Measuring kinetic energy changes in the mesoscale with low acquisition rates

© 2014 AIP Publishing. LLC. E.R., I.A.M., and R.A.R. acknowledge financial support from the Fundació Privada Cellex Barcelona, Generalitat de Catalunya Grant No. 2009-SGR-159, and from the MICINN (Grant No. FIS2011-24409). L.D. and E.R. acknowledge financial support from the Spanish Government (ENFASIS). L.D. acknowledges financial support from Comunidad de Madrid (MODELICO). We thank Antonio Ortiz-Ambriz, Juan M. R. Parrondo, and Félix Carrique for fruitful discussions. Dedicated to the memory of Professor D. Petrov.
We report on the measurement of the average kinetic energy changes in isothermal and nonisothermal quasistatic processes in the mesoscale, realized with a Brownian particle trapped with optical tweezers. Our estimation of the kinetic energy change allows to access to the full energetic description of the Brownian particle. Kinetic energy estimates are obtained from measurements of the mean square velocity of the trapped bead sampled at frequencies several orders of magnitude smaller than the momentum relaxation frequency. The velocity is tuned applying a noisy electric field that modulates the amplitude of the fluctuations of the position and velocity of the Brownian particle, whose motion is equivalent to that of a particle in a higher temperature reservoir. Additionally, we show that the dependence of the variance of the time-averaged velocity on the sampling frequency can be used to quantify properties of the electrophoretic mobility of a charged colloid. Our method could be applied to detect temperature gradients in inhomogeneous media and to characterize the complete thermodynamics of biological motors and of artificial micro and nanoscopic heat engines.
Comunidad de Madrid (MODELICO)
Spanish MICINN
Fundació Privada Cellex Barcelona, Generalitat de Catalunya
Spanish Government (ENFASIS)
Depto. de Estructura de la Materia, Física Térmica y Electrónica
Fac. de Ciencias Físicas
TRUE
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