Water Wettability That Performs Under

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Sustainable Biomimicked Oil/Water Wettability That Perform Under Severe Challenges Avijit Das, Dibyangana Parbat, Arpita Shome, and Uttam Manna ACS Sustainable Chem. Eng., Just Accepted Manuscript • DOI: 10.1021/ acssuschemeng.9b00881 • Publication Date (Web): 06 May 2019 Downloaded from http://pubs.acs.org on May 7, 2019

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ACS Sustainable Chemistry & Engineering

Sustainable Biomimicked Oil/Water Wettability That Perform Under Severe Challenges Avijit Das,a Dibyangana Parbat,a Arpita Shome a and Uttam Manna a,b* a

Department of Chemistry, Indian Institute of Technology-Guwahati, Kamrup, Assam 781039, India

b

Centre for Nanotechnology , Indian Institute of Technology-Guwahati, Amingaon, Kamrup, Assam 781039, India

Correspondence and requests for materials should be addressed to U.M. (email: [email protected])

ABSTRACT: In the recent past, biomimicked super-liquid repellent interfaces were recognized as the prospective and energy efficient solution for remediation of such oil-contamination, and mostly two phase oil/water mixtures that are either composed of light oil or heavy oil are demonstrated for gravity driven and environmentally friendly oil/water separation. In the reality, aqueous phase is contaminated with both heavy and light oils. Moreover, the demonstration of common oil/water separation with two phase system under physically/chemically challenging settings is rare, due to poor durability of the synthesized biomimicked membranes. Here in this report, a chemically reactive and covalently crosslinked multilayers of chemically reactive polymeric nanocomplex/aminographene oxide nanosheets is adopted for fabricating durable and tensile deformation tolerant two distinct selective-liquid-permeable membranes. Further these biomimicked membranes are exploited in the gravity driven selective filtration of oil and aqueous phase from the three phase oil/water mixture under practically relevant diverse and severe challenging settings, unprecedentedly. A prototype was developed through strategic association of both fish scale and lotus leaf inspired stretchable membranes, for simultaneous and active filtration of both heavy/light oils and aqueous phases—from their respective mixtures, and both the separated oil and aqueous phases were collected in two individual containers. Both the light/heavy oil phases selectively passed through the stretchable superhydrophobic membrane and the aqueous phase filtrated through the underwater superoleophobic membrane. The developed prototype is highly efficient in repetitive (at least 25 times) separation and collection of both oil and water phases—simultaneously, irrespective of density, surface tension and viscosity of the oil phase and chemical complexity in the aqueous phase. Keywords: Chemically Reactive Nanocomplex, Amino Graphene Oxide, Oil/Water Separation, Superoleophobicity, Superhydrophobicity, Selective filtration. INTRODUCTION Lotus leaf and Fish scale inspired, superhydrophobic and underwater superoleophobic interfaces1-4 have immense potential for wide range of practically relevant applications—including antibiofouling coating, oil/water separation, sustained drug delivery, open microfluidics etc.5-15 These interfaces are artificially synthesized by trapping the third external phases (water/air)16-17 in the hierarchically featured interfaces—which is rationally modulated with essential chemical functionalities. 1-5 The hierarchical topography that is topped with inert low surface energy coatings, allow to trap metastable air phase and eventually conferred lotus-leaf inspired superhydrophobicity— and such interfaces have an inherently strong affinity towards oil/oily phase.1,3 Whereas, highly water compatible—fish scale inspired interfaces that are efficient in confining an aqueous phase display super oil repellency under water. 2,4 In the past, these two distinct biomimicked wettabilities were rationally associated for developing membranes for gravity driven oil/water separations—from mostly two phase oil/water mixtures. In 2004, a seminal report from Liang and coworkers18 demonstrated the rational integration of lotus leaf inspired superhydrophobicity with metal mesh for gravity driven removal of oil spills from contaminated aqueous phase, where the separated aqueous phase was accumulated on top of the metal mesh. Thus, this approach introduced an early basis for energy and environment friendly remediation of oil spills 11,18-20—that are severely affecting the aqueous eco-system around the globe.21 Later, another membrane, decorated with fish-scale inspired underwater superoleophobicity, was independently and successfully exploited for gravity-driven selective filtration of aqueous phase

from oil/water mixture, and oil/oily phase piled up on top of the membrane.22-23 Both of these approaches are highly efficient in gravity driven active filtration/collection of a single liquid (either oil or water) phase from the respective two phase oil/water mixtures, however, the other liquid phase accumulates on top of the nature-inspired selective liquid repellent membrane.18-23 This accumulated liquid phase on the top of the biomimicked individual membrane in such previously reported filtration based separation set-ups is likely to block the immediate filtration of the selective liquids—on further addition of any oil/water mixture again. Thus, the removal of that accumulated liquid phase from top of the liquid repellent membrane is essential prior to perform any further filtration based oil/water separation, and this obvious interrupted oil/water separation process is likely to impose a severe inconvenience/challenge for its practical utility. Moreover, in reality polluted aqueous phase consists of both light and heavy oil/oily contaminates. Thus, the separation of oil/oily contaminants from three phase oil/water mixtures—that consists of heavy oil, light oil and aqueous phases, under practically relevant severe settings, is more relevant to the existing practical challenge of remediation of oil spillage under diverse scenarios. In general, the demonstration of oil/water separation—even with two phase mixtures under harsh and challenging settings, is rare in the literature as the durability of the reported biomimicked membranes is the major concern.24-25 To combat the durability issues, some important designs, including external stimuli assisted self-healing and self-repairable approaches are introduced.26-30 Such designs are fundamentally interesting and important, however the external stimuli dependent restoration of biomimicked wettability in the practically relevant diverse settings is less appropriate for real

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world applications.26-30 In the recent past, the concept of bulkbiomimicked wettability that consists of essential topography and appropriate chemistry—three dimensionally in the reported materials is a highly promising approach for addressing the existing durability issues,31-33 and such designs are inherently ca-

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continued to perform oil/water separation—even after incurring various severe physical/chemical challenges—including large tensile deformation (150%), creasing, winding, twisting, sand paper abrasion, sand drop test, adhesive tape peeling test, knife scratch test and prolonged (20 days) exposures to extreme

Scheme 1. A) Representing the amine reactive polymeric multilayers of amino-garphene oxide (AGO) and chemically reactive polymeric nanocomplex (CRPNC) on stretchable fibrous membranes, where residual acrylate groups in the multilayers coating allowed to post modify the multilayers coating s—with octadecylamine (B) and glucamine (C). These octadecylamine and glucamine treatments provided both superhydrophobic membrane (SHM , B) and underwater superoleophobic membrane (UWSOM, C), respectively.

pable of sustaining various abrasive exposures and continued to display uninterrupted biomimicked wettability even after removal of the top interface, without the aid of any external intervention.31-34 Such coating with bulk liquid wettability are mostly developed on the geometrically simple—planar substrates,31-34 any report on semipermeable membranes that are embedded with such bulk biomimicked wettability is yet to be introduced in the literature, and such a material would be appropriate for 1) sustaining various abrasive exposures and 2) separating oil/water mixture successfully, under various severe settings. Here, in this current study, an early attempt is made to address three practically relevant and challenging aspects. Firstly, a common and facile synthetic procedure was adopted for developing two distinct and stretchable biomimicked membranes, where two different nanomaterials—chemically reactive polymeric nanocomplex (CRPNC) and amino graphene oxide (AGO) nanosheets are rationally integrated into multilayers functional coating on selected fibrous substrate. The rational post chemical modifications of the covalently cross-linked and chemically reactive multilayers of CRPNC/AGO with primary amine containing selected small molecules (i.e.; octadecylamine and glucamine) provided stretchable and durable a) superhydrophobic membrane (referred as SHM) and underwater superoleophobic membrane (denoted as UWSOM) as shown in Scheme 1. Secondly, synthesized membranes that are embedded with two distinct durable biomimicked liquids wettability were extended for demonstration of instant separation and collection of three phase oil/water mixtures under challenging scenarios. The extreme and selective liquids (oil/water) repellent selective-liquid-permeable membranes (SHM and UWSOM)

acidic pH, basic pH, artificial sea water, river water and UV radiation. Thirdly, a lab-made prototype was developed using such durable nature inspired stretchable membranes (SHM and UWSOM), which was capable of selective separation/collection (above 98%) of oil/oily phase and aqueous phase—from three phases (light oil, heavy oil and aqueous phase) oil/water mixture, under practically relevant severe settings. RESULTS AND DISCUSSIONS Synthesis of Stretchable Biomimicked Membranes In general, separate approaches were adopted for optimizing essential topography and appropriate chemistry, which eventually provided two distinct nature inspired superhydrophobic (in air) and superoleophobic (under water) interfaces.1-4 Furthermore, the report on the design of stretchable and durable membranes that are embedded with such two distinct biomimicked wettability—following single synthetic procedure is unprecedented in the literature. Recently, our research group introduced chemically reactive polymeric nanocomplex (CRPNC) through strategic use of catalyst free and rapid Michael addition reaction for developing different nature-inspired functional materials.34-37 In this current design, this CRPNC and primary amine grafted graphene oxide (AGO) are rationally integrated into an amine reactive multilayers following a facile layer-by-layer deposition process.37-39 In the past, chemically reactive multilayers of polymer and reactive nanocomplex provided hydrophobic interfaces, where contact angle of beaded water droplet was below


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140°.37,39 Inspired from these early designs, the multilayer construction of CRPNC and AGO was unprecedentedly exploited for synthesizing stretchable and durable both SHM and UWSOM, where CRPNC and AGO was consecutively (for 10

substrate with significantly lesser deposition steps. After repeating the deposition cycles of CRPNC and AGO for 10 times, the morphology of the fibrous substrate was examined with FESEM study, and it was compared with native featureless fi-

Figure 1. (A) The DLS study illustrating the growth of nano-complexes in the BPEI/5Acl mixture with increasing the number of bilayers deposition cycles. (B-C) FESEM images of the fibrous substrate before (B) and after (C) deposition of the multilayers (10 bilayers) coating. (D) FT IR spectra of the multilayers coating before (black) and after post-treatment with octadecylamine (red) and glucamine (gray) molecules. (E-H) Digital image (E,G) and contact angle image (F, H) of beaded water (in air) and oil (under water) droplets on the multilayers coated fibrous substrate , after post-treatment with octadecylamine (E-F) and glucamine (G-H) respectively.

cycles) deposited on the strategically selected stretchable and fibrous substrate. The size of the amine reactive nanocomplex was noticed to increase rapidly (from 60 nm to 465 nm) with increasing the deposition cycle as confirmed with dynamic light scattering study (Figure 1A). Compare to earlier design37,39 the desired liquid repellent properties were optimized in the fibrous

bers of the selected substrate (Figure 1B). Random granular domains on the each fibers of the selected substrate was observed under FESEM (Figure 1C)—after the deposition of multilayers of CRPNC/AGO. Besides, the Raman spectral analysis revealed the successful integration of AGO in the multilayers



coatings, where both the D and G bands—that are characteristics of AGO, were appeared as shown in Figure S2. Further, this multilayer coating was examined with standard FTIR spectral analysis,34-37 where the characteristic IR signatures at 1410 cm1 and 1735 cm-1 that are corresponding to i) the C–H stretching

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beaded liquids (oil/water) droplets are readily rolled off on the slightly tilted interfaces (5° for SHM and 4° for UWSOM) as shown in Figure S 3A-H (see movie 1-2 for more details). Moreover, both streams of water (in air) and oil (under water) bounced away from the nature inspired SHM and UWSOM re-

Figure 2. A-D) Digital image (A,C) and contact angle image (B,D) of beaded water (A,B; in air) and oil (C,D; under water) droplets on the stretched (with 150% tensile stain) SHM (A-B) and UWSOM (C-D). E) The plot accounting the change in static contact angle of beaded water (black line indicating water wettability in air) and oil (red line denoting oil wettability under water) droplets on the SHM (black) and SOM (red)—during gradual increment of the tensile strain from 0% to150%. F-I) Digital (F,H) and contact angle (G,I) images of beaded water (in air; F-G) and oil (under water; H-I) droplet on SHM and UWSOM—that are repetitively (1000 times) deformed with 150% tensile strain. J) In the plot, black and red lines illustrating the changes in water (in air) and oil (under water) wettability during successive (1000 times) tensile deformations of SHM and UWSOM, respectively.

of the β-carbon of the vinyl group and ii) carbonyl stretching, respectively, confirmed the existence of residual acrylate groups. Furthermore, these residual acrylate groups are capable of readily react with primary amine containing two distinct small molecules—that are octadecylamine (hydrophobic small molecule) and glucamine (hydrophilic small molecule). After the post modifications with these selected small molecules, a significant change in IR peak intensity was noted at 1410 cm-1, and this change was normalized with respect to the IR peak intensity for carbonyl group at 1735 cm-1 as the carbonyl groups remained unperturbed during the 1,4-conjugate addition reaction between the amine containing small molecules and the residual acrylate groups of the multilayers (Figure 1D). Thus, the simple demonstration revealed the ability of residual acrylate functional groups in modulating the essential chemistry of the hierarchically featured multilayers coatings which eventually allowed to associate distinct liquid wettability to the selected fibrous substrate. The octadecylamine treated membrane repelled water in air with contact angle of ~157˚ (Figure 1E-F), whereas same multilayer coated membrane became underwater superoleophobic with advancing contact angle of ~161˚, after post-treatment with glucamine as shown in (Figure 1G-H). The embedded liquid wettability was highly non-adhesive as the

spectively, as shown in Figure S3 J, L, which suggested the existence of durable nature-inspired wettability (see movie 3-4). The biomimicked interfaces were tilted with large angle for improve visual inspection of this bouncing phenomena of water and oil on SHM (in air) and UWSOM (underwater), respectively. As expected, the streams of oil and water failed to bounce on bare fibrous substrate as shown in Figure S3 I,K. Further, the synthesized SHM and UWSOM were exposed to more challenging settings for investigating the durability of the embedded super-liquid-repellency and the detail durability studies are discussed in the following section. Investigation of the Physical/Chemical Durability of Biomimicked Wettability. These extreme and selective liquid repellent membranes were exposed to physically more severe challenging setting like tensile deformation—which is generally known to perturb the extreme liquid wettability and eventually few separate designs are introduced in the literature to achieve stretchable super liquid wettability.28-29 In contrast to our earlier reported chemically re-


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active multilayers,37,39 this current polymeric coating on stretchable fibrous substrate, required less bilayer depositions (‘only’ 10 bilayers)) for adopting durable super liquids (oil/water) repellent membranes (SHM, UWSOM), and the synthesized biomimicked interfaces are capable of incurring more tensile strain (total 150%), without compromising the embedded nature inspired extreme liquid (oil/water) wettabilities—that are superhydrophobicity (in air) and superoleophobicity under water, where both the aqueous (in air) and the oil (under water) droplets beaded on the octadecylamine (SHM) and glucamine (UWSOM) treated multilayer coating with liquid contact angle above 150° as shown in Figure 2A-E. Furthermore, these superliquid wettabilities remained unperturbed—even after exposing

(Figure S4-5). Further, such nature inspired wettabilities in SHM and UWSOM were examined after performing various other severe physical abrasive tests (Figure S6-7)—following standard reported protocols.24 First, both SHM and UWSOM was immobilized on the double sided adhesive surface and then brought in contact with an abrasive sand paper, then both the biomimicked membranes were rubbed manually with back and forth motion (with an average speed of ~ 4 cm/s, this speed can be manually tailored) for 20 times under applied pressure of 110 kPa—and this applied pressure is significantly higher compare to the pressure (below 15 kPa) imposed in the commonly reported demonstrations.24 During this severe physical abrasion process, the top portion of the coating was affected as shown in

Figure 3. A-L) Digital image (A,E,I) and contact angle (B,F,J) images of the beaded water droplet on the SHM in air, after performing san d paper abrasion test (A-B), adhesive tape peeling test (E-F), knife test (I-J). Further, the water wettability examined after exposing these treated SHM to 150 % tensile deformations (C-D,G-H,K-L). M-X) Digital image (M,Q,U) and contact angle (N,R,V) images of the beaded oil droplet on the UWSOM, after performing sand paper abrasion test (M-N), adhesive tape peeling test (Q-R), knife test (U-V). Further, the oil wettability examined after exposing these SOM to 150 % tensile deformations (O P,S-T,W-X). Y-Z) Plots accounting the embedded water (in air, Y) and oil (under water, Z) wettabilities on the SHM (Y) and UWSOM (Z) after exposures to various chemically and radiative severe conditions—including extremes of pH (1 &12), River water, artificial sea water and UV irradiation (at λmax =254 nm and 365 nm) for prolonged duration (25 days).

these nature inspired extremely liquid repellent membranes (SHM and UWSOM) to large (with 150%) tensile deformation for 1000 times as shown in Figure 2F-J. Thus, current single chemical approach provided highly stretchable two distinct super liquid repellent membranes (SHM and UWSOM), such demonstration is unprecedented in literature.34-39 Then, both the SHM and UWSOM were exposed to various common and practically relevant physical manipulations, including creasing, winding, and twisting each for ten times (Figure S4-5), however, both oil (under water) and water (in air) repellency remained unaffected with the liquid contact angles above 150˚

Movie 5-6, however, both nonadhesive super liquid wettabilities of the membranes (SHM and UWSOM) remained unaltered with liquid contact angle above 150˚ as shown in Figure 3A-B, M-N. Moreover, the nonadhesive superhydrophobicity and underwater superoleophobicity remained unaltered—even after performing the adhesive tape peeling test on the synthesized stretchable membranes (SHM and UWSOM) as shown in Figure 3E-F, Q-R, where freshly exposed adhesive tape was brought in contact with SHM and UWSOM—with an applied pressure of 110 kPa for 1 min for improve contact between ad-



hesive surface and biomimicked membranes, and the synthesized SHM and UWSOM faced severe abrasive challenge during the process of peeling the biomimicked membranes from the adhesive surface as shown in Movie 7-8. Further, knife scratch test was performed on the synthesized SHM and UWSOM, where top surface of the biomimiked coatings were exposed to manual and random physical scratches as shown in Movie 9-10, however that embedded liquid repellency remained unaffected as shown in Figure 3I-J, U-V. All the SHM and UWSOM that were exposed to severe physical abrasive tests, were further exposed to large (150%) tensile strain, and the physically deformed membranes (SHM and UWSOM) dis-

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Figure S9A, E. However, the physically damaged interior of the multilayers coatings continued to display extreme liquid repellency as shown in Figure S9A-B, E-F. Further, the arbitrarily cleaved multilayers that were transferred to the adhesive tape (see Figure S9C,G) also displayed extreme liquid repellency as shown in Figure S9C-D, G-H. This control study confirmed that the multilayers coatings are embedded with bulk super liquid wettability. As a consequence, the current synthesized membranes that are coated with such multilayers are capable of sustaining various practically relevant severe physical challenges and abrasions. Next, a stream of a 150 g sand grains was separately dropped

Figure 4. A) Schematic illustrating the selective and simultaneous collection of both oil and aqueous phases from its mixture using lab -made prototype, where superhydrophobic membrane (SHM) and under water superoleophobic membrane (SOM) selectively allowed to pass separated oil and aqueous phase respectively. (B-D) Digital images illustrating the collection of light oil (kerosene) and water from its mixtures, whereas (E -G) Digital images describing the collection of heavy oil (dichloro ethane, DCE) and water.

played extreme liquid repellency as shown in Figure 3C-D,GH,K-L, O-P,S-T,W-X. Such impeccable durability of the synthesized biomimicked membranes is rare in the literature. The exemplary tolerance of the biomimicked wettability in the synthesized SHM and UWSOM under various severe physical abrasive settings is likely due to bulk (both top interface and interior) optimization of essential chemistry and topography in the polymeric multilayers coatings through 1,4 conjugate addition reaction between amine and acrylate groups. Eventually, both the top interface and interior of the coating is inherently capable of displaying super liquid wettability, which is denoted as bulk super-liquid wettability. Thus, the exposed interior of the coating after performing the severe physical abrasions tests, remained efficient in displaying extreme liquid repellency. To examine the existence of bulk super-liquid wettability in the synthesized multilayers, a similar multilayers construction, which was deposited on the planar glass slide, was appropriately post modified separately with ODA and glucamine, prior to expose to adhesive tape with applied load of 110 kPa. After the peeling process, a freshly exposed interior of the multilayers coating on a flat substrate (i.e., microscopic glass slide) was obtained, and the top of the multilayers coating was uniformly transferred onto the adhesive tape as shown in

on both the UWSOM and SHM from a height of 20cm, however, any apparent change in liquid wettabilities was not observed (Figure S6K-P, S7K-P). Next, the chemical durability of the embedded liquid (oil/water) wettabilities of SHM and UWSOM was investigated in details, where both of these membranes (i.e.; UWSOM and SHM) were continuously exposed to various chemically harsh aqueous phases—including highly acidic (pH 1)/alkaline (pH 12) water, artificial sea water, river water (Brahmaputra river water, Assam, India) for 25 days. However, both SHM and UWSOM continued to display the embedded nonadhesive superhydrophobicity (in air) and superoleophobicity (under water), respectively, with liquid contact angle above 150˚ as shown in Figure 3Y-Z. At the end, both SHM and UWSOM were exposed to another practically relevant challenge—that is prolonged UV radiation, where both the membranes were placed under UV radiation at two different maximum wavelengths ( i.e.; 254nm and 365nm)—simultaneously—for 25 days. However, both the membranes remained efficient to display nonadhesive superhydrophobicity/underwater superoleophobicity, with liquid contact angle above 150° (Figure 3Y-Z). Further, these membranes—that were exposed to UV radiation for 25 days, were also exposed to high tensile deformation, and physically deformed both SHM and UWSOM


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displayed extreme water (in air) and oil (under water) repellency with liquid contact angle above 150° as shown in Figure S10C-D, G-H. Parallel Collection of Oil and Aqueous Phases from Oil/Water Mixtures The highly durable and stretchable synthesized membranes (SHM and UWSOM)— that are capable of displaying uninterrupted extreme water (in air, under oil; Figure S11) and oil (under water) repellency— even after exposures to severe physical and chemical challenges, were explored in developing a prototype—for proof of concept demonstration of simultaneous separation followed by collection of two distinct separated liquid phases (oil and water) in individual containers. So, a polypropylene tube (diameter 3 cm, length 4.3 cm) with one surface hole (1.5 mm) at the middle of the tube was selected for preparing the above mentioned prototype, where both ends opening of the tube were closed with SHM and UWSOM as depicted in Figure 4A, and the surface hole was used for pouring different oil/water mixtures. Then, oil/water mixture consisting of 10 ml aqueous phase (colored with added dye for improved visualization) and 10 ml of kerosene (model light oil) were transferred into the prototype using glass a funnel as shown in Figure 4B-C, the aqueous phase was selectively passed through the UWSOM— which was attached at the right end of the prototype, and the oil-free aqueous phase was collected in a container that was placed under the prototype. Simultaneously, kerosene also selectively passed through the SHM that was attached at the other end of the prototype and the selectively filtrated oil phase was collected in another container right under the prototype as shown in Figure 4B-C. Thus, two different liquid phases were separated from the oil/water mixture and collected in individual containers (see movie 11), and no accumulation of any liquid phase was noted on the top of the used membranes at the end as shown in Figure 4D, and this unprecedented successes is attributed to the rational and combinatorial function of two distinct nature-inspired interfaces. Further, this prototype was explored for separating/collecting heavy oil (dichloromethane (DCE), model heavy oil) and aqueous phase—simultaneously (see movie 12)— from the respective oil/water mixture as shown in Figure 4E-G. The efficiency of separated water/oil phase is calculated following given equation; Vc S = 𝑥100 Vs

Where, S = separation efficiency of the liquids and Vc and Vs are representing the volume of the corresponding liquid after selective filtration and the actual volume that present in the mixture before active separation, respectively. The lab made prototype was also found to be highly efficient

Figure 5. (A) The plot accounting the efficiency of simultaneous oil (red) and aqueous (blue) phases separation efficiency—from various oil/water mixtures, irrespective of the viscosity, surface tension and density of used oils. (B) Plot illustrating the successful separation, followed by collection of two distinct liquid phases (oil (red) and water (blue)) from respective oil/water mixtures—where the aqueous phase was varied from highly acidic, alkaline, artificial sea water to river water, and the effect of large (150%) physical deformation on its separation performance is also examined. (C) Bar graph representing the ability of repetitive (minimum 25 times) oil (red) and aqueous (blue) phase separation using the same lab-made prototype.

(above 98 %) in separating and collecting various other



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oil/aqueous mixtures—irrespective of a) density, b) surface tenthrough same 1,4-conjugate addition reaction. Most of the desion and c) viscosity of the used oil phases (vegetable oil, silisigns of biomimicked interfaces are optimized by associating delicate chemistries (i.e., metal-thiol bond and metal-ion intercone oil, motor oil, dichloromethane and chloroform, Table S1) as shown in Figure 5A and Figure S12. After the oil/water sepaction, UV sensitive silane chemistry etc.) and such designs are aration, the underwater superoleophobic membranes continued inappropriate for application in diverse challenging settings. 4049 As a consequence, the demonstration of oil/water separation to repel non-volatile used oils—extremely, and thus, the synthesized biomimicked membranes remained appropriate and efperformance with the reported materials under severe scenarios ficient for long term use in oil/water separation. Further, variare rare in the literature.50-52 Whereas, the current approach alous oil/water mixtures contaminated with highly acidic (pH 1) lowed to utilize these nature-inspired interfaces in remediation and alkaline (pH 12) aqueous phase, artificial sea water, river of oil spillages under various severe practically relevant scenarwater, were successfully separated using this same prototype as ios. shown in Figure 5B. Furthermore, the membranes (SHM and UWSOM) that were exposed to prolonged (25 days) UV irradiation (simultaneously at at λmax =254 nm and 365 nm) and successively (1000 times) stretched with 150% TS, were also found to be efficient in isolating/collecting oil and aqueous phases—simultaneously. The current prototype allowed selective and simultaneous filtration of both oil and aqueous phases, without accumulating any single phase on top of the used membranes. After performing the simultaneous separation and followed by collection of oil/water—from oil/water mixture, the membrane was air-dried before repeating this oil/water separation process with the same SHM and UWSOM and this oil/water separation process was repeated successfully for minimum 25 times, without the aid of any external interventions as shown in Figure 5C. The successive wetting and drying of biomimicked membranes with respective liquid phase has no noticeable impact on the oil/water separation performance. Moreover, the uninterrupted oil/water separation in various harsh settings is likely due to the existence of a) covalent Figure 6. (A-C) Digital images illustrating the separation of three phases (light oil/water/ heavy oil) oil/water mixture using the prototype made out of stretchable membranes (SHM and UWSOM) that are embedded with two distinct bio-mimicked liquid optimization of essential wettabilities. C) Both the heavy (DCE, red colour) and light (kerosene; blue colour) oils selectively passed through the SHM and chemistry and b) robust the colourless aqueous phase was filtrated through the UWSOM and collected in two separate containers. D) The graph accounting for the covalent cross-linkages separation efficiency of both aqueous phase (blue) and oil phase (red) under various severe settings, where the DI water was replaced with various chemically complex aqueous phase. in the multilayers


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Separation Oil and Water from Three Phases Oil/Water Mixture The demonstration of parallel collection of oil and aqueous phase from the respective oil/water mixtures, and the performance of stretchable biomimicked membranes (SHM and UWSOM) in oil/water separation under practically relevant severe settings, inspired to extend this approach for separation of oil and aqueous phase from three phases (light oil, aqueous phase and heavy oil) oil/water mixture. The oil/water mixture that consisted of three phases—kerosene (top layer, blue), DI water (middle layer, colorless) and DCE (bottom layer, added red color aids visual inspection) was poured into the lab-made prototype, and instantly both the heavy and light oil phases selectively passed through the SHM, whereas aqueous phase was collected in a separate beaker after selective filtration through the UWSOM as shown in Figure 6A-C. The collected aqueous phase was found to be completely colorless (Figure 6C), which strongly suggested that the separated aqueous phase is free from both heavy and light oils. The collection efficiency of the separated oils and DI water were estimated to be above 98% as shown in Figure 6D. Moreover, this separation performance remained unaffected, even after replacing the DI water with practically relevant and more complex aqueous phases (e.g.; highly acidic, strongly basic, artificial sea water, river water) as shown in Figure 6D. Such unprecedented demonstration is highly relevant for remediation of water pollution that is caused due to frequent oil spillages at practical and diverse settings. CONCLUSION In conclusion, the current communication introduced a facile and single chemical approach for the synthesis of durable and stretchable superhydrophobic (in air) and superoleophobic (under water) membranes—for the first time. These synthesized membranes were strategically exploited in a combinatorial act of two distinct nature inspired (lotus leaf and fish-scale) wettabilities—that are superhydrophobicity and superoleophobicity—for parallel and selective separation of various oil/water mixtures repetitively—irrespective of surface tension, density and viscosity of used oil phase and chemical complexity in the aqueous phase. This current approach does not demand any external intervention. Such energy efficient and unprecedented approach was further successfully extended for the separation of oil and aqueous phases from three phases oil/water mixtures and the separation performance was remained unperturbed even after associating practically relevant severe and complex aqueous phases (i.e.; extremes of pH, artificial sea water, river water) to the prototype. ASSOCIATED CONTENT Supporting Information

The Supporting Information is available free of charge on the ACS Publications website, the attached supporting informations accounting the detailed description of material and methods for the synthesis of material and related demonstrations, different physical and chemical durability of the synthesized material and demonstration of light and heavy oil separation and collection in air and underwater, respectively. AUTHOR INFORMATION

Corresponding Author *[email protected].

Notes There are no conflicts to declare.

ACKNOWLEDGMENT We acknowledge the financial support from Science and Engineering Research Board (YSS/2015/000818), Department of Science and Technology, Government of India. We thank Ms. Jumi Deka and Dr. Kalyan Raidongia for their generous help in synthesizing AGO. We thank CIF and Department of Chemistry, Indian Institute of Technology-Guwahati, for their generous assistance in executing various experiments and for the infrastructure. Avijit Das thanks CSIR for PhD fellowship, and Arpita Shome and Dibyangana Parbat are thankful to IIT G for their doctoral fellowships.

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TOC Use only: A common and facile synthetic approach is introduced to synthesize highly tolerant and two distinct biomimicked membranes for simultaneous separation and collection of aqueous and oil/oily phases at severe settings.


Water Wettability That Performs Under

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