Article pubs.acs.org/IECR
Assembled Block Copolymer Stabilized High Internal Phase Emulsion Hydrogels for Enhancing Oil Safety Tao Zhang,† Zhiguang Xu,† Yuanpeng Wu,‡ and Qipeng Guo*,† †
Polymers Research Group, Institute for Frontier Materials, Deakin University, Locked Bag 20000, Geelong, Victoria 3220, Australia School of Materials Science and Engineering, Southwest Petroleum University, Chengdu, Sichuan 610500, China
‡
S Supporting Information *
ABSTRACT: Accidental spills and subsequent fires during oil storage and transportation periods cause serious damage to environments. Herein, we present a novel route to enhance oil safety by transforming oils into high internal phase emulsion (HIPE) hydrogels. These HIPE hydrogels are stabilized by solvent- or pH-driven assembled block copolymer (BCP), namely poly(4-vinylpyridine)-block-poly(ethylene glycol)-block-poly(4-vinylpyridine) (4VPmEGn-4VPm). The assembled BCP shows high efficiency to stabilize HIPE hydrogels with a low concentration of 1.0 (w/v) % relative to the continuous aqueous phase. The volume fraction of the dispersed organic phase can be as high as 89% with a variety of oils, including toluene, xylene, blended vegetable oil, canola oil, gasoline, diesel, and engine oil. These smelly and flammable liquids were formed into HIPE hydrogels and thus their safety was enhanced. As the assembly is pH sensitive, oils trapped in the HIPE hydrogels can be released by simply tuning pH values of the continuous aqueous phase. The aqueous phase containing BCP can be reused to stabilize HIPE hydrogels after naturalization. These assembled BCP stabilized HIPE hydrogels offer a novel and safe approach to preserve and transport these smelly and flammable liquid oils, avoiding environmental damage.
1. INTRODUCTION
Stabilizers are vital for the preparation of HIPEs, and most HIPEs are stabilized by solid particles and surfactants. However, most solid particles suffer from phase inversion with increasing the volume fraction of the internal phase though some solid particles function as HIPE stabilizers successfully.9−11 Surfactants including block copolymers (BCPs) usually show low efficiency, where a high concentration of 5−50 (w/v) % of the continuous phase is required to stabilize HIPEs.12−16 Recently, some efficient HIPE stabilizers, including polymer microgels,17−20 ionomers,21 and core crosslinked star (CCS) polymers22−24 have been reported. Conventional BCPs are also able to stabilize emulsions, but they are inefficient, where as high as 5−50 (w/v) % of BCPs in the continuous phase is required.8,25,26 As a particulate emulsifier for HIPEs, it is noted that the reported polymer emulsifiers are usually cross-linked, such as chemical or physical cross-linked gels,7,8,17,18,27−29 chemical cross-linked hybrid copolymer,30 CCS polymer,22−24 and branched copolymer.31 To our best knowledge, no assembled BCPs have been reported as HIPE stabilizers. We recently reported HIPE organogels stabilized by assembled polymer organogels,27,28,32 and these HIPE organogels have also been investigated for oil spill recovery and oil− water separation.28,33 We present herein a new approach to
Oils such as liquid fuels and some organic solvents are of vital importance in current life, but they may become great hazards to environment. With growing production of liquid fuels and organic solvents, the storage and transportation of these liquids arouse many issues about accidental spills and subsequent fires.1,2 These oil spills and fires cause serious and irrecoverable damage to ecosystem, environment, and even human health. One promising method to prepare safe oils is to transfer them into oil-in-water emulsions, and these emulsions have been found with the following properties: (a) the volatility of the emulsified oil is much lower than that of pure oil; (b) viscous emulsions are much less likely to spill, slosh, or splash; (c) emulsified oil is much less flammable than pure oil.3,4 However, these emulsions are still stored and transported in liquid form which is prone to accidental spills.3 These emulsified fuels are usually used directly, although pure liquids are required in some circumstances. High internal phase emulsions (HIPEs) are emulsions with a high volume fraction of the internal/dispersed phase, that is, at least 74%.5 HIPEs usually exhibit high viscosity due to the high volume fraction of the internal phase, and thus they are also called gel emulsions.6 HIPEs without liquid-like flow behavior are also called HIPE organogels or hydrogels based on the type of the continuous phase, and they can be obtained by applying organic particles as stabilizers.7,8 These HIPE hydrogels have several advantages over common emulsions for oil safety as they trap more oils and have a higher viscosity. © XXXX American Chemical Society
Received: January 4, 2016 Revised: March 14, 2016 Accepted: March 28, 2016
A
DOI: 10.1021/acs.iecr.6b00039 Ind. Eng. Chem. Res. XXXX, XXX, XXX−XXX
Article
Industrial & Engineering Chemistry Research
dynamic size of the assembled BCP. SAXS data were collected at the Australian Synchrotron on the small/wide-angle X-ray scattering (SAXS/WAXS) beamline. The samples were injected into 1.0 mm quartz capillaries, and the background correction was conducted by measuring the scattering of air with the same sample holder. Gel formation was determined using a tube inversion methodology: All samples were prepared in a 7 mL vial with a diameter of 16 mm, and the formation of gels was defined that no flow behavior was observed in an inversed tube for at least 10 min. The conductivities of emulsions and HIPE hydrogels prepared from assembled BCP solution and toluene were measured by a SevenEasy conductivity meter (MettlerToledo GmbH, Switzerland) at 25 °C. The conductivities of toluene and water were also tested for comparison. HIPE hydrogels with different volume fractions of toluene were stored in closed vials to observe their stability at 0 and 20 °C. Rheological experiments were carried out on a TA DHR 3 rheometer using a plate geometry with a diameter of 40 mm. The measurements were conducted at 25 °C and gap was set to be 1000 μm. A solvent trap was used to minimize the effect of evaporation. Frequency sweeps with an angular frequency from 0.3 to 500 rad s−1 were performed at a strain of 1%.
prepare safe oil by transforming liquid oils into HIPE hydrogels stabilized by assembled BCPs. HIPE hydrogels have been developed to be stabilized by a type of novel and efficient stabilizers, assembled BCPs, namely poly(4-vinylpyridine)block-poly(ethylene glycol)-block-poly(4-vinylpyridine) (4VPmEGn-4VPm). These HIPE hydrogels can trap a variety of oils such as smelly and highly flammable organic solvents and fuels, including toluene, xylene, gasoline, diesel, and engine oil. The trapped oils can be released by simply tuning the pH values of the continuous phase in the as-prepared HIPE hydrogels, and the continuous aqueous phase with assembled BCP can be reused to stabilize HIPE hydrogels. As the assembly of BCPs is pH responsive, they are efficient HIPE stabilizer in the assembled state, and dissolve into the aqueous phase at relative low pH. The aqueous phase and stabilizers are reusable and thus the cost of using assembled BCPs to stabilize HIPEs for enhancing oil safety can be reduced. Therefore, this approach can be practically used to enhance oil safety during storage and transportation periods.
2. EXPERIMENTAL SECTION 2.1. Materials. Block copolymers poly(4-vinylpyridine)block-poly(ethylene glycol)-block-poly(4-vinylpyridine) (4VPmEGn-4VPm ) were synthesized by atom transfer radical dispersion polymerization according to the procedure reported in our previous paper,34 and the copper was removed by basic or neutral alumium oxide column. A slight amount of alkali such as triethylamine was added to BCP solution in DMF if the neutral alumina column was used to remove copper. The subscripts denote the degree of polymerization (DP) of the corresponding blocks based on 1H NMR. N,N-dimethylformamide (DMF), styrene, toluene, and xylene were purchased from Sigma-Aldrich. Blended vegetable oil and canola oil (Homemaker) were purchased from Woolworths. Gasoline, diesel, and engine oil were bought from Shell local store. The other reagents and solvents were analytical grade and used directly. Deionized water was used throughout the experiments. 2.2. Preparation of Assembled BCP Solutions. Assembled BCP solutions were prepared in two methods. In method one, solvent-driven assembly was applied, where BCPs were dissolved into DMF to obtain 10 (w/v) % solution and subsequently water was added to the as-prepared DMF solution slowly to drive the assembly of BCP. The final concentration of the assembled BCP solution was kept at 1 (w/v) % in water/ DMF (9/1, v/v), and the solution was used directly to stabilize HIPE hydrogels. In method two, pH-driven assembly was used, where BCPs were dissolved into water (pH = 1), then adjusted to pH 9 with NaOH (0.01 M) aqueous solution, and finally diluted the solution to 1 (w/v) % with water. 2.3. Preparation of HIPE Hydrogels. HIPE hydrogels were prepared by increasing the volume fraction of the dispersed phase in the as-obtained assembled BCP solution step by step. Common emulsions with 33% and 50% of the dispersed phase were obtained by shearing the mixture of hydrophobic solvents or oils and the assembled BCP solutions in a 7 mL vial with a Vortex mixer at 3400 rpm. HIPE hydrogels were formed by further increasing the volume fraction of solvents or oils to 80%, 83%, 86%, and 89% in these emulsions. The fractions of all samples are by volume. 2.4. Characterization. Dynamic light scattering measurements were carried out at 25 °C on a Malvin Zetasizer Nano ZS apparatus. Scattering intensity autocorrelation functions were analyzed with the Cumulant method to calculate the hydro-
3. RESULTS AND DISCUSSION 3.1. Assembled BCP Solutions. Emulsions are commonly formed with oil/water/stabilizer, and stabilizer dispersing into water can be used directly to support emulsions. Water is a good solvent for PEG block but cannot dissolve P4VP blocks, and thus assures the assembly and dispersity of 4VPm-EGn4VPm. In the preparation of solvent-driven assembled BCP solutions, DMF was selected as solvent since it dissolves both PEG block and P4VP blocks. As a water-miscible solvent, DMF facilitates solvent-driven assembly of BCP and the preparation of emulsions. After dissolving BCP into DMF, a transparent solution with a low viscosity was obtained, indicating that no macrophase separation occurred. The solution becomes translucent after the addition of water to the DMF solution slowly. To prepare pH-driven assembled BCP solutions, BCP was first dissolved into water with pH 1. After BCP was totally dissolved, the aqueous solution was adjusted to pH 9 with NaOH solution, and then diluted to 1 (w/v) %. Similar to solvent-driven assembled BCP solutions, the pH-driven BCP solutions become translucent. Four BCPs with different PEG and P4VP block lengths were used to prepare solvent- and pH-driven assembled aqueous solutions, and then these solutions were used for the continuous phase to prepare HIPEs. From the results shown in Table 1, the BCP 4VP82-EG136-4VP82 is the most efficient to stabilize HIPE hydrogels. Thus, this BCP was used in this paper. In experiments, to reduce uncertainty on measurements, we used high-accuracy instruments such as balance (0.0001 g) and pipettes (0.001 mL), and we also repeated experiments for several times. The values such as 89%, 80% are based on calculation but omit decimal fraction to maintain their precision. The solvent- and pH-driven assembly of assembled BCP was studied by DLS, and it can be seen from the results in Figure 1a that the sizes of solvent- and pH-driven assembled 4VP82EG136-4VP82 are 131.9 and 179.4 nm, respectively. The assembly of 4VP82-EG136-4VP82 was further investigated by SAXS. It has been reported that no phase separation was observed for 4VPm-EGn-4VPm solution in DMF.34 From the SAXS profiles shown in Figure 1b, it can be seen that B
DOI: 10.1021/acs.iecr.6b00039 Ind. Eng. Chem. Res. XXXX, XXX, XXX−XXX
Article
Industrial & Engineering Chemistry Research
thus its solutions were investigated to stabilize emulsions, and typical photos of emulsions formed from toluene and assembled BCP aqueous solutions are shown in Figure 2a. It can be seen that ordinary emulsions were formed with a low ratio of toluene, such as 50%. This emulsion is separated into two layers after several hours, and the separation of these emulsions is totally reversible at least for 20 times. It is believed that the separation is induced by density differences between the continuous phase and the dispersed phase.21 Similar to other emulsions,29,39 viscosities of these emulsions increase with the gradual increase the volume fraction of the dispersed phase such as toluene to these ordinary emulsions. These emulsions with 80%, 83%, 86%, or 89% of toluene do not show flow behavior anymore in an inversed vial, showing the formation of three-dimensional networks. The formation of networks should greatly avoid spill, slosh, and splash. The formations of these emulsions and HIPEs were also observed when toluene was replaced by other organic solvents such as xylene and various oils including blended vegetable oil, canola oil, diesel, engine oil, and gasoline. The type of these emulsions was determined by conductivity measurements and drop test measurements, and the results of conductivity measurements are shown in Figure 2b. Toluene is a nonpolar solvent and its conductivity is 0 μS cm−1 at room temperature. While the conductivity of the assembled BCP aqueous solution is greater than that of pure water, at about 300 μS cm−1, perhaps because the presence of DMF in water enhances the conductivity. From the results, it is observed that conductivities of these emulsions are much higher than that of toluene, indicating these emulsions were formed with toluene dispersed into water. The results are agreeable with those observed in drop test measurements. The conductivities of these emulsions decline with the increase of toluene volume fractions in emulsions, and this decline may be explained by the the thinner membrane between oil droplets and the difficulty of movement in emulsions with high toluene fraction. Since the continuous phase is aqueous, the formed gels can be called high internal phase hydrogels. The oil droplets are dispersed in the water, and due to the immiscibility between the dispersed phase and the continuous phase, the volatility decreases greatly.
Table 1. Assembled BCPs Used for Preparation of HIPEs solvent-driven assembly
1
2
3
4
maximum internal phase fraction
pH-driven assembly
appearance
maximum internal phase fraction
BCPs
appearance
4VP82EG1364VP82 4VP87EG2274VP87 4VP50EG2274VP50 4VP36EG4544VP36
translucent
89%
translucent
89%
translucent
80%
translucent
80%
translucent
75%
translucent
75%
transparent
∼50%
transparent
∼50%
microphase separation occurred upon the addition of water into DMF solution. From these fittings, it can be known that the radius of assembled BCPs are 20.5, 20.0, and 18.5 nm for solvent-induced assembly before and after dialysis and pHinduced assembly of 4VP82-EG136-4VP82, respectively, showing assembly occurred in these solutions. The SAXS data were fitted with a form factor as detailed in the Supporting Information, but the accurate structures of these BCPs cannot be elicited. It is noted that the size ranges of assembled BCPs from SAXS are much smaller than those from DLS; such large discrepancy was also observed by others35,36 as well as in our previous work.37 3.2. Formation of HIPE Hydrogels. It is known that formation of oil-in-water (high internal phase) emulsion requires partial wettability of the particles with positive adhesion energy EAdh(o/w) and negative spreading coefficient S(o/w):38 S(o/w) = −EAdh(w/o) = γs − w − γo − w − γs − o < 0
(1)
EAdh(o/w) = −S(w/o) = γs − w + γo − w − γs − o > 0
(2)
where γp‑o, γp‑w, and γw‑o stand for interfacial energies of the following three interfaces: particle−oil, particle−water, and water−oil, respectively. The assembled BCP is amphiphilic and
Figure 1. (a) Size distribution of pH-driven (hollow) and solvent-driven (filled) assembled 4VP82-EG136-4VP82 and (b) SAXS profiles for solventdriven assembly before and after dialysis and pH-induced assembly of 4VP82-EG136-4VP82, respectively. The red lines fit to the corresponding experimental data (hollow dotted lines). C
DOI: 10.1021/acs.iecr.6b00039 Ind. Eng. Chem. Res. XXXX, XXX, XXX−XXX
Article
Industrial & Engineering Chemistry Research
Figure 2. (a) Photos of emulsion and HIPE hydrogels with 50%, 80%, 83%, 86%, and 89% of toluene after 24 h storage; (b) conductivities of assembled BCP stabilized emulsions.
(w/v) % of the aqueous phase in these HIPE hydrogels, and that diesel was used as the dispersed phase as it is of low smell. It can be observed from the Figure 5 that G′ is higher than the corresponding G″ for all the HIPE hydrogels under study,
The morphology of these newly formed HIPE hydrogels was observed by optical microscopy. Figure 3 shows the optical
Figure 3. Optical images of HIPE hydrogels with toluene fractions of 83%, 86%, and 89% as internal phase.
images of HIPE hydrogels with different volume fractions of toluene. The sizes of these dispersed droplets vary from tens of micrometres to a little over 100 μm, falling in the size range of emulsions. With the increase of the internal phase, the sizes of the internal phase increase and some of them get deformed. It is noted that the dispersed droplets in HIPEs are typically deformed into a polygonal shape,40 while here almost all the dispersed droplets are perfect spheres. It should be noted that the high volatility of the dispersed phase (toluene) facilitates the evaporation of the dispersed droplets during observation, which has been confirmed by the observation of a same sample with time. It can be seen from Figure 4 that the number of droplet decreased and the droplets separated from each other, indicating droplets evaporated and small ones disappeared during observation. The formation of these assembled BCP stabilized HIPE hydrogels was verified by rheological measurement. For all the samples under study, the concentration of BCP was kept at 1.0
Figure 5. Dynamic moduli G′ (filled) and G″ (hollow) of HIPE hydrogels with 80%, 83%, and 86% of diesel as the dispersed phase as a function of oscillatory shear frequency.
indicating that these HIPE hydrogels have viscoelastic property dominated by elasticity. No crossover is observed between G′ and G″ within the range of frequency from 0.3 to 500 rad s−1. The G′ values of these HIPE hydrogels with different volume fractions of the dispersed phase show weak dependence on frequencies, indicating that these HIPE hydrogels under study exhibit good tolerance to strain at the frequency range (Figure S4). It also can be seen that both the G′ and G″ increase with the rise of volume fraction of the internal phase in these HIPE hydrogels, consistent with the properties of the conventional HIPEs.41,42 Therefore, the formation of three-dimensional networks should be induced by the dispersed droplets interaction. 3.3. Efficiency and Stability. The formation of these HIPE hydrogels are stabilized by assembled BCP, and the BCP assembled into particles to stabilize the HIPE hydrogels. Therefore, these HIPE hydrogels are Pickering emulsions. It is believed that appropriate surface wettability is required for a particulate stabilizer in order to be strongly absorbed onto emulsions droplets. The increase of the deprotonation in the P4VP blocks enhances the hydrophobicity of the assembled
Figure 4. Optical images of HIPE hydrogel with 89% of toluene at after (a) 45, (b) 90, and (c) 180 s of evaporation. D
DOI: 10.1021/acs.iecr.6b00039 Ind. Eng. Chem. Res. XXXX, XXX, XXX−XXX
Article
Industrial & Engineering Chemistry Research particles, and these particles have to be absorbed on the surface of oils, leading to the formation of stable emulsions. Protonation of P4VP blocks with HCl as appropriate leads to dissolution of the P4VP blocks and failure of HIPE hydrogels. Conventional BCPs are also able to stabilize emulsions,25 but they are inefficient, where as high as 5−50 w/v % of the continuous phase is required. As a particulate emulsifier for HIPEs, it is noted that the reported polymer emulsifiers are usually cross-linked, such as chemical or physical cross-linked gels,7,8,17,18,27−29 chemical cross-linked hybrid copolymer,30 CCS polymer,22−24 and branched copolymer.31 To our best knowledge, no assembled BCPs have been reported as HIPE stabilizers. In the present work, the assembled BCPs are absolutely efficient to stabilize HIPEs. The emulsifying efficiency of the assembled BCP as HIPE stabilizers was studied by calculating the total toluene/water interfacial area (S) of these HIPE hydrogels from the following formulate: S = 4πR2 ×
3VT 3
4πR
=
3VT R
Scheme 1. (a) pH-Induced Assembly of BCPs and (b) pHInduced Formation of HIPE Hydrogels
oils and organic solvents, it means that these liquids can be transformed into hydrogels. As a result, it is believed that volatility of these HIPE hydrogels is much lower than that of pure oil; HIPE hydrogels are much less likely to spill, slosh, or splash, and that HIPE hydrogels are much less flammable than pure oils. Therefore, they would be less hazardous. However, it may be required that these organic solvents and oils can be separated easily from these HIPE hydrogels. As these HIPE hydrogels are stabilized by assembled BCP and it is well-known that the assembly of 4VPm-EGn-4VPm in water is responsive to pH value, the solvents and oils can be released by tuning pH values of the continuous phase in HIPE hydrogels, since the BCP can totally dissolve into water, leading to the collapse of these HIPE hydrogels. This process is called pH-triggered demulsification. The pH-triggered demulsification system has been mentioned in delivery of crude oil,30 and only a safe and odorless solvent dodecane has been studied so far.24 Figure 6a shows the process of pH-triggered demulsification, where a HIPE hydrogel was prepared with 86% of gasoline (dyed with oil red O), 14% of aqueous solution with 2% of assembled BCP (higher than 1% for reuse). The HIPE hydrogel separated into red upper (gasoline) layer and clear lower (BCP aqueous solution) layer after 1 min upon the addition of HCl (1 M) to tune the pH to 5. This result is consistent with the fact that no HIPE was formed using the BCP solution at pH 5. Control experiment showed that with the addition of the same amount of water into the HIPE hydrogel, no obvious change was observed, as the water just slightly decreased the volume fraction of the dispersed phase. It was also noted that no precipitant was observed as the BCP is totally dissolved into water, which should facilitate the purification of oils. After the removal of the upper layer, the pH of the aqueous solution can be adjusted back with the addition of NaOH (1 M), and the aqueous solution containing assembled BCP could be reused to stabilize HIPE hydrogels again by the addition of gasoline. As HCl reacts with NaOH to form NaCl, BCP solutions with different NaCl concentrations were used to prepare HIPE hydrogels. The mechanical properties of HIPE hydrogels with 83% of diesel as the dispersed phase with 0.2 and 0.5 M of NaCl in the continuous were measured by dynamic frequency measurements, and the results are shown in Figure 6b. From the results, it can be seen that after the addition of salt to the continuous aqueous phase, the G′ and G″ of hydrogels declined in comparison with HIPE hydrogels without salt. With the frequency reaching to 300 rad s−1, the elasticity of the HIPE hydrogels becomes sensitive to rapid movement, which may indicate that the physical junctions start to break at the critical
(3)
where R is the average toluene droplet radius, and VT is the volume of toluene included in the HIPE hydrogels. The total interfacial areas (S) of the HIPE hydrogels prepared with various dispersed phase volume ratios (σ) were calculated according to the above equation. The value of the interfacial area of toluene/water is about 5 × 105 μm2, which is much higher than the corresponding unassembled BCPs. The stability of the HIPE hydrogels as-prepared were investigated at 20 and 0 °C in closed vials. No change was observed over 12 months at 0 °C for HIPE hydrogels with 75%, 80%, 83%, 86%, and 89% of toluene in closed vials, showing that these HIPE hydrogels are stable at 0 °C. However, about 2% of the dispersed phase was separated from HIPE hydrogels in the first week although no further separation was observed at 20 °C. In all, these HIPE hydrogels showed high stability. The stability of emulsions could be classified into the stability of droplets and dispersion stability.43 The stability of droplets can be destroyed by coalescence and coarsening. The gel state of HIPE organogels suppresses the Brownian motions and collision of these dispersed droplets and thus hinders coalescence. The immiscibility of the continuous phase and dispersed phase creates a barrier to the diffusion of the organic phase and prevents coarsening. Thus, the HIPE hydrogels exhibit high droplet stability. The stability has been confirmed by optical microscopy and no obvious differences were observed for HIPE organogels freshly prepared and stored for 10 months. The high stability of dispersion might be explained by the interdroplets repulsion which could be indicated by the elasticity of HIPE hydrogel.43 The middle EG block in BCPs 4VPm-EGn-4VPm is completely soluble in water, but the end 4VP blocks cannot dissolve into water at neutral or basic condition, leading to assembly of the BCPs. The 4VP blocks react with H+, and then the protonated 4VP blocks are hydrophilic, resulting in total dissolution in water (as shown in Scheme 1a). The BCPs become amphiphilic and assembled at relative high pH, and the assembled BCPs tend to aggregate at interface to stabilize oil droplets dispersed in aqueous solution. The volume fraction of the dispersed phase is over the geometrical limit (74% for monodisperse droplets) for a dispersed phase, resulting in the formation of self-standing oil-in-water hydrogels (Scheme 1b). 3.4. Demulsification and Reusability. As these HIPE hydrogels can be prepared from smelly and highly flammable E
DOI: 10.1021/acs.iecr.6b00039 Ind. Eng. Chem. Res. XXXX, XXX, XXX−XXX
Article
Industrial & Engineering Chemistry Research
Figure 6. (a) A typical procedure for preparation and separation of gasoline (dyed with oil red O) by BCP stabilized HIPE hydrogels and (b) dynamic modulus G′ and G″ of HIPE hydrogels with 83% engine oil at NaCl concentrations of 0, 0.2, and 0.5 M as a function of oscillatory shear frequency.
■
frequency. Three dimensional networks still exist in the hydrogels, and the G′ and G″ of HIPE hydrogels with 0.2 and 0.5 M salt in their aqueous phases have similar values. The reusability of the aqueous phase (containing BCP) decreases the cost of the oil transformation and provides the possibility of practical use.
(1) Fay, J. A. Unusual Fire Hazard of LNG Tanker Spills. Combust. Sci. Technol. 1973, 7, 47−49. (2) Luketa-Hanlin, A. A review of large-scale LNG spills: experiments and modeling. J. Hazard. Mater. 2006, 132, 119−40. (3) Lee, J. C. Y.; Felske, J. D.; Ashgriz, N. Flame Propagation Across Gelled Alkane-In-Water Emulsions. Spill Sci. Technol. Bull. 2003, 8, 391−398. (4) Beerbower, A.; Nixon, J.; Philippoff, W.; Wallace, T. Thickened Fuels for Aircraft Safety. SAE Tech. Rep. 670364 1967, 670364. (5) Silverstein, M. S. PolyHIPEs: Recent advances in emulsiontemplated porous polymers. Prog. Polym. Sci. 2014, 39, 199−234. (6) Menner, A.; Powell, R.; Bismarck, A. Open Porous Polymer Foams via Inverse Emulsion Polymerization: Should the Definition of High Internal Phase (Ratio) Emulsions Be Extended? Macromolecules 2006, 39, 2034−2035. (7) Chen, Y.; Ballard, N.; Bon, S. A. F. Moldable high internal phase emulsion hydrogel objects from non-covalently crosslinked poly(Nisopropylacrylamide) nanogel dispersions. Chem. Commun. 2013, 49, 1524−1526. (8) Chen, Y.; Ballard, N.; Gayet, F.; Bon, S. A. F. High internal phase emulsion gels (HIPE-gels) from polymer dispersions reinforced with quadruple hydrogen bond functionality. Chem. Commun. 2012, 48, 1117−1119. (9) Ikem, V. O.; Menner, A.; Bismarck, A. High Internal Phase Emulsions Stabilized Solely by Functionalized Silica Particles. Angew. Chem., Int. Ed. 2008, 47, 8277−8279. (10) Menner, A.; Ikem, V.; Salgueiro, M.; Shaffer, M. S. P.; Bismarck, A. High internal phase emulsion templates solely stabilised by functionalised titania nanoparticles. Chem. Commun. 2007, 4274− 4276. (11) Zhou, J.; Qiao, X.; Binks, B. P.; Sun, K.; Bai, M.; Li, Y.; Liu, Y. Magnetic Pickering emulsions stabilized by Fe3O4 nanoparticles. Langmuir 2011, 27, 3308−16. (12) Lim, H.; Kassim, A.; Huang, N.; Ambar Yarmo, M. Palm-Based Nonionic Surfactants as Emulsifiers for High Internal Phase Emulsions. J. Surfactants Deterg. 2009, 12, 355−362. (13) Barbetta, A.; Cameron, N. R. Morphology and Surface Area of Emulsion-Derived (PolyHIPE) Solid Foams Prepared with Oil-Phase Soluble Porogenic Solvents: Span 80 as Surfactant. Macromolecules 2004, 37, 3188−3201. (14) Mork, S. W.; Rose, G. D.; Green, D. P. High-Performance Poly(butylene oxide)/Poly(ethylene oxide) Block Copolymer Surfactants for the Preparation of Water-in-Oil High Internal Phase Emulsions. J. Surfactants Deterg. 2001, 4, 127−134. (15) Williams, J. M. High Internal Phase Water-in-Oil Emulsions: Influence of Surfactants and Cosurfactants on Emulsion Stability and Foam Quality. Langmuir 1991, 7, 1370−1377.
4. CONCLUSIONS The assembled BCP-stabilized HIPE hydrogels exhibit high efficiency, easy recovery, and high reusability for a variety of smelly and flammable oils, enhancing oil safety during storage and transportation periods. The HIPE hydrogels are stabilized by solvent- or pH-driven assembled BCP 4VPm-EGn-4VPm, and the assembled BCP shows a high efficiency, where 1.0% of the continuous aqueous phase is enough to stabilize HIPE hydrogels. The HIPE hydrogels can trap a variety of organic solvents and oils, such as toluene, xylene, blended vegetable oil, canola oil, diesel, gasoline, and engine oil, and the volume fraction of the dispersed organic phase can be as high as 89%. The trapped organic solvents or oils can be released by simply tuning the pH value of the continuous phase to pH = 5, and the continuous aqueous phase containing BCP can be reused after neutralization. The transition of liquid oils into HIPE hydrogels is suitable for practical use to enhance oil safety and to prevent environmental damage.
■
ASSOCIATED CONTENT
* Supporting Information S
The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.iecr.6b00039. Characterization of triblock copolymer; SAXS fitting; formulation of HIPE hydrogels; strain sweeps (PDF)
■
REFERENCES
AUTHOR INFORMATION
Corresponding Author
*E-mail:
[email protected]. Fax: +61 3 5227 1103. Tel: +61 3 5227 2802. Notes
The authors declare no competing financial interest.
■
ACKNOWLEDGMENTS The SAXS measurements were conducted on the SAXS beamline at the Australian Synchrotron, Victoria, Australia. F
DOI: 10.1021/acs.iecr.6b00039 Ind. Eng. Chem. Res. XXXX, XXX, XXX−XXX
Article
Industrial & Engineering Chemistry Research (16) Viswanathan, P.; Johnson, D. W.; Hurley, C.; Cameron, N. R.; Battaglia, G. 3D Surface Functionalization of Emulsion-Templated Polymeric Foams. Macromolecules 2014, 47, 7091−7098. (17) Li, Z.; Ming, T.; Wang, J.; Ngai, T. High Internal Phase Emulsions Stabilized Solely by Microgel Particles. Angew. Chem., Int. Ed. 2009, 48, 8490−8493. (18) Sun, G.; Li, Z.; Ngai, T. Inversion of Particle-Stabilized Emulsions to Form High-Internal-Phase Emulsions. Angew. Chem., Int. Ed. 2010, 49, 2163−2166. (19) Li, Z.; Wei, X.; Ming, T.; Wang, J.; Ngai, T. Dual templating synthesis of hierarchical porous silica materials with three orders of length scale. Chem. Commun. 2009, 46, 8767−9. (20) Li, X.; Sun, G.; Li, Y.; Yu, J. C.; Wu, J.; Ma, G. H.; Ngai, T. Porous TiO(2) materials through Pickering high-internal phase emulsion templating. Langmuir 2014, 30, 2676−83. (21) Zhang, T.; Xu, Z.; Cai, Z.; Guo, Q. Phase inversion of ionomerstabilized emulsions to form high internal phase emulsions (HIPEs). Phys. Chem. Chem. Phys. 2015, 17, 16033−16039. (22) Chen, Q.; Xu, Y.; Cao, X.; Qin, L.; An, Z. Core cross-linked star (CCS) polymers with temperature and salt dual responsiveness: synthesis, formation of high internal phase emulsions (HIPEs) and triggered demulsification. Polym. Chem. 2014, 5, 175−185. (23) Chen, Q.; Deng, X.; An, Z. pH-induced inversion of water-in-oil emulsions to oil-in-water high internal phase emulsions (HIPEs) using core cross-linked star (CCS) polymer as interfacial stabilizer. Macromol. Rapid Commun. 2014, 35, 1148−52. (24) Chen, Q.; Cao, X.; Liu, H.; Zhou, W.; Qin, L.; An, Z. pHresponsive high internal phase emulsions stabilized by core crosslinked star (CCS) polymers. Polym. Chem. 2013, 4, 4092−4102. (25) Wu, R.; Menner, A.; Bismarck, A. Tough Interconnected Polymerized Medium and High Internal Phase Emulsions Reinforced by Silica Particles. J. Polym. Sci., Part A: Polym. Chem. 2010, 48, 1979− 1989. (26) Hughes, J. M.; Budd, P. M.; Tiede, K.; Lewis, J. Polymerized High Internal Phase Emulsion Monoliths for the Chromatographic Separation of Engineered Nanoparticles. J. Appl. Polym. Sci. 2015, 132, 41229. (27) Zhang, T.; Guo, Q. High internal phase emulsion (HIPE) organogels prepared from charge-driven assembled polymer organogels. Chem. Commun. 2013, 49, 11803−5. (28) Zhang, T.; Wu, Y.; Xua, Z.; Guo, Q. Hybrid high internal phase emulsion (HIPE) organogels with oil separation properties. Chem. Commun. 2014, 50, 13821−13824. (29) Chen, X.; Liu, K.; He, P.; Zhang, H.; Fang, Y. Preparation of Novel W/O Gel-Emulsions and Their Application in the Preparation of Low-Density Materials. Langmuir 2012, 28, 9275−9281. (30) Sun, J.; Yi, C.; Wei, W.; Zhao, D.; Hu, Q.; Liu, X. Nanohybrids from direct chemical self-assembly of poly(styrene-alt-maleic anhydride) as pH-responsive particulate emulsifiers. Langmuir 2014, 30, 14757−64. (31) Wei, W.; Wang, T.; Yi, C.; Liu, J.; Liu, X. Self-assembled micelles based on branched poly(styrene-alt-maleic anhydride) as particulate emulsifiers. RSC Adv. 2015, 5, 1564−1570. (32) Zhang, T.; Guo, Q. A new route to prepare multiresponsive organogels from a block ionomer via charge-driven assembly. Chem. Commun. 2013, 49, 5076−5078. (33) Wu, Y.; Zhang, T.; Xu, Z.; Guo, Q. High internal phase emulsion (HIPE) xerogels for enhanced oil spill recovery. J. Mater. Chem. A 2015, 3, 1906−1909. (34) Zhang, T.; Guo, Q. Polyoxometalate-based hybrid organogels prepared from a triblock copolymer via chargedriven assembly. RSC Adv. 2014, 4, 35055−35058. (35) Obeid, R.; Maltseva, E.; Thünemann, A. F.; Tanaka, F.; Winnik, F. M. Temperature Response of Self-Assembled Micelles of Telechelic Hydrophobically Modified Poly(2-alkyl-2-oxazoline)s in Water. Macromolecules 2009, 42, 2204−2214. (36) Li, Y.; Peng, B.; Chen, Y. Kinetically Trapped Block Copolymer Nano-Objects with Cylinder to Sphere Shape Transition Properties. Macromol. Chem. Phys. 2015, 216, 495−503.
(37) Salim, N. V.; Guo, Q. Multiple vesicular morphologies in AB/ AC diblock copolymer complexes through hydrogen bonding interactions. J. Phys. Chem. B 2011, 115, 9528−36. (38) Chevalier, Y.; Bolzinger, M.-A. Emulsions stabilized with solid nanoparticles: Pickering emulsions. Colloids Surf., A 2013, 439, 23−34. (39) Lissant, K. J. The geometry of high-internal-phase-ratio emulsions. J. Colloid Interface Sci. 1966, 22, 462−468. (40) Capron, I.; Cathala, B. Surfactant-free high internal phase emulsions stabilized by cellulose nanocrystals. Biomacromolecules 2013, 14, 291−6. (41) Pal, R. Rheology of high internal phase ratio emulsions. Food Hydrocolloids 2006, 20, 997−1005. (42) Binks, B. P.; Clint, J. H.; Whitby, C. P. Rheological Behavior of Water-in-Oil Emulsions Stabilized by Hydrophobic Bentonite Particles. Langmuir 2005, 21, 5307−5316. (43) Foudazi, R.; Qavi, S.; Masalova, I.; Malkin, A. Y. Physical chemistry of highly concentrated emulsions. Adv. Colloid Interface Sci. 2015, 220, 78−91.
G
DOI: 10.1021/acs.iecr.6b00039 Ind. Eng. Chem. Res. XXXX, XXX, XXX−XXX
