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Electronic Supplementary Information

Janus Membranes with Controllable Asymmetric Configuration

for Highly Efficient Separation of Oil-in-Water Emulsions

Jing Yang†, Hao-Nan Li†, Zhi-Xiong Chen, Ai He, Qi-Zhi Zhong, Zhi-Kang Xu*

MOE Key Laboratory of Macromolecular Synthesis and Functionalization, and Key Laboratory of

Adsorption and Separation Materials & Technologies of Zhejiang Province, Department of Polymer

Science and Engineering, Zhejiang University, Hangzhou 310027, China

*E-mail: xuzk@zju.edu.cn

†These authors contributed equally to this work

Electronic Supplementary Material (ESI) for Journal of Materials Chemistry A.This journal is © The Royal Society of Chemistry 2019

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Table of Contents

Figure S1 – Figure S2----------------------------------------------------------------------------------------S3

Figure S3 – Figure S4----------------------------------------------------------------------------------------S4

Figure S5--------------------------------------------------------------------------------------------------------S5

Table S1---------------------------------------------------------------------------------------------------------S6

Figure S6 – Figure S7---------------------------------------------------------------------------------------S7

Figure S8 – Figure S9---------------------------------------------------------------------------------------S8

Figure 10 and Table S2---------------------------------------------------------------------------------S9

Figure S11 --------------------------------------------------------------------------------------------S10

Figure S12 – Figure S13---------------------------------------------------------------------------------S11

Figure S14-----------------------------------------------------------------------------------------------------S12

References--------------------------------------------------------------------------------------------------------S12

S3

Figure S1. 3D LSCM images of PDA/PSS JMs constructed by varing co-deposition time (from

15 min to 120 min) and thus with different hydrophilization depths (from 7.2 μm to 30.0 μm)

wetted by the rhodamine B solution.

Figure S2. FT-IR/ATR spectra of (a) PDA/PDDA JMs and (b) PDA/PSS JMs for both the

hydrophilic side and the hydrophobic side with different co-deposition periods.

15 min

60 min 90 min 120 min

30 min 45 min

Thickness = 7.2 μm Thickness = 10.8 μm Thickness = 16.0 μm

Thickness = 18.8 μm Thickness = 22.5 μm Thickness = 30.0 μm

1800 1600 1400 1200 1000

Wavenumbers (cm-1

)

120 min

90 min

60 min

30 min

15 min

PPMM

Hydrophilic Side of PDA/PDDA JMs

45 min

1800 1600 1400 1200 1000

30 min

Wavenumbers (cm-1

)

120 min

90 min

60 min

45 min

15 min

PPMM

Hydrophobic Side of PDA/PDDA JMs

1800 1600 1400 1200 1000

15 min

45 min

Wavenumbers (cm-1

)

120 min

90 min

60 min

30 min

PPMM

Hydrophilic Side of PDA/PSS JMs

1800 1600 1400 1200 1000

15 min

Wavenumbers (cm-1

)

45 min

120 min

90 min

60 min

30 min

PPMM

Hydrophobic Side of PDA/PSS JMs

(a)

(b)

S4

Figure S3. XPS spectra of (a) PDA/PDDA JMs and (b) PDA/PSS JMs for both the hydrophilic

side and the hydrophobic side.

0

20

40

60

80

100

120

140

160

Wa

ter

co

nta

ct

an

gle

(o)

Thickness of hydrophilic portion (m)

hydrophilic side hydrophobic side

0 7.2 10.8 16.0 18.8 22.5 30.0

Figure S4. WCA on the hydrophilic side and the hydrophobic side of PDA/PSS JMs with

different hydrophilization depths.

600 500 400 300 200 100

PDA/PDDA JMs

1 h-hydropilic side

0.5 h-hydrophilic side

2 h-hydrophobic side

PPMM

C 1s

N 1s

O 1s

Binding Energy (eV)600 500 400 300 200 100

PDA/PSS JMs

1 h-hydrophilic side

0.5 h-hydrophilic side

2 h-hydrophobic side

PPMM

C 1s

N 1s

O 1s

Binding Energy (eV)

S 2p3S 2s

(a) (b)

S5

Figure S5. SEM images of the hydrophilic side of (a) PDA/PDDA JMs and (b) PDA/PSS JMs

with different hydrophilization depths.

(a)

(b) 7.2 μm0 μm 10.8 μm 16.0 μm

18.8 μm 22.5 μm 30.0 μm

12.1 μm0 μm

16.9 μm 20.0 μm 27.3 μm

7.8 μm 14.8 μm

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Table S1. Average pore diameter and porosity of nascent PPMM and JMs with different

hydrophilization depths.

Samples

Bulk Surface

Average pore diameter (nm)

Porosity (%) Average pore diameter (nm)

Porosity (%)

Nascent PPMMs 245.4 73.2 190.2 30.7

PDA/PDDA JMs (7.8 μm) --- --- 157.3 28.5

PDA/PDDA JMs (12.1 μm) 262.3 73.2 185.5 37.1

PDA/PDDA JMs (14.3 μm) 276.3 73.4 236.9 39.8

PDA/PDDA JMs (16.9 μm) --- --- 167.5 31.0

PDA/PDDA JMs (20.0 μm) --- --- 178.2 31.1

PDA/PDDA JMs (27.3 μm) 260.0 73.0 147.7 27.4

PDA/PSS JMs (7.2 μm) --- --- 197.4 36.7

PDA/PSS JMs (10.8 μm) 242.0 72.8 174.7 29.9

PDA/PSS JMs (16.0 μm) 250.7 73.1 189.9 36.6

PDA/PSS JMs (18.8 μm) --- --- 208.0 39.2

PDA/PSS JMs (22.5 μm) --- --- 243.9 39.4

PDDA/PSS JMs (30.0 μm) 273.2 73.4 179.9 24.1

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Figure S6. Dynamic UOCA and oil drop CD on the hydrophilic side of PDA/PSS JMs with

different hydrophilization depths.

Figure S7. LSCM images of emulsion separation processes using PDA/PSS JMs with

different hydrophilization depths: (a) H1 = 0 μm (neat PPMM), (b) H1 = 10.8 μm, (c) H1 = 30.0

μm. The oil-in-water emulsions are stabilized by hexadecyl trimethyl ammonium bromide

(CTAB) and dyed by Nile red.

0

30

60

90

120

150

180

7.2 m 10.8 m 16.0 m 18.8 m 22.5 m 30.0 m

UW

OC

A (

o)

Time (s)

0 10 20 30 40 50 60 70 80 90 100 110 120

0.0

0.2

0.4

0.6

0.8

1.0

Dro

p C

D (

mm

)

40 μm

(a)

(b)

(c)

0 s 200 s50 s 100 s 150 s

0 s 260 s65 s 130 s 195 s

0 s 200 s50 s 100 s 150 s

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Figure S8. Optical microscopic photos (left) and DLS graph (right) of (a) Tween 80 stabilized

and (b) CTAB stabilized emulsions. The oil contents are 100 mg/mL and 15 mg/mL for (a) and

(b), respectively.

Figure S9. DLS graphs of feed after separation for (a) PDA/PDDA JMs toward SDS stabilized

emulsions, (b) PDA/PSS JMs toward CTAB stabilized emulsions, (c) PDA/PDDA JMs toward

Tween 80 stabilized emulsions, and d) PDA/PSS JMs toward Tween 80 stabilized emulsions.

The corresponding DLS graphs of filtrate after separation for (a), (b), (c) and (d) are shown in

(e), (f), (g) and (h).

20 30 40 50 60 70

0

10

20

30

Nu

mb

er

(%)

Droplet size (nm)

50 100 150 200 250

0

10

20

30

Droplet size (nm)

Nu

mb

er

(%)

(a)

(b)

50 μm

50 μm

25 50 75 100 125 1500

10

20

30

Filtrate

Size (d. nm)

Nu

mb

er

(%)

30 60 90 120 1500

10

20

30

Feed after separation

Size (d. nm)

Nu

mb

er

(%)

25 50 75 100 125 1500

10

20

30

Filtrate

Size (d. nm)

Nu

mb

er

(%)

5 10 15 20 250

10

20

30

Feed after separation

Size (d. nm)

Nu

mb

er

(%)

25 50 75 100 125 1500

10

20

30

Filtrate

Size (d. nm)

Nu

mb

er

(%)

30 60 90 120 1500

10

20

30

Feed after separation

Size (d. nm)

Nu

mb

er

(%)

25 50 75 100 125 1500

10

20

30

Filtrate

Size (d. nm)

Nu

mb

er

(%)

5 10 15 20 250

10

20

30

Feed after separation

Size (d. nm)

Nu

mb

er

(%)

(a) (b) (c) (d)

(e) (f) (g) (h)

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Figure S10. Optical microscopic images of feed after separation for (a) PDA/PDDA JMs

toward SDS stabilized emulsions, (b) PDA/PSS JMs toward CTAB stabilized emulsions, (c)

PDA/PDDA JMs toward Tween 80 stabilized emulsions, and (d) PDA/PSS JMs toward Tween

80 stabilized emulsions. The corresponding optical microscopic images of filtrate after

separation for (a), (b), (c) and (d) are shown in (e), (f), (g) and (h).

Table S2. Purities of collected oils using different Janus membranes after separation.

Sample Oil purity (%)

PDA/PDDA JM (H1 = 12.1μm) / SDS emulsion 98.8

PDA/PSS JM (H1 = 10.8 μm) / CTAB emulsion 99.9

PDA/PDDA JM (H1 = 12.1 μm) / Tween 80 emulsion 99.6

PDA/PSS JM (H1 = 10.8 μm) / Tween 80 emulsion 99.5

(a) (b) (c) (d)

(e) (f) (g) (h)

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Figure S11. Photographs of petroleum ether separation status at time t=0, 10, 30 min for oil-

in-water emulsions stabilized by (a) SDS using PDA/PDDA JMs (H1 = 12.1 μm) and by (b)

CTAB using PDA/PSS JMs (H1 = 10.8 μm). The optical microscopic images and DLS graphs

of feed before and after separation as well as filtrate after separation are shown

correspondingly.

0 min 30 min10 min

(a)

50 μm 50 μm 50 μm

50 μm 50 μm 50 μm

(b)

50 100 150 200 2503000

10

20

30

Size (d. nm)

Nu

mb

er

(%)

0.1 1 10 1000

10

20

30

Size (d. nm)

Nu

mb

er

(%)

0.1 1 10 1000

10

20

30

Size (d. nm)

Nu

mb

er

(%)

50 100 150 200 2503000

10

20

30

Size (d. nm)

Nu

mb

er

(%)

0 min 30 min10 min

10 1000

10

20

30

Size (d. nm)

Nu

mb

er

(%)

10 1000

10

20

30

Size (d. nm)

Nu

mb

er

(%)

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0 2 4 6 8 10 12 14 16 18

0

20

40

60

80

100

PDA/PDDA JM for Tween 80 emulsions

Oil r

eco

very

rati

o (

%)

Time (min)

PDA/PDDA JM for SDS emulsions

PDA/PSS JM for Tween 80 emulsions

PDA/PSS JM for CTAB emulsions

Figure S12. Comparison of separation data for oil-in-water emulsions stabilized by different

surfactants using PDA/PDDA or PDA/PSS JMs with ~10 μm of hydrophilization depth.

Figure S13. Surface zeta potential of the hydrophilic side as a function of the hydrophilization

depth for (a) PDA/PDDA JMs and (b) PDA/PSS JMs.

In the case of coexisted DA and polyelectrolytes in aqueous solution, the oxidative

polymerization of DA can produce two kinds of PDA-based colloidal particles. One is neat PDA

aggregates containing covalently bonded PDA and physically self-assembled trimers [1]. The

other one is charged hybrid PDA/polyelectrolyte clusters formed through electrostatic

interactions because PDA owns negatively charged catechol groups as well as positively

charged amino groups [2]. Both polycations and polyanions are able to inhibit the growth of

PDA aggregates due to the electrostatic stabilization effect [3]. The size of hybrid clusters is

thus smaller than that of neat PDA aggregates. Under an electric field, these relatively small

and charged hybrid clusters preferentially migrate to the oppositely charged electrode and

(a) (b)

-40

-30

-20

-10

0

10

20

30

40

50

60

pH = 7.00

Zeta

Po

ten

tial

(mV

)

hydrophilic side

0 7.8 12.1 14.8 16.9 20.0 27.3

Thickness of PDA/PDDA hydrophilic portion (m)

0

-10

-20

-30

-40

-50

-60

-70

hydrophilic side

Zeta

Po

ten

tial

(mV

)

0 7.2 10.8 16.0 18.8 22.5 30.0

Thickness of PDA/PSS hydrophilic portion (m)

pH = 7.00

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adhere onto the membrane surface and inside wall of the pores. However, the deposition of

the neat PDA aggregates cannot be accelerated due to their neutral and large-sized profiles. It

means that the electric field-accelerating deposition of charged PDA/electrolyte clusters is

dominant during the first 30 min until an equilibrium is reached. The deposition of neat PDA

aggregates, however, is still in progress afterwards. Such difference in the kinetics of

deposition thus causes a maximum value of the surface zeta potential when the membrane

was deposited for 30 min (Figure S13). Therefore, those Janus membranes with the most

enriched surface charge (H1 ≈ 10 μm) significantly facilitate the deemulsification process,

exhibiting excellent separation performances mentioned above. Further, the efficiency of

emulsion separation becomes depressed with thickening the hydrophilic depth because the

directional oil delivery is hindered gradually.

Figure S14. Oil flux and recovery ratio evolutions under repeated cycles when PDA/PSS JMs

(H1 = 10.8 μm) were used to separate the CTAB stabilized oil-in-water emulsions. 1,2-

Dichloroethane (a) and petroleum ether (b) were used as the heavy oil and the light oil,

respectively.

References

[1] S. Hong, Y. S. Na, S. Choi, I. T. Song, W. Y. Kim, H. Lee, Adv. Funct. Mater. 2012, 22,

4711-4717.

[2] H.-C. Yang, R. Z. Waldman, M.-B. Wu, J. Hou, L. Chen, S. B. Darling, Z.-K. Xu, Adv.

Funct. Mater. 2018, 28, 1705327.

[3] M. Mateescu, M. H. Metz-Boutigue, P. Bertani, V. Ball, J. Colloid Interf. Sci. 2016, 469,

184-190.

0

5000

10000

15000

20000

10 2

Cycle number

Oil

flu

x (

Lh

-1m

-2 b

ar-1

)

oil flux

3 4 5 6 7 8 9 100

20

40

60

80

100

oil recovery ratio

O

il r

eco

very

rati

o (

%)

(a) (b)

0

10

20

30

40

50

10 2

Cycle number

Oil

flu

x (

Lh

-1m

-2)

oil flux

3 4 5 6 7 8 9 100

10

20

30

40

50

60

70

80oil recovery ratio

O

il r

eco

very

rati

o (

%)