Charge Controlled Swelling of Microgel Particles

Fernández‐Nieves, Alberto; Fernández-Barbero, A.; Vincent, Brian; Nieves, FJ de las

doi:10.1021/ma991520l

Cited by 221 publications

(193 citation statements)

References 24 publications

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“…We directly image the noncoalescence of these oppositely charged droplets in a microfluidic device (7)(8)(9). In our study, the charges of the droplets originate from the chemical composition of the stabilizing microgel particles that sit on the droplet surface (10). The stabilization of emulsions through the use of these microgels is at first glance very similar to Pickering emulsions (11)(12)(13)(14), which are solid-stabilized emulsions discovered a century ago (15,16).…”

mentioning

confidence: 86%

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

Liu

Seiffert

Thiele

et al. 2011

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

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: 86%

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

Liu

Seiffert

Thiele

et al. 2011

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

102

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“…[1,[17][18][19][20], which leads not only to thermo-responsive microgels but also to pH responsive ones. There are some theoretical and experimental publications studying the influence of the co-monomer type and concentration on swelling/deswelling behaviour of charged microgel particles [17][18][19][20][21]. Due to the deprotonation of carboxylic (-COOH) groups, the interchain electrostatic repulsion and the increase in osmotic pressure lead to an increase in particle size [1,12,18].…”

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confidence: 99%

The Effect of Co-Monomer Content on the Swelling/Shrinking and Mechanical Behaviour of Individually Adsorbed PNIPAM Microgel Particles

et al. 2011

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Abstract:The swelling/deswelling behaviour of microgel particles in the bulk and at the surface was studied and correlated to their mechanical properties. We focused on two kinds of particles: pure PNIPAM and PNIPAM-co-AAc particles. It was shown that the two step volume phase transition found for PNIPAM-co-AAc particles in the bulk disappears after the adsorption at the surface and only a one step transition was identified. The transition temperature increased strongly with increasing the co-monomer content. The dependence of the Young's modulus of the adsorbed microgel particles on the temperature and the co-monomer content was discussed. The investigations were performed via DLS and SFM.

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“…Remarkably, these restrictions do not necessarily apply to suspensions of soft microgels, which are cross-linked polymer particles immersed in a solvent that can exist in either swollen or deswollen states, depending on external conditions like temperature (6) and pH (7). Indeed, microgel suspensions containing a small fraction of larger particles can crystallize without defects by shrinking the larger particles to a size that is identical to that of the smaller and more abundant microgel particles (8).…”

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confidence: 99%

The role of ions in the self-healing behavior of soft particle suspensions

Scotti

Gasser

Herman

et al. 2016

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

185

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Impurities in crystals generally cause point defects and can even suppress crystallization. This general rule, however, does not apply to colloidal crystals formed by soft microgel particles [Iyer ASJ, Lyon LA (2009) Angew Chem Int Ed 48:4562-4566], as, in this case, the larger particles are able to shrink and join the crystal formed by a majority of smaller particles. Using small-angle X-ray scattering, we find the limit in large-particle concentration for this spontaneous deswelling to persist. We rationalize our data in the context of those counterions that are bound to the microgel particles as a result of the electrostatic attraction exerted by the fixed charges residing on the particle periphery. These bound counterions do not contribute to the suspension osmotic pressure in dilute conditions, as they can be seen as internal degrees of freedom associated with each microgel particle. In contrast, at sufficiently high particle concentrations, the counterion cloud of each particle overlaps with that of its neighbors, allowing these ions to freely explore the space outside the particles. We confirm this scenario by directly measuring the osmotic pressure of the suspension. Because these counterions are then no longer bound, they create an osmotic pressure difference between the inside and outside of the microgels, which, if larger than the microgel bulk modulus, can cause deswelling, explaining why large, soft microgel particles feel the squeeze when suspended with a majority of smaller particles. We perform small-angle neutron scattering measurements to further confirm this remarkable behavior.oint defects in crystalline materials disrupt the crystal structure and often prevent crystallization. This is the case, for instance, when large particles are introduced in a crystal of smaller particles. Bragg illustrated the consequences of this disruption using soap bubbles (1). In metal melts, a size mismatch of 15% between the atoms suppresses crystallization (2), and, in hard spheres, which constitute an important model system for condensed matter, a polydispersity above 12% also prevents crystallization (3). Furthermore, the polydispersity in hard sphere crystals does not exceed 5.7%, due to local segregation of dissimilar particles during crystallization (4, 5).Remarkably, these restrictions do not necessarily apply to suspensions of soft microgels, which are cross-linked polymer particles immersed in a solvent that can exist in either swollen or deswollen states, depending on external conditions like temperature (6) and pH (7). Indeed, microgel suspensions containing a small fraction of larger particles can crystallize without defects by shrinking the larger particles to a size that is identical to that of the smaller and more abundant microgel particles (8). This deswelling was hypothesized to result either from the direct interaction between large and small particles or from the osmotic pressure exerted by the small microgels on the larger ones (2). Here, we show that none of these effects drive this proces...

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Charge Controlled Swelling of Microgel Particles

Cited by 221 publications

References 24 publications

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

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

The Effect of Co-Monomer Content on the Swelling/Shrinking and Mechanical Behaviour of Individually Adsorbed PNIPAM Microgel Particles

The role of ions in the self-healing behavior of soft particle suspensions

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