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Micro-rheology of a sticking transition

We have studied the sticking process of a colloid, suspended in a fluid medium by an optical tweezer, to a rigid substrate. The evolution of the frictional coupling between the two as a function of their separation is detected by the diffusivity of the particle and also by its phase sensitive response to an in-plane external oscillatory drive applied to the substrate. Upon contact, the coupling changes abruptly from viscous to elastic for a rigid silica particle, while it evolves slowly with time, similar to aging in glassy systems, for a soft and deformable polystyrene particle. Depending on the relative strengths of the particle-substrate interaction, the tweezer-potential and the external drive, three regimes of dynamics - stuck, aging and non-stuck – are observed in the dynamical phase diagram.

P. Sharma , S. Ghosh , S. Bhattacharya “Microrheology of a sticking transition” Nature Physics 4, 960(2008)[supplementary]

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