Temperature-jump relaxation kinetics at liquid/solid interfaces: fluorescence thermometry of porous silica heated by a Joule discharge

Abstract

Abstract : Temperature-jump relaxation techniques are adapted to measuring the kinetics of reversible reactions at interfaces of liquid phases/solid phases. In the present work, we determine whether fast temperature changes can be created within a packed bed of silica gel using Joule discharge heating. Fast heating of the surface of porous silica depends on the solution within the pores carrying current through the particle, since heat flow from the surrounding solution into the interior of the silica particle would generally be slow. To characterize the rate of heating of the silica surface, fluorescence thermometry was employed to measure the temperature rise at a liquid/solid interface on a microsecond time- scale. 9,10 dichloroanthracene (9,10 DCA) was found to be a suitable probe molecule for fast fluorescence measurement of temperature changes at alkylated silica surfaces. For 10 micrometers silica particles, we observe an exponential relaxation of the temperature-dependent fluorescence intensity with a decay time that corresponds to the rate of energy deposition in the sample. These results indicate that ionic current flows through the silica, uniformly heating the surface area of smaller particle-size silica, uniformly heating the surface area of smaller particle-size silica. Larger particle silica shows a slower thermal relaxation indicating non-conductive domains which are heated on a slower time- scale by thermal conduction.