Thursday, August 11, 2016

Precise control and measurement of solid-liquid interfacial temperature and viscosity with dual-beam femtosecond optical tweezers in condensed phase

Dipankar Mondal, Paresh Mathur and Debabrata Goswami

We present a novel method of microrheology based on femtosecond optical tweezers, which in turn enables us to directly measure and control in situ temperature at microscale volumes at solid-liquid interface. A noninvasive pulsed 780 nm trapped bead spontaneously responds to its changes in environment induced by a co-propagating 1560 nm pulsed laser due to mutual energy transfer between solvent molecules and trapped bead. Strong absorption of the hydroxyl group by the 1560 nm laser creates local heating in individual and binary mixtures of water and alcohols. “Hot Brownian motion” of the trapped polystyrene bead gets reflected in the corner frequency deduced from power spectrum. Changes in corner frequency values enable us to calculate the viscosity as well as temperature at the solid-liquid interface. We show that these experimental results can also be theoretically ratified.

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