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Université de Fribourg

Giant enhanced diffusion of gold nanoparticles in optical vortex fields

Albaladejo, Silvia ; Marqués, Manuel I. ; Scheffold, Frank ; Sáenz, Juan Jose

In: Nano Letters, 2009, vol. 9, no. 10, p. 3527–3531

We study the diffusion of a metal nanoparticle in the nonconservative force field of an optical vortex lattice. Radiation pressure in the vortex array is shown to induce a giant enhancement over the free thermal diffusion. Langevin dynamics simulations show that the diffusion coefficient of (50 nm radius) gold particles at room temperature is enhanced by 2 orders of magnitude at power densities...

Université de Fribourg

Photocount statistics in mesoscopic optics

Balog, Sandor ; Zakharov, Pavel ; Scheffold, Frank ; Skipetrov, S. E.

In: Physical Review Letters, 2006, vol. 97, p. 103901

We report the first observation of the impact of mesoscopic fluctuations on the photocount statistics of coherent light scattered in a random medium. A Poisson photocount distribution of the incident light widens and gains additional asymmetry upon transmission through a suspension of small dielectric spheres. The effect is only appreciable when the average number of photocounts becomes...

Université de Fribourg

Modulated 3D cross-correlation light scattering: Improving turbid sample characterization

Block, Ian D. ; Scheffold, Frank

In: Review of Scientific Instruments, 2010, vol. 81, no. 12, p. 123107

Accurate characterization using static light scattering (SLS) and dynamic light scattering (DLS) methods mandates the measurement and analysis of singly scattered light. In turbid samples, the suppression of multiple scattering is therefore required to obtain meaningful results. One powerful technique for achieving this, known as 3D cross-correlation, uses two simultaneous light scattering...

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

Controlling dispersion forces between small particles with artificially created random light fields

Brügger, Georges ; Froufe-Pérez, Luis S. ; Scheffold, Frank ; Sáenz, Juan José

In: Nature Communications, 2015, vol. 6, p. 7460

Appropriate combinations of laser beams can be used to trap and manipulate small particles with optical tweezers as well as to induce significant optical binding forces between particles. These interaction forces are usually strongly anisotropic depending on the interference landscape of the external fields. This is in contrast with the familiar isotropic, translationally invariant, van der Waals...

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

Quasi-real-time analysis of dynamic near field scattering data using a graphics processing unit

Cerchiari, Giovanni ; Croccolo, Fabrizio ; Cardinaux, Frédéric ; Scheffold, Frank

In: Review of Scientific Instruments, 2012, vol. 83, no. 10, p. 106101

We present an implementation of the analysis of dynamic near field scattering (NFS) data using a graphics processing unit. We introduce an optimized data management scheme thereby limiting the number of operations required. Overall, we reduce the processing time from hours to minutes, for typical experimental conditions. Previously the limiting step in such experiments, the processing time is now...

Université de Fribourg

Jamming and overpacking fuzzy microgels: Deformation, interpenetration, and compression

Conley, Gaurasundar M. ; Aebischer, Philippe ; Nöjd, Sofi ; Schurtenberger, Peter ; Scheffold, Frank

In: Science Advances, 2017, vol. 3, no. 10, p. e1700969

Tuning the solubility of fuzzy polymer microgels by external triggers, such as temperature or pH, provides a unique mechanism for controlling the porosity and size of colloidal particles on the nanoscale. As a consequence, these smart microgel particles are being considered for applications ranging from viscosity modifiers and sensing to drug delivery and as models for the glass and the...

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

Superresolution microscopy of the volume phase transition of pNIPAM microgels

Conley, Gaurasundar M. ; Nöjd, Sofi ; Braibanti, Marco ; Schurtenberger, Peter ; Scheffold, Frank

In: Colloids and Surfaces A: Physicochemical and Engineering Aspects, 2016, vol. 499, p. 18–23

Hierarchical polymer structures such as pNIPAM microgels have been extensively studied for their ability to undergo structural and physical transformations that can be controlled by external stimuli such as temperature, pH or solvent composition. However, a direct three-dimensional visualization of individual particles in-situ has so far been hindered by insufficient resolution, with optical...