Dual Superlyophobic Aliphatic Polyketone Membranes for Highly

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Surfaces, Interfaces, and Applications

Dual Superlyophobic Aliphatic Polyketone Membranes for Highly Efficient Emulsified Oil-Water Separation: Performance and Mechanism Liang Cheng, Da-Ming Wang, Abdul Rajjak Shaikh, Li-Feng Fang, Sungil Jeon, Daisuke Saeki, Lei Zhang, Cui-Jing Liu, and Hideto Matsuyama ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.8b09687 • Publication Date (Web): 15 Aug 2018 Downloaded from http://pubs.acs.org on August 23, 2018

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ACS Applied Materials & Interfaces

Dual Superlyophobic Aliphatic Polyketone Membranes for Highly Efficient Emulsified Oil-Water Separation: Performance and Mechanism Liang Cheng,† Da-Ming Wang,‡ Abdul Rajjak Shaikh,§ Li-Feng Fang,† Sungil Jeon,† Daisuke Saeki,† Lei Zhang,† Cui-Jing Liu,† Hideto Matsuyama*†

†

Center for Membrane and Film Technology, Department of Chemical Science and Engineering, Kobe

University, Kobe 657-8501, Japan ‡

Department of Chemical Engineering, National Taiwan University, Taipei 10617, Taiwan

§

Department of Chemistry, King Fahad University of Petroleum and Minerals, Dhahran 31261,

Kingdom of Saudi Arabia *E-mail: [email protected]

Keywords: dual superlyophobicity, aliphatic polyketone, re-entrant geometry, phase separation, oil/water separations

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Abstract: Efficient treatment of difficult emulsified oil/water wastes is a global challenge. Membranes exhibiting unusual dual superlyophobicity (combined underwater superoleophobicity and underoil superhydrophobicity) are intriguing to realize high efficiency separation of both oil-in-water and water-in-oil emulsions. For the first time, a robust polymeric membrane demonstrating dual superlyophobicity to common apolar oils was facilely fabricated via a simple one-step phase separation process using an aliphatic polyketone (PK) polymer, thanks to a conjunction of intermediate hydrophilicity and re-entrant fibril-like texture upon the prepared PK membrane. Further chemical modification to improve surface hydrophilicity slightly can enable dual superlyophobicity to both apolar and polar oils. It is found that a non-wetting composite state of oil against water or water against oil was obtainable on the membrane surfaces only when the probe liquids possess an equilibrium contact angle (θow or θwo) larger than the critical re-entrant angle of the textured surfaces (73°), which can explain the existences of dual superlyophobicity and also the non-wetting to fully wetting transitions. A simple design chart was developed to map out the operational windows of material hydrophilicity and reentrant geometry, i.e. a possible zone, to help rational design of similar interfacial systems from various materials. Switchable filtrations of oil-in-water and water-in-oil nano-emulsions were achieved readily with both high flux and high rejection. The simplicity and scalability of the membrane preparation process and the well-elucidated underlying mechanisms illuminate the great application potential of the PK-based superwetting membranes.

1. INTRODUCTION Interfacial material systems with superwettability have attracted tremendous interests of academic researchers and engineers for understanding special wetting mechanism and designing advanced interfacial devices.1 Natural surfaces such as self-cleaning lotus leaves (by superhydrophobicity in air) and fish scales (by superoleophobicity in water),2 have revealed the key role of cooperative combination of surface chemistry and texture in creating robust coatings, films and membranes with 2


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superwettability.3,4 For membranes capable of separating particles, molecules or ions with relatively low energy consumption, incorporating superwettability can help realizing outperforming permeability and selectivity,5 fouling-resistance,6 and other valuable functionalities such as stimuli-responsiveness.7,8 Recently, several intriguing solid surfaces,9,10 fabric,11 and membranes,12,13 have been reported to possess both underwater superoleophobicity and underoil superhydrophobicity, namely dual superlyophobicity in oil-water systems. This switchable oil/water repellency in oil-in-water (OW) and water-in-oil (WO) systems is of great value to design intelligent surface microfluidics, microdroplet reactors, oil/water separators and other unexpected functional systems.14,15 However the preparation methods were usually complicated with complex manipulations of surface chemistries13 and applying tedious microfabrication processes9,10 or template-assistance13 to create special surface texture. A simple and scalable method to create dual superlyophobic interfacial systems is highly desired to realize largescale production and practical applications. On the other hand, the underlying mechanism and controlling material parameters need to be clarified more clearly for better understanding and design of similar systems from various materials. Especially, the membrane-type surfaces usually exhibiting fractal-like non-uniform bulk morphology formed by the classical phase separation process are more difficult to characterize and model to distinguish the roles of material chemistry and geometry. In principle, a super-antiwetting state on a rough solid surface in either solid-liquid-air or solid-liquid-liquid systems can be realized by forming a thermodynamically stable composite interface in the Cassie-Baxter (CB) regime.16 It requires the equilibrium contact angle θ on the smooth surface with the same chemistry to be larger than a certain threshold θc (>90°); otherwise, the transition from the non-wetting CB state to the fully-wetting Wenzel state will occur.17 However, it has been found that many natural and artificial surfaces with re-entrant curvature can support a stable or metastable composite interface with extremely high apparent contact angle θ* even for θψ, where ψ is the local geometrical angle of the texture (the angle between the horizontal and the local tangent to solid surface). This mechanism has inspired successful 3



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development of extremely rare superoleophobic surfaces in air against even low-surface-tension liquids (e.g. methanol) through independent control of surface chemistry and morphology (to give the equilibrium oil contact angle in air θo>ψ).17 Then, Tian et al. extended the idea to design surfaces with dual superlyophobicity in oil-water systems and proposed two principal criteria, namely, the water/oil filling criterion (the equilibrium water contact angle in air θwψ).9 Upon a hexagonally arrayed microposts with a re-entrant geometry (ψ=76°), dual superlyophobicity for a model oil (hexadecane) was realized with materials having intermediate surface chemistry with θw in between 56° and 74°. A more comprehensive theoretical analysis on the interplay of θw and ψ variables for a more wide scope of oils including both apolar and polar ones can be very helpful to design more robust systems for real applications. The objectives addressed and also the highlighted novelties of this study are: 1) facile synthesis of dual superlyophobic polymeric membrane based on a simple one-step non-solvent induced phase separation process (NIPS) with aliphatic polyketone (hereafter referred to as PK), for switchable filtrations of oil-in-water (OW) and water-in-oil (WO) nano-emulsions, 2) clarification of the underlying mechanism and controlling parameters that determine dual superlyophobicity to apolar oils and polar oils by investigating the interplay of surface chemistry and surface morphology, and 3) development of a simple design chart to help engineering similar superwetting systems from various materials. Note that PK is an engineering thermoplastic with a perfectly alternating sequence of ethylene and carbon monoxide, usually regarded as a homopolymer of repeat unit −(CH2CH2CO). It has a high crystalline melting point of around 260 °C, strong mechanical strength and resistance to most organic solvents,18-20 thus is promising for long-term operations even in harsh conditions. For the first time, PK has been utilized to prepare interfacial systems exhibiting superwettability.

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2. EXPERIMENTAL SECTION 2.1 Materials. Aliphatic polyketone (PK; Mw=200,000 g mol-1) was kindly provided by Asahi Kasei Co. (Japan). Resorcinol, methanol, acetone, hexane (C6), hexadecane (C16), chloroform (CF), dichloroethane (DCE), dichloromethane (DCM), toluene (T) and soybean oil (SO) were purchased from Wako Pure Chemical Industries Co. (Japan). Sodium borohydride (NaBH4), 1H,1H,2H,2Hperfluorooctyltrichlorosilane (FOTS), sodium dodecyl sulfate (SDS), Tween-80, and Span-80 were bought from Sigma-Aldrich Japan. Asahiklin AK-225 was obtained from Asahi Glass Co. (Japan). Milli-Q water (Milli-Q integral 3, Millipore SAS, France) was prepared in our lab. 2.2 Fabrication of Pristine and Modified PK Membranes and Dense Films. A PK membrane was prepared by the typical non-solvent induced phase separation (NIPS) process. PK powder at a concentration of 10 wt% was dissolved in resorcinol/water (65/35 w/w) mixture by stirring at 80 °C for 3 h to form a clear dope solution. After degassing the polymer solution was cast onto a clean glass plate and immediately immersed into a methanol/water (30/70 w/w) coagulation bath. The formed membrane was then subjected to washing baths in the sequences of acetone and hexane with 20 min for each, and finally air-dried for storage and test. Since usual solvent casting-evaporation method is not feasible to PK that has excellent resistance to almost all organic solvent, a dense and smooth PK film for contact angle analysis was prepared by a well-controlled melting-cooling process using differential scanning calorimeter (DSC) under nitrogen gas protection to avoid possible oxidation or contamination that may change the surface chemistry. An appropriate size, typically 0.5×0.5 cm2, of a dried membrane sample was sealed in an aluminum pan and placed in the heating chamber. A fixed melting-cooling thermoscan was carried out, with first heating from 25°C to 270°C by 30°C min-1, then keeping at 270°C for 10 min, and finally cooling down to 25°C by 30°C min-1. Optionally, the prepared PK membrane and film were immersed into a 0.5 wt% NaBH4 aqueous solution for several minutes to carry out reduction modification, then silanized in a solution of FOTS in Asahiklin AK-225 for 6 h at room temperature, and finally air dried for further tests. 5



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2.3 Preparation of Oil/water Emulsions. Surfactant-stabilized oil-in-water (OW) and water-in-oil (WO) nano-emulsions were prepared for membrane filtration tests. Following the previous study,21 hexadecane-in-water (named as C16/W) was prepared by adding 1 mL C16 into the mixture of 0.1 mg sodium dodecyl sulfate and 99 mL water under one-day stirring and then diluting 15 times; the same procedure was applied to soybean oil-in-water (named as SO/W). For chloroform-in-water emulsion (named as CF/W), 2 mL CF was added into the mixture of 500 mL water and 0.21 g Tween-80 with following 3 h stirring. For water-in-chloroform (named as W/CF) and water-in-hexane (named as W/C6), 1 mL water was added into 100 mL solvent containing 0.06 g and 0.02 g Span-80, respectively, according to the study.22 For water-in-toluene (named as W/T), 2 mL water was added into the mixture of 0.3 g Span-80 and 228 mL toluene as described previously.23 2.4 Instruments and Characterizations. Contact angles were measured by a contact angle goniometer (Drop Master 300, Kyowa Interface Science, Japan) to evaluate surface wettability. The probe water, air and oil droplets (4~12 µL) were carefully dispensed onto the sample surface in other medium. The data reported was averaged on at least six measurements at different locations. Membrane tensile strength tests were conducted by a tensile testing apparatus (AGS-J, Shimadzu, Japan) with vertically mounted membrane samples between two pairs of pneumatic clamps at a testing speed of 10 mm min-1. Surface morphology and roughness were characterized by a field-emission scanning electron microscope (FE-SEM; JSF-7500F, JEOL, Japan) and an atomic force microscope (AFM; SPA-400, Hitachi High-Tech Science, Japan) with a SI-DF40P2 cantilever in tapping mode. Surface chemical composition was analyzed by Fourier-transform infrared spectroscopy with attenuated total reflectance (FTIR-ATR; ALPHA, Bruker, USA) and X-ray photoelectron spectroscopy (XPS; JPS-9010 MC, JEOL, Japan) with Al Kα X-ray (1486.6 eV) and a detection depth of ~6 nm. All samples were freeze-dried before measurements. Differential scanning calorimeter (DSC; 8500, PerkinElmer, USA) was used to measure PK’s melting point and prepare dense film under nitrogen atmosphere. Dynamic light scattering (DLS; ELSZ-1000ZS, Otsuka Electronics, Japan) was used to measure the oil/water nanoemulsions. Average pore size and pore size distribution of the prepared PK membrane were measured 6 ACS Paragon Plus Environment

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by a capillary flow porometer (CFP-1500AXLC, Porous Materials Inc., USA) according to the bubble point method of ASTM F316-86. The oil content in permeate was measured by a Total Organic Carbon analyzer (TOC-VCSH, Shimadzu, Japan). The water content in feed solutions and corresponding permeate was checked by a Karl Fischer moisture analyzer (MKH-700, Kyoto Electronics, Japan). The oil/water separations were conducted by pouring oil/water free-mixtures or emulsions directly into a membrane filtration apparatus (KG25, ADVANTEC MFS, Inc., Japan) with effective filtration area of 2.1 cm2 and then pressured by vacuum (~0.9 bar) or gravity (10 cm liquid column, ~0.01 bar). The flux was calculated by the time needed for the first 5 mL permeation. 2.5 Computational Methods. Molecular Dynamics (MD) simulation was used to analyze the surface interaction of PK film with solution-phase molecule (water or hexane). The initial polymer models were build using Materials Visualizer’s polymer building tools in Material Studio version 7.0 (BIOVIA DASSAULT SYSTEMS) program. Long PK chain was built and packed in a periodic box using Amorphous Cell module in Materials Studio. All MD simulations were carried out using Gromacs 5.0.4 program. More details on simulation conditions are described in the supporting Information.

3. RESULTS AND DISCUSSION 3.1. Dual Superlyophobicity to Common Apolar Oils. A one-step NIPS process without any template-assistance and chemical modification was utilized to prepare a PK membrane with dual superlyophobicity to common apolar oils. Figure 1 displays the apparent contact angles of oil against water (θ∗ow) and water against oil (θ∗wo) on the PK membrane prepared. The properties of the probe liquids used in this work are shown in Table S1. For apolar oils such as hexane (C6) and hexadecane (C16), both θ∗ow and θ∗wo are as high as 160°, and small sliding angles of 9° and 15° to allow oil or water droplets rolling-off are observed. This confirms dual superlyophobicity of the pristine PK membane to commonm apolar oils. However, the PK membrane loses dual superoleophobicity when tested with polar oils: in water it can be partially wetted by dichloroethane (DCE) and fully wetted by 7



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chloroform (CF) and dichloromethane (DCM), corresponding to underwater superoleophilicity; while in oil it shows remarkable water repellency with extremely small sliding angles (0°-4°), corresponding to underoil superhydrophobicity. Such oil polarity-sensitive dual superlyophobicity has yet been reported.

Figure 1. Oil-in-water (OW) and water-in-oil (WO) contact angles tests for polar and apolar oils on the aliphatic polyketone (PK) membrane prepared by nonsolvent induced phase separation process (NIPS). The color scheme shows how the contact angles were determined. Figure 2a depicts the surface morphology of the PK membrane surface. The SEM and AFM images reveal the highly porous textured surface consisting of interconnected microfibrils with 100-300 nm varying diameter. Note that the fibril-like structure is inherently re-entrant. Not only the surface, the membrane cross-section also features similar morphology, as shown in Figure S1. Figure 2b shows the digital photos of the robust PK membrane without any mechanical support prepared and the polymer raw material used. The stress-strain curves of the membrane samples indicate a superior tensile strength of 3.5±0.2 MPa. Furthermore, it is found that the membrane is superhydrophilic in air (θ*w=0°) and superaerophobic in water (θ*a=158°). Figure 2c shows a dense and smooth PK film prepared by a wellcontrolled melting-cooling process (see Figure S2) to evaluate the equilibrium contact angles of waterin-air (θw), air-in-water (θa), oil-in-water (θow), and water-in-oil (θwo). The measured θw=69° and 8


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θa=125° suggest that PK has an intermediate hydrophilicity. Table 1 summarizes all θow and θwo tested with different oils on the dense films, along with θ*ow and θ*wo tested on the porous membranes. The PK film demonstrates θow90° for polar oils (DCE, CF and DCM), and θow, θwo>90° for apolar oils (C6 and C16), indicating the higher affinity of PK for polar oils than for apolar oils. The apparent contact angles of the PK membrane combining PK’s intrinsic wettability and rough texture have very high values (159°-170°) for θow, θwo>90°, and go to zero for θow≤74°.

Figure 2. a) SEM (top row) and AFM (bottom row) images of the PK membrane surface, the inset roughness profile corresponds to Line 1 in the AFM image. b) Photos of the PK raw material and the prepared PK membrane with the tested stress-strain curves and droplet profiles of water-in-air and airin-water on it. c) Photos of a dense PK film and the droplet profiles of water-in-air and air-in-water on it.

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Table 1. Summary of the measured equilibrium contact angles and apparent contact angles on the PKbased membranes and films with different surface chemistries. OW (°)

Surface chemistry

WO (°)

C6

C16

DCE

CF

DCM

C6

C16

DCE

CF

DCM

PK

θ

*

163

162

132

0

0

162

159

165

170

170

(θw=69°)

θ

106

100

78

74

67

116

120

132

136

145

PK-F

θ

*

165

170

167

165

166

160

159

170

170

170

(θw=64°)

θ

125

113

113

107

94

88

108

110

106

120

PK-OH

θ

*

171

171

168

166

163

0

0

142

143

154

(θw=48°)

θ

135

127

133

125

109

69

64

75

77

94

3.2. Dual Superlyophobicity to Both Apolar and Polar Oils. Through easy manipulation of PK chemistry via specific reduction reaction, the surface hydrophilicity of the PK membrane can be further tuned to realize dual superlyophobicity to all oils irrespective of polarity. Figure 3a depicts that the pendant carbonyl group of PK can be converted to secondary alcohol using NaBH4 and then be coupled with fluorine moieties by silanization. The modified PK carrying hydroxyl groups is referred as PK-OH and that carrying fluorine groups as PK-F. FTIR-ATR and XPS analyses confirm the successful modifications (Figure S3). These three materials show increasing hydrophilicity in the order of PK (θw=69°) ψmin. A fully wetting transition will happen only when the pressure difference across the composite caused by internal and external force is large enough. The relationship of θ∗ versus θ can be calculated by the CB relation, cosθ * = rφs cosθ + φs − 1 , where r is the roughness of the wetted solid area, r = (π − ψ ) / sinψ , φs the area fraction of the liquid-liquid interface occluded by the solid surface texture in solid-oil-water systems, φ s = R sinψ /( R + D ) .29 The CB relation can then be rewritten as

cos θ ∗ = −1 +

1 [(π − θ ) cos θ + sin θ ] D∗

(1)

where D*=(R+D)/R is the geometrical spacing ratio. It is found that D*=7.54 gives the best data fitting. The SEM image analysis of the PK membrane surface (see Figure S4) indicates a very similar value of D*≈7.15 based on the estimated R≈0.13 µm and 2D≈1.6 µm.

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Figure 4. a) Contact angle analysis by plotting cosθ∗ (i.e. θ*ow and θ*wo on porous membranes) versus cosθ (i.e. θow and θwo on smooth films), with the calculated robustness factors A∗ for a possible soil-oilwater composite interface as described in (b), taking chloroform (CF) as an example. b) Schematic cartoons of a sagging solid-oil-water composite interface at θ=ψ formed on a non-ideal bottomtruncated cylindrical texture with radius R, intercylinder spacing 2D and the minimum geometric angle

ψmin. Rsag is the radius of curvature of the sagging composite interface, δθ the sagging angle, h1 the sagging height and h2 the maximum pore depth. For the ideal cylindrical texture, ψmin =0°. The ability of a possible solid-oil-water composite interface to withstand external pressure can then be estimated by a general robustness factor (A∗) that combines robustness height (H∗) and robustness angle (T∗) as proposed in previous studies.29,30,31 H∗ compares the pressure PH required to force the sagging height h1 to reach the maximum pore depth h2, with the minimum pressure difference across the composite interface Pref=2γow/lcap. T∗ compares the pressure Pθ required to force a sagging angle of

δθ=θ-ψmin with Pref. It is considered that a stable or metastable CB composite is possible only when A∗>>1. For the non-ideal model with ψmin>0°, the robust factor A*ψmin can be expressed as

1 A∗ψ min

=

1 H ∗ψ min

+

sin 2 θ (cosψ min − cos θ )T ∗ψ min

(2)

13



where H ∗ψ =

lcap (cosψ min − cos θ ) ∗

R ( D − 1)

min

2

and T ∗ψ =

lcap sin(θ −ψ min )

2 R( D∗ − 1)

min

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. lcap = γ ow / ( ρ w − ρo g ) is the capillary

length of the fluid in oil-water systems, ρw is the water density, ρo the oil density, g the gravity acceleration, and γow the oil-water interfacial tension. For ψmin=0° the expressions reduce to the original ∗ ones for ideal cylinder texture,30,31 i.e. Aideal =

  1 − cos θ  ∗  . Figure 4a displays the calculated R ( D − 1)  ( D − 1 + 2sin θ )  lcap ∗

A*ideal and A*ψmin for chloroform (CF). It is found that A*ideal,CF is larger than 100 for any θ>0°, while A*ψmin=73°,CF declines to zero sharply when θ approaches 73°, which correlates well with the observations. The A*ideal and A*ψmin values calculated for all the oil/water systems studied are summarized in Table 2. Only A*ψmin=73° can reason all the wetting behaviors observed by giving A*ψmin=73°ψ) with applying Equation (5) gives

cos(θ w + θ h )
ψ). The potential point (ψ, θw) need to locate in the shaded region. Curve ③ is shown with cosψ versus cos(θw +θh) with θh=15° to demonstrate the effect of contact angle hysteresis. The three points indicated are corresponding to the PK, PK-F and PK-OH membranes.

3.4. Switchable Oil/water Filtrations. Figure 7 further demonstrates oil/water separations by the PK membrane (with a mean pore size around 80 nm, see Figure S8). Figure 7a displays that fast oil removal for water/DCE free-mixture and water removal for C6/water free-mixture can be accomplished under vacuum suction without any detectable impurity in the filtrate. Figure 7b shows gravity-driven dead-end filtrations of oil/water nano-emulsions. Three oil-in-water (OW) emulsions including C16/W, soybean oil (SO)/W and CF/W, and three water-in-oil (WO) emulsions including W/C6, W/toluene(T) and W/CF were tested. Dynamic light scattering (DLS) measurements (Figure S9) indicate that the droplet sizes of the nano-emulsions are about 100-500 nm, except for CF/W (~50 nm). Ultralow oil impurity (~1 ppm) and ultrahigh oil purity (>99.95%) in the filtrates can be acchieved for the switchable oil/water filtrations, except the relatively high oil permeation (~100 ppm) observed for CF/W. Ultrahigh fluxes (60-120 Lm-2h-1, equivalent to 6000~12000 Lm-2h-1bar-1) were obtained for filtrations of C16/W, SO/W and W/CF, in contrast to the relatively low flux for W/C6 and W/T. In the latter two cases, the

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rejected heavier water layer will easily accumulate on the membrane surface in the dead-end filtration mode and thus cause severe pore blockage and flux decline.

Figure 7. a) Photos of dead-end filtrations of water/DCE (water dyed blue) and C6/water (C6 dyed red) free mixtures under vacuum suction. b) Filtration performances of gravity-driven dead-end filtrations of oil/water nano-emulsions (10 cm liquid column, ~0.01 bar). Oil impurity in filtrate is presented for OW, while oil purity in filtrate is presented for WO. The digital photos show the filtration apparatus used and the solutions before and after filtration. The pristine PK membrane was used for all tests.

It has been demonstrated that the three PK, PK-F and PK-OH membranes exhibiting the same surface morphology but different surface chemistry display increasing hydrophilicity (and thus underwater oleophobicity and underoil hydrophilicity). Figure 8 compares their filtration performances for the same oil/water nano-emulsions. In the case of SO/W, the less hydrophilic PK membrane displays slightly lower oil impurity in filtrate (Figure 8a) but higher flux decline (Figure 8b) due to the relatively stronger adhesion between the PK membrane and soybean oil (i.e. membrane fouling). Similarly, in the 20


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case of W/CF (Figure 8d), the less hydrophilic PK membrane display both high operation flux and higher oil purity in permeate because of its superior underoil superhydrophobicity. Severe irreversible fouling is observed with the PK-OH membrane. As for CF/W (Figure 8c), the PK-F and PK-OH membranes with improved underwater superoleophobicity show higher oil rejection but severe flux decline, which can be attributed to pore blockage by accumulation of the rejected heavier oil on the membrane surfaces. Simple water rinsing can dislodge the adhered oil layer and restore membrane flux substantially. By contrast, the PK membrane shows gradual but irreversible flux decline by absorbing oil foulants throughout the membrane matrix. Overall, the filtration performances can be well explained by considering both surface wettability and membrane separation mechanism. The PK-F membrane allows low fouling (i.e. low irreversible flux decline) switchable oil/water filtrations involving either apolar or polar oils.

Figure 8. Comparing performances of gravity-driven dead-end filtrations (10 cm liquid column, ~0.01 bar) of oil/water nano-emulsions using the PK, PK-OH and PK membranes. a) The oil impurity in filtrate for the filtrations of SO/W and CF/W, and the oil purity in filtrate for the filtrations of W/CF. c)d) The flux variation with filtrate volume for the filtrations of b) SO/W, c) CF/W and d) W/CF.

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Finally, it is worth pointing out the benefits and limitations of the developed PK-based membranes. Knowing that a number of superwetting membranes have been developed for efficient separation of either oil-in-water or water-in-oil emulsions, there are few reports on unusual dual superlyophobic membranes that enable switchable filtrations for both types of emulsions.[12,

13]

This class of

superwetting membranes can also contribute to design novel intelligent interfacial systems. The preparation approach of PK membrane is very simple, without applying any template-assistance and post-modification. The filtration performances for oil/water nano-emulsions in terms of both flux and rejection are superior as compared to the previous studies.[12, 13] However, to obtain dual superlyophobic membrane covering both apolar and polar oils, e.g. the PK-F membrane, additional chemical modification was performed in this study, which limits the preparation scalability and stability. Thanks to the good membrane formation ability of PK, a better and simpler alternative approach can be used to manipulate membrane surface morphology and/or surface chemistry, i.e. adjusting the phase separation conditions including dope solution recipe (e.g. polymer concentration, solvent and additives) and coagulation bath conditions (e.g. non-solvent composition and temperature). This would be the next topic in the following research.

4. CONCLUSIONS A robust PK membrane possessing dual superlyophobicity to common apolar oils can be facilely prepared by the simple one-step phase separation process. After suitable chemical modification of the membrane surface, dual superlyophobicity to both apolar and polar oils can be achieved. Experimental and theoretical contact angle analyses reveal that how the intermediate hydrophilicity and re-entrant geometry of the fractal-like membrane surfaces, along with contact angle hysteresis, synergistically determine the existence and robustness of dual superlyophobicity and the otherwise fully wetting transition. A simple design chart can be used to easily map out the windows of suitable surface hydrophilicity (θw) and re-entrant geometry (ψ) that make the dual superlyophobicity possible by 22


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engineering various materials. It is believed that the simple and scalable membrane manufacturing strategy reported in this study will boost the practical application of advanced interfacial systems relying on switchable superwettability. ASSOCIATED CONTENT

Supporting Information. Support information is available free of charge via the Internet at http://pubs.acs.org. More details on the MD simulations, SEM images of the membrane cross-section, image analysis, membrane chemical compositions, pore size distribution, simulation results, droplet size distributions of the oil-in-water and water-in-oil emulsions before and after filtration, properties of the probe liquids used.

AUTHOR INFORMATION Corresponding Author *E-mail: [email protected]

Notes The authors declare no competing financial interest.

ACKNOWLEDGEMENTS We gratefully acknowledge material support from Asahi Kasei Co., Ltd. This research is funded by Grants-in-Aid from the Special Coordination Funds for Promoting Science and Technology, Creation of Innovation Centers for Advanced Interdisciplinary Research Areas (Innovative Bioproduction, Kobe) from the Ministry of Education, Culture, Sports, Science and Technology, Japan.

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REFERENCES (1)

Tian, Y.; Su, B.; Jiang, L., Interfacial Material System Exhibiting Superwettability. Adv. Mater.

2014, 26, 6872-6897. (2)

Liu, M.; Wang, S.; Wei, Z.; Song, Y.; Jiang, L., Bioinspired Design of a Superoleophobic and

Low Adhesive Water/Solid Interface. Adv. Mater. 2009, 21, 665-669. (3)

Tuteja, A.; Choi, W.; McKinley, G. H.; Cohen, R. E.; Rubner, M. F., Design Parameters for

Superhydrophobicity and Superoleophobicity. MRS Bull. 2011, 33, 752-758. (4)

Su, B.; Guo, W.; Jiang, L., Learning from Nature: Binary Cooperative Complementary

Nanomaterials. Small 2015, 11, 1072-1096. (5)

Shi, Z.; Zhang, W.; Zhang, F.; Liu, X.; Wang, D.; Jin, J.; Jiang, L., Ultrafast Separation of

Emulsified Oil/Water Mixtures by Ultrathin Free-Standing Single-Walled Carbon Nanotube Network Films. Adv. Mater. 2013, 25, 2422-2427. (6)

Rana, D.; Matsuura, T., Surface Modifications for Antifouling Membranes. Chemical Reviews

2010, 110, 2448-2471. (7)

Zhang, L.; Zhang, Z.; Wang, P., Smart Surfaces with Switchable Superoleophilicity and

Superoleophobicity in Aqueous Media: toward Controllable Oil/Water Separation. NPG Asia Mater.

2012, 4, e8. (8)

Kwon, G.; Kota, A. K.; Li, Y.; Sohani, A.; Mabry, J. M.; Tuteja, A., On-Demand Separation of

Oil-Water Mixtures. Adv. Mater. 2012, 24, 3666-3671. (9)

Tian, X.; Jokinen, V.; Li, J.; Sainio, J.; Ras, R. H. A., Unusual Dual Superlyophobic Surfaces in

Oil-Water Systems: The Design Principles. Adv. Mater. 2016, 28, 10652-10658. (10)

Zhang, P.; Wang, S.; Wang, S.; Jiang, L., Superwetting Surfaces under Different Media: Effects

of Surface Topography on Wettability. Small 2015, 11, 1939-1946.

24


Page 25 of 27 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

(11)


Cho, J. H.; Katsumata, R.; Zhou, S. X.; Kim, C. B.; Dulaney, A. R.; Janes, D. W.; Ellison, C. J.,

Ultrasmooth Polydopamine Modified Surfaces for Block Copolymer Nanopatterning on Flexible Substrates. ACS Appl. Mater. Interfaces 2016, 8, 7456-7463. (12)

Lo, Y.H.; Yang, C.Y.; Chang, H.K.; Hung, W.C.; Chen, P.Y., Bioinspired Diatomite Membrane

with Selective Superwettability for Oil/Water Separation. Sci. Rep. 2017, 7, 1426. (13)

Tao, M.; Xue, L.; Liu, F.; Jiang, L., An Intelligent Superwetting PVDF Membrane Showing

Switchable Transport Performance for Oil/Water Separation. Adv. Mater. 2014, 26, 2943-2948. (14)

Wang, B.; Liang, W.; Guo, Z.; Liu, W., Biomimetic Super-lyophobic and Super-lyophilic

Materials Applied for Oil/Water Separation: A New Strategy Beyond Nature. Chem. Soc. Rev. 2015, 44, 336-361. (15)

Wen, L.; Tian, Y.; Jiang, L., Bioinspired Super-Wettability from Fundamental Research to

Practical Applications. Angew. Chem. Int. Ed. 2015, 54, 3387-3399. (16)

Cassie, A. B. D.; Baxter, S., Wettability of Porous Surfaces. Trans. Faraday Soc. 1944, 40, 546-

551. (17)

Tuteja, A.; Choi, W.; Ma, M.; Mabry, J. M.; Mazzella, S. A.; Rutledge, G. C.; McKinley, G. H.;

Cohen, R. E., Designing Superoleophobic Surfaces. Science 2007, 318, 1618-1622. (18)

Lagaron, J. M.; Powell, A. K.; Davidson, N. S., Characterization of the Structure and Crystalline

Polymorphism Present in Aliphatic Polyketones by Raman Spectroscopy. Macromolecules 2000, 33, 1030-1035. (19)

Ohsawa, O.; Lee, K.-H.; Kim, B.-S.; Lee, S.; Kim, I.-S., Preparation and Characterization of

Polyketone (PK) Fibrous Membrane via Electrospinning. Polymer 2010, 51, 2007-2012. (20)

Gupta, P.; Schulte, J. T.; Flood, J. E.; Spruiell, J. E., Development of High-strength Fibers from

Aliphatic Polyketones by Melt Spinning and Drawing. J. Appl. Polym. Sci. 2001, 82, 1794-1815.. (21)

Hu, L.; Gao, S.; Ding, X.; Wang, D.; Jiang, J.; Jin, J.; Jiang, L., Photothermal-responsive Single-

walled Carbon Nanotube-based Ultrathin Membranes for On/Off Switchable Separation of Oil-in-Water Nanoemulsions. ACS Nano 2015, 9, 4835-4842. 25



(22)

Page 26 of 27

Chen, L.; Si, Y.; Zhu, H.; Jiang, T.; Guo, Z., A Study on the Fabrication of Porous PVDF

Membranes by In-situ Elimination and Their Applications in Separating Oil/Water Mixtures and Nanoemulsions. J. Membr. Sci. 2016, 520, 760-768. (23)

Shi, Z.; Zhang, W.; Zhang, F.; Liu, X.; Wang, D.; Jin, J.; Jiang, L., Ultrafast Separation of

Emulsified Oil/Water Mixtures by Ultrathin Free-standing Single-walled Carbon Nanotube Network Films. Adv. Mater. 2013, 25, 2422-2427. (24)

Zhang, W.; Zhu, Y.; Liu, X.; Wang, D.; Li, J.; Jiang, L.; Jin, J., Salt-Induced Fabrication of

Superhydrophilic and Underwater Superoleophobic PAA-g-PVDF Membranes for Effective Separation of Oil-in-Water Emulsions. Angew. Chem. Int. Ed. 2014, 53, 856-860. (25)

Zhang, F.; Gao, S.; Zhu, Y.; Jin, J., Alkaline-induced Superhydrophilic/Underwater

Superoleophobic Polyacrylonitrile Membranes with Ultralow Oil-adhesion for High-efficient Oil/Water Separation. J. Membr. Sci. 2016, 513, 67-73. (26)

Zhu, Y.; Zhang, F.; Wang, D.; Pei, X. F.; Zhang, W.; Jin, J., A Novel Zwitterionic

Polyelectrolyte Grafted PVDF Membrane for Thoroughly Separating Oil from Water with Ultrahigh Efficiency. J. Mater. Chem. A 2013, 1, 5758-5765. (27)

Xue, Z.; Cao, Y.; Liu, N.; Feng, L.; Jiang, L., Special Wettable Materials for Oil/Water

Separation. J. Mater. Chem. A 2014, 2, 2445-2460. (28)

David, Q., Non-sticking Drops. Rep. Prog. Phys. 2005, 68, 2495-2532.

(29)

Chhatre, S. S.; Choi, W.; Tuteja, A.; Park, K.C.; Mabry, J. M.; McKinley, G. H.; Cohen, R. E.,

Scale Dependence of Omniphobic Mesh Surfaces. Langmuir 2010, 26, 4027-4035. (30)

Tuteja, A.; Choi, W.; Mabry, J. M.; McKinley, G. H.; Cohen, R. E., Robust Omniphobic

Surfaces. Proc. Natl. Acad. Sci. 2008, 105, 18200-18205. (31)

Choi, W.; Tuteja, A.; Chhatre, S.; Mabry, J. M.; Cohen, R. E.; McKinley, G. H., Fabrics with

Tunable Oleophobicity. Adv. Mater. 2009, 21, 2190-2195. (32)

Bartell, F. E.; Osterhof, H. J., Determination of the Wettability of A Solid by A Liquid. Ind. Eng.

Chem. 1927, 19, 1277-1280.

26


Page 27 of 27 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

(33)


van Dijke, M. I. J.; Sorbie, K. S., The Relation between Interfacial Tensions and Wettability in

Three-phase Systems: Consequences for Pore Occupancy and Relative Permeability. J. Pet. Sci. Eng.

2002, 33, 39-48. (34)

van Damme, H. S.; Hogt, A. H.; Feijen, J., Surface Mobility and Structural Transitions of

Poly(n-alkyl methacrylates) Probed by Dynamic Contact Angle Measurements. J. Colloid Interface Sci.

1986, 114, 167-172. (35)

Chhatre, S. S.; Tuteja, A.; Choi, W.; Revaux, A.; Smith, D.; Mabry, J. M.; McKinley, G. H.;

Cohen, R. E., Thermal Annealing Treatment to Achieve Switchable and Reversible Oleophobicity on Fabrics. Langmuir 2009, 25, 13625-13632. (36)

Shaikh, A. R.; Rajabzadeh, S.; Matsuo, R.; Takaba, H.; Matsuyama, H., Hydration Effects and

Antifouling Properties of Poly(vinyl chloride-co-PEGMA) Membranes Studied Using Molecular Dynamics Simulations. Appl. Surf. Sci. 2016, 369, 241-250.

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Dual Superlyophobic Aliphatic Polyketone Membranes for Highly

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