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Université de Fribourg

Pathways and challenges towards a complete characterization of microgels

Scheffold, Frank

In: Nature Communications, 2020, vol. 11, no. 1, p. 4315

Due to their controlled size, sensitivity to external stimuli, and ease-of-use, microgel colloids are unique building blocks for soft materials made by crosslinking polymers on the micrometer scale. Despite the plethora of work published, many questions about their internal structure, interactions, and phase behavior are still open. The reasons for this lack of understanding are the...

Université de Fribourg

Colloidal gelation, a means to study elasto-capillarity effects in foam

Mikhailovskaya, Alesya ; Trappe, Véronique ; Salonen, Anniina

In: Soft Matter, 2020, vol. 16, no. 9, p. 2249–2255

We explore the evolution of the mechanical properties of a coarsening foam containing colloidal particles that undergo a sol–gel transition in the continuous phase. This enables us to investigate the impact of elasto-capillarity on foam mechanics over a wide range of elasto-capillary numbers. Right after initiating aggregation the foam mechanics is predominantly determined by the elasticity...

Université de Fribourg

Chemistry of alkaline earth metals: It is not all ionic and definitely not boring!

Fromm, Katharina M.

In: Coordination Chemistry Reviews, 2020, vol. 408, p. 213193

Some scientists might consider group 2 chemistry as “boring, closed shell and all ionic, aqueous chemistry, where everything is known! It is not worth investigating”. How wrong they are! Far from forming only purely ionic compounds, this review will shed light on some spectacular molecules, showing that alkaline earth metal ions can behave similar to transition metal ions. After general...

Université de Fribourg

Accounting for effective interactions among charged microgels

Aguirre-Manzo, L. A. ; Ledesma-Motolinía, Mónica ; Rojas-Ochoa, Luis Fernando ; Trappe, Véronique ; Callejas-Fernández, J. ; Haro-Pérez, Catalina ; González-Mozuelos, P.

In: Physical Review E, 2019, vol. 100, no. 3, p. 032602

We introduce a theoretical approach to describe structural correlations among charged permeable spheres at finite particle concentrations. This theory explicitly accounts for correlations among microions and between microions and macroions and allows for the proposal of an effective interaction among macroions that successfully captures structural correlations observed in poly- N -isopropyl...

Université de Fribourg

Relationship between rheology and structure of interpenetrating, deforming and compressing microgels

Conley, Gaurasundar M. ; Zhang, Chi ; Aebischer, Philippe ; Harden, James L. ; Scheffold, Frank

In: Nature Communications, 2019, vol. 10, no. 1, p. 2436

Thermosensitive microgels are widely studied hybrid systems combining properties of polymers and colloidal particles in a unique way. Due to their complex morphology, their interactions and packing, and consequentially the viscoelasticity of suspensions made from microgels, are still not fully understood, in particular under dense packing conditions. Here we study the frequency-dependent...

Université de Fribourg

Observation of strongly heterogeneous dynamics at the depinning transition in a colloidal glass

Şenbil, Nesrin ; Gruber, Markus ; Zhang, Chi ; Fuchs, Matthias ; Scheffold, Frank

In: Physical Review Letters, 2019, vol. 122, no. 10, p. 108002

We study experimentally the origin of heterogeneous dynamics in strongly driven glass-forming systems. Thereto, we apply a well-defined force with a laser line trap on individual colloidal polystyrene probe particles seeded in an emulsion glass composed of droplets of the same size. Fluid and glass states can be probed. We monitor the trajectories of the probe and measure displacements and...

Université de Fribourg

Effect of anisotropic diffusion on spinodal decomposition

Vuijk, Hidde Derk ; Brader, Joseph M. ; Sharma, Abhinav

In: Soft Matter, 2019, vol. 15, no. 6, p. 1319–1326

We study the phase transition dynamics of a fluid system in which the particles diffuse anisotropically in space. The motivation to study such a situation is provided by systems of interacting magnetic colloidal particles subject to the Lorentz force. The Smoluchowski equation for the many-particle probability distribution then acquires an anisotropic diffusion tensor. We show that in...

Université de Fribourg

Tunable 2D binary colloidal alloys for soft nanotemplating

Fernández-Rodríguez, Miguel Ángel ; Elnathan, Roey ; Ditcovski, Ran ; Grillo, Fabio ; Conley, Gaurasundar Marc ; Timpu, Flavia ; Rauh, Astrid ; Geisel, Karen ; Ellenbogen, Tal ; Grange, Rachel ; Scheffold, Frank ; Karg, Matthias ; Richtering, Walter ; Voelcker, Nicolas H. ; Isa, Lucio

In: Nanoscale, 2018, vol. 10, no. 47, p. 22189–22195

The realization of non-close-packed nanoscale patterns with multiple feature sizes and length scales via colloidal self-assembly is a highly challenging task. We demonstrate here the creation of a variety of tunable particle arrays by harnessing the sequential self-assembly and deposition of two differently sized microgel particles at the fluid–fluid interface. The two-step process is...