduced then these factors also reach a critical value when plasma power input increasing C onclusions The characterization of the composite membranes prepared by the deposition of plasma polymer top-layer formed from organic monomers onto the porous membranes substrates depends highly on the preparation conditions The separation efficiency of these membranes is influenced much not only by the plasma parameters but also by the nature of substrates and monomers using for plasma polymerization The salt rejection increases and the water flux decreases with the increasing of the top-layer thickness and the plasma polymer cross-linking degree, which involves the plasma polymerization time and the effective plasma energy transferred into monomer molecules during plasma polymerization A cknow ledgem ents The authors would like to thank Vietnam Ministry of Science and Technology (MOST) and Japan Society for the Promotion of Science (JSPS) as the financial support for this work References [1] J Y Lai, c c Chou, J Appl Polym Sci 37 (1989) 1465 [2] Y J Wang c H Chen, M L Yell, G H Hsiue, B c Yu J Membr Sci 53 (1990) 275 [3] K Okita, S Asako, Selectivity 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