Osmotic pressure of suspensions comprised of charged microgels

Scotti, Andrea; Peláez-Fernández, Miguel; Gasser, Urs; Fernández‐Nieves, Alberto

doi:10.1103/physreve.103.012609

Cited by 22 publications

(36 citation statements)

References 83 publications

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“…This method concentrates the microgels slowly, with the system being allowed to equilibrate for multiple weeks in each case. [ 11 ] This method also avoids the potential for aggregation or poor redispersion of particles that can arise when samples are prepared from dried solids in experiments where volume fraction is controlled gravimetrically. As compared to other methods of tuning the microgel volume fraction, external osmotic pressure variation allows us to control the concentration of ULC particles reproducibly and reliably.…”

Section: Resultsmentioning

confidence: 99%

Emergence of Non‐Hexagonal Crystal Packing of Deswollen and Deformed Ultra‐Soft Microgels under Osmotic Pressure Control

Islam

Nguyen

Lyon

2021

Macromol. Rapid Commun.

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Highly solvent swollen poly(N‐isopropylacrylamide‐co‐acrylic acid) microgels are synthesized without exogenous crosslinker, making them extremely soft and deformable. These ultralow crosslinked microgels (ULC) are incubated under controlled osmotic pressure to provide a slow (and presumably thermodynamically controlled) approach to higher packing densities. It is found that ULC microgels show stable colloidal packing over a very wide range of osmotic pressures and thus packing densities. Surprising observation of co‐existence between hexagonal and square lattices is also made over the lower range of studied osmotic pressures, with microgels apparently changing shape from spheres to cubes in defects or grain boundaries. It is proposed that the unusual packing behavior observed for ULC microgels is due to the extreme softness of these particles, where deswelling causes deformation and shrinking of the particles that result in unique packing states governed by contributions to the entropy at the colloidal system, single particle and ionic levels. These observations further suggest that more detailed experimental and theoretical studies of ultra‐soft microgels are required to obtain a complete understanding of their behavior in packed and confined geometries.

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Section: Resultsmentioning

confidence: 99%

Emergence of Non‐Hexagonal Crystal Packing of Deswollen and Deformed Ultra‐Soft Microgels under Osmotic Pressure Control

Islam

Nguyen

Lyon

2021

Macromol. Rapid Commun.

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“…As the PNIPAm particles deform and deswell at large volume fractions, an effective volume fraction is conventionally used defined by ζ = N •V (T ), with N the particle number concentration and V (T ) the volume fraction of a particle in a dilute dispersion at temperature T as obtained by dynamic light scattering [39,45,46]. Values around and above ζ = 1 are possible with deformed particles and interpenetration of the PNIPAm shell [12,13,45,[47][48][49][50].…”

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confidence: 99%

“…Values around and above ζ = 1 are possible with deformed particles and interpenetration of the PNIPAm shell [12,13,45,[47][48][49][50]. Depending on the softness of pure PNIPAm particles the real volume fraction matches ζ up to approximately ζ = 0.8 [46,51]. At higher volume fractions the particles are not in swelling equilibrium [31].…”

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confidence: 99%

Glass-liquid and glass-gel transitions of soft-shell particles

et al. 2021

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We study the structure and dynamics of colloidal particles with a spherical hard core and a thermo-responsive soft shell over the whole phase diagram by means of small-angle X-ray scattering and X-ray photon correlation spectroscopy. By changing the effective volume fraction by temperature and particle concentration, liquid, repulsive glass and attractive gel phases are observed. The dynamics slow down with increasing volume fraction in the liquid phase and reflect a Vogel-Fulcher-Tamann behaviour known for fragile glass formers. We find a liquid-glass transition above 50 vol.% that is independent from the particles' concentration and temperature. In an overpacked state at effective volume fractions above 1, the dispersion does not show a liquid phase but undergoes a gel-glass transition at an effective volume fraction of 34 vol.%. At the same concentration, extrema of subdiffusive dynamics are found in the liquid phase at lower weight fractions.We interpret this as dynamic precursors of the glass-gel transition.

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“…As the dextran concentration increases, the nanogels experience increasing osmotic pressures, π , which can be measured by means of a membrane osmometer. 28,37 Then, multi-angle dynamic light scattering (DLS) measurements of dextran solutions and dextran-nanogel solutions allowed them to decouple the nanogel and dextran contribution to the scattering signal. In this way, the nanogel hydrodynamic radius and thus the nanogel volume, v , can be determined at different π .…”

Section: Introductionmentioning

confidence: 99%