Interpenetrating Janus Membrane for High. Rectification Ratio Liquid Unidirectional

Transcription

1 SUPPORTING INFORMATION Interpenetrating Janus Membrane for High Rectification Ratio Liquid Unidirectional Penetration Lanlan Hou, 1, Nü Wang, 1, Xingkun Man, 2 Zhimin Cui, 1 Jing Wu, 3 Jingchong Liu, 1 Shuai Li, 1 Yuan Gao, 1 Dianming Li, 1 Lei Jiang, 1, 4 Yong Zhao 1, * 1 Key Laboratory of Bioinspired Smart Interfacial Science and Technology of Ministry of Education, Beijing Key Laboratory of Bioinspired Energy Materials and Devices, School of Chemistry, Beijing Advanced Innovation Center for Biomedical Engineering, Beihang University, Beijing , P. R. China. 2 Center of Soft Matter Physics and its Applications, School of Physics and Nuclear Energy Engineering, Beihang University, Beijing , P. R. China 3 Beijing Key Laboratory of Clothing Materials R&D and Assessment, Beijing Engineering Research Center of Textile Nanofiber, School of Materials Science and Engineering, Beijing Institute of Fashion Technology, Beijing , P. R. China. 4 Laboratory of Bio-inspired Smart Interface Science, Technical Institute of Physics and Chemistry, Chinese Academy of Sciences, Beijing , P. R. China. These two authors contributed equally to this work. Corresponding * zhaoyong@buaa.edu.cn 1

2 Supplementary Video 1: An uninterrupted video shows tetrachloromethane unidirectional penetration on Janus M5/1/Cu(OH)2 membrane. Supplementary Video 2: An uninterrupted video shows formamide unidirectional penetration on Janus M0/Cu(OH)2 membrane. Supplementary Video 3: Various liquids unidirectional penetration on Janus membrane: water and formamide on M0/Cu(OH)2 membrane; ethylene glycol and hexadecane on M 15/1/Cu(OH)2 membrane; tetradecane and dimethylbenzene on M 5/1/Cu(OH)2 membrane. 2

3 Figure S1. The morphology and diameter distribution of three kinds of lyophobic membranes. (a, b, c) Pure PVDF-HFP nanofibers and its diameter distribution. (d, e, f) PFDTMS doped PVDF-HFP nanofibers with weight ratio of 1 to 15 of M15/1 and its diameter distribution. (g, h, i) M5/1 and its diameter distribution. The diameter histograms of M0, M15/1 and M5/1 fibers show uniform normal distribution. The average diameters are nm, nm, and nm, separately. 3

4 Figure S2. The pore size and morphology of the copper mesh before and after oxidation. The pore diameter frequency distribution histograms of (a) original copper mesh with average pore diameter of ± 3.37 and (b) Cu(OH)2 mesh after oxidation of ± 3.51 μm. The result revealed the reduction of pore size after oxidation. (c, d) The nano-needles presented an average diameter of ± nm and average length of 9.83 ± 2.72 μm, the diameter and length distributions of the nano-needles were shown. (e) The SEM images of original copper mesh with relatively smooth surface and (f) the nanoneedle structured Cu(OH)2 mesh. (g, h) As the increasing of oxidation reaction time, the structures are no longer nanoneedle arrays individual, but nano-flower clusters coexisting (oxidation time of 60 min). 4

5 Figure S3. The SEM images of Cu(OH)2 nanoneedles and its corresponding nanoneedle length distribution at oxidation time of (a, b, c) 5 min, (d, e, f) 10 min, (g, h, i) 15 min, (j, k, l) 20 min, (m, n, o) 30 min, (p, q, r) 45 min. The morphology of Cu(OH)2 nanoneedles and its 5

6 nanoneedle length distribution with increasing oxidation time of 5 min (a, b, c), 10 min (d, e, f), 15 min (g, h, i), 20 min (j, k, l), 30 min (m, n, o) and 45 min (p, q, r). 6

7 Figure S4. The average nanoneedle length at oxidation time of 5 min, 10 min, 15 min, 20 min, 30 min, and 45 min. The average nanoneedle length are 2.31 ± 0.63 μm (5 min), 6.14 ± 1.21 μm (10 min), ± 1.85 μm (15 min), 9.94 ±1.69 μm (20 min), 9.83 ± 2.72 μm (30 min), and 9.84 ± 1.94 μm (45 min). 7

8 Figure S5. The interpenetrating structured PVDF-HFP/Cu(OH)2 Janus membrane. (a, b) The cross section of the PVDF-HFP/Cu(OH)2 composite membrane observed by focused ion beam. It directly demonstrated the overlapping structure that nanoneedle is inserted through PVDF-HFP fibers. (c) The origin image of Figure 1i. In order to have a better observation of the interface structure, we prepared a PVDF-HFP nanofiber only with a few layers (electrospinning time for 15 s). The Cu(OH)2 nanoneedles are interpenetrating with the bottommost layers of fibers. This image indicates the interpenetrating structure of the nanoneedles/nanofibers Janus membrane. 8

9 Figure S6. The morphology of PVDF-HFP after soaking and stirring for 24 h in (a) Propylene glycol, (b) Dimethylbenzene, (c) Tetradecane, (d) Hexadecane, (e) Hexane, (f) Ethanol. The results showed the PVDF-HFP kept intact fiber morphology, without fracture or dissolution, demonstrating its good solvent resistance. 9

10 Figure S7. The SEM of Cu(OH)2 nanoneedles after liquid penetration tests (a) water, (b) formamide, (c) ethylene glycol, and (d) tetradecane. It showed the Cu(OH)2 morphology after liquid breakthrough tests through the Janus membrane in LI to LO direction. As illustrated that water on M 0/Cu(OH)2 (Figure S7a, ± Pa), formamide on M15/1/Cu(OH)2 (Figure S7b, ± 85.4 Pa), ethylene glycol on M 15/1/Cu(OH)2 (Figure S7c, ± 50.8 Pa), and tetradecane on M 5/1/Cu(OH)2 (Figure S7d, ± 61.3 Pa). The results demonstrated that Cu(OH)2 mesh still keep the original nanoneedle morphology after use. 10

11 Figure S8. The liquid unidirectional penetration on the Janus membrane. (a, b) The formamide was intercepted to form a liquid column on M0/Cu(OH)2 in the lyophilic to lyophobic (LI to LO) direction while can penetrate the Janus membrane in the LO to LI direction. (c, d) The ethylene glycol was intercepted and to form a liquid column on M15/1/Cu(OH)2 in the LI to LO direction while can penetrate the Janus membrane in the LO to LI direction. (e, f) The hexadecane was intercepted to form a liquid column on M15/1/Cu(OH)2 in the LI to LO direction while can penetrate the Janus membrane in the LO to LI direction. 11

12 Figure S9. Mechanism of liquid on porous lyophobic membrane and Janus membrane without interpenetrating structure. The illustrations of moving and breakthrough process of fluid on (a, b) a lyophobic porous membrane, (c, d) and a Janus membrane with opposite wettability on its two surfaces in a lyophobicity to lyophilicity direction. There is relationship of r1 > r3 > r(min). Understanding the gas/liquid/solid interface dynamics of droplet on porous lyophobic material is of critical important in a wide range of applications. Liquid cannot penetrate the porous lyophobic membrane unless the applied pressure is higher than the Laplace pressure force (PL). The droplet on a lyophobic membrane is forced by the Laplace pressure that PL = -2γlg/r, γlg is the gas/liquid interface tension, and r is the meniscus radius of curvature. Figure S9b shows the liquid is forced by the maximum Laplace pressure when the gas/liquid meniscus displaying a hemisphere shape (the r reaches its minimum value). With the hydrostatic pressure (PH) increases and exceeds the 12

13 maximum PL, the liquid breaks through the membrane. The derivation of Laplace pressure is expressed in Figure S10 as follow: Figure S10. The Laplace pressure detailed formula derivation process for a droplet on a porous lyophobic membrane with force analysis. P L 2 lg (1) r curvature r curvature d sin (2) - (3) From (1) (2) (3), can derive (4) P L 2 sin( ) lg (4) d d D R 1 (5) 13

14 R R - R R - Rsin (6) 1 2 d D ( R - Rsin ) (7) From (4) (5) (6) (7), can derive (8) P L 2 lg sin( ) D ( R - R sin ) (8) D* D R R (9) D ( D*-1) R (10) From (8) (9) (10), can derive (11) P L 2 sin( ) lg (11) RD ( *-sin ) The 2d is the local distance between two of the gas/liquid/solid three-phase contact points, and 2D is the minimum distance between the perpendicular tangents of two adjacent fibers as illustrated in Figure S9. The D* is the interspace ratio that defined as D * = (D+R)/R, when α, θ, and φ are the extruded angle, contact angle and the local geometrical angle (the angle between horizontal line and tangent line of the cylindrical fiber). There is a relation of θ = φ + α. As previous studies demonstrated that liquid on a Janus membrane, is more easily penetrate in the lyophobic to lyophilic side (LO to LI) than it is in the lyophilic to lyophobic direction (LI to LO). It is important to point out, destroying the gas/liquid interface will resulted in the disappearing of Laplace pressure. This principle is also very important for the liquid penetration performance on 14

15 the anisotropic wettability Janus membrane. In the LO to LI direction, the gas/liquid interface is destroyed as when it moves to contact with the lyophilic layer, and PL disappeared. Then liquid can spread over the lyophilic layer and penetrate the composite membrane (Figure S9c, d). The liquid/gas interface was damaged and the penetration process was greatly accelerated before the PL reaches its maximum value. That is to say, the distance of the two layers plays an important role in liquid unidirectional penetration through Janus membrane. While in the LI to LO, it can simply consider the liquid penetration as on a single porous lyophobic membrane. It is because they follow the same movement model, and the lyophilic layer has no resistance for droplet to contact the lyophobic layer. The liquid pressure ratio (k) is defined to divide the liquid breakthrough pressure in LI to LO direction (φ and θ) by in LO to LI direction (φ' and θ'). The maximum Laplace pressure is PL(max) = 2γlg/R(1 - D * ) (the gas/liquid interface shows a hemisphere shape, the rmin equal to D and α = 90 o. Thus, k is defined as: P k P D -sin ' * H ( LI LO) = ( * -1) sin( ) H ( LO LI ) D '- ' The k is determined by the lyophobic fiber spacing and the meniscus of gas/liquid interface in LO to LI direction (D * and α'). 15

16 Figure S11. Liquid penetration mechanism on porous Janus membranes with interpenetrating microstructure. (a) The Cu(OH)2 nanoneedles will form an interpenetrating structure with the bottommost layers of fiber, rather than a piercing structure. The schematic diagram reveals the interpenetrating structure of the nanofibers into the nanoneedles array. (b, c) The mechanism of liquid penetration process on the PVDF- HFP/Cu(OH)2 in LI to LO direction. (d) The interconnected structure of the anisotropic membrane. (e, f) The liquid penetration analysis on designed PVDF-HFP/Cu(OH)2 Janus membrane in LO to LI direction. Figure S11g is an enlargement of Figure S11f. (h) The liquid penetrated the Janus membrane under the capillary effect of superlyophilic Cu(OH)2 nanoneedle. 16

17 On the Janus membrane in LO to LI direction, as the hydraulic pressure increases due to continuously drop of droplet, the contact line keeps a moving state. The Figure S11e, f illustrated the moving of contact line, which lead to the changes of Laplace pressure before contacting the Cu(OH)2 nanoneedle. The breakthrough pressure is dependent on when the liquid/gas contact line to be touched but not yet touched the Cu(OH)2 nanoneedle (Figure S11g). When the liquid contacted the Cu(OH)2 nanoneedle, the liquid could spontaneously wet and penetrate the Janus membrane owing to the capillary effect of superlyophilic Cu(OH)2 nanoneedle (Figure S11h). 17

18 Figure S12. The liquid rectification ration of formamide on M0/Cu(OH)2 with nanoneedle length of (a) 2.31 ± 0.63 μm for 5 min oxidation time, (b) 9.83 ± 2.72 μm for 30 min oxidation time. The electrospinning time range from 20 s to 150 s in Figure S13a, and 20 s to 240 s in Figure S13b. (c) The M0 thickness corresponding to electrospinning time from 30 s to 240 s. (d) The formamide pressure ratio on M0/Cu(OH)2 Janus membrane with lyophilic layer of different oxidation time (5 min, 15 min, 30 min, 45min), the M0 thickness is 6 μm (electrospinning time of 1 min). To investigated the different gap distances on directional liquid penetration performance, here we selected a control M0/Cu(OH)2 Janus membranes with shorter nanoneedle length of 2.31 ± 0.63 μm (oxidation time of 5 min) to control the gap distances between two layers. As for the liquid unidirectional penetration (formamide as the test liquid) on the Janus membrane that Cu(OH) 2 18

19 nanoneedle length of 2.31 ± 0.63 μm (Figure S12a, oxidation time of 5 min), and 9.83 ± 2.72 μm (Figure S12b, oxidation time of 30 min), the pressure rectification ratios (k) were tested with different electrospinning time. With the thickness of lyophobic fibrous layer increases, the k revealed a first increase and then decrease tendency. When the electrospinning time is below 10 s, the sparse nanofibers cannot prevent liquid penetration through both directions. At the electrospinning time of 20 s, the formamide begins to show a penetration difference from two directions, showing a rectification ratio (k) of 2.5 (Figure S12a) and 3.8 (Figure S12b). The electrospinning time of 20 s is regarded as the thinner critical thickness. When the electrospinning time less than 1.0 min, the M0 is too thin to withstand too much liquid and showed a small hydraulic pressure in both direction. As the M0 thickness continue to increase beyond 1.0 min, it shown different maximum critical M0 thickness for nanoneedle length of 2.31 ± 0.63 μm and 9.83 ± 2.72 μm. On the M0/Cu(OH)2 Janus membranes with nanoneedle length of 2.31 ± 0.63 μm, the results show that the maximum critical electrospinning time is 150 s (membrane thickness of 17.0 ± 0.6 μm). When k tends to 1 that Janus membrane lost its liquid unidirectional penetration ability (Figure S12a). As it turns to M0/Cu(OH)2 with nanoneedle length of 9.83 ± 2.72 μm, when the electrospinning time exceeded 210 s (M 0 thickness of 25.8 ± 0.7 μm), the unidirectional penetration property of Janus membrane decayed that k approaches 1 (Figure S12b). Therefore, the maximum nanofibers membrane critical thickness for nanoneedle length of 2.31 ± 0.63 μm and 9.83 ± 2.72 μm are 17.0 μm and 25.8 μm. The results demonstrated the interpenetrating depth has positive effect on the performance of directional liquid penetration. That is to say, the narrow gap between the lyophilic and lyophobic layer facilitated and improved the liquid unidirectional penetration performances. Figure S12c illustrated the M0 thickness of electrospinning time range from 30 s to 240 s. When the electrospinning time are 10 s and 20 s, there are only a few layers of 19

20 fibers, it is difficult to measure the fibrous membrane thickness from the section SEM image (Figure S13). Because the membrane is achieved through a continuous deposition process, the original thickness at beginning is 0, it is rational to deduce the thickness through fitting curve. Here, according to the data fitting between the fibrous membrane thickness and electrospinning time, the fitting equation revealed: T = t t, R 2 = 0.999, where T represents the fibrous membrane thickness (unit: μm), and t represents the electrospinning time (unit: s). It was inferred that the fibrous membrane thickness was 0.9 μm at 10 s and 1.8 μm at 20 s. Figure S12d exhibited an increasing tendency of k, that formamide liquid on M0/copper Janus membrane, to M0/Cu(OH)2 Janus membrane with oxidation time for 5 min, and 15 min. The results demonstrate that the length of nanoneedle has a positive correlation effect on the performances of liquid unidirectional penetration. Meanwhile, when the nanoneedle length is almost the same, the two Janus membranes produce similar pressure ratios to the formamide liquid at oxidation time of 15 min, 30 min (the selected experiment condition), and 45 min. 20

21 Figure S13. The SEM images of M0/Cu(OH)2 with M0 thickness of 10 s and 20 s. The oxidation time of the Cu(OH)2 mesh is 30 min. 21

22 Figure S14. The liquid rectification ratio of previous works and our work. S1 Janus membranes with anisotropic wettability and unidirectional penetration property have been reported. However, some works only show liquid unidirectional penetration phenomenon, while didn t specify the rectification ratio value. S2, 23, 29 Few works illustrated the liquid pressure data as we illustrated in Figure S14. The rectification ratio of water is k ~ 9.0 with water column height at one direction 2 cm and another direction of 18 cm; 26 water of k ~ 7, soybean oil of k ~ 4, hexadecane of k ~ 2 (no specific data, estimated from the figure points); S1 diesel of k ~ 9.5 (one direction 2.3 kpa and another direction of 22 kpa), 28 water of k ~ 7.3 and k ~ 10.2 for dual-layer and tri-layer Janus membrane (1021%). 43 In our work, various liquids with broad surface tension range showed rather high k on Janus membranes [water (10.5), formamide (11.6), propylene glycol (8.2), ethylene glycol (9.0), hexadecane (9.0), tetrachloromethane (10.3), dimethylbenzene (16.8), and tetradecane (17.1)]. The data were tested on LO layer with thickness ~ 6 μm, thinner LO layer thickness could bring higher k but lower absolute hydraulic pressure value. Therefore, the ~6 μm LO layer thickness was 22

23 selected as demonstration after balancing the trade-off of high hydraulic pressure and high rectification ratio. 23

24 Figure S15. The packing effect of nanofibers. A scheme illustrates the decreasing of effective pore size of the electrospinning membrane due to the nanofibers packing effect with the increases of time. As casting the shadows of fibers on a screen, Figure S15d-f are obtained, which infer the effective pore size of the fibrous membrane for Figure S15a-c. Here we assume m of fibers with diameter of b randomly distributed in an area A. The ya is the average length of fibers shadow on each screen, there is given by: ya y (sin ) b y 0 4 The δ is the angle between fiber and the light ray. Thus, the sum areas of all shadows are πmby/4, then the total covering area fraction (denoted by x) can by illustrated as x = πmby/4a. S3, S4 This relational shown that that x is proportional to the fibers total length of ym. Therefore, it infers that as the increases of membrane thickness (number of fibers increases), the fraction of the area covered by the fibers increases, resulting in a decrease in the pore size of the fibrous membrane. Here, the lyophobic layer thickness (T) and the overlapped nanoneedle length (l) have effects on liquid penetration performances. The membrane s pore size (d) has inverse function with the membrane thickness that d e -βt, here β is a fitting parameter to indicate the decrease rate with 24

25 its value of according to the experimental results. In addition, we use the symbol n to indicate the nanoneedle effect. According these two effects mentioned above, the actual effective pore size (de) can be illustrated in form of de = ne -βt. As Young s equation described, there is relation: Hc 4 lg cos exp( T) n g In the LO to LI direction, there are two cases: (i) when the lyophobic thickness is less than the nanoneedle s length (T < l), the nanoneedle dominate the physical penetration process, and then set n equals to the nanoneedle s length of ; (ii) when the lyophobic thickness exceeds the nanoneedle s length (T > l), the nanoneedle s effect is independent of membrane s thickness anymore and is a constant number. We then take n = l/t to fit our experimental results, and T take the minimum thickness of the lyophobic membrane (n = 9.8/3.0 3). However, there is no needling effect for liquid penetrate in the opposite LI to LO direction, and n equals to 1. It is worth noting that, as the electrospun fibrous membrane increases to a certain thickness, the nanoneedle effect does not work and the liquid pressure on both sides is equal (n = 1). This theoretical formula can be used to infer the critical liquid column pressure as a function of membrane s thickness. 25

26 Figure S16. Loss of unidirectional penetration function of Janus membrane with enhancement of lyophobic properties. (a) The dropped water on M15/1/Cu(OH)2 membranes of the lyophobic side, (b) ethylene glycol and (c) propylene glycol on M 5/1/Cu(OH)2 membranes of the lyophobic side, while be blocked and maintain a liquid column in a glass tube. The length of glass tube is 500 mm. In the article of Table 1, it proved the water exhibited good unidirectional performances on M0/Cu(OH)2. The result indicate water didn t show a unidirectional penetration on M 15/1/Cu(OH)2, but was blocked from either two directions. Even in the lyophobic to lyophilic direction, the water 26

27 can be supported a height that exceeding 500 mm while remaining impermeable on M 15/1/Cu(OH)2 (Figure S16a). As above discussion revealed, the lyophobic abilities of electrospinning membranes are successively enhanced form M0, M15/1 to M5/1. The ultra-water-repellent ability generated large Laplace pressure, while the large wetting difference made the composite film to lose the liquid unidirectional penetration property. Moreover, there are also water, formamide, ethylene glycol, and propylene glycol, that showed the similar performances on M5/1/Cu(OH)2 membranes with high columns more than 500 mm in Lyophobic to lyophilic direction (Figure S16b, c). Thus, the wettability difference of Janus membrane determines a corresponding applicable range towards liquid. These results are in agreement with other previous studies. In addition, it was seen each of the Janus M/Cu(OH)2 has its application range in liquid unidirectional penetration in Table 1. To be noted, results show the M15/1/Cu(OH)2 has an application scope for liquid with surface tension from mn m -1, while liquids such as benzene (and other liquid after the benzene sequence in Table 1 has the same surface tension range) was not applicable. It was because that liquids show lyophilic and can be spread on the M 15/1 membrane, however, the hexadecane, tetradecane, and dodecane with relatively large viscosity, which has a certain influence on the wettability, shows lyophobicity on the M15/1 membrane. 27

28 Figure S17. Potential applications of the Janus membrane. (a-c) The water unidirectional penetration in a water/hexadecane two-phase liquid mixture system through the M0/Cu(OH)2 membrane with the superhydrophilic layer faces upwards. The water was dyed by methylene blue for better visual effects. (d-g) The water unidirectional penetration from an oil/water mixture system and its expanded programming applications. It can be used for controlled output of signals. A lab-made device integrating the Janus membrane and the signal reception/display system was prepared in a two-phase liquid mixture system. As shown in Figure S17a-c, a M0/Cu(OH)2 membrane was fixed at the bottom of the tube to control 28

29 whether the liquid can penetrate upwards through the orientation of the membrane. Once the water is upwards penetration to contact with the circuit, the circuit turns on and the signal was shown on the display. Here we define the circuit switch-on signal as 1, and the switch-off signal as 0. As the result was shown, according to the international ASCII code, represents B (Figure S17d), represents U (Figure S17e), and represents A (Figure S17f, g), the signal of BUAA was detected and shown in the screen. Therefore, we can realize a ASCII code programming for signal input and output. This strategy offers a possibility of a liquid unidirectional membrane in fluidic detection applications. 29

30 References (S1) Zhou, H.; Wang, H.; Niu, H.; Lin, T. Superphobicity/Philicity Janus Fabrics with Switchable, Spontaneous, Directional Transport Ability to Water and Oil Fluids. Sci. Rep. 2013, 3, (S2) Wang, H.; Zhou, H.; Yang, W.; Zhao, Y.; Fang, J.; Lin, T. Selective, Spontaneous One- Way Oil-Transport Fabrics and Their Novel Use for Gauging Liquid Surface Tension. ACS Appl. Mater. Interfaces 2015, 7, (S3) Parkhouse, J. G.; Kelly, A. The Random Packing of Fibres in Three Dimensions. Proc. R. Soc. London, Ser. A 1995, 451, (S4) Jin, B.; Pelegri, A. A. Three-Dimensional Numerical Simulation of Random Fiber Composites with High Aspect Ratio and High Volume Fraction. J. Eng. Mater. Technol. 2011, 133,