Light‐induced self‐thermophoresis of Janus spheroidal nanoparticles

Abstract

A theoretical framework is provided for determining the self-thermophoretic velocity of a light irradiated spheroidal Janus nanoparticle consisting of symmetric dielectric and perfectly conducting semi-spheroids. The analysis is based on solving the linearized Joule heating problem due to uniform laser irradiance and on explicitly determining the temperature fields inside and outside the particle. We employ the thermoelectric (Peltier- Seebeck) methodology to find the surface self - induced temperature gradient and the related slip velocity which determines the autonomous phoretic (self - propulsion) mobility of the Janus particle. Simplified explicit expressions for the self - thermophoretic velocities of spheroidal (prolate and oblate) Janus particles in terms of their aspect ratios are found and few practical limiting cases (i.e., sphere, disk and needle) are also discussed.

Light-induced thermoosmosis about conducting ellipsoidal nanoparticles

“…Janus type) light-irradiated spherical [7,8] or non-spherical (e.g. spheroidal [10]) particles can in principle acquire a finite thermophoretic velocity.…”

AC Electrokinetics of Polarizable Tri-Axial Ellipsoidal Nano-Antennas and Quantum Dot Manipulation

“…The ACEO velocity field in Equation (43) decays to zero for large values of Ω∗ and has a maximum at Ω∗=0. The analytic expression for the Stokes stream-function Equation (42) and the associated velocity components Equation (43) for an induced ACEO flow past a sphere are identical with those given in [32]. A Cartesian leading-order representation of the same quadrupole-type velocity field in the DC limit (i.e., Ω∗=0) which is similar to Equation (41) (but without the last Faxen’s term), has been also obtained in [46].…”

“…In addition, the polarizability of the NP generates a tangential component of the electric field along the surface of the particle, which under the assumption of a thin Debye or electric double layer (EDL) results in a surface-slip velocity according to the Helmholtz Smoluchowski (HS) model [23] which drives a quadrupole-type ACEO motion in the solute (Figure 1). Since for typical micro-fluid applications, inertia effects can be neglected with respect to viscous ones, the long-range ACEO [24] or opto- [31,32] induced flow fields (forced by HS slippage), can be modeled by the Stokes momentum equation. Finally, treating the small-size QDs as free tracers, it is assumed that they are simply carried by the induced ACEO fluid motion (typical velocities of the order of few μm/s).…”

“…In this context, most fluorophores are characterized by two distinct emission and absorption frequency bands which are separated by the Stokes drift [33] (e.g., typical wave lengths of 346 nm and 445 nm for Alexa 532-type fluorophore) and for this reason ellipsoidal NAs possessing at least two resonant frequencies, are considered more effective NAs compared to the commonly used spherical NAs. It is also worth mentioning that non-spherical laser-heated conducting nanoparticles immersed in electrolyte (unlike spherical NPs), are generally subjected to a non-vanishing self-induced thermoosmotic (quadrupole-type) flow driven by the Seebeck effect [32]. Thus, it is easier to manipulate and control optical-induced thermoosmotic flow fields about orthotropic (ellipsoidal) NPs compared to say around a perfectly symmetric spherical particle.…”

Photoactivated Polymersome Nanomotors: Traversing Biological Barriers

“…Theh ypothesized mechanism of propulsion, which was previously shown to drive motility of Janus motors, [24] is photo-induced thermophoresis. [25] TheA u-hemisphere undergoes plasmonic absorbance,r esulting in an increase of the particle temperature and subsequent generation of at emperature gradient, which results in positive thermodiffusion (particles move from hot to cold regions). [26] Due to their high temperature,particles acquire sufficient kinetic energy to drive their propulsion.…”