Photophoresis - a Forgotten Force ??

Autor(en)

Helmuth Horvath

Abstrakt

In general a force will act on a particle illuminated by light or other radiation and absorbing part of the flux, and as a consequence a motion will result. It is caused by the interaction of gas molecules with the particle’s surface, which is hotter than the surroundings. This surface must be inhomogeneous with respect to accommodation and/or temperature. Gas molecules, impacting and reflected from the particle’s surface with accommodation, transfer some momentum from the particle and thus cause the force. For a temperature variation on the particle’s surface, the force points from the hot to the cold part, thus in the direction of the incident radiation, and under very special conditions it can be the opposite. A particle’s surface having a variation in accommodation coefficient will cause a force from the locations of higher to lower accommodation. Usually this will cause both a linear force and a torque. The latter in combination with Brownian rotation will result in a zero net force. But it is possible that an external torque acting on the particles causes an orientation. The torque can be caused by magnetic or electric fields on magnetic or electric dipoles in the particles or by gravity orienting inhomogeneous particles. For micrometer- and nanometer-sized particles, the photophoretic force can exceed gravity. Photophoresis is important for levitation in the stratosphere and for planet formation, it can also be used for on-line particle separation, or in clean-room technology or in geo-engineering.

Organisation(en)

Aerosolphysik und Umweltphysik

Journal

KONA: powder and particle journal

Band

31

Seiten

181-199

Anzahl der Seiten

19

ISSN

0288-4534

DOI

https://doi.org/10.14356/kona.2014009

Publikationsdatum

2014

Peer-reviewed

Ja

ÖFOS 2012

103039 Aerosolphysik

Schlagwörter

ASJC Scopus Sachgebiete

Allgemeiner Maschinenbau, Allgemeine chemische Verfahrenstechnik, Allgemeine Chemie, Allgemeine Materialwissenschaften

Link zum Portal

https://ucrisportal.univie.ac.at/de/publications/24fbc774-78cf-4535-9195-4beaaf2a0cf6