Surfactant-Free Emulsions with Erasable Triggered Phase Inversions

Subscriber access provided by CORNELL UNIVERSITY LIBRARY

Article

Surfactant-free emulsions with erasable triggered phase inversions Yiwen Chen, Zhen Wang, Dingguan Wang, Ning Ma, Cancan Li, and Yapei Wang Langmuir, Just Accepted Manuscript • DOI: 10.1021/acs.langmuir.6b03189 • Publication Date (Web): 28 Sep 2016 Downloaded from http://pubs.acs.org on September 29, 2016

Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a free service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are accessible to all readers and citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.

Langmuir is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.

Page 1 of 17

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

Langmuir

Surfactant-free emulsions with erasable triggered phase inversions Yiwen Chen,† Zhen Wang,‡ DingguanWang,‡ Ning Ma,*, †, § Cancan Li,† and Yapei Wang*, ‡ †

School of Materials Science and Engineering, University of Science and Technology

Beijing, Beijing 100083, China. ‡

Department of Chemistry, Renmin University of China, Beijing 100872, China.

§

College of Materials Science and Chemical Engineering, Harbin Engineering

University, Harbin 150001, China.

ACS Paragon Plus Environment

Langmuir

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

Page 2 of 17

ABSTRACT: Complex emulsions including double emulsions and high-internal-phase emulsions (HIPEs) are wonderful templates for producing porous polymeric materials. Yet surfactants and multiple emulsifications are generally needed. In this work, surfactant-free

complex

emulsions

are

successfully

prepared

by

using

a

CO2-responsive block copolymer through one-step emulsification. Phase inversion from HIPEs to double emulsions happens in one system upon the change of polymer amphiphilicity as a result of CO2 triggering. The one-step emulsion method offers great convenience for converting the block copolymer into porous 3D scaffolds and particles. Moreover, CO2 triggering is erasable so that the polymer can be repeatedly used for controllable complex emulsions as well as porous materials.


Page 3 of 17

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

Langmuir

Emulsions have been extensively used as soft templates for materials with massive production and special function. In particular, complex emulsions including double emulsions and high internal phase emulsions (HIPEs) are especially at the forefront of devising solid materials with well-defined porous morphologies.1-4 Interfacial active surfactants are generally needed to maintain the long-term stability of emulsion systems at early stage. Yet their difficulty of removal may cause risks to the application of emulsion-templated materials.5,

6

Surfactant-free emulsification is

coming into focus for fabricating complex emulsions by using amphiphilic polymers.7-10 The polymers acting as both the emulsifier at interface and emulsion matrix in disperse phase should have ideal amphiphilicity to induce the phase inversion and stabilize the whole emulsion system. In addition to synthetic strategies for precisely tailoring polymer amphiphilicity, supramolecular routes with the use of stimuli-responsive polymers are superior on account of convenience and economy cost.11-17 Though many stimuli-responsive polymers have been exploited, only a few of them were successfully extended to build surfactant-free emulsions.18 More insights and attempts are expected to readily expand this field and build new polymer porous matrix. Tailoring the polymer amphiphilicity by carbon dioxide (CO2) is rising as a new choice for directing controllable self-assembly.19 The precise regulation of polymer amphiphilicity by changing the purging amount of CO2 also affords great opportunities for exploiting controllable emulsions.20 There have been studies that emulsification and demulsification processes can be reversed by CO2 or N2 bubbling


Langmuir

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

using CO2-responsive surfactant or particles.5,

Page 4 of 17

21-23

However, the preparation of

multiple complex emulsions in one polymer system without the help of surfactants is more challenging. To do that, the polymer amphiphilicity has to locate within a wide range for triggering different phase inversion. In this communication, a CO2-responsive block copolymer was synthesized intending to build surfactant-free complex emulsions by only adjusting the amount of CO2. Complex emulsions including HIPE (W/O) and double emulsion (W/O/W) were successfully formed which could be subsequently solidified into porous networks or particles, respectively. More importantly, the CO2 triggering is erasable in this system so that the polymer can be recycled upon removal of CO2. The CO2-responsive block copolymer of polymethylmethacrylate-b-dimethylamino propyl methacrylamide (PMMA-b-PDMAPMA) was synthesized by reversible addition fragmentation chain transfer polymerization (RAFT) of the corresponding monomers.

The

PMMA block

provides hydrophobic

contribution

to

the

amphiphilicity and also improves mechanical performance of the solidified matrix. It should be properly long to be steadily trapped in the oil phase. Meanwhile, long PMMA chain could also enhance the steric repulsion among emulsion droplets and thus prevent their coalescence.6,

24

The PDMAPMA block is CO2-responsive and

provides hydrophilic contribution to the amphiphilicity when the tertiary amine moieties are protonated. The change of polymer amphiphilicity relies on the protonation degree of tertiary amine groups in the PDMAPMA blocks. If necessary, CO2 that has been associated with PDMAPMA can be erased by heating or purging


Page 5 of 17

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

Langmuir

inert gas into the system. Specifically, the block ratio and molecular weight of the block copolymer (PMMA-b-PDMAPMA) were carefully determined by NMR spectroscopy and gel permeation chromatography (see details in Supporting Information). For preparing surfactant-free emulsions, the PMMA-b-PDMAPMA diblock copolymer together with a probing dye of Nile Red was dissolved in chloroform as an oil phase. Without addition of any other surfactants, this polymer solution was emulsified in water straightforwardly with a water/oil ratio of 5:1 via high-speed homogenization. In contrast, the oil phase is imaged as red color and the water phase is dark under fluorescent microscopy observation. A gel-like W/O emulsion with microscopic polyhedral structure was obtained, where the internal water phase was surrounded by thin film of external oil phase (Figure 1b, 1e and Figure S3). These results conform to the features of HIPE, indicating the formation of a complex emulsion of W/O HIPE. The PDMAPMA segment turns more hydrophilic when it is protonated upon bubbling CO2 in the water-oil system. The change of polymer amphiphilicity as a result of PDMAPMA protonation causes the phase inversion. As shown in Figure 1d, 1g and Figure S4, after purging CO2 with a flow rate of 80 mL/min for one minute or longer time, the oil phase is inversed as the dispersion phase with loading multiple water droplets in each oil droplet, representing a transition from W/O HIPE to W/O/W double emulsion. According to Bancroft rule, the formation of more internal W/O interfaces for stabilizing internal water droplets in the double emulsion can be attributed to the increased hydrophilicity of copolymer.


Langmuir

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

Page 6 of 17

Figure 1. (a) Schematic illustration of emulsion phase inversions triggered by CO2. (b-d) Bright-field microscopy images and (e-g) fluorescence microscopy images (under

excitation

of

blue

channel)

of

emulsions

prepared

by

using

PMMA-b-PDMAPMA under different CO2 bubbling time: 0 s (b, e); 10 s (c, f); 60 s (d, g).

It is interestingly found that decreasing the purging amount of CO2 leads to a different emulsion morphology. As shown in Figure 1c and 1f, W/O/W double emulsion was still obtained when CO2 was purged for only 10 s. However, the number of inner water droplets is remarkably reduced and most oil droplets contain only one water droplet. It is assumed that the amphiphilicity as a result of partial protonation of tertiary amine groups in the PDMAPMA block with purging less CO2 is not enough to stabilize the inner water/oil interfaces, which induces Ostwald ripening and the


Page 7 of 17

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

Langmuir

subsequent coalescence of internal water droplets. To confirm that the internal phase of double emulsions is composed of water but not CO2 gas, the water phase was loaded with a water-soluble dye of sodium fluorescein before emulsification. Fluorescence microscopy reveals that the internal phases are green, corresponding to the imaging colour of sodium fluorescein under excitation of blue channel (Figure S5). It should be noted that CO2 flowing through the emulsion system can take away some organic solvent, which may change the water-oil ratio and cause emulsion phase inversion based on the Ostwald packing theory. As a control experiment, the emulsion system was purged by nitrogen with the same flowing rate as CO2 for 10 s. A W/O HIPE was formed (Figure S6), indicating that the slight evaporation of oil phase has no evident effect on the emulsion morphology. In other words, it is the change of amphiphilicity that mainly contributes to the phase inversion upon CO2 purging.

Figure 2. (a) Schematic change of molecular structure of the PMMA-b-PDMAPMA copolymer in the process of protonation. 1H NMR studies of the copolymer in D2O with the CO2 purging time of 0 s (b); 10 s (c); 60 s (d), respectively.


Langmuir

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

Page 8 of 17

Great insights were provided into the protonation process of PMMA-b-PDMAPMA upon the stepwise introduction of CO2. The copolymers were typically dispersed in deuteroxide (D2O) and bubbled by CO2 with different time for

1

H NMR

measurements. The protons marked as e, f, g and h are ascribed to tertiary amine group on PDMAPMA block (Figure 2a). As shown in Figure 2b, proton signals at 1.83 ppm, 2.27 ppm, 3.02 ppm, and 3.05 ppm referring to the unprotonated PDMAPMA block are relatively weak because of hydrophobic nature of PMMA-b-PDMAPMA in D2O. Chemical shifts of the protons marked as e and f in PDMAPMA segments are expected to move downfield if the nitrogen atom of tertiary amine group was protonated.25 A tiny peak at 2.68 ppm illustrates that PDMAPMA has been slightly protonated before CO2 triggering, which may be due to the partial protonation of tertiary amine groups in neutral water. Yet this slight protonation is extremely important to provide appropriate amphiphilicity for satisfying the formation of W/O HIPE. When the PMMA-b-PDMAPMA-D2O solution was purged with CO2 for 10 s, the proton signal marked as e’ downshifts and is also intensified due to the enhanced protonation of the PDMAPMA segments. In addition, the appearance of the peak at 3.26 ppm marked as f’ further indicates the protonation of tertiary amine groups (Figure 2c). Upon purging CO2 for 60 s, the proton signals are significantly strengthened due to the increased solubility of copolymer in D2O (Figure 2d). The evolution of chemical shifts accounts for the change of polymer amphiphilicity by CO2 triggering. Moreover, distinguished decrease of pH and rise of polymer charge provide additional evidences for supporting the protonation of PDMAPMA in


Page 9 of 17

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

Langmuir

aqueous solution upon CO2 purging (Figure S7).

Figure 3. (a) Optical photograph and (b) scanning electron microscopy (SEM) images of HIPE-based material after crosslinking by dibromobutane. (c-d) Scanning electron microscopy (SEM) images of emulsion-based materials prepared by using PMMA-b-PDMAPMA under different CO2 bubbling time: 10 s (c); 60 s (d).

To realize their full potential, the surfactant-free complex emulsions as stated above were solidified into porous matrix upon the removal of organic solvents. PMMA-b-PDMAPMA in the W/O HIPE was cross-linked with the addition of dibromobutane which is supposed to react with the tertiary amine groups to form quaternary ammonium salt (Figure 3a). As a consequence of cross-linking, the polymer network structure was maintained after the complete removal of chloroform, yielding a kind of three-dimensional scaffold with porous structure (Figure 3b). Drying the double emulsions could produce hollow particles and porous particles depending on the morphology of inner water droplets (Figure 3c and 3d).


Langmuir

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

Figure 4. (a) Schematic illustration of the removal of CO2 and the reuse of PMMA-PDMAPMA for controllable emulsion. (b-d) Bright-field microscopy and (e-g) fluorescence microscopy images of emulsions prepared by using recycled PMMA-b-PDMAPMA under different CO2 bubbling time: 0 s (b, e); 10 s (c, f); 60 s (d, g).

Notably, CO2 as a form of carbonic acid that is associated with PDMAPMA can be fully erased under heating or purging inert gas such as nitrogen. In this regard, these porous structures composed of protonated copolymers (before cross-linking) are expected to be reused without residual effect on the emulsion inversions. As shown in Figure 4, CO2 was removed under heating in a vacuum oven at 70oC and the


Page 10 of 17

Page 11 of 17

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

Langmuir

PMMA-b-PDMAPMA copolymers were reused to experience emulsification and CO2 triggering for another time. After protonating and erasing the copolymer for three cycles, the same trend of phase inversions was maintained, repeatedly generating W/O HIPE and double emulsion before and after CO2 purging, respectively. These results indicate the great advantage of this CO2-responsive block copolymer for building recyclable porous polymeric materials by using the templates of complex emulsions. In summary, we presented a versatile strategy for preparing complex emulsions without the use of surfactants. The building block of PMMA-b-PDMAPMA is ultra-sensitive to CO2 stimulus and becomes amphiphilic along with the protonation of tertiary amine groups in PDMAMPA segments. The change of polymer amphiphilicity based on the protonation degree directs the phase inversion from W/O HIPE to W/O/W double emulsion, enabling the easy preparation of well-defined porous polymeric materials. Moreover, the block copolymers can be fully recovered once the bound CO2 is removed and reformed into specific porous materials via emulsion method. It is envisioned that these porous materials could be readily used as scaffolds for loading functional substances. We also believe that this study will lay the groundwork and provide valuable inspirations for controllable emulsions based on the concept of tuning polymer amphiphilicity.


Langmuir

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

ASSOCIATED CONTENT Supporting Information. This material is available free of charge via the Internet at http://pubs.acs.org. Materials, instruments and characterizations, experimental details and supplementary figures are included here.

AUTHOR INFORMATION Corresponding Author Email: [email protected]; [email protected]. Author Contributions Y.C. and Z.W. contributed equally to this work. Notes The authors declare no competing financial interest.

ACKNOWLEDGMENT This work was financially supported by the National Natural Science Foundation of China (51373197, 21422407, 21674127, and 21404008).

REFERENCES (1) Garti, N.; Bisperink, C. Double Emulsions: Progress and Applications. Curr. Opin.

Colloid In. 1998, 3, 657-667. (2) Khan, A. Y.; Talegaonkar, S.; Iqbal, Z.; Ahmed F. J.; Khar, R. K. Multiple


Page 12 of 17

Page 13 of 17

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

Langmuir

Emulsions: An Overview. Curr. Drug Deliv. 2006, 3, 429-443. (3) Datta, S. S.; Abbaspourrad, A.; Amstad, E.; Fan, J.; Kim, S. H.; Romanowsky, M.; Shum, H. C.; Sun, B. J.; Utada, A. S.; Windbergs, M.; Zhou S. B.; Weitz, D. A. 25th Anniversary Article: Double Emulsion Templated Solid Microcapsules: Mechanics and Controlled Release. Adv. Mater. 2014, 26, 2205-2218. (4) Wang, Y.; Zhang, C.; Tang, C.; Li, J.; Shen, K.; Liu, J.; Qu, X.; Li, J.; Wang, Q.; Yang,

Z.

Emulsion Interfacial Synthesis of

Asymmetric

Janus Particles.

Macromolecules 2011, 44, 3787-3794. (5) Jiang, J.; Zhu, Y.; Cui, Z.; Binks, B. P. Switchable Pickering Emulsions Stabilized by Silica Nanoparticles Hydrophobized In Situ with a Switchable Surfactant. Angew.

Chem., Int. Ed. 2013, 52, 12373-12376. (6) Huang, X.; Fang, R.; Wang, D.; Wang, J.; Xu, H.; Wang Y.; Zhang, X.Tuning Polymeric Amphiphilicity via Se-N Interactions: Towards One-Step Double Emulsion for Highly Selective Enzyme Mimics. Small 2015, 11, 1537-1541. (7) Hanson, J. A.; Chang, C. B.; Graves, S. M.; Li, Z. B.; Mason, T. G.; Deming, T. J. Nanoscale Double Emulsions Stabilized by Single-Component Block Copolypeptides.

Nature 2008, 455, 85-88. (8) Hong, L.; Sun, G.; Cai, J.; Ngai, T. One-Step Formation of W/O/W Multiple Emulsions Stabilized by Single Amphiphilic Block Copolymers. Langmuir 2012, 28, 2332-2336. (9) Huang, X.; Yang, Y.; Shi, J.; Ngo, H. T.; Shen, C.; Du, W.; Wang, Y. High-Internal-Phase Emulsion Tailoring Polymer Amphiphilicity towards an Efficient


Langmuir

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

NIR-Sensitive Bacteria Filter. Small 2015, 11, 4876-4883. (10) Wu, D.; Xu, F.; Sun, B.; Fu, R.; He, H.; Matyjaszewski, K. Design and Preparation of Porous Polymers. Chem. Rev. 2012, 112, 3959-4015. (11) Chen, D.; Jiang, M. Strategies for Constructing Polymeric Micelles and Hollow Spheres in Solution via Specific Intermolecular Interactions. Acc. Chem. Res. 2005,

38, 494-502. (12) Ge, Z.; Liu, S. Functional Block Copolymer Assemblies Responsive to Tumor and Intracellular Microenvironments for Site-Specific Drug Delivery and Enhanced Imaging Performance. Chem. Soc. Rev. 2013, 42, 7289-7325. (13) Zhang, Z.; Ma, R.; Shi, L. Cooperative Macromolecular Self-Assembly toward Polymeric Assemblies with Multiple and Bioactive Functions. Acc. Chem. Res. 2014,

47, 1426-1437. (14) Sanchez-Sanchez, A.; Fulton, D. A.; Pomposo, J. A. pH-Responsive Single-Chain Polymer Nanoparticles Utilizing Dynamic Covalent Enamine Bonds.

Chem. Commun. 2014, 50, 1871-1874. (15) Thompson, K. L.; Fielding, L. A.; Mykhaylyk, O. O.; Lane, J. A.; Derry, M. J.; Armes, S. P. Vermicious Thermo-Responsive Pickering Emulsifiers. Chem. Sci. 2015,

6, 4207-4214. (16) Stuart, M. A. C.; Huck, W. T. S.; Genzer, J.; Mueller, M.; Ober, C.; Stamm, M.; Sukhorukov, G. B.; Szleifer, I.; Tsukruk, V. V.; Urban, M.; Winnik, F.; Zauscher, S.; Luzinov, I.; Minko, S. Emerging Applications of Stimuli-Responsive Polymer Materials. Nature Mater. 2010, 9, 101-113.


Page 14 of 17

Page 15 of 17

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

Langmuir

(17) Xu, H.; Cao, W.; Zhang, X. Selenium-Containing Polymers: Promising Biomaterials for Controlled Release and Enzyme Mimics. Acc. Chem. Res. 2013, 46, 1647-1658. (18) Besnard, L.; Marchal, F.; Paredes, J. F.; Daillant, J.; Pantoustier, N.; Perrin, P.; Guenoun, P. Multiple Emulsions Controlled by Stimuli-Responsive Polymers. Adv.

Mater. 2013, 25, 2844-2848. (19) Yan, Q.; Zhou, R.; Fu, C.; Zhang, H.; Yin, Y.; Yuan, J. CO2-Responsive Polymeric Vesicles that Breathe. Angew. Chem., Int. Ed. 2011, 50, 4923-4927. (20) Xiong, D.; Cui, G.; Wang, J.; Wang, H.; Li, Z.; Yao, K.; Zhang, S. Reversible Hydrophobic–Hydrophilic Transition of Ionic Liquids Driven by Carbon Dioxide.

Angew. Chem., Int. Ed. 2015, 54, 7265-7269. (21) Liu, Y.; Jessop, P. G.; Cunningham, M.; Eckert, C. A.; Liotta, C. L. Switchable Surfactants. Science 2006, 313, 958-960. (22) Qian, Y.; Zhang, Q.; Qiu, X.; Zhu, S. CO2-Responsive DiethylaminoethylModified Lignin Nanoparticles and Their Application as Surfactants for CO2/N2-SwitchablePickering Emulsions. Green Chem. 2014, 16, 4963-4968. (23) Liu, P.; Lu, W.; Wang, W.-J.; Li, B.-G.; Zhu, S. Highly CO2/N2-Switchable Zwitterionic Surfactant for Pickering Emulsions at Ambient Temperature. Langmuir 2014, 30, 10248-10255. (24) Garti, N.; Aserin, A. Double Emulsions Stabilized by Macromolecular Surfactants. Adv. Colloid Interface Sci. 1996, 65, 37-69. (25) Das, A.; Ghosh, S.; Ray, A. R. Unveiling the Self-Assembly Behavior of


Langmuir

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

Copolymers of AAc and DMAPMA in Situ to Form Smart Hydrogels Displaying Nanogels-within-Macrogel Hierarchical Morphology. Polymer 2011, 52, 3800-3810.


Page 16 of 17

Page 17 of 17

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

Langmuir

Table of Contents


Surfactant-Free Emulsions with Erasable Triggered Phase Inversions

Recommend Documents