Université de Fribourg

Diffusing wave microrheology of highly scattering concentrated monodisperse emulsions

Kim, Ha Seong ; Şenbil, Nesrin ; Zhang, Chi ; Scheffold, Frank ; Mason, Thomas G.

In: Proceedings of the National Academy of Sciences, 2019, vol. 116, no. 16, p. 7766–7771

Motivated by improvements in diffusing wave spectroscopy (DWS) for nonergodic, highly optically scattering soft matter and by cursory treatment of collective scattering effects in prior DWS microrheology experiments, we investigate the low-frequency plateau elastic shear moduli G′p of concentrated, monodisperse, disordered oil-in- water emulsions as droplets jam. In such experiments, the...

Université de Fribourg

Brownian dynamics of colloidal microspheres with tunable elastic properties from soft to hard

Yoon, Jiwon ; Cardinaux, Frédéric ; Lapointe, Clayton ; Zhang, Chi ; Mason, Thomas G. ; Ahn, Kyung Hyun ; Scheffold, Frank

In: Colloids and Surfaces A: Physicochemical and Engineering Aspects, 2018, vol. 546, p. 360–365

We study the Brownian thermal motion of a colloidal model system made by emulsifying hot liquid α-eicosene wax into an aqueous surfactant solution of sodium dodecyl sulfate (SDS). When this waxy oil-in-water emulsion is cooled below α- eicosene's melting point of Tc ≃ 25 °C, the microscale emulsion droplets solidify, effectively yielding a dispersed particulate system. So, the...

Université de Fribourg

The liquid-glass-jamming transition in disordered ionic nanoemulsions

Braibanti, Marco ; Kim, Ha Seong ; ªenbil, Nesrin ; Pagenkopp, Matthew J. ; Mason, Thomas G. ; Scheffold, Frank

In: Scientific Reports, 2017, vol. 7, no. 1, p. 13879

In quenched disordered out-of-equilibrium many-body colloidal systems, there are important distinctions between the glass transition, which is related to the onset of nonergodicity and loss of low-frequency relaxations caused by crowding, and the jamming transition, which is related to the dramatic increase in elasticity of the system caused by the deformation of constituent objects. For...

Université de Fribourg

Entropic, electrostatic, and interfacial regimes in concentrated disordered ionic emulsions

Kim, Ha Seong ; Scheffold, Frank ; Mason, Thomas G.

In: Rheologica Acta, 2016, vol. 55, no. 8, p. 683–697

We develop a free energy model that describes two key thermodynamic properties, the osmotic pressure Π and the linear elastic shear modulus G′p (i.e. plateau storage modulus), of concentrated monodisperse emulsions which have isotropic, disordered, droplet structures, and are stabilized using ionic surfactants. This model effectively incorporates the concept of random close packing or...

Université de Fribourg

Structure of marginally jammed polydisperse packings of frictionless spheres

Zhang, Chi ; O'Donovan, Cathal B. ; Corwin, Eric I. ; Cardinaux, Frédéric ; Mason, Thomas G. ; Möbius, Matthias E. ; Scheffold, Frank

In: Physical Review E, 2015, vol. 91, no. 3, p. 032302

We model the packing structure of a marginally jammed bulk ensemble of polydisperse spheres. To this end we expand on the granocentric model [Clusel et al., Nature (London) 460, 611 (2009)], explicitly taking into account rattlers. This leads to a relationship between the characteristic parameters of the packing, such as the mean number of neighbors and the fraction of rattlers, and the radial...

Université de Fribourg

The jamming elasticity of emulsions stabilized by ionic surfactants

Scheffold, Frank ; Wilking, James N. ; Haberko, Jakub ; Cardinaux, Frédéric ; Mason, Thomas G.

In: Soft Matter, 2014, vol. 10, no. 28, p. 5040–5044

Oil-in-water emulsions composed of colloidal-scale droplets are often stabilized using ionic surfactants that provide a repulsive interaction between neighboring droplet interfaces, thereby inhibiting coalescence. If the droplet volume fraction is raised rapidly by applying an osmotic pressure, the droplets remain disordered, undergo an ergodic–nonergodic transition, and jam. If the applied...

Université de Fribourg

Crossover between entropic and interfacial elasticity and osmotic pressure in uniform disordered emulsions

Mason, Thomas G. ; Scheffold, Frank

In: Soft Matter, 2014, vol. 10, no. 36, p. 7109–7116

We develop a simple predictive model of the osmotic pressure Π and linear shear elastic modulus G′p of uniform disordered emulsions that includes energetic contributions from entropy and interfacial deformation. This model yields a smooth crossover between an entropically dominated G′p ∼...

Université de Fribourg

Linear and nonlinear rheology of dense emulsions across the glass and the jamming regimes

Scheffold, Frank ; Cardinaux, Frédéric ; Mason, Thomas G.

In: Journal of Physics: Condensed Matter, 2013, vol. 25, no. 50, p. 502101

We discuss the linear and nonlinear rheology of concentrated microscale emulsions, amorphous disordered solids composed of repulsive and deformable soft colloidal spheres. Based on recent results from simulation and theory, we derive quantitative predictions for the dependences of the elastic shear modulus and the yield stress on the droplet volume fraction. The remarkable agreement with...

Université de Fribourg

Elasticity and glassy dynamics of dense emulsions

Cardinaux, Frédéric ; Mason, Thomas G. ; Scheffold, Frank

In: AIP Conference Proceedings, 2013, vol. 1518, p. 222–226

We present a rheology and light scattering study of the dynamical properties of dense emulsions at volume fractions ranging from viscous liquid to deeply jammed states. From temporally and spatially revolved dynamic light scattering we obtain detailed information about the internal dynamics. Our measurements thus allow a direct study of heterogeneous nature of the relaxation processes involved in...

Université de Fribourg

Star colloids in nematic liquid crystals

Lapointe, Clayton P. ; Mayor, Kenny ; Mason, Thomas G.

In: Soft Matter, 2013, vol. 9, no. 32, p. 7843–7854

We present a study of the elastic alignment, accompanying director field distortions, and elastic pair interactions of star-shaped colloids suspended in aligned nematic liquid crystals. We design and fabricate lithographic colloids, “N-stars”, containing N rod-like protrusions (i.e. “rays” or “arms”) each having a constant angle between adjacent rays. N-star geometries contain concave...