2019 

Guillaume Duclos; Raymond Adkins; Debarghya Banerjee; Matthew S E Peterson; Minu Varghese; Itamar Kolvin; Arvind Baskaran; Robert A Pelcovits; Thomas R Powers; Aparna Baskaran; Federico Toschi; Michael F Hagan; Sebastian J Streichan; Vincenzo Vitelli; Daniel A Beller; Zvonimir Dogic Topological structure and dynamics of three dimensional active nematics Journal Article arXiv, 2019, (13 pages, 5 figures, plus Supplementary Information of 12 pages, 4 figures). Abstract  BibTeX  Tags: condmat.soft @article{e86486974c294689ad18cb25f012fe2e, title = {Topological structure and dynamics of three dimensional active nematics}, author = {Guillaume Duclos and Raymond Adkins and Debarghya Banerjee and {Matthew S E } Peterson and Minu Varghese and Itamar Kolvin and Arvind Baskaran and {Robert A } Pelcovits and {Thomas R } Powers and Aparna Baskaran and Federico Toschi and {Michael F } Hagan and {Sebastian J } Streichan and Vincenzo Vitelli and {Daniel A } Beller and Zvonimir Dogic}, year = {2019}, date = {20190101}, journal = {arXiv}, publisher = {Cornell University Library}, abstract = {Pointlike motile topological defects control the universal dynamics of diverse twodimensional active nematics ranging from shaken granular rods to cellular monolayers. A comparable understanding in higher dimensions has yet to emerge. We report the creation of threedimensional active nematics by dispersing extensile microtubule bundles in a passive colloidal liquid crystal. Lightsheet microscopy reveals the millimeterscale structure of active nematics with a single bundle resolution and the temporal evolution of the associated nematic director field. The dominant excitations of threedimensional active nematics are extended chargeneutral disclination loops that undergo complex dynamics and recombination events. These studies introduce a new class of nonequilibrium systems whose turbulentlike dynamics arises from the interplay between internally generated active stresses, the chaotic flows and the topological structure of the constituent defects.}, note = {13 pages, 5 figures, plus Supplementary Information of 12 pages, 4 figures}, keywords = {condmat.soft}, pubstate = {published}, tppubtype = {article} } Pointlike motile topological defects control the universal dynamics of diverse twodimensional active nematics ranging from shaken granular rods to cellular monolayers. A comparable understanding in higher dimensions has yet to emerge. We report the creation of threedimensional active nematics by dispersing extensile microtubule bundles in a passive colloidal liquid crystal. Lightsheet microscopy reveals the millimeterscale structure of active nematics with a single bundle resolution and the temporal evolution of the associated nematic director field. The dominant excitations of threedimensional active nematics are extended chargeneutral disclination loops that undergo complex dynamics and recombination events. These studies introduce a new class of nonequilibrium systems whose turbulentlike dynamics arises from the interplay between internally generated active stresses, the chaotic flows and the topological structure of the constituent defects.  
Xiao Xue; Luca Biferale; Mauro Sbragaglia; Federico Toschi Particle settling in a fluctuating multicomponent fluid under confinement Journal Article arXiv, 2019, (12pages, 7 figures). Abstract  BibTeX  Tags: condmat.soft, physics.compph, physics.fludyn @article{d03238a0027f4132ad45a1d7327e35d7, title = {Particle settling in a fluctuating multicomponent fluid under confinement}, author = {Xiao Xue and Luca Biferale and Mauro Sbragaglia and Federico Toschi}, year = {2019}, date = {20190101}, journal = {arXiv}, publisher = {Cornell University Library}, abstract = {We study the motion of a spherical particle driven by a constant volume force in a confined channel with a fixed square crosssection. The channel is filled with a mixture of two liquids under the effect of thermal fluctuations. We use the lattice Boltzmann method to simulate a fluctuating multicomponent fluid in the mixedphase, and particlefluid interactions are tuned to reproduce different wetting properties at the particle surface. The numerical setup is first validated in the absence of thermal fluctuations; to this aim, we quantitatively compute the drift velocity at changing the particle radius and compare it with previous experimental and numerical data. In the presence of thermal fluctuations, we study the fluctuations in the particle's velocity at changing thermal energy, applied force, particle size, and particle wettability. The importance of fluctuations with respect to the mean drift velocity is quantitatively assessed, especially in comparison to unconfined situations. Results show that confinement strongly enhances the importance of velocity fluctuations, which can be one order of magnitude larger than what expected in unconfined domains. The observed findings underscore the versatility of the lattice Boltzmann simulations in concrete applications involving the motion of colloidal particles in a highly confined environment in the presence of thermal fluctuations.}, note = {12pages, 7 figures}, keywords = {condmat.soft, physics.compph, physics.fludyn}, pubstate = {published}, tppubtype = {article} } We study the motion of a spherical particle driven by a constant volume force in a confined channel with a fixed square crosssection. The channel is filled with a mixture of two liquids under the effect of thermal fluctuations. We use the lattice Boltzmann method to simulate a fluctuating multicomponent fluid in the mixedphase, and particlefluid interactions are tuned to reproduce different wetting properties at the particle surface. The numerical setup is first validated in the absence of thermal fluctuations; to this aim, we quantitatively compute the drift velocity at changing the particle radius and compare it with previous experimental and numerical data. In the presence of thermal fluctuations, we study the fluctuations in the particle's velocity at changing thermal energy, applied force, particle size, and particle wettability. The importance of fluctuations with respect to the mean drift velocity is quantitatively assessed, especially in comparison to unconfined situations. Results show that confinement strongly enhances the importance of velocity fluctuations, which can be one order of magnitude larger than what expected in unconfined domains. The observed findings underscore the versatility of the lattice Boltzmann simulations in concrete applications involving the motion of colloidal particles in a highly confined environment in the presence of thermal fluctuations.  
Roberto Benzi; Thibaut Divoux; Catherine Barentin; S é; Mauro Sbragaglia; Federico Toschi Unified theoretical and experimental view on transient shear banding Journal Article arXiv, 2019, (5 pages, 4 figures  supplemental 5 pages, 4 figures). Abstract  BibTeX  Tags: condmat.soft, condmat.statmech, physics.fludyn @article{67228bed5d894c6688f967ac3899f499, title = {Unified theoretical and experimental view on transient shear banding}, author = {Roberto Benzi and Thibaut Divoux and Catherine Barentin and S é and Mauro Sbragaglia and Federico Toschi}, year = {2019}, date = {20190101}, journal = {arXiv}, publisher = {Cornell University Library}, abstract = {Dense emulsions, colloidal gels, microgels, and foams all display a solidlike behavior at rest characterized by a yield stress, above which the material flows like a liquid. Such a fluidization transition often consists of longlasting transient flows that involve shearbanded velocity profiles. The characteristic time for full fluidization, $tau_textf$, has been reported to decay as a powerlaw of the shear rate $dot gamma$ and of the shear stress $sigma$ with respective exponents $alpha$ and $beta$. Strikingly, the ratio of these exponents was empirically observed to coincide with the exponent of the HerschelBulkley law that describes the steadystate flow behavior of these complex fluids. Here we introduce a continuum model based on the minimization of an outofequilibrium free energy that captures quantitatively all the salient features associated with such textittransient shearbanding. More generally, our results provide a unified theoretical framework for describing the yielding transition and the steadystate flow properties of yield stress fluids.}, note = {5 pages, 4 figures  supplemental 5 pages, 4 figures}, keywords = {condmat.soft, condmat.statmech, physics.fludyn}, pubstate = {published}, tppubtype = {article} } Dense emulsions, colloidal gels, microgels, and foams all display a solidlike behavior at rest characterized by a yield stress, above which the material flows like a liquid. Such a fluidization transition often consists of longlasting transient flows that involve shearbanded velocity profiles. The characteristic time for full fluidization, $tau_textf$, has been reported to decay as a powerlaw of the shear rate $dot gamma$ and of the shear stress $sigma$ with respective exponents $alpha$ and $beta$. Strikingly, the ratio of these exponents was empirically observed to coincide with the exponent of the HerschelBulkley law that describes the steadystate flow behavior of these complex fluids. Here we introduce a continuum model based on the minimization of an outofequilibrium free energy that captures quantitatively all the salient features associated with such textittransient shearbanding. More generally, our results provide a unified theoretical framework for describing the yielding transition and the steadystate flow properties of yield stress fluids. 
publications
2019 

Topological structure and dynamics of three dimensional active nematics Journal Article arXiv, 2019, (13 pages, 5 figures, plus Supplementary Information of 12 pages, 4 figures).  
Particle settling in a fluctuating multicomponent fluid under confinement Journal Article arXiv, 2019, (12pages, 7 figures).  
Unified theoretical and experimental view on transient shear banding Journal Article arXiv, 2019, (5 pages, 4 figures  supplemental 5 pages, 4 figures). 