Violation of the fluctuation-dissipation theorem in confined driven colloids

¹ Dipartimento di Ingegneria Chimica, DICCISM, Università di Pisa I-56126 Pisa, Italy
² Dipartimento di Fisica “Enrico Fermi”, Università di Pisa Largo B. Pontecorvo 3, I-56127 Pisa, Italy
³ SOFT-INFM-CNR - P.zza A. Moro 2, I-00185, Roma, Italy

Corresponding authors: r.mauri@ing.unipi.it dino.leporini@df.unipi.it

Received: 27 July 2006
Accepted: 20 October 2006

Abstract

Analytical models describing a colloidal particle confined in a harmonic well, e.g. provided by an optical trap, and driven by shear flows are presented. Violation of both static and dynamic fluctuation-dissipation theorem (FDT) is clearly seen, thus clarifying the connection between such FDT violation and the breakdown of the detailed balance. The simple shear and Taylor-Couette velocity fields are studied in detail, showing that loosening confinement enhances FDT violations. In addition, cases violating FDT but not energy equipartition are presented. For the cases under study, an effective temperature is defined via the static FDT, which appears to be more physically sound than the one defined via the time-dependent FDT. Confining sheared colloidal particles by optical tweezers yields considerable FDT violation.