Magnetic, Thermosensitive Microgels as Stimuli‐Responsive Emulsifiers Allowing for Remote Control of Separability and Stability of Oil in Water‐Emulsions

Brugger, Bastian; Richtering, Walter

doi:10.1002/adma.200700487

Cited by 188 publications

(178 citation statements)

References 32 publications

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“…More interestingly, by changing the pH, the noncoalescence can be switched to coalescence. The resultant pH-triggered coalescence holds promises for the invention of new "smart" materials and process enhancement in many emulsion-related applications (23)(24)(25).…”

mentioning

confidence: 99%

Non-coalescence of oppositely charged droplets in pH-sensitive emulsions

Liu

Seiffert

Thiele

et al. 2011

Proc. Natl. Acad. Sci. U.S.A.

100

102

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Like charges stabilize emulsions, whereas opposite charges break emulsions. This is the fundamental principle for many industrial and practical processes. Using micrometer-sized pH-sensitive polymeric hydrogel particles as emulsion stabilizers, we prepare emulsions that consist of oppositely charged droplets, which do not coalesce. We observe noncoalescence of oppositely charged droplets in bulk emulsification as well as in microfluidic devices, where oppositely charged droplets are forced to collide within channel junctions. The results demonstrate that electrostatic interactions between droplets do not determine their stability and reveal the unique pH-dependent properties of emulsions stabilized by soft microgel particles. The noncoalescence can be switched to coalescence by neutralizing the microgels, and the emulsion can be broken on demand. This unusual feature of the microgel-stabilized emulsions offers fascinating opportunities for future applications of these systems.stimuli-sensitive emulsions | limited coalescence | poly (N-isopropylacrylamide) microgels | Pickering emulsions | lab-on-a-chip E mulsions are multiphase systems, which consist of two immiscible liquids, one dispersed in another in the form of small droplets with submicron to micron sizes. Emulsions are used in food, cosmetics, medicine, coatings, paints, and a large number of other technical applications (1). Due to their large interfacial area, emulsions are thermodynamically unstable and have a tendency to undergo coalescence, a process during which two droplets merge into a bigger one, minimizing the surface energy (2). Certain molecules or materials, such as surfactants or solid particles, can be added to prevent coalescence, making emulsions kinetically stable. These emulsion stabilizers usually provide electrostatic repulsion, steric repulsion, and/or strength to the interfacial layer of the droplets, according to widely accepted theories. For example, when emulsion droplets are covered with an ionic surfactant, they carry like charges; these charges repel each other due to electrostatic interaction, which prevents droplet aggregation or coalescence. By contrast, when oppositely charged droplets are generated in an emulsion, they attract each other and coalescence is hastened; this phenomenon is the key event in processes like electrocoalescence (3, 4).In contrast to this classical behavior, unexpected noncoalescence of two oppositely charged droplets has been reported very recently (5, 6); these investigations show that under the influence of an electric field of sufficient strength, two oppositely charged water droplets recoil after contact rather than coalesce, depending on the curvature and local capillary pressure at the liquid bridge between two adjacent droplets. However, these studies were conducted with drops that were formed temporarily under the influence of an electric field in a continuous phase of air rather than with drops that are dispersed in a liquid. By contrast, stable emulsions, which consist of oppositely charg...

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mentioning

confidence: 99%

Non-coalescence of oppositely charged droplets in pH-sensitive emulsions

Liu

Seiffert

Thiele

et al. 2011

Proc. Natl. Acad. Sci. U.S.A.

100

102

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“…Exposed to heat, the gel changes conformation to open pores (Reproduced with kind permission from Reference [29]). …”

Section: Magnetic Field-responsivementioning

confidence: 99%

“…Also popular, is the synthesis of superparamagnetic iron oxide nanoparticles (SPION) of 10-20 nm diameter, carefully well dispersed in organic solvents. Interestingly, these SPIONs have been FDA approved as MRI contrast agents [25][26][27][28][29][30].…”

Section: Magnetic Field Responsive Polymersmentioning

confidence: 99%

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Responsive Polymers for Crop Protection

et al. 2010

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This review outlines the responsive polymer methods currently in use with their potential application to plant protection and puts forward plant-specific mechanisms as stimuli in newly devised methods for smart release of crop protection agents (CPAs). CPAs include chemicals (fungicides, insecticides, herbicides), biochemicals (antibiotics, RNAbased vaccines for plant viruses), semiochemicals (pheromones, repellents, allomones), microbial pesticides, growth regulators (insect and plant) or micronutrients, all with crop protection effects. This appraisal focuses on emerging uses of polymer nano-encapsulated CPAs. Firstly, the most interesting advances in controlled release methods are critically discussed with their advantages and drawbacks. Secondly, several plant-specific stimulibased smart methods are anticipated for use alongside the polymer nano-or microcapsules. These new CPA release methods are designed to (i) protect plants against infection produced by fungi or bacteria, and (ii) apply micro-nutrients when the plants need it the most. Thus, we foresee (i) the responsive release of nano-encapsulated bioinsecticides regulated by plant stress enzymes, and (ii) the delivery of micro-nutrients synchronized by the nature or intensity of plant root exudates. Such continued advances of nano-scale smart polymer-based CPAs for the protection of crops herald a "small revolution" for the benefit of sustainable agriculture.Keywords: responsive polymers; crop protection agent (CPA); CPA nanocapsule; nanoscience; nanotechnology; plant-specific stimuli; intelligent self-regulated release OPEN ACCESSPolymers 2010, 2 230 Glossary of TermsAllomone: a pheromone that induces a behavioral or physiological change in a member of another species that is of benefit to the producer. Bio-insecticide: the natural substance made and used for eliminating plant-eating insects. Cuticle: the layer of cutin (waxy waterproof substance, consisting of derivatives of fatty acids) covering the epidermis of the aerial parts of plants. Elicitor: a substance that induces the defense mechanisms in higher plants. Epidermis: the outer protective layer of plant cells. Parasitic plant: a plant that derives some or all of its sustenance from another plant. Perennial plant: a plant that lives for more than two years. Phloem: a plant tissue that conducts organic nutrients substances to all parts of the plant. Phytopathogen: an organism that causes a disease in a plant. RNA-based vaccines for plant viruses: Double-stranded RNA (dsRNA) is a RNA with two complementary strands, which is converted to small interfering (siRNA), involved in the RNA interference (RNAi) pathway, including plant viruses RNA silencing. Root exudate: any substance released through the pores of a diseased or injured plant root.

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“…To solve this problem, a few methods applying external forces such as electronic, magnetic, acoustic, and optical sources have been introduced. [12][13][14] Of these external force sources, an optical source that uses light as the energy source makes the fast analysis available, as it can produce ultra-high speed reaction. The light source with high resolution to control the microdroplet can be achieved by using the objective lens, which makes it another important strength of optical force.…”

Section: Introductionmentioning

confidence: 99%

Study for optical manipulation of a surfactant-covered droplet using lattice Boltzmann method

2014

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In this study, we simulated deformation and surfactant distribution on the interface of a surfactant-covered droplet using optical tweezers as an external source. Two optical forces attracted a single droplet from the center to both sides. This resulted in an elliptical shape deformation. The droplet deformation was characterized as the change of the magnitudes of surface tension and optical force. In this process, a non-linear relationship among deformation, surface tension, and optical forces was observed. The change in the local surfactant concentration resulting from the application of optical forces was also analyzed and compared with the concentration of surfactants subjected to an extensional flow. Under the optical force influence, the surfactant molecules were concentrated at the droplet equator, which is totally opposite to the surfactants behavior under extensional flow, where the molecules were concentrated at the poles. Lastly, the quasi-equilibrium surfactant distribution was obtained by combining the effects of the optical forces with the extensional flow. All simulations were executed by the lattice Boltzmann method which is a powerful tool for solving micro-scale problems. V C 2014 AIP Publishing LLC.

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Magnetic, Thermosensitive Microgels as Stimuli‐Responsive Emulsifiers Allowing for Remote Control of Separability and Stability of Oil in Water‐Emulsions

Cited by 188 publications

References 32 publications

Non-coalescence of oppositely charged droplets in pH-sensitive emulsions

Non-coalescence of oppositely charged droplets in pH-sensitive emulsions

Responsive Polymers for Crop Protection

Study for optical manipulation of a surfactant-covered droplet using lattice Boltzmann method

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