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Université de Fribourg

Light induced inverse-square law interactions between nanoparticles: “mock gravity” at the nanoscale

Luis-Hita, J. ; Marqués, M. I. ; Delgado-Buscalioni, R. ; Sousa, N. de ; Froufe-Pérez, L. S. ; Scheffold, Frank ; Sáenz, J. J.

In: Physical Review Letters, 2019, vol. 123, no. 14, p. 143201

The interaction forces between identical resonant molecules or nanoparticles, optically induced by a quasimonochromatic isotropic random light field, are theoretically analyzed. In general, the interaction force exhibits a far-field oscillatory behavior at separation distances larger than the light wavelength. However, we show that the oscillations disappear when the frequency of the random...

Université de Fribourg

Colloidal dynamics and elasticity of dense wax particle suspensions over a wide range of volume fractions when tuning the softness by temperature

Yoon, Jiwon ; Scheffold, Frank ; Ahn, Kyung Hyun

In: Colloids and Surfaces A: Physicochemical and Engineering Aspects, 2019, vol. 576, p. 1–8

We report on the colloidal dynamics and rheology of liquid droplet emulsions and solid particle suspensions over a wide range of volume fractions. Diffusing wave spectroscopy and rheometry were utilized to study the micro/macroscale properties of 1-eicosene wax particles dispersed in water. By changing the temperature, the wax droplets change their properties from soft to hard or vice versa,...

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

When black and white make green: the surprising interplay of structure and pigments

Sai, Tianqi ; Wilts, Bodo D. ; Sicher, Alba ; Steiner, Ullrich ; Scheffold, Frank ; Dufresne, Eric R.

In: CHIMIA International Journal for Chemistry, 2019, vol. 73, no. 1, p. 47–50

The natural world is teeming with color, which originates either from the wavelength- dependent absorp- tion of light by pigments or from scattering from nanoscale structures, or both. While the latter ' structural color ' has been a topic of intense study in recent years, the most vibrant colors in nature involve contributions from both structure and pigment. The study of structure–pigment...

Université de Fribourg

Structure and sedimentation kinetics of dense suspensions of fibroblast cells

Zenuni, Arbnor ; Zhang, Chi ; Haeni, Laetitia ; Rothen-Rutishauser, Barbara ; Scheffold, Frank

In: CHIMIA International Journal for Chemistry, 2019, vol. 73, no. 1, p. 43–46

We investigate the structure and the dynamics of dense suspensions of NIH 3T3 fibroblast cells. Using two-photon microscopy we obtain three dimensional (3D) images from which the size and the packing structure of the dense cell suspensions can be extracted. In addition, we analyse the global time-dependent behaviour of the suspensions by time-lapse measurements of cell sedimentation. Since...

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

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

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...

Université de Fribourg

Nonequilibrium solid-solid phase transition in a lattice of liquid jets

Croccolo, Fabrizio ; Castellini, Stefano ; Scheffold, Frank ; Vailati, Alberto

In: Physical Review E, 2018, vol. 98, no. 6, p. 063104

Solid-solid phase transitions are commonly encountered at the atomic scale in alloys and in superatomic mesoscopic systems of colloidal particles. Here we investigate a solid-solid phase transition occurring at the macroscopic scale between lattices of liquid jets with different symmetries generated by convection in a horizontal layer of a binary liquid mixture. In the absence of a shear...