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Preparation of Patterned Isopore Poly(urethane acrylate) and Microporous Poly(vinylidene fluoride) Membranes by Soft Lithography and Their Application to Water Treatment : 소프트 리소그래피 방법을 이용한 패턴형 등방공경 PUA 분리막과 패턴형 PVDF 정밀여과막의 제작 및 수처리에의 적용

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dc.contributor.advisor이정학-
dc.contributor.author최동찬-
dc.date.accessioned2017-07-13T08:40:55Z-
dc.date.available2017-07-13T08:40:55Z-
dc.date.issued2015-08-
dc.identifier.other000000056859-
dc.identifier.urihttps://hdl.handle.net/10371/119749-
dc.description학위논문 (박사)-- 서울대학교 대학원 : 화학생물공학부, 2015. 8. 이정학.-
dc.description.abstractMembrane filtration process is widely used for water and wastewater treatments because of numerous advantages it offers. Critical issues in membrane processes are membrane fouling as well as broad pore size distribution. In this study, patterned isopore membrane with high fouling resistance was fabricated combining soft lithographic method with UV-curable polymer and the effect of pattern on particle deposition were elucidated.
First, membrane with uniform pore size was fabricated using a soft-lithographic method. Due to the precisely controlled pore size by micro size patterns, the membrane presented narrow pore size distribution comparing with conventional membrane. Furthermore, because the UV-curable polyurethane acrylate with releasing agent which decreases surface energy of PUA was used as the membrane material, it gave rise to better anti-biofouling performance than materials of commercial isopore membrane such as polycarbonate.
Second, a patterned isopore membrane with reverse-pyramid patterns was prepared from UV-curable polyurethane acrylate by the soft lithographic method and extent of particle deposition was investigated during microfiltration. The extent of particle deposition was dependent on not only the ratio of crossflow velocity to permeation velocity, but also the size of particles in the feed. Three dimensional modeling based on computational fluid dynamics was also conducted to predict the vortex formation and elucidate the anti-fouling mechanisms of reverse-pyramid patterned membranes. The vortex was in accordance with the trends of particle depositions during the microfiltration.
Third, correlations between pattern shape and extent of particle deposition were investigated experimentally and were elucidated through three dimensional modeling. The extent of particle deposition on patterned membranes was dependent on both pattern shape and orientation. Three dimensional modeling predicted velocity profile and shear stress distribution on patterned membrane surface. The changes in hydraulic trait at each pattern affected particle deposition. In particular, maximum shear stress mostly governed the extent of particle depositions on the membrane surface.		-
dc.description.tableofcontentsTable of Contents
Abstract…………………………………………………… i
Table of contents………………………………………… iii
List of Figures………………………………………………x
List of Tables………………………………………………xx

I. Introduction……………………………………………… 1
I.1. Backgrounds……………………………………… 2
I.2. Objectives………………………………………… 4
II. Literature Review……………………………………… 7
II.1. Soft-lithography………………………………… 8
II.1.1. Introduction……………………………… 8
II.1.2. Materials for soft-lithography………… 9
II.1.2.1. Hard molds………………………… 9
II.1.2.2. Soft molds………………………… 11
II.1.2.3. Rigiflex molds…………………… 14
II.1.3. Diverse patterning techniques of soft-lithography… 15
II.1.3.1. Soft molding……………………… 15
II.1.3.2. Capillary force lithography application……… 18
II.2. Isopore membranes…………………………………20
II.2.1. Introduction…………………………………………… 20
II.2.2. History of isopore membranes…………………… 21
II.2.2.1. Track etched membrane………………………… 21
II.2.2.2. Focused ion beam method……………………… 24
II.2.2.3. Micro molding……………………………………… 26
II.2.2.4. Self-assembly……………………………………… 31
II.2.3. Application of isopore membranes…… 33
II.3. Patterned membranes………………………………… 37
II.3.1. History of patterned membranes…………………… 37
II.3.2. Micro patterned hollow fiber membrane………… 39
II.3.3. Micro patterned flat sheet membrane…………… 43
II.3.4. Sub-micro patterned flat sheet membrane……… 46
II.3.5. Confirmation of antifouling property of patterned membrane …………………………………………………… 48
II.4. Computational fluid dynamics at membrane………49
II.4.1. Introduction…………………………………………… 49
II.4.2. CFD for crossflow membrane filtration system… 50
II.4.2.1. Crossflow membrane filtration system without spacer………………………………………………………… 50
II.4.2.2. Crossflow membrane filtration system with spacer…………………………………………………………53
II.4.3. CFD in Membrane bioreactor…………………… 56
III. Tunable Pore Size Micro/Submicron-sieve Membranes by Soft Lithography .……………………………………… 59
III.1. Introduction …………………………………………… 60
III.2. Experimental section ……………………………… 63
III.2.1. Preparation of PUA membranes ………………… 63
III.2.2. Water flux test ……………………………………… 65
III.2.3. Particle separation test …………………………… 67
III.2.4. CDC biofouling test ………………………………… 68
III.2.5. Membrane characterization ……………………… 70
III.3. Results and discussion …………………………… 71
III.3.1. Preparation of Tunable Pore Size Micro-sieve membrane…………………………………………………… 71
III.3.2. Surface pore characteristics of micro-sieve Membrane …………………………………………………… 74
III.3.3. Submicron-sieve Membrane Preparation and Surface Pore Characterization ……………………………77
III.3.4. Effect of straight pore structure and uniform pore size
………………………………………………………………… 79
III.3.5. Anti-biofouling property of PUA material ………… 81
III.4. Conclusion ……………………………………………… 84
IV. Three-dimensional hydraulic modeling of particle deposition on the patterned isopore membrane in crossflow microfiltration………………………………………………… 85
IV.1. Introduction …………………………………………… 86
IV.2. Materials and Methods ……………………………… 89
IV.2.1. Fabrication of patterned isopore membrane …… 89
IV.2.2. Particle depositions during crossflow microfiltration………………………………………………… 92
IV.2.3. Numerical method ………………………………… 95
IV.3. Results and discussion ……………………………… 98
IV.3.1. Conformation of a reverse-pyramid patterned membrane …………………………………………………… 98
IV.3.2. Deposition of 2 ㎛ particles on the patterned isopore membrane surface ………………………………………… 102
IV.3.3. Deposition of 5 ㎛ particles or mixture of 2 and 5 ?㎛ particles on the patterned isopore membrane surface …………………………………………………………………105
IV.3.4. Hydraulic flow characteristics on the patterned membrane surface ………………………………………… 109
IV.4. Conclusions.……………………………………………114
V. Effects of pattern shape and orientation on fouling behavior……………………………………………………… 115
V.1. Introduction …………………………………………… 116
V.2. Materials and Methods ……………………………… 118
V.2.1. Materials …………………………………………… 118
V.2.2. Preparation of patterned MF membrane ………… 119
V.2.3. Pure water flux measurement of MF membrane … ……………………………………………………………………121
V.2.4. Particle deposition experiment …………………… 123
V.2.5. Numerical method ………………………………… 124
V.3. Results and discussion ……………………………… 126
V.3.1. SEM images and pure water flux of flat and patterned membrane …………………………………………………… 126
V.3.2. Particle deposition on flat and patterned membrane surface ……………………………………………………… 129
V.3.3. Wall shear stress near the flat and patterned membrane surface ………………………………………… 131
V.3.4. Stream line near the flat and patterned membrane surface ……………………………………………………… 134
V.3.5. Relationship between particle deposition and wall shear stress ………………………………………………… 136
V.3.6. Relationship between particle deposition and stream line………………………………………………………………138
V.4. Conclusions …………………………………………… 139
VI. Conclusion ……………………………………………… 141

List of Figures
Figure II-1. Demensial stability (Rogers and Lee 2009) …………………………………………………………………… 13
Figure II-2 Schematic diagram of soft molding ………… 17
Figure II-3 Schematic diagram of capillary force lithography application (a) thick polymer, (b) thin polymer ………… 19
Figure II-4 SEM images of track etched membrane with (a) 200 X magnification and (b) 500X magnification ………… 22
Figure II-5 SEM image of silicon nitride isopore membrane with 25 nm pore size (H. D. Tong 2004) ………………… 25
Figure II-6 SEM images of (a) line and space micro structure and (b) several micrometer isopore membrane fabricated by micromolding method. (L. Vogelaar 2003) …………………………………………………………………… 28
Figure II-7 SEM images of (a) accumulated silica particles and (b) isopore membrane after removing silica particles and photo polymerization (F. Yan 2004) ………………… 29
Figure II-8 SEM image of isopore membrane prepared by combining micromolding and float casting method after particle separation experiment. Several micrometer pore was shown behind of sub-micro meter pores (F. Yan 2012) …………………………………………………………………… 30
Figure II-9 SEM images of (a) top view and (b) cross section of AAO membrane (W. Lee 2006) ……………… 32
Figure II-10 SEM images mixed cell before filtration (left) and cells after filtration (right) (Y. Ou 2014) ……………… 35
Figure II-11 SEM images of arrayed nanodots. (H. Masuda 2000) …………………………………………………………… 36
Figure II-12 SEM images of patterned hollow fiber membrane at (a) 5 mm, (b) 12 mm, (c) 32 mm and (d) 58 mm air gap (Culfaz et al. 2010) ……………………………41
Figure II-13 Schematic diagram of patterned hollow fiber membrane fabrication (Kim et al. 2015) ………………… 42
Figure II-14 SEM images of (a) pyramid, and (b) prism patterned membrane (Won et al. 2012) ………………… 44
Figure II-15 SEM images of patterned membrane prepared from (a) 180 kDa, (b) 275 kDa, and (c) 430 kDa molecular weight polymer (Won et al. 2014) ………………………… 45
Figure II-16 (a) Schematic diagram of sub-micro patterned UF membrane preparation step and AFM images of (b) flat and (c) patterned membrane (S.H. Maruf et al. 2013)… 47
Figure II-17 Pressure distribution on the membrane surface (Rahimi et al. 2005) ………………………………………… 52
Figure II-18 Experimental and modeling results of particle deposition experiment (Radu et al. 2014) ……………… 55
Figure II-19 Relationship between bubble size and average wall shear stress (Wei et al. 2013) ……………………… 58
Figure III-1. SEM images of master mold with a pyramid pattern. The base length and height of the pyramids are 28 μm and 10 μm, respectively ……………………………… 64
Figure III-2. Schematic diagram of the stirred cell for water flux measurements. To measure the flux of each membrane, membranes were installed in the stirred cell and the reservoir was filled with distilled water. Then, pressurized N2 gas was used to deliver water to the stirred cell. The weight of the effluent was measured using a balance ……………………………………………………… 66
Figure III-3. Schematic diagram and operating conditions of the biofouling test with the CDC reactor ………………… 69
Figure III-4. Schematic representation of the process steps for the fabrication of soft-lithographically patterned micro/submicron-sieve membranes. A PDMS stamp that is replicated from a master mold is used to generate a working PSMAH stamp. Then UV-curable PUA oligomer solution is dispensed onto the working stamp and scraped with a casting knife. Finally, the fully cured PUA isopore membrane layer with the working stamp is dissolved on a fabric support, where the dissolving PSMAH material acts as a glue to attach the membrane onto the support. The same procedures can also be applied for master mold with submicron-sized features. Note here that the pore size of the isopore membrane can be easily be varied by adjusting the height of the casting knife in the fourth step for this pyramid-shaped master mold …………………………… 73
Figure III-5. Scanning electron microscopy (SEM) images of membranes. a) Commercial PVDF(polyvinylidene fluoride), and b) Commercial track-etched membranes, respectively. The red circles in b) show defective pores with doublets or triplets. c) and d) PUA isopore membranes with different pore sizes fabricated by simply adjusting the vertical height of the casting knife		-
dc.description.tableofcontentspore size ~2.6 μm for c) and ~6.3 μm for d). e) Plot of pore size and porosity as a function of the vertical height of the casting knife. Values for the track-etched membrane shown in (b) are indicated in the plot for comparison purposes ………………………… 75
Figure III-6. SEM images of soft-lithographically fabricated micro-sieve membranes. The height of the casting knife was varied (manually) to obtain isopore micro-sieve membranes with different pore sizes, (a) ~2.7 μm, (b) ~3.5 μm, (c) ~5.9 μm and (d) ~6.4 μm, respectively. The pyramid-patterned Si master mold was used for these membranes. The final thicknesses of the micro-sieve membrane layer on the porous polyester support varied as well, from ~1 μm for (a) up to ~2.3 μm for (d) ………… 76
Figure III-7. SEM images of soft-lithographically fabricated submicron-sieve membranes. (a) Si master mold having vertical array of ~700nm Si pillars, (b) PUA membrane, and (c) Track-etched membrane, respectively. (d) Comparison of pore or pattern size in track-etched and PUA membranes. (e) Plot of the measured porosities for both membranes. Scale bars are 1μm for (a), (b), and (c) ………………………………………………………………… 78
Figure III-8. a) Comparison of water flux through various membranes with different porosity by the stirred cell test. b) Semi-log plot of the normalized water flux based on the porosity of each membrane used in the flux measurements. c) SEM images of colloidal particles (mixture of 1.1 μm and 300 nm polystyrene colloids) before separation by the isopore membrane, on the membrane surface, and in the permeate after filtration, from left to right, respectively ………………………………………………… 80
Figure III-9. CLSM images of biofilm on the a) PUA and b) track-etched microsieve membrane surfaces after 48 h of operation in CDC reactor. Green color indicates the P. aeruginosa in biofilm. Imaging area is ~1.2 mm*1.2 mm for both cases. c) ζ-potential of membranes and anti-biofouling characteristics. Variation of zeta-potential of PUA and TE membranes as a function of solution pH. d) Surface energy of PUA and track-etched membranes ………… 83
Figure IV-1. Schematic diagram of fabrication steps for the patterned isopore membrane. UV-curable PUA precursor solution was (a) dispensed on a pyramid-patterned PDMS replica mold and (b) spin-coated at 1850 rpm. (c) The PUA oligomer solution was polymerized by UV-curing at 365 nm for 2 h. (d) Finally, reverse-pyramid patterned PUA membrane was detached from the PDMS mold ……… 91
Figure IV-2. Schematic diagram of the crossflow filtration experimental set-up. A peristaltic pump was connected to the permeation line of membrane module to control the pore water flux………………………………………………… 94
Figure IV-3. Overall domain of computational fluid dynamics modeling . The overall domain size was 75 μm × 150 μm × 2000 μm (width × length × height) and the size of each pattern was 25 μm × 25 μm × 16 μm. The number of elements was 57,864 and fine meshes were generated near the membrane surface to solve complicate flow behavior with accuracy …………………………… 97
Figure IV-4. SEM images of (a, b) surface (c) cross-section, and (d) rear of the patterned isopore membrane ………………………………………………………………… 99
Figure IV-5. SEM images of PUA membrane prepared at different rotation rates. (a) 2400 and (b) 2500 rpm. Higher rotation rate gave rise to larger membrane pore size ………………………………………………………………… 100
Figure IV-6. Average pore size and pore size distribution of PUA membrane. The average pore size of PUA membrane was around 0.8 ?m and its deviation was 0.08 μm ……101
Figure IV-7. SEM images of particle depositions on the membrane surfaces after crossflow microfiltration of 2 μm particles (a) at Vc = 0.25 m/s with low Jp (=Vc/1000 = 2.5 X 10-4 m/s), (b) Vc =0.42 m/s with low Jp (=Vc/1000 = 4.2 X 10-4 m/s), (c) Vc = 0.25 m/s with high Jp (=Vc /100 = 2.5 X 10-3 m/s), and (d) Vc =0.42 m/s with high Jp (=Vc /100 = 4.2 X 10-3 m/s ) …………………………… 104
Figure IV-8. SEM images of particle depositions on the membrane surfaces after crossflow microfiltration of 5 μm particles (a) at Vc = 0.25 m/s with low Jp (Jp = Vc 1000 = 2.5 X 10-4 m/s), and (b) Vc = 0.42 m/s with low Jp ( = Vc /1000 = 4.2 X 10-4 m/s) ……………………………… 107
Figure IV-9. SEM images of particle depositions on the membrane surfaces after crossflow microfiltration of mixture of 2 and 5 μm particles (a) at Vc = 0.25 m/s with low Jp (Jp = Vc /1000 = 2.5 X 10-4 m/s), and (b) Vc = 0.42 m/s with low Jp ( = Vc /1000 = 4.2 X 10-4 m/s). Magnified SEM images are presented at right side of each SEM image ………………………………………………………… 108
Figure IV-10. Stream lines estimated by 3-D modeling near the patterned isopore membrane surface: (a) Vc = 0.25 m/s with low Jp (=Vc /1000 = 2.5 X 10-4 m/s), (b) Vc = 0.42 m/s with low Jp (=Vc /1000 = 4.2 X 10-4 m/s), (c) Vc = 0.25 m/s with high Jp (=Vc /100 = 2.5 X 10-3 m/s), and (d) Vc = 0.42 m/s with high Jp (=Vc /100 = 4.2 X 10-3 m/s), (a) Vc = 0.25 m/s with low Jp (=Vc /1000 = 2.5 X 10-4 m/s) and (b) Vc = 0.42 m/s with low Jp (=Vc /1000 = 4.2 X 10-4 m/s). For (a) and (b), the stream lines were estimated, assuming that a 5 μm particle was trapped around the pore in each reverse-pyramid pattern. The blue and red colors of the horizontal spectrum indicate the lower and higher water stream velocity, respectively ………………………………………………………………… 113
Figure V-1. Schematic diagram of patterned membrane fabrication (Won et al. 2012) ……………………………… 120
Figure V-2. Schematic diagram of crossflow microfiltration system ………………………………………………………… 122
Figure V-3. SEM images of (a) flat membrane (X1000), (b) flat membrane (X2500), (c) reverse-pyramid membrane (X1000), (d) reverse-pyramid membrane (X2500), (e) pyramid membrane (X1000), and (f) pyramid membrane (X2500) ………………………………………………………127
Figure V-4. Water fluxes of flat and patterned membranes ………………………………………………………………… 128
Figure V-5. Amounts of particle deposition at each membrane surface ……………………………………………130
Figure V-6. Wall shear stresses at each membrane surface. The red and blue colors of the vertical bar indicate higher and lower wall shear stress, respectively …………………………………………………………………… 133
Figure V-7. Stream lines at each membrane surface … 135
Figure V-8. Maximum wall shear stresses of each pattern shape …………………………………………………………… 137

List of Tables
Table II-1 Pore density and mean porosity of various commercial track etched membrane(J. I. Calvo et al. 1995) …………………………………………………………………… 23		-
dc.formatapplication/pdf-
dc.format.extent5491679 bytes-
dc.format.mediumapplication/pdf-
dc.language.isoen-
dc.publisher서울대학교 대학원-
dc.subjectIsopore membrane-
dc.subjectPatterned membrane-
dc.subjectAnti-fouling-
dc.subjectParticle deposition-
dc.subjectThree dimensional modeling-
dc.subjectSoft lithography-
dc.subjectShear stress-
dc.subjectVortex-
dc.subject.ddc660-
dc.titlePreparation of Patterned Isopore Poly(urethane acrylate) and Microporous Poly(vinylidene fluoride) Membranes by Soft Lithography and Their Application to Water Treatment-
dc.title.alternative소프트 리소그래피 방법을 이용한 패턴형 등방공경 PUA 분리막과 패턴형 PVDF 정밀여과막의 제작 및 수처리에의 적용-
dc.typeThesis-
dc.contributor.AlternativeAuthorChoi, Dong-Chan-
dc.description.degreeDoctor-
dc.citation.pagesxx, 156-
dc.contributor.affiliation공과대학 화학생물공학부-
dc.date.awarded2015-08-
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