Biomedical subjects

Jesús Santana-Solano

Publications and source records attributed to Jesús Santana-Solano.

4 recordsLinked to original sources

PubMed2006

Direct measurement of colloidal particle rotation and field dependence in alternating current electrohydrodynamic flows.

We have measured the influence of both applied alternating current (AC) field strength and frequency on the electrohydrodynamic (EH) flows present in colloidal systems near an electrode surface. The effect of the flows is visualized by the rotation of the colloids, fluorescently labeled by a novel technique involving EH-driven aggregation of much smaller tracer colloids to the surface of the larger colloids. Our results show an E2 dependence of these flows, consistent with an induced charge mechanism for effective colloidal interactions. We have also observed a crossover in frequency that suggests a change in the origin of the induced charge, consistent with predictions from available theory. The EH flows appear to be hydrodynamically screened inside clusters, as evidenced by the lack of rotation of interior colloids and the cluster-size independent rotation rate of colloids on the boundary.

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PubMed2005

Short-time dynamics in quasi-two-dimensional colloidal suspensions.

The short-time dynamic properties of colloidal particles in quasi-two-dimensional geometries are studied by digital video microscopy. We demonstrate experimentally that the effective-two-dimensional physical quantities such as the dynamic structure factor, the hydrodynamic function, and the hydrodynamic diffusion coefficients are related in exactly the same manner as their three-dimensional counterparts.

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PubMed2003

Effective pair potential between confined charged colloidal particles.

The pair correlation function g(r) between like-charged colloidal particles in quasi-two-dimensional geometries is measured by optical microscopy for a wide range of particle concentrations and various degrees of confinement. The effective pair potential u(r) is obtained by deconvoluting g(r) via Monte Carlo computer simulations. Our results confirm the existence of a long-range attractive component of u(r) and the appearance of an extra attractive term under stringent confinement.

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PubMed2002

Short-time dynamics of colloidal particles confined between two walls.

The short-time dynamics of colloidal particles in a quasi-two-dimensional geometry is studied by digital video microscopy. The particles (polystyrene spheres) are suspended in water and confined between two parallel glass plates, forming an effective two-dimensional system. The (effective) two-dimensional van Hove function G(r,t) and its self and distinct part are measured with a time resolution of 1/30 s. We found that the general behavior of these time-correlation functions (and their Fourier transforms) is quite similar to that of their three-dimensional counterparts. The effects of the strong hydrodynamic coupling of the particles motion to the walls and that due to the hydrodynamic interactions between particles are contained in the (effective) hydrodynamic function H(k) obtained from the initial slope of F(k,t) [the Fourier transform of G(r,t)]. We found that H(k), as a function of the wave vector k and particle concentration, exhibits a similar qualitative behavior to the hydrodynamic function in homogeneous three-dimensional suspensions of hard spheres. We also found in our systems that the particle fluctuations relax only by self-diffusion for wave vectors where the static structure factor S(k)=1. This result is important for measurements of self-diffusion dynamics in three-dimensional systems by light scattering techniques.

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