Engineering Selective Desalination Membranes via Molecular Control

Full text access provided via ACS AuthorChoice

Energy and the Environment

Engineering Selective Desalination Membranes via Molecular Control of Polymer Functional Groups Hongxi Luo, Kevin Chang, Kevin Bahati, and Geoffrey M. Geise Environ. Sci. Technol. Lett., Just Accepted Manuscript • DOI: 10.1021/acs.estlett.9b00351 • Publication Date (Web): 10 Jul 2019 Downloaded from pubs.acs.org on July 18, 2019

Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.

is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.

Page 1 of 20

Environmental Science & Technology Letters

1

Engineering Selective Desalination Membranes via

2

Molecular Control of Polymer Functional Groups

3

Hongxi Luo,+ Kevin Chang,+ Kevin Bahati, Geoffrey M. Geise*

4

Department of Chemical Engineering, University of Virginia, 102 Engineers’ Way, P.O. Box

5

400741, Charlottesville, VA 22904, USA

6 7

+Authors

contributed equally

8

9

10

KEYWORDS. Desalination; Selectivity; Water Purification; Membrane; Dielectric

1 ACS Paragon Plus Environment


Page 2 of 20

12

ABSTRACT

13

Membrane-based desalination processes are used widely to address increasing global demand for

14

purified water. To continue to meet increasing demand, advanced and highly selective

15

desalination membranes are needed to effectively and efficiently purify water that is increasingly

16

contaminated and saline. A general lack of fundamental structure-property relationships

17

frustrates the development of these membranes. Advanced polymer synthesis capabilities that

18

enable increasingly precise molecular control over the position of functional groups on a

19

polymer backbone could be instrumental in engineering advanced desalination membranes, but

20

little is known about how the position of functional groups influences water and salt transport

21

properties. In this study, we prepared and characterized a series of equivalent water content co-

22

polymers to determine how the functional group configuration along the polymer backbone

23

influences desalination-relevant transport properties. Shifting the co-polymer composition from

24

one rich in vicinal diol groups to one rich in side chains with a single hydroxyl group drove an

25

increase in the water/salt permeability selectivity, which is directly related to desalination-critical

26

salt rejection. The results suggest that controlled placement of functional groups within a

27

polymer could be a viable strategy for preparing advanced and highly selective desalination

28

membrane materials.


Page 3 of 20

30 31


Introduction Meeting global demand for clean water is a pressing engineering challenge.1 Membrane-

32

based technologies are used widely to desalinate water, and more efficient membranes are

33

needed to meet growing demand for purified water from increasingly contaminated and/or saline

34

water.2-6 Water purification membranes are generally polymeric, and highly selective membranes

35

are needed to meet the growing separation challenges in desalination technologies including

36

reverse osmosis and nanofiltration.6-10 The selective properties of these desalination membranes

37

result from the preferential transport of water relative to hydrated ions.11 Engineering highly

38

selective materials has been frustrated by a lack of fundamental structure-property relationships

39

to guide the design of advanced polymer membranes to address global water needs.

40

The ability to precisely place functional groups along a polymer backbone, with a high

41

degree of molecular control over functional group position, is becoming increasingly viable.12, 13

42

This structural control, facilitated by advances in synthesis capabilities, could be important for

43

engineering advanced desalination membranes. Little is known, however, about how functional

44

group placement within a polymer influences water/salt selectivity.

45

We report the desalination (i.e., water/salt) selectivity properties of a series of model

46

materials where the distribution of hydroxyl functional groups along the polymer backbone was

47

varied from a clustered to a more uniform configuration. Importantly, this series of materials was

48

prepared such that the membrane water content did not change as the distribution of the hydroxyl

49

groups changed. Membrane water content has a significant influence on water/salt selectivity

50

properties,9, 14 so the ability to vary the distribution of functional groups within the material

51

without perturbing the water content enabled us to ascribe the observed results to changes in the

52

functional group configuration.



53

Page 4 of 20

Shifting the functional group configuration to space the hydroxyl groups out more evenly

54

(compared to the more clustered configuration) resulted in increased water/salt permeability

55

selectivity, which is directly related to desalination-critical salt rejection.11 This increase in

56

selectivity was largely driven by sorption, or thermodynamic, effects. The results suggest that an

57

even distribution of hydrophilic chemical functionality in polymers may lead to more selective

58

membranes to address global demand for desalinated water.

59 60

Materials and Methods

61

HEMA:GMA:GMAOH Co-Polymers

62

Five co-polymers containing 2-hydroxyethyl methacrylate (HEMA), glycidyl methacrylate

63

(GMA), and glycerol methacrylate (GMAOH) co-monomers and cross-linked using

64

poly(ethylene glycol) dimethacylate (PEGDMA) were prepared via UV-initiated free radical

65

polymerization. These model materials are chemically different from the aromatic polyamide-

66

based membranes commonly used in reverse osmosis and nanofiltration membranes.15 The

67

structure of these materials (i.e., the choice of co-monomers) was chosen to enable preparation of

68

a series of materials where the distribution of hydrophilic functional groups (in this case,

69

hydroxyl groups) could be varied by changing the composition of the co-polymer without

70

changing the water content of the polymer.

71

The hydroxyl group distribution in the co-polymer was varied by changing co-monomer

72

composition of the pre-polymerization solution used to prepare the materials (Table 1). The

73

sample nomenclature, HEMA:GMA:GMAOH x:y:z, reflects the composition (by mass) of the

74

pre-polymerization solution used to prepare that material (e.g., 15:55:30 was prepared from a

75

pre-polymerization solution containing 15%, 55%, and 30%, by mass, of HEMA, GMA, and


Page 5 of 20


76

GMAOH, respectively). The PEGDMA cross-linker and initiator (1-hydroxycyclohexyl phenyl

77

ketone) were added to the co-monomer solution at compositions of 0.1 and 0.01 g/g(total co-

78

monomer), respectively, to form the pre-polymerization solution, which was stirred for 30 min at

79

room temperature to ensure the solution was well-mixed. The pre-polymerization solution was

80

degassed (via sonication for 10 min), confined between quartz plates (separated by spacers to

81

control film thickness), and irradiated, for 5 min, with 120 µJ/cm2 of 312 nm light to form

82

transparent and homogeneous polymer films that were approximately 100 m thick. The

83

chemical structure and additional information about the co-polymers are reported in Section S1

84

of the Supporting Information.

85 86

Table 1. Co-monomer mass fraction in the pre-polymerization solution used to prepare the

87

HEMA:GMA:GMAOH co-polymers defines the sample nomenclature. The water uptake and dry

88

density data were measured at ambient temperature, and the water sorption coefficient, 𝐾𝑤, was

89

calculated using the water uptake and dry polymer density. Uncertainty in the measured data is

90

one standard deviation from the mean of at least three measurements, and the uncertainty in the

91

water sorption coefficient was calculated using standard propagation of error.16 CoPolymer Sample

92

0:60:40 15:55:30 30:50:20 45:45:10 60:40:0 aUnits:

Co-Monomer Mass Fraction in the Pre-Polymerization Solution HEMA

GMA

GMAOH

0.0 0.15 0.30 0.45 0.60

0.60 0.55 0.50 0.45 0.40

0.40 0.30 0.20 0.10 0.0

Water Uptakea

Dry Polymer Density (g/cm3)

𝑲𝒘

0.24 ± 0.02 0.24 ± 0.01 0.24 ± 0.01 0.23 ± 0.01 0.23 ± 0.01

1.29 ± 0.02 1.30 ± 0.03 1.27 ± 0.01 1.27 ± 0.01 1.26 ± 0.02

0.23 ± 0.01 0.24 ± 0.01 0.23 ± 0.01 0.23 ± 0.01 0.23 ± 0.01

g(water) / g(dry polymer)

93 94 95 96

Water and Salt Transport Property Characterization To characterize the potential desalination performance of the HEMA:GMA:GMAOH copolymers, we measured water uptake, salt sorption coefficient, and water and salt permeability 5 ACS Paragon Plus Environment


Page 6 of 20

97

properties at ambient temperature. Water uptake was combined with dry polymer density to

98

calculate the water sorption coefficient, 𝐾𝑤 (Table 1).17 Water (i  w) and salt (i  s) sorption

99

coefficients, 𝐾𝑖, were combined with permeability properties, 𝑃𝑖, to calculate, via the solution-

100

diffusion model,18 apparent diffusion coefficients, 𝐷𝑖, as:19

101

𝐷 𝑖 = 𝑃𝑖 𝐾 𝑖

102

At least three measurements, per sample, were made for each property, and the uncertainty in the

103

measurement was one standard deviation from the mean. Standard propagation of error was used

104

to quantify the uncertainty in calculated quantities.16 Details about the specific methods used to

105

measure water uptake, salt sorption, pure water permeability, salt permeability, and hydrated

106

polymer dielectric properties are reported in Section S2 of the Supporting Information.

(1)

107 108 109

Results and Discussion Each composition of HEMA:GMA:GMAOH had equivalent water content (Table 1). Water

110

content affects the transport (and, thus, desalination) selectivity of hydrated polymers, and

111

increases in water content often correlate with decreases in selectivity.9, 14 Therefore, preparing

112

materials with equivalent water content is critical for decoupling the influence of functional

113

group configuration on water/salt transport selectivity from the influence of changing water

114

content on water/salt transport selectivity.

115

The equivalent water content of this series of HEMA:GMA:GMAOH co-polymers likely

116

results from subtle changes in the extent of cross-linking and hydroxyl group content across the

117

series of co-polymers. These changes were estimated to be reasonably small, as discussed in

118

Section S1.1 of the Supporting Information. Ultimately, maintaining equivalent water content in


Page 7 of 20


119

the series of materials was prioritized due to the strong influence of water content on the water

120

and salt transport properties of hydrated polymers.9, 14

121

We compared the HEMA:GMA:GMAOH transport properties to those of cross-linked

122

poly(ethylene glycol) diacrylate (PEG) hydrogels, as these materials also preferentially transport

123

water over salt via a solution-diffusion mechanism.20 The water content of these hydrogels can

124

be manipulated by changing the ethylene glycol chain length or by adding a diluent to the pre-

125

polymerization mixture.20 Thus, the PEG materials illustrate how transport properties change

126

with water content to contrast the situation in equivalent water content HEMA:GMA:GMAOH.

127

The water/salt transport selectivity is defined as the ratio of water to salt permeability, 𝑃𝑤 𝑃𝑠,

128

sorption 𝐾𝑤 𝐾𝑠, or diffusion, 𝐷𝑤 𝐷𝑠, coefficients, and the three selectivity values are related via

129

the solution-diffusion model:9

130

𝑃𝑤 𝑃 = (𝐾𝑤 𝐾 ) × (𝐷𝑤 𝐷 ) 𝑠 𝑠 𝑠

131

This water/salt permeability selectivity can be directly related to salt rejection, which is a critical

132

characteristic of effective desalination membranes.11 The salt rejection, R, is defined as the salt

133

concentration reduction from the bulk solution on the feed side of the membrane, 𝑐𝑠,𝑓𝑒𝑒𝑑, to the

134

bulk solution on the permeate (or product) side of the membrane normalized by 𝑐𝑠,𝑓𝑒𝑒𝑑 and

135

depends on the water/salt permeability selectivity: 𝑃𝑤𝑉𝑤

136

𝐑=

𝑐𝑠,𝑓𝑒𝑒𝑑 ― 𝑐𝑠,𝑝𝑒𝑟𝑚𝑒𝑎𝑡𝑒 𝑐𝑠,𝑓𝑒𝑒𝑑

=

𝑃𝑠 𝑅𝑇 (∆𝑝

1+

𝑃𝑤𝑉𝑤

― ∆𝜋)

𝑃𝑠 𝑅𝑇 (∆𝑝

(2)

(3)

― ∆𝜋)

137

where 𝑉𝑤 is the molar volume of water, ∆𝑝 is the hydraulic pressure difference across the

138

membrane, ∆𝜋 is the osmotic pressure difference across the membrane, R is the gas constant, and

139

T is the absolute temperature.9



Page 8 of 20

140

Water/salt permeability selectivity depends on a combination of both water/salt sorption

141

and diffusivity selectivity properties (Equation 2). Functional group configuration significantly

142

influenced the water/salt sorption selectivity of HEMA:GMA:GMAOH (Figure 1A). A

143

distributed hydroxyl group configuration (HEMA-rich co-polymer) led to higher sorption

144

selectivity compared to a vicinal-diol rich configuration (GMAOH-rich co-polymer), and this

145

result can be attributed to more effective exclusion of salt from the HEMA-rich co-polymer

146

compared to the GMAOH-rich co-polymer.

147

A 0

B

148 149

Figure 1. Water/salt sorption selectivity (A) and water/salt diffusivity selectivity (B) as a

150

function of water sorption coefficient and apparent water diffusion coefficient, respectively, for

151

HEMA:GMA:GMAOH ( ) and PEG ( )20 materials. For HEMA:GMA:GMAOH, the HEMA co-

152

monomer composition of the pre-polymerization solution used to prepare the co-polymer is

153

reported for each data point. The dashed lines represent reported empirical sorption (left) and

154

diffusivity (right) trade-off frontiers for desalination membrane materials,21, 22 and the solid lines

155

are least-squares fits to the data.

156


Page 9 of 20

157


Comparing HEMA:GMA:GMAOH water/salt sorption selectivity with that of

158

poly(ethylene glycol) diacrylate (PEG) hydrogels, we observed that the HEMA:GMA:GMAOH

159

data points move vertically upwards as HEMA content increases in a manner different from the

160

PEG materials (Figure 1A). The PEG result is expected if water content primarily drives sorption

161

selectivity properties.20 The HEMA:GMA:GMAOH result suggests that polymer chemistry, not

162

changing water content, is responsible for the change in sorption selectivity of

163

HEMA:GMA:GMAOH. Thus, preparing polymers with a distributed functional group

164

configuration may be a viable strategy to increase the water/salt sorption selectivity.

165

The HEMA:GMA:GMAOH materials are approximately an order of magnitude more

166

water/salt diffusion selective compared to the PEG materials (Figure 1B). This result may be due

167

to the glassy nature of hydrated HEMA:GMA:GMAOH compared to the rubbery nature of PEG

168

(see Section S1.3 of the Supporting Information).23 More rigid (glassy) polymer backbones are

169

often more diffusion selective compared to more flexible (rubbery) polymer backbones.24-26

170

The apparent water diffusion coefficient decreases and the water/salt diffusivity selectivity

171

increases as the co-polymer composition shifts toward a more HEMA rich (or distributed

172

hydroxyl group configuration). This observed trend is similar to that observed for PEG. The

173

water content of the PEG materials was varied systematically, and the explanation for the

174

observed relationship between water/salt diffusivity selectivity and water diffusion coefficient is

175

that reduction in the free volume of the polymer (as water content decreases) causes a general

176

reduction in diffusion that influences the larger hydrated ions to a greater extent than water.20 In

177

HEMA:GMA:GMAOH, the change in co-monomer composition (and thus, distribution of

178

hydroxyl groups) results in a situation where water diffusion slows as HEMA content increases.

179

This reduction in water diffusivity is accompanied by an increase in water/salt diffusion



Page 10 of 20

180

selectivity that is similar in proportion to that of PEG. Therefore, changes in water diffusivity,

181

due to compositional changes in the HEMA:GMA:GMAOH materials, may influence water/salt

182

diffusivity selectivity in a manner similar to that in the free volume-based explanation where

183

water diffusion depends strongly on free volume.9, 14

184

Water/salt diffusivity selectivity is affected to a lesser extent, compared to water/salt sorption

185

selectivity, by changing the HEMA content of the pre-polymerization solution. The water/salt

186

diffusivity selectivity increases by 26% over the range of HEMA compositions considered. The

187

water/salt sorption selectivity, by comparison, increases by 53% over the range of HEMA

188

compositions considered. Importantly, the 53% increase in sorption selectivity comes without a

189

change in the water sorption coefficient, which as discussed subsequently, means that, as co-

190

polymer composition changes, the water permeability will not change because of sorption

191

effects.

192

The decrease in the apparent water diffusivity as the co-polymer composition changes at

193

constant water content could be considered unexpected, as diffusivity in hydrated polymers is

194

often a strong function of water content.9, 14, 27-29 Dielectric permittivity properties, however,

195

provide insight into the observed water diffusivity. As further discussed in Section S3 of the

196

Supporting Information, the dielectric loss spectra can be interpreted in terms of time constants,

197

which describe the dipole relaxation dynamics of different modes of water motion, and the

198

dielectric strengths of those relaxations, which describe the relative amount of water in the

199

material that is participating in each relaxation mode.30

200

Dielectric spectroscopy suggests three populations of dipolar water motion: highly restricted

201

motion that relaxes on an order 0.1 ns timescale, less restricted motion that relaxes with a time

202

constant of approximately 45 ps, and non-restricted (i.e., bulk water) motion that relaxes with a


Page 11 of 20


203

time constant of 8.8 ps (see Supporting Information for additional discussion). In general, the

204

dielectric strength associated with each mode of motion decreases as HEMA content increases

205

(Table S1), though the reduction is more pronounced for the non-restricted relaxation mode

206

compared to the other two modes. This decrease in the dielectric strength associated with all

207

three relaxation modes, coupled with the statistically equivalent water content of the materials,

208

suggests that increasing HEMA content promotes water-polymer interactions that relax at

209

frequencies lower than that probed in our experiments.

210

An example of such interactions would be water that is very tightly associated with the

211

hydroxyl groups. Such (effectively immobile) water will not be detected by dielectric

212

spectroscopy in the frequency range considered here.31 As such, the dielectric strength data

213

suggests that distributing the hydroxyl groups in the polymer causes more water to tightly

214

associate with hydroxyl groups compared to the situation in the vicinal diol-rich materials.

215

This molecular picture is consistent with a steric explanation suggesting that water molecules

216

may be able to hydrate the hydroxyl group on a HEMA side chain to a greater extent compared

217

to the more sterically hindered GMAOH side chain. This explanation is also consistent with

218

estimates of the enthalpy of hydration for the hydroxyl groups on the side chains (see Section S4

219

of the Supporting Information). Ultimately, this reduction in water motion within the polymer

220

appears to have a similar effect on both water and salt diffusion as reducing the water content of

221

the polymer (as supported by the similar slopes of the data in Figure 1B).

222

Primarily due to the strong increase in water/salt sorption selectivity at constant water

223

content, the HEMA:GMA:GMAOH water/salt permeability selectivity increases as the HEMA

224

content of the pre-polymerization solution used to prepare the materials increases (Figure 2). A

225

distributed hydroxyl group configuration (HEMA-rich) is more selective for water over salt



Page 12 of 20

226

transport compared to the vicinal-diol rich configuration (GMAOH-rich). The overall selectivity

227

of the HEMA:GMA:GMAOH series of materials is greater than that of the PEG materials due to

228

the previously discussed differences in the diffusivity selectivity properties.

229

230 231 232 233 234 235 236 237

Figure 2. Water/salt permeability selectivity as a function of diffusive water permeability for HEMA:GMA:GMAOH ( ) and PEG ( )20 materials. For HEMA:GMA:GMAOH, the HEMA comonomer composition of the pre-polymerization solution used to prepare the co-polymer is reported for each data point. The dashed line represents a reported empirical permeability tradeoff frontier for desalination membrane materials,21, 22 and the solid lines are least-squares fits to the data.

238

The PEG materials exhibit a typical tradeoff relationship whereby water/salt selectivity tends

239

to decrease as materials become more permeable to water. This tradeoff is often observed in cases


Page 13 of 20


240

where the water content of a series of materials is varied systematically.22 In these cases, the higher

241

water content polymers tend to have higher water permeability and lower water/salt selectivity

242

compared to the lower water content polymers.

243

The HEMA:GMA:GMAOH materials suffer less of a reduction in the diffusive water

244

permeability as water/salt selectivity increases compared to the PEG materials (i.e., the slope of

245

the HEMA:GMA:GMAOH dashed line is steeper than that of the PEG dashed line in Figure 2).

246

This result stems from the equivalent water content nature of the HEMA:GMA:GMAOH series of

247

materials and the fact that both water/salt sorption and diffusivity selectivity increase with

248

increasing content of HEMA in the pre-polymerization solution.

249

Chemical modification of a series of water content equivalent co-polymers, from a vicinal

250

diol-rich to a distributed hydroxyl group-rich configuration, increased water/salt permeability

251

selectivity with a smaller water permeability penalty compared to that often observed in hydrated

252

polymers. These results, obtained using a model series of co-polymers, suggest that controlling

253

the spatial arrangement of functional groups in hydrated membrane materials may be important

254

for engineering highly selective polymers for desalination applications. The results on these

255

model materials represent a step toward establishing general water and salt transport structure-

256

property relationships for membrane materials including polymers that are more chemically

257

similar to commercial desalination membranes than those materials considered here. The results

258

suggest that distributed hydrophilic functional groups may lead to increased selectivity and may

259

represent a strategy for improving water/salt selectivity of advanced membrane materials to

260

address global water shortages.

261



Page 14 of 20

262

ASSOCIATED CONTENT

263

Supporting Information. Additional information regarding experimental methods, material

264

properties and characterization (molar composition, hydroxyl group content, FT-IR, and glass

265

transition temperature analysis), microwave dielectric spectroscopy data analysis, and hydroxyl

266

group hydration analysis. This material is available free of charge via the Internet at

267

http://pubs.acs.org.

268

AUTHOR INFORMATION

269

Corresponding Author

270

*102 Engineers’ Way, P.O. Box 400741, Charlottesville, VA 22904 USA, [email protected]

271

Funding Sources

272

This material is based upon work supported in part by the National Science Foundation (NSF)

273

Faculty Early Career Development (CAREER) Program (CBET-1752048).

274

Notes

275

The authors declare no competing financial interest.

276

REFERENCES

277 278

1.

Mekonnen, M. M.; Hoekstra, A. Y., Four billion people facing severe water scarcity. Sci. Adv. 2016, 2, e1500323.

279 280 281

2.

Tang, C. Y.; Yang, Z.; Guo, H.; Wen, J. J.; Nghiem, L. D.; Cornelissen, E., Potable water reuse through advanced membrane technology. Environ. Sci. Technol. 2018, 52, 1021510223.

282 283

3.

Miller, S.; Shemer, H.; Semiat, R., Energy and environmental issues in desalination. Desalination 2015, 366, 2-8.

284 285

4.

Subramani, A.; Jacangelo, J. G., Emerging desalination technologies for water treatment: A critical review. Water Res. 2015, 75, 164-187. 14 ACS Paragon Plus Environment

Page 15 of 20


286 287 288

5.

Amy, G.; Ghaffour, N.; Li, Z.; Francis, L.; Linares, R. V.; Missimer, T.; Lattemann, S., Membrane-based seawater desalination: Present and future prospects. Desalination 2017, 401, 16-21.

289 290

6.

Cohen, Y.; Semiat, R.; Rahardianto, A., A perspective on reverse osmosis water desalination: Quest for sustainability. AlChE J. 2017, 63, 1771-1784.

291 292 293

7.

Werber, J. R.; Deshmukh, A.; Elimelech, M., The critical need for increased selectivity, not increased water permeability, for desalination membranes. Environ. Sci. Technol. Lett. 2016, 3, 112-120.

294 295 296

8.

Park, H. B.; Kamcev, J.; Robeson, L. M.; Elimelech, M.; Freeman, B. D., Maximizing the right stuff: The trade-off between membrane permeability and selectivity. Science 2017, 356, 1-10.

297 298

9.

Geise, G. M.; Paul, D. R.; Freeman, B. D., Fundamental water and salt transport properties of polymeric materials. Prog. Polym. Sci. 2014, 39, 1-42.

299 300 301

10.

Geise, G. M.; Lee, H.-S.; Miller, D. J.; Freeman, B. D.; McGrath, J. E.; Paul, D. R., Water purification by membranes: The role of polymer science. J. Polym. Sci., Part B: Polym. Phys. 2010, 48, 1685-1718.

302

11.

Baker, R. W., Membrane Technology and Applications. 3rd ed.; Wiley: New York, 2012.

303 304 305

12.

Solleder, S. C.; Zengel, D.; Wetzel, K. S.; Meier, M. A. R., A scalable and high-yield strategy for the synthesis of sequence-defined macromolecules. Angew. Chem. Int. Ed. 2016, 55, 1204-1207.

306 307

13.

Lutz, J.-F., Defining the field of sequence-controlled polymers. Macromol. Rapid Commun. 2017, 38, 1700582.

308 309 310

14.

Yasuda, H.; Lamaze, C. E.; Ikenberry, L. D., Permeability of solutes through hydrated polymer membranes Part I. Diffusion of sodium chloride. Die Makromolekulare Chemie 1968, 118, 19-35.

311 312

15.

Petersen, R. J., Composite reverse osmosis and nanofiltration membranes. J. Membr. Sci. 1993, 83, 81-150.

313 314

16.

Bevington, P. R.; Robinson, D. K., Chapter 4: Propagation of errors. In Data reduction and error analysis for the physical sciences, McGraw Hill: New York, 2003; pp 56-65.

315 316

17.

Chang, K.; Luo, H.; Geise, G. M., Water content, relative permittivity, and ion sorption properties of polymers for membrane desalination. J. Membr. Sci. 2019, 574, 24-32.

317 318 319 320

18.

Wijmans, J. G.; Baker, R. W., The solution-diffusion model: A unified approach to membrane permeation. In Materials Science of Membranes for Gas and Vapor Separation, Yampolskii, Y. P.; Pinnau, I.; Freeman, B. D., Eds. John Wiley & Sons, Ltd: West Sussex, 2006; pp 159-189. 15 ACS Paragon Plus Environment


Page 16 of 20

321 322

19.

Geise, G. M.; Freeman, B. D.; Paul, D. R., Sodium chloride diffusion in sulfonated polymers for membrane applications. J. Membr. Sci. 2013, 427, 186-196.

323 324 325

20.

Ju, H.; Sagle, A. C.; Freeman, B. D.; Mardel, J. I.; Hill, A. J., Characterization of sodium chloride and water transport in crosslinked poly(ethylene oxide) hydrogels. J. Membr. Sci. 2010, 358, 131-141.

326 327

21.

Zhang, H.; Geise, G. M., Modeling the water permeability and water/salt selectivity tradeoff in polymer membranes. J. Membr. Sci. 2016, 520, 790-800.

328 329 330

22.

Geise, G. M.; Park, H. B.; Sagle, A. C.; Freeman, B. D.; McGrath, J. E., Water permeability and water/salt selectivity tradeoff in polymers for desalination. J. Membr. Sci. 2011, 369, 130-138.

331 332 333

23.

Ju, H.; McCloskey, B. D.; Sagle, A. C.; Kusuma, V. A.; Freeman, B. D., Preparation and characterization of crosslinked poly(ethylene glycol) diacrylate hydrogels as foulingresistant membrane coating materials. J. Membr. Sci. 2009, 330, 180-188.

334 335 336

24.

Chang, K.; Korovich, A.; Xue, T.; Morris, W. A.; Madsen, L. A.; Geise, G. M., Influence of rubbery versus glassy backbone dynamics on multiscale transport in polymer membranes. Macromolecules 2018, 51, 9222-9233.

337 338

25.

Chang, K.; Xue, T.; Geise, G. M., Increasing salt size selectivity in low water content polymers via polymer backbone dynamics. J. Membr. Sci. 2018, 552, 43-50.

339 340

26.

Paul, D. R.; Yampol'skii, Y. P., Polymeric Gas Separation Membranes. CRC Press: Boca Raton, 1994.

341 342 343

27.

Yasuda, H.; Ikenberry, L. D.; Lamaze, C. E., Permeability of solutes through hydrated polymer membranes Part II. Permeability of water soluble organic solutes. Die Makromolekulare Chemie 1969, 125, 108-118.

344 345

28.

Mackie, J. S.; Meares, P., The diffusion of electrolytes in a cation-exchange resin membrane. I. Theoretical. Proc. R. Soc. London, Ser. A 1955, 232, 498-509.

346 347

29.

Meares, P., The mechanism of water transport in membranes. Philos. Trans. R. Soc., B 1977, 278, 113-150.

348 349 350

30.

Lu, Z.; Polizos, G.; Macdonald, D. D.; Manias, E., State of water in perfluorosulfonic ionomer (Nafion® 117) proton exchange membranes. J. Electrochem. Soc. 2008, 155, B163-B171.

351 352

31.

Smith, G.; Duffy, A. P.; Shen, J.; Olliff, C. J., Dielectric relaxation spectroscopy and some applications in the pharmaceutical sciences. J. Pharm. Sci. 1995, 84, 1029-1044.

353


Page 17 of 20


Table of Contents (TOC) Graphic 47x39mm (300 x 300 DPI)

ACS Paragon Plus Environment


Figure 1. Water/salt sorption selectivity (A) and water/salt diffusivity selectivity (B) as a function of water sorption coefficient and apparent water diffusion coefficient, respectively, for HEMA:GMA:GMAOH (■) and PEG (□)20 materials. For HEMA:GMA:GMAOH, the HEMA co-monomer composition of the pre-polymerization solution used to prepare the co-polymer is reported for each data point. The dashed lines represent reported empirical sorption (left) and diffusivity (right) trade-off frontiers for desalination membrane materials,21, 22 and the solid lines are least-squares fits to the data. 207x191mm (300 x 300 DPI)


Page 18 of 20

Page 19 of 20


Figure 1. Water/salt sorption selectivity (A) and water/salt diffusivity selectivity (B) as a function of water sorption coefficient and apparent water diffusion coefficient, respectively, for HEMA:GMA:GMAOH (■) and PEG (□)20 materials. For HEMA:GMA:GMAOH, the HEMA co-monomer composition of the pre-polymerization solution used to prepare the co-polymer is reported for each data point. The dashed lines represent reported empirical sorption (left) and diffusivity (right) trade-off frontiers for desalination membrane materials,21, 22 and the solid lines are least-squares fits to the data. 218x207mm (300 x 300 DPI)



Figure 2. Water/salt permeability selectivity as a function of diffusive water permeability for HEMA:GMA:GMAOH (■) and PEG (□)20 materials. For HEMA:GMA:GMAOH, the HEMA co-monomer composition of the pre-polymerization solution used to prepare the co-polymer is reported for each data point. The dashed line represents a reported empirical permeability trade-off frontier for desalination membrane materials,21, 22 and the solid lines are least-squares fits to the data. 215x205mm (300 x 300 DPI)


Page 20 of 20

Engineering Selective Desalination Membranes via Molecular Control

Recommend Documents