new research article surface modification of asymmetric...

Research ArticleSurface Modification of Asymmetric PolysulfonePolyethyleneGlycol Membranes by DC Ar-Glow Discharge Plasma

Chalad Yuenyao12 Thawat Chittrakarn34

Yutthana Tirawanichakul134 and Suksawat Sirijarukul34

1National Research University Project 2014 Prince of Songkla University Hat Yai Songkhla 90112 Thailand2Material Chemistry Research Center Department of Chemistry Faculty of Science Khon Kaen University MuangKhon Kaen 40002 Thailand3Department of Physics Faculty of Science Prince of Songkla University Hat Yai Songkhla 90112 Thailand4Membrane Science and Technology Research Center Faculty of Science Prince of Songkla University Hat YaiSongkhla 90112 Thailand

Correspondence should be addressed to Chalad Yuenyao pannatornyhotmailcom

Received 1 September 2016 Revised 9 November 2016 Accepted 29 November 2016

Academic Editor Mohd H D Othman

Copyright copy 2016 Chalad Yuenyao et alThis is an open access article distributed under theCreativeCommonsAttribution Licensewhich permits unrestricted use distribution and reproduction in any medium provided the original work is properly cited

Polysulfonepolyethylene glycol (PSFPEG)membranes were prepared by drywet phase inversionmethod Effects of direct currentglow discharge plasma using argon as working gas on morphological structures and gas separation properties of membraneswere studied Alteration of membrane characteristics were analyzed by various techniques like contact angle scanning electronmicroscope Fourier transform infrared spectroscopy and dynamic mechanical thermal analysis Gas separation properties weremeasured in terms of permeation and ideal O2N2 selectivity Results showed that hydrophilic and gas separation properties ofPSFPEG membranes increased by plasma surface modification It was also shown that the dosage of PEG and plasma treatmentaffected themorphological structures andmechanical and gas separation propertiesThemacro voids and transmembrane structuredisappeared with a little amount of PEG dosage Pore size andmechanical strength tend to decrease with increasing PEG dosage upto 10wt Glass transition temperature (119879119892) receded from 2018 to 1437∘C for pure PSF and PSFPEG with PEG dosage of 10wtO2 and N2 gases permeation through the 10-minute plasma treated membranes tend to increase However the permeation stronglydispersed when treatment time was more extended

1 Introduction

Plasma surface modification is one of the processes withhigh potential that can be used to raise the utility ofmembrane materials in diverse technical applications Glowdischarge plasma at low pressures is one of the severalphysical techniques utilized to modify the morphology andproperties of polymeric membrane surfaces [1] Most glowdischarge plasmas used for these aims are generated fromradio frequency (1356MHz) and microwave (245GHz)power sources However DC glow discharge is the easiestamong these techniques as there is no need for complexelectronic circuits As already presented by various refer-ences polymericmembranemodification is the integration ofchemical and physical techniques [2ndash4] Addition of organic

or inorganic particle as a third component of the castingsolution is one of the most important chemical techniqueswhile the plasma surface modification is a physical (plasmatreatment) and physicochemical (plasma polymerization andgrafting) technique Membrane performance obtained bythe incorporation of these two techniques is quite high[5] Typically the permeability of asymmetric polymeric gasseparation membranes prepared by phase inversion tech-niques is quite low and unsuitable for practical use In orderto increase the permeability of gas hydrophilic propertiesselective layer thickness and porosity of the membraneshave to be improved In general to increase the permeationrate the selective layer should be thin For the CO2CH4separation the hydrophilic property of themembrane surfacehas an influence on the CO2 permeation rate Therefore

Hindawi Publishing CorporationInternational Journal of Polymer ScienceVolume 2016 Article ID 4759150 8 pageshttpdxdoiorg10115520164759150

2 International Journal of Polymer Science

the permeation rate of CO2 was enhanced by increasingthe hydrophilic property of the membrane surface [3 4]However the increase of gas permeation rate depends onmany parameters like kinetic diameter quadrupole momentand polarizability of gas as well as the polarity of polymericmembrane surfaces Generally etching and deposition pro-cesses occur at the same timewhen the polymericmembranesare treated with the discharge plasma from non-polymerforming gases [1] Nevertheless these processes are dependedon the initial plasma conditions

For the addition of the third component in the polymersolution polyethylene glycol (PEG) is one of the mostimportant additives used Several research groups have inves-tigated the effect of PEG and both molecular weight anddosage on themorphology structuremechanical propertiesand performance as well as the formation of membranesIn 1998 Kim and Lee [5] studied the effect of PEG onmembrane formation by phase inversion They found thatthe PEG behaves as a pore-forming agent The water fluxincreases and solute rejection and coagulation value decreasewith increasing PEG to NMP ratio Also porosity of thebottom sublayer increased with the use of the PEG additiveBesides the free fractional volume is uplifted as the glasstransition temperature (119879119892) themodulus and tensile strengthdeclined after PEG was incorporated in the casting solution[6 7] Shieh et al [7] found that PEG can be used toimprove the membrane selectivity due to its hydrophilicnature Chakrabarty et al [8] reported that the membraneswhich incorporated PEG of higher molecular weights showhigher pure water flux and porosity than the membraneswith low molecular weight PEG Zuo et al [9] investigatedthe influence of PEG molecular weight on morphologiesand properties of PVDF membranes They found that PEGwith a relatively low molecular weight acts as a pore-formingagent while PEG with high molecular weight behaves as apore-suppressing agent They also found that the viscosity ofcasting solutions increased with increasing PEG molecularweight Furthermore Yunos et al [10] investigated the effectof PEG molecular weight and dosage on the properties andperformance of PSF membranes They found that pure waterflux and mean pore radius of membranes increased with anincrease of PEG content as well as the hydrophilic componentappearance in PSFPEG blend membranes

This work studied the effects of PEG as a polymericadditive and of low temperature and pressure DC glowdischarge plasma on the morphological structures and sur-face properties of polysulfonepolyethylene glycol (PSFPEG)membranes Additionally the permeation of N2 and O2gases through PSFPEG membranes before and after plasmatreatment was measured and appraised

2 Experimental Method

21 Materials Polysulfone (UDEL 3500 LCD MB) in pelletform was supplied from Solvay China Solvents includingDMAC (99 119872119882 = 8712 gmol) 1-methyl-2-pyrrolidone(NMP) tetrahydrofuran (THF) and acetone (995) werepurchased from Fluka Riedel-deHaen Sigma-Aldrich (Thai-land) Co Ltd and Ajax Finechem Pty Ltd respectively PSF

pellets were weighed by 001 g weighing scale (AND and GF-3000) from AampD (Thailand) Co Ltd A hot plate magneticstirrer of VS-130SH from Vision Scientific (Thailand) CoLtd was used for dissolving PSF Hot plate temperature wasset at 55ndash60∘C PEG (119872119882 = 1000 gmol) purchased fromFluka Riedel-deHaen was used as additive in this study

22 Preparation of Flat Sheet Membranes Polysulfonepoly-ethylene glycol (PSFPEG) asymmetric membrane was pre-pared by drywet phase inversion method Pellets of PSFwere dried by an electrical oven at 85∘C for 24 hr beforeusage All ingredients were weighed corresponding to thegiven formula In the preparation of the casting solution PEGwas first dissolved in the solvents Afterwards PSF materialsare carefully poured into the solution of PEG and solventsTo remove air bubbles the dissolved casting solutions weresubjected to the ultrasonic bath for 15minThen the obtainedcasting solution was casted on a clear and smooth glassplate The wet thickness of casted membranes was controlledat about 150 120583m To obtain the asymmetric membrane thenascent membranes were placed in the normal air for oneminute before they were immersed in the coagulation bath ofionized water for 24 hr After that the membrane was driedin normal air for 24 hr

23 Plasma Treatment of PSFPEG Membranes A lab-scalelow pressure DC glow discharge plasma system was usedfor the treatment of PSFPEG membranes Details of thisplasma system are explained in previous work [11] In briefthe plasma system as shown in Figure 1 consisted of vacuumchamber power supply and electrode and rotary pumpBefore generating plasma discharges the pressure inside theplasma reactor was pumped down to about 55 times 10minus2mbarIn the present work the initial plasma gas pressure anddischarge power were controlled at about 25 times 10minus1mbar and150W respectively Samples of PSFPEG membranes werefixed on an acrylic plate of 15mm thickness and then placedon the anode electrodeThe interelectrode gap was controlledat about 30 plusmn 01 cm To study the effect of glow dischargeplasma on the surface and gas permeation properties ofPSFPEG membranes plasma treatment time was varied

24 Characterization of PSFPEG Membranes First PSFmembranes with different PEG concentrations were testedfor their hydrophilic properties by water contact anglemeasurements in sessile drop mode using a video basedoptical contact angle measuring instrument (Model OCA15EC DataPhysics Intruments GmbH Germany) Samples ofplasma treated PSFPEGmembranes were subjected to watercontact anglemeasurements as well Physical andmechanicalproperties of polymeric membrane were investigated bydynamic mechanical thermal analysis (DMTA) technique intensile mode During the DMTA test the frequency and tem-perature were controlled at 1Hz and 20ndash300∘C respectivelyFor the observation of morphological patterns and structuresby SEM samples of PSFPEG membranes were immersed inliquid nitrogen for 5ndash10 minutes and then coated by gold atlow pressure Furthermore the creation of functional groups

International Journal of Polymer Science 3

Cathode

Anode

Vacuum chamber

Rotary pump

Membrane

DC

12

kVm

ax3

A

Figure 1 DC-plasma system and components

Feed Retentate

Permeate

O-Ring

Stainless steel ringMembrane

Supporting mesh

Stainless steel housing

Figure 2 Components of the permeation module

was verified by attenuated reflectance Fourier transforminfrared (ATR-FTIR) spectroscopy in the range of 400ndash4000 cmminus1 for the wave number with a resolution of 4 cmminus1

25 Gas Permeation Measurement The permeation rate ofpure O2 and N2 gases through PSFPEG membrane samplesbefore and after plasma treatment was measured at differentpressure levels at 2 4 6 and 8 bar The permeation moduleas a critical component of the testing setup is presentedin Figure 2 Samples of membrane were cut into circularform with the diameter of 57 cm and effective area of about1736 cm2 To prevent any leakage of gas rubber O-rings witha thickness of 05 cm were utilized Permeation rates wereread from the soap bubble flow rate meter five times foreach sample with the average value calculatedThe pressure-normalized flux or permeability value in the unit of GPU(1GPU = 10minus6 cm3 (STP)cm2 s cmHg) was determined byusing (1) [4 12ndash14] In addition the ideal gas separation factoror the O2N2 selectivity was estimated by (2) [3 10 14]

(119875119897 ) =119876119860Δ119901 (1)

prop119894119895 = (119875119897)119894(119875119897)119895 =119875119894119875119895 (2)

where 119876 is the volumetric flow rate 119875 is the permeability 119897is the skin layer thickness 119860 is the membrane effective area(119875119897) is the permeance in the unit of GPU and Δ119901 is thetransmembrane pressure 119875119894 and 119875119895 are the permeability of 119894and 119895 gases respectively

70

75

80

85

90

95

100

0 10 20 30 40PEG dosage (wt)

Wat

er co

ntac

t ang

le (∘

)

Figure 3 Water contact angle versus an increase in the PEGconcentration (wt)

3 Results and Discussion

31 Effect of PEG Concentration Results of the water contactangle measurement of PSF membranes at different PEGdosages show a decreasing trend especially when the PEGconcentration increased to 30wt as shown in Figure 3 Thewater contact angle decreased from905 to 754 or about 170while the PEG dosage increased to about 30wtThis meansthat the PEG concentration has an effect on the hydrophilicproperties of PSF membranes

Figures 4(a)ndash4(c) show morphological patterns andstructures of pure PSF PSFPEG 5wt and PSFPEG 10wtrespectively It can be seen that the macro voids disappearedwhen PEG was incorporated in the PSF membrane Inthis study the pore size was estimated through the SEMmicrograph It was found that the average pore size of PSFmembranes approximated by Carnoy Program 20 versionincorporated with SEM micrographs tends to decrease withincreasing PEG dosage The average pore size of pure PSF(included macro voids) PSFPEG 5wt and PSFPEG10wtwas about 337 311 and 309120583m respectively Furtherit can be seen that the small transition layer which appearedin the pure PSF membrane was completely suppressed whenPEG was incorporated Figure 5 shows the pore diameterdistribution of pure PSF membranes and PSFPEG mem-branes with a loading of 5 and 10wt Distribution of thepore size is narrower when PEG (119872119882 = 1000 dalton) wasincorporated in the casting solutionThismeans that the poresize of PSFPEG membranes is more uniform than that ofpure PSF ones

In addition to the hydrophilic properties andmorpholog-ical structuresmechanical strengths and glass transition tem-peratures (119879119892) of PSF membranes were studied using DMTAtechnique Results show thatmechanical strengths in terms ofstorage modulus and loss modulus of the membrane samplestend to decrease while the PEGdosage increased up to 10wt


(a) (b)

(c)

Figure 4 SEMmicrographs cross-sectional structure of pure PSF (a) PSFPEG 5wt (b) and PSFPEG 10wt (c) membranes

0

50

100

150

200

250

Num

ber o

f por

es

Pure_PSF

Maximum pore diameter (120583m)

0-1

1-2

2-3

3-4

4-5

5-6

6-7

7-8

8-9

9-10

10-11

11ndash5

0

PEG 10wtPEG 5wt

Figure 5 Comparison of themaximumpore diameter distributionsbetween pure PSF membranes and PSFPEG membranes with aloading of 5 and 10wt respectively

as illustrated in Figures 6(a) and 6(b) respectively Figure 6(c)shows that 119879119892 decreased from 2018∘C for a membrane with-out PEG to 1437∘C for a PSFPEG membrane with 10wtPEG Decreasing of mechanical strengths and 119879119892 may reflectthe degradation of membrane structure caused from plasmatreatment and the negative alteration influenced from aggre-gation of PEG dosage These results are in accordance withKim and Lee [5] Ma et al [15] and Chakrabarty et al [16]

32 Effect of DC-Plasma Treatment In addition to the effectof PEG dosage Ar-plasma also has an effect on the physicalproperties of PSFPEG The storage and loss modulus ofplasma treated PSFPEG membranes decreased as shown inFigures 6(a) and 6(b) This indicates that Ar-plasma at about15W can degrade PSFPEG membranes Figure 7 shows themodification of water contact angle of PSFPEG membranes(PEG concentration of 5 and 10wt) both before and afterplasma treatment at about 15W and at different treatmenttimes It can be seen that the water contact angle of PSFPEGmembrane surfaces decreased sharply at the beginning ofthe treatment and dispersed for a prolong treatment timeThese changes indicated a competition between etching and


0

200

400

600

800

0 100 200 300 400

PEG0_UPEG5_U

PEG10_UTemperature (∘C)

Stor

age m

odul

us (E

998400 MPa

)

PEG10_Ar5m

(a)

0

10

20

30

40

50

0 100 200 300 400

Loss

mod

ulus

(E998400998400

MPa

)

Temperature (∘C)PEG0_UPEG5_U

PEG10_UPEG10_Ar5m

(b)

00

05

10

15

20

25

30

35

0 100 200 300 400

Loss

tang

ent


PEG10_UPEG10_Ar5m

(c)

Figure 6 Variation of storage and loss modulus loss tangent and 119879119892 of membrane samples with PEG concentration (wt)

deposition processes in the plasma treatment For a prolongtreatment time the etching effect and deposition processare comparable For this treatment the optimized plasmatreatment time is in the range of 1ndash3min It was shown thatlow pressure DC Ar-plasma can improve the hydrophilicproperties of PSFPEG membrane surfaces From literaturethe improvement of the hydrophilic property of polymericmembrane surfaces can increase both permeation rate andideal selectivity of CO2CH4 [3]

Figure 8 shows the FTIR spectra of PSFPEGmembranesbefore and after Ar-plasma treatment For the PSFPEGuntreated membranes it can be seen that the characteristicabsorption peaks of PEG at around 2885 cmminus1 (O-H) and1110 cmminus1 (C-O) do not appear This suggested that most ofthe PEG is not apparent in the membrane top layer However

a low absorption peak appeared at around 2872 2920and 2965 cmminus1 After Ar-plasma treatment the new lowabsorption peak appeared at around 2357 and 2368 cmminus1Also very low absorption peaks at around 3140ndash4000 cmminus1are in the opposite direction when compared with thePSFPEG untreated membranes The intensity of absorptionpeaks at around 2872 and 2965 cmminus1 decreased after plasmatreatment whereas the peak at around 2920 cmminus1 increasedclearly Decreasing of absorption peaks may reflect thedecomposition or degradation of functional groups whereasthe increase of absorption bands was attributed to thedeposition or creation of functional groups

New absorption peaks correspond to the creation ofC-H bonds of aldehyde groups After plasma treatmentmembrane samples were exposed to the air and the oxidation


20

40

60

80

100

0 5 10 15 20 25Plasma treatment time (min)

Wat

er co

ntac

t ang

le (∘

)

PEG 10wtPEG 5wt

Figure 7 Water contact angle of PSFPEGmembranes after being treated with low temperature DC Ar-plasma at treatment time of 0 1 3 510 15 and 20min

30405060708090

100

600 800 1000 1200 1400 1600 1800

Tran

smitt

ance

()

PEG10_UPEG10_Ar5min

Wavenumber (cmminus1)

(a)

95

96

97

98

99

100

1800 2300 2800 3300 3800

Tran

smitt

ance

()

PEG10_UPEG10_Ar5min


2872 2920 2965 cmminus1

2357 2368 cmminus1

(b)

Figure 8 FTIR spectra of PSFPEG membranes before (black) and after (orange) plasma treatment (a) wavenumber 600 to 1800 and (b)1800 to 4000

of methyl group in the structure of PSF was then initiatedThe oxidation at the position of methyl group yields analdehyde which can further be oxidized to yield a carboxylicpolar group The increase of hydrophilic properties may bethe result from these polar groups Furthermore the O-H and C-H bonds at around 3000 to 3900 cmminus1 bandof plasma treated membranes are more active than theuntreated ones For this reason the hydrophilic property wasimproved according to the results of the water contact anglemeasurements mentioned above

Figure 9 shows the top skin surface of PSFPEG 10wtmembranes It can be seen that the number of pores decreasedafter plasma treatment This may due to the effect that thedeposition processes are more dominant than the plasmaetching processes This result is according to the gas perme-ation testing results as the permeation of O2 and N2 gasesthrough PSFPEG 10wt decreased after being treated byplasmaThis leads to an increase of the idealO2N2 selectivity

33 Gas Permeation Property The permeation of O2 andN2 gases through PSF and PSFPEG membranes was mea-sured using different transmembrane gas pressuresThe idealO2N2 separation factor was evaluated The experimentalresults of these measurements are shown in Figure 10 Itcan be seen that the permeance in the unit of GPU ofO2 and N2 is strongly dispersed However the permeancetends to decrease with increasing plasma treatment timeThe gas permeation through ten-minute plasma treatedmembranes increased clearly This can be explained that theplasma etching process ismore dominant than the depositionprocess The variation of O2 and N2 permeability affectedthe ideal separation factor or selectivity of these two gasesThe ideal O2N2 selectivity increased to about 3 as shownin Figure 10 when PSFPEG membranes were treated withglow discharge plasma of Ar gas for 20 minutes Results fromthis study also showed that the gas permeation of PSFPEGmembranes is significantly higher than that of PSF pure


(a) (b)

Figure 9 SEMmicrographs of top skin layers of PSFPEG 10wtmembranes untreated (a) and Ar-plasma treated at a discharge power andtreatment time of 15W and 5min (b) respectively

00

05

10

15

20

25

30

0

50

100

150

200

250

0 5 10 15 20 25

Gas

per

mea

nce (

GPU

)

Plasma treatment time (min)

O2N

2se

lect

ivity

N2 permeanceO2 permeanceO2N2 selectivity

Figure 10 O2 andN2 gases permeance and ideal O2N2 selectivity ata pressure of 3 bar for plasma treated PSF membrane with differenttreatment times

membranes For the asymmetric polymeric membrane withdense skin layer the permeation of gas depended on the skinlayer thickness Referring to the SEM micrographs as shownin Figures 4(a)ndash4(c) the skin layer thickness decreased whenPEG was incorporated in PSF membranes Typically skinlayer thickness affected to the permeation rate of gases [4]Furthermore incorporation of PEG into the PSF castingsolution affected the formation of porous top layer as shownin Figure 9 Formation of pore on top skin layer leads toincrease of permeation rate of gases anddecrease of selectivityof O2N2 gases

4 ConclusionsIn summary the morphological structure and physicalproperty of PSF changed when PEG was incorporated in

the casting solution The pore size distribution was opti-mized clearly Macro voids were suppressed and insteadsponge like structures appeared The hydrophilic propertieswere improved with incorporation of PEG The level ofhydrophilicity was enhanced with increasing PEG dosageIn addition to the change of morphological structures thephysical properties in terms of glass transition temperatureand viscoelastic modulus were modified The hydrophilicproperty was further increased by glow discharge plasmaat low pressures because the polar group like O-H andC-H bonds increased after plasma treatment For the gasseparation property it was shown that the incorporation ofPEG can increase the permeation rate of O2 and N2 gasesHowever the O2N2 separation factor is quite lowThismightbe because the coupling agent is not incorporated in thecasting solution The separation factor was enhanced afterPSFPEG membranes were treated with DC glow dischargeplasma

Competing Interests

The authors declare that they have no competing interests

Acknowledgments

Financial support from National Research University Princeof Songkla University (NRUrsquo58 PSU) and ThEP Cen-ter CHE Thailand is acknowledged The authors wishto thank the Membrane Science and Technology ResearchCenter (MSTRC) Department of Physics and Prince ofSongkla University for providing infrastructure and facilitiesrequired

References

[1] E F CastroVidaurre C A Achete F Gallo DGarcia R Simaoand A C Habert ldquoSurface modification of polymeric materialsby plasma treatmentrdquoMaterials Research vol 5 no 1 pp 37ndash412002


[2] D Hegemann H Brunner and C Oehr ldquoPlasma treatmentof polymers for surface and adhesion improvementrdquo NuclearInstruments and Methods in Physics Research Section B BeamInteractions with Materials and Atoms vol 208 pp 281ndash2862003

[3] S Modarresi M Soltanieh S A Mousavi and I ShabanildquoEffect of low-frequency oxygen plasma on polysulfone mem-branes for CO2CH4 Separationrdquo Journal of Applied PolymerScience vol 124 no 1 pp E199ndashE204 2012

[4] C Yuenyao Y Tirawanichakul and T Chittrakarn ldquoAsymmet-ric polysulfone gas separation membranes treated by low pres-sure DC glow discharge plasmasrdquo Journal of Applied PolymerScience vol 132 no 24 article no 42116 2015

[5] J-H Kim and K-H Lee ldquoEffect of PEG additive on membraneformation by phase inversionrdquo Journal of Membrane Sciencevol 138 no 2 pp 153ndash163 1998

[6] G D Vilakati E M V Hoek and B B Mamba ldquoProbing themechanical and thermal properties of polysulfone membranesmodified with synthetic and natural polymer additivesrdquo Poly-mer Testing vol 34 pp 202ndash210 2014

[7] J-J Shieh T-S Chung R Wang M P Srinivasan andD R Paul ldquoGas separation performance of poly(4-vinylpyridine)polyetherimide composite hollow fibersrdquoJournal of Membrane Science vol 182 no 1-2 pp 111ndash123 2001

[8] B Chakrabarty A K Ghoshal and M K Purkait ldquoEffectof molecular weight of PEG on membrane morphology andtransport propertiesrdquo Journal of Membrane Science vol 309 no1-2 pp 209ndash221 2008

[9] D-Y Zuo Y-Y Xu W-L Xu and H-T Zou ldquoThe influence ofPEGmolecularweight onmorphologies andproperties of PVDfasymmetric membranesrdquo Chinese Journal of Polymer Sciencevol 26 no 4 pp 405ndash414 2008

[10] M Z Yunos Z Harun H Basri and A F Ismail ldquoStudieson fouling by natural organic matter (NOM) on polysulfonemembranes effect of polyethylene glycol (PEG)rdquo Desalinationvol 333 pp 36ndash44 2014

[11] C Yuenyao T Chittrakarn Y Tirawanichakul P Saeung andWTaweepreda ldquoThe effects of oxygen and argon plasmas on thesurface morphology of polysulfone membranerdquoThai Journal ofPhysics vol 8 pp 41ndash44 2012

[12] A F Ismail and P Y Lai ldquoDevelopment of defect-free asymmet-ric polysulfone membranes for gas separation using responsesurface methodologyrdquo Separation and Purification Technologyvol 40 no 2 pp 191ndash207 2004

[13] M A Aroon A F Ismail M M Montazer-Rahmati and TMatsuura ldquoMorphology and permeation properties of polysul-fone membranes for gas separation effects of non-solvent addi-tives and co-solventrdquo Separation and Purification Technologyvol 72 no 2 pp 194ndash202 2010

[14] R W Baker Membrane Technology and Applications JohnWiley amp Sons Chichester UK 2nd edition 2004

[15] Y Ma F Shi J Ma MWu J Zhang and C Gao ldquoEffect of PEGadditive on the morphology and performance of polysulfoneultrafiltration membranesrdquo Desalination vol 272 no 1ndash3 pp51ndash58 2011

[16] B Chakrabarty A K Ghoshal and M K Purkait ldquoSEManalysis and gas permeability test to characterize polysulfonemembrane prepared with polyethylene glycol as additiverdquoJournal of Colloid and Interface Science vol 320 no 1 pp 245ndash253 2008

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the permeation rate of CO2 was enhanced by increasingthe hydrophilic property of the membrane surface [3 4]However the increase of gas permeation rate depends onmany parameters like kinetic diameter quadrupole momentand polarizability of gas as well as the polarity of polymericmembrane surfaces Generally etching and deposition pro-cesses occur at the same timewhen the polymericmembranesare treated with the discharge plasma from non-polymerforming gases [1] Nevertheless these processes are dependedon the initial plasma conditions

For the addition of the third component in the polymersolution polyethylene glycol (PEG) is one of the mostimportant additives used Several research groups have inves-tigated the effect of PEG and both molecular weight anddosage on themorphology structuremechanical propertiesand performance as well as the formation of membranesIn 1998 Kim and Lee [5] studied the effect of PEG onmembrane formation by phase inversion They found thatthe PEG behaves as a pore-forming agent The water fluxincreases and solute rejection and coagulation value decreasewith increasing PEG to NMP ratio Also porosity of thebottom sublayer increased with the use of the PEG additiveBesides the free fractional volume is uplifted as the glasstransition temperature (119879119892) themodulus and tensile strengthdeclined after PEG was incorporated in the casting solution[6 7] Shieh et al [7] found that PEG can be used toimprove the membrane selectivity due to its hydrophilicnature Chakrabarty et al [8] reported that the membraneswhich incorporated PEG of higher molecular weights showhigher pure water flux and porosity than the membraneswith low molecular weight PEG Zuo et al [9] investigatedthe influence of PEG molecular weight on morphologiesand properties of PVDF membranes They found that PEGwith a relatively low molecular weight acts as a pore-formingagent while PEG with high molecular weight behaves as apore-suppressing agent They also found that the viscosity ofcasting solutions increased with increasing PEG molecularweight Furthermore Yunos et al [10] investigated the effectof PEG molecular weight and dosage on the properties andperformance of PSF membranes They found that pure waterflux and mean pore radius of membranes increased with anincrease of PEG content as well as the hydrophilic componentappearance in PSFPEG blend membranes

This work studied the effects of PEG as a polymericadditive and of low temperature and pressure DC glowdischarge plasma on the morphological structures and sur-face properties of polysulfonepolyethylene glycol (PSFPEG)membranes Additionally the permeation of N2 and O2gases through PSFPEG membranes before and after plasmatreatment was measured and appraised

2 Experimental Method

21 Materials Polysulfone (UDEL 3500 LCD MB) in pelletform was supplied from Solvay China Solvents includingDMAC (99 119872119882 = 8712 gmol) 1-methyl-2-pyrrolidone(NMP) tetrahydrofuran (THF) and acetone (995) werepurchased from Fluka Riedel-deHaen Sigma-Aldrich (Thai-land) Co Ltd and Ajax Finechem Pty Ltd respectively PSF

pellets were weighed by 001 g weighing scale (AND and GF-3000) from AampD (Thailand) Co Ltd A hot plate magneticstirrer of VS-130SH from Vision Scientific (Thailand) CoLtd was used for dissolving PSF Hot plate temperature wasset at 55ndash60∘C PEG (119872119882 = 1000 gmol) purchased fromFluka Riedel-deHaen was used as additive in this study

22 Preparation of Flat Sheet Membranes Polysulfonepoly-ethylene glycol (PSFPEG) asymmetric membrane was pre-pared by drywet phase inversion method Pellets of PSFwere dried by an electrical oven at 85∘C for 24 hr beforeusage All ingredients were weighed corresponding to thegiven formula In the preparation of the casting solution PEGwas first dissolved in the solvents Afterwards PSF materialsare carefully poured into the solution of PEG and solventsTo remove air bubbles the dissolved casting solutions weresubjected to the ultrasonic bath for 15minThen the obtainedcasting solution was casted on a clear and smooth glassplate The wet thickness of casted membranes was controlledat about 150 120583m To obtain the asymmetric membrane thenascent membranes were placed in the normal air for oneminute before they were immersed in the coagulation bath ofionized water for 24 hr After that the membrane was driedin normal air for 24 hr

23 Plasma Treatment of PSFPEG Membranes A lab-scalelow pressure DC glow discharge plasma system was usedfor the treatment of PSFPEG membranes Details of thisplasma system are explained in previous work [11] In briefthe plasma system as shown in Figure 1 consisted of vacuumchamber power supply and electrode and rotary pumpBefore generating plasma discharges the pressure inside theplasma reactor was pumped down to about 55 times 10minus2mbarIn the present work the initial plasma gas pressure anddischarge power were controlled at about 25 times 10minus1mbar and150W respectively Samples of PSFPEG membranes werefixed on an acrylic plate of 15mm thickness and then placedon the anode electrodeThe interelectrode gap was controlledat about 30 plusmn 01 cm To study the effect of glow dischargeplasma on the surface and gas permeation properties ofPSFPEG membranes plasma treatment time was varied

24 Characterization of PSFPEG Membranes First PSFmembranes with different PEG concentrations were testedfor their hydrophilic properties by water contact anglemeasurements in sessile drop mode using a video basedoptical contact angle measuring instrument (Model OCA15EC DataPhysics Intruments GmbH Germany) Samples ofplasma treated PSFPEGmembranes were subjected to watercontact anglemeasurements as well Physical andmechanicalproperties of polymeric membrane were investigated bydynamic mechanical thermal analysis (DMTA) technique intensile mode During the DMTA test the frequency and tem-perature were controlled at 1Hz and 20ndash300∘C respectivelyFor the observation of morphological patterns and structuresby SEM samples of PSFPEG membranes were immersed inliquid nitrogen for 5ndash10 minutes and then coated by gold atlow pressure Furthermore the creation of functional groups


Cathode

Anode

Vacuum chamber

Rotary pump

Membrane

DC

12

kVm

ax3

A


Feed Retentate

Permeate

O-Ring


Supporting mesh





(119875119897 ) =119876119860Δ119901 (1)

prop119894119895 = (119875119897)119894(119875119897)119895 =119875119894119875119895 (2)


70

75

80

85

90

95

100

0 10 20 30 40PEG dosage (wt)

Wat

er co

ntac

t ang

le (∘

)







(a) (b)

(c)


0

50

100

150

200

250

Num

ber o

f por

es

Pure_PSF


0-1

1-2

2-3

3-4

4-5

5-6

6-7

7-8

8-9

9-10

10-11

11ndash5

0

PEG 10wtPEG 5wt





0

200

400

600

800

0 100 200 300 400

PEG0_UPEG5_U


Stor

age m

odul

us (E

998400 MPa

)

PEG10_Ar5m

(a)

0

10

20

30

40

50

0 100 200 300 400

Loss

mod

ulus

(E998400998400

MPa

)


PEG10_UPEG10_Ar5m

(b)

00

05

10

15

20

25

30

35

0 100 200 300 400

Loss

tang

ent


PEG10_UPEG10_Ar5m

(c)







20

40

60

80

100


Wat

er co

ntac

t ang

le (∘

)

PEG 10wtPEG 5wt


30405060708090

100

600 800 1000 1200 1400 1600 1800

Tran

smitt

ance

()

PEG10_UPEG10_Ar5min


(a)

95

96

97

98

99

100

1800 2300 2800 3300 3800

Tran

smitt

ance

()

PEG10_UPEG10_Ar5min


2872 2920 2965 cmminus1

2357 2368 cmminus1

(b)






(a) (b)


00

05

10

15

20

25

30

0

50

100

150

200

250

0 5 10 15 20 25

Gas

per

mea

nce (

GPU

)


O2N

2se

lect

ivity






Competing Interests


Acknowledgments


References

























CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials




Cathode

Anode

Vacuum chamber

Rotary pump

Membrane

DC

12

kVm

ax3

A


Feed Retentate

Permeate

O-Ring


Supporting mesh





(119875119897 ) =119876119860Δ119901 (1)

prop119894119895 = (119875119897)119894(119875119897)119895 =119875119894119875119895 (2)


70

75

80

85

90

95

100

0 10 20 30 40PEG dosage (wt)

Wat

er co

ntac

t ang

le (∘

)







(a) (b)

(c)


0

50

100

150

200

250

Num

ber o

f por

es

Pure_PSF


0-1

1-2

2-3

3-4

4-5

5-6

6-7

7-8

8-9

9-10

10-11

11ndash5

0

PEG 10wtPEG 5wt





0

200

400

600

800

0 100 200 300 400

PEG0_UPEG5_U


Stor

age m

odul

us (E

998400 MPa

)

PEG10_Ar5m

(a)

0

10

20

30

40

50

0 100 200 300 400

Loss

mod

ulus

(E998400998400

MPa

)


PEG10_UPEG10_Ar5m

(b)

00

05

10

15

20

25

30

35

0 100 200 300 400

Loss

tang

ent


PEG10_UPEG10_Ar5m

(c)







20

40

60

80

100


Wat

er co

ntac

t ang

le (∘

)

PEG 10wtPEG 5wt


30405060708090

100

600 800 1000 1200 1400 1600 1800

Tran

smitt

ance

()

PEG10_UPEG10_Ar5min


(a)

95

96

97

98

99

100

1800 2300 2800 3300 3800

Tran

smitt

ance

()

PEG10_UPEG10_Ar5min


2872 2920 2965 cmminus1

2357 2368 cmminus1

(b)






(a) (b)


00

05

10

15

20

25

30

0

50

100

150

200

250

0 5 10 15 20 25

Gas

per

mea

nce (

GPU

)


O2N

2se

lect

ivity






Competing Interests


Acknowledgments


References

























CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials




(a) (b)

(c)


0

50

100

150

200

250

Num

ber o

f por

es

Pure_PSF


0-1

1-2

2-3

3-4

4-5

5-6

6-7

7-8

8-9

9-10

10-11

11ndash5

0

PEG 10wtPEG 5wt





0

200

400

600

800

0 100 200 300 400

PEG0_UPEG5_U


Stor

age m

odul

us (E

998400 MPa

)

PEG10_Ar5m

(a)

0

10

20

30

40

50

0 100 200 300 400

Loss

mod

ulus

(E998400998400

MPa

)


PEG10_UPEG10_Ar5m

(b)

00

05

10

15

20

25

30

35

0 100 200 300 400

Loss

tang

ent


PEG10_UPEG10_Ar5m

(c)







20

40

60

80

100


Wat

er co

ntac

t ang

le (∘

)

PEG 10wtPEG 5wt


30405060708090

100

600 800 1000 1200 1400 1600 1800

Tran

smitt

ance

()

PEG10_UPEG10_Ar5min


(a)

95

96

97

98

99

100

1800 2300 2800 3300 3800

Tran

smitt

ance

()

PEG10_UPEG10_Ar5min


2872 2920 2965 cmminus1

2357 2368 cmminus1

(b)






(a) (b)


00

05

10

15

20

25

30

0

50

100

150

200

250

0 5 10 15 20 25

Gas

per

mea

nce (

GPU

)


O2N

2se

lect

ivity






Competing Interests


Acknowledgments


References

























CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials




0

200

400

600

800

0 100 200 300 400

PEG0_UPEG5_U


Stor

age m

odul

us (E

998400 MPa

)

PEG10_Ar5m

(a)

0

10

20

30

40

50

0 100 200 300 400

Loss

mod

ulus

(E998400998400

MPa

)


PEG10_UPEG10_Ar5m

(b)

00

05

10

15

20

25

30

35

0 100 200 300 400

Loss

tang

ent


PEG10_UPEG10_Ar5m

(c)







20

40

60

80

100


Wat

er co

ntac

t ang

le (∘

)

PEG 10wtPEG 5wt


30405060708090

100

600 800 1000 1200 1400 1600 1800

Tran

smitt

ance

()

PEG10_UPEG10_Ar5min


(a)

95

96

97

98

99

100

1800 2300 2800 3300 3800

Tran

smitt

ance

()

PEG10_UPEG10_Ar5min


2872 2920 2965 cmminus1

2357 2368 cmminus1

(b)






(a) (b)


00

05

10

15

20

25

30

0

50

100

150

200

250

0 5 10 15 20 25

Gas

per

mea

nce (

GPU

)


O2N

2se

lect

ivity






Competing Interests


Acknowledgments


References

























CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials




20

40

60

80

100


Wat

er co

ntac

t ang

le (∘

)

PEG 10wtPEG 5wt


30405060708090

100

600 800 1000 1200 1400 1600 1800

Tran

smitt

ance

()

PEG10_UPEG10_Ar5min


(a)

95

96

97

98

99

100

1800 2300 2800 3300 3800

Tran

smitt

ance

()

PEG10_UPEG10_Ar5min


2872 2920 2965 cmminus1

2357 2368 cmminus1

(b)






(a) (b)


00

05

10

15

20

25

30

0

50

100

150

200

250

0 5 10 15 20 25

Gas

per

mea

nce (

GPU

)


O2N

2se

lect

ivity






Competing Interests


Acknowledgments


References

























CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials




(a) (b)


00

05

10

15

20

25

30

0

50

100

150

200

250

0 5 10 15 20 25

Gas

per

mea

nce (

GPU

)


O2N

2se

lect

ivity






Competing Interests


Acknowledgments


References

























CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials


























CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials



new research article surface modification of asymmetric...

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