Orientation of Janus particles under thermal fields: The role of internal mass anisotropy

Olarte-Plata, Juan D.; Bresme, Fernando

doi:10.1063/5.0008237

Cited by 17 publications

(23 citation statements)

References 19 publications

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“…[24][25][26] Very recently, we demonstrated that the mass anisotropy, an intrinsic property of heterogeneous JNPs, couples with the heat flux to impart a thermophoretic torque on the JNP, and the particles adopt a preferential orientation in the direction of the thermal field. 27 This thermal-orientation e↵ect has been reported at molecular scales, in water and other polar molecules. 28,29 In this work, we investigate JNPs immersed in liquids as a model system to achieve anisotropic heating.…”

Section: Introductionmentioning

confidence: 63%

Spatial Control of Heat Flow at the Nanoscale Using Janus Particles

et al. 2021

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Janus Nanoparticles (JNP) feature heterogeneous compositions bringing opportunities in technological and medical applications. We investigate using non-equilibrium molecular dynamics simulations the temperature field generated around heated spherical Janus Nanoparticles to assess the performance of the particles in the generation of anisotropic heating. We demonstrate that the contrasting interfacial thermal conductances of the fluid-material interfaces arising from the heterogeneous composition of the JNP can be exploited to control the thermal fields around the nanoparticle leading to a temperature di↵erence between both sides of the nanoparticle (temperature contrast) that is significant for particles comprising regions with disparate hydrophilicity.We illustrate this idea using simplified atomistic and complex models of gold nanoparticles passivated with hydrophobic and hydrophilic ligands in water. Furthermore, we introduce a continuum model to predict the temperature contrast as a function of the interfacial thermal conductance and nanoparticle size. We further show that, unlike 1 homogeneous nanoparticles, the interfacial fluid temperature depends on the interfacial thermal conductance of Janus nanoparticles.

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Section: Introductionmentioning

confidence: 63%

Spatial Control of Heat Flow at the Nanoscale Using Janus Particles

et al. 2021

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“…Hence, irrespective of the negligible temperature gradient on the gold side, the rotational velocity is sensitive to the thermo-osmotic mobility coefficient , which can thus confidently be inferred from the measurement. Compared to the substantial thermal-conductivity contrast, the role of mass anisotropy, which can lead to similar polarization effects [ 89 – 91 ], plays presumably a negligible role in our experiments, as the thin gold cap makes the Janus particle only slightly bottom heavy.…”

Section: Resultsmentioning

confidence: 95%

Thermotaxis of Janus particles

et al. 2021

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The interactions of autonomous microswimmers play an important role for the formation of collective states of motile active matter. We study them in detail for the common microswimmer-design of two-faced Janus spheres with hemispheres made from different materials. Their chemical and physical surface properties may be tailored to fine-tune their mutual attractive, repulsive or aligning behavior. To investigate these effects systematically, we monitor the dynamics of a single gold-capped Janus particle in the external temperature field created by an optically heated metal nanoparticle. We quantify the orientation-dependent repulsion and alignment of the Janus particle and explain it in terms of a simple theoretical model for the induced thermoosmotic surface fluxes. The model reveals that the particle’s angular velocity is solely determined by the temperature profile on the equator between the Janus particle’s hemispheres and their phoretic mobility contrast. The distortion of the external temperature field by their heterogeneous heat conductivity is moreover shown to break the apparent symmetry of the problem. Graphic abstract

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“…Density ratio and total polarization a. Density ratio: Introducing the auxiliary quantities β A,a ≡ p max v A,a λ A,a /[Dρ(0)], Eqs. (26) and (27) evaluated at x = 0 and x → ∞, respectively, yield…”

Section: Vanishing Integralmentioning

confidence: 99%

“…On one hand, physical modelling aimed at a better understanding and characterization of types of activity and propulsion of individual active particles [9][10][11][12][13][14][15][16][17] and their interactions upon mutual encounters [18][19][20], encounters with walls [21,22] or when exposed to external fields [23][24][25][26][27]. On the other hand, a huge body of simulations and theories (e.g., [4,6,[28][29][30][31][32][33][34][35][36][37][38][39][40][41][42][43][44][45][46]) has aimed at the emerging collective properties of very large assemblies of active particles.…”

Section: Introductionmentioning

confidence: 99%

Polarization-Density Patterns of Active Particles in Motility Gradients

Auschra,

Holubec,

Söker

et al. 2020

Preprint

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The co-localization of density modulations and emerging particle polarization is a characteristic feature of active matter in the vicinity of motility gradients. It therefore provides a robust tool to detect intrinsic microscopic activity by mesoscale observations. We employ the active-Brownianparticle model to address the density and polarization profiles of a single Janus-type swimmer in the vicinity of an abrupt activity step. The derived results nicely agree with measurements of polarization and density modulations of a single hot microswimmer at a motility step presented in the accompanying experimental paper [1]. Qualitative similarities to interfacial properties at motilityinduced phase separations are observed. We generalize the theoretical framework to situations where the swimmer's propulsion speed depends on its orientation. Theory results are discussed and explained within a simplified two-species model.

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Orientation of Janus particles under thermal fields: The role of internal mass anisotropy

Cited by 17 publications

References 19 publications

Spatial Control of Heat Flow at the Nanoscale Using Janus Particles

Spatial Control of Heat Flow at the Nanoscale Using Janus Particles

Thermotaxis of Janus particles

Polarization-Density Patterns of Active Particles in Motility Gradients

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