Biomedical subjects

E Ramé

Publications and source records attributed to E Ramé.

3 recordsLinked to original sources

PubMed2005

Wetting by simple room-temperature polymer melts: deviations from Newtonian behavior.

The hydrodynamics near moving contact lines of two room-temperature polymer melts, polyisobutylene (PIB) and polystyrene (PS), are different from those of a third polymer melt, polydimethylsiloxane (PDMS). While all three fluids exhibit Newtonian behavior in rotational rheological measurements, a model of the hydrodynamics near moving contact lines which assumes Newtonian behavior of the fluid accurately describes the interface shape of a variety of PDMS fluids but fails to describe the interface deformation by viscous forces in PIB and PS. The magnitude of the deviations from the model and the distance along the liquid-vapor interface over which they are seen increase with increasing capillary number. We conclude that the wetting behaviors of PIB and PS are influenced by weak elasticity in these low molecular weight melts and that dynamic wetting is more sensitive to this elasticity than standard rheometric techniques.

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PubMed2004

Characterizing the microscopic physics near moving contact lines using dynamic contact angle data.

Directly probing the fluid flow and liquid-vapor interface shape in the microscopic immediate vicinity of the moving contact line can only be accomplished in very specific and isolated cases. Yet this physics is critical to macroscopic dynamic wetting. Here we examine the microscopic (or inner) physics of spreading silicone fluids using data of macroscopic dynamic contact angle versus Capillary number Ca=U mu/sigma. This dynamic contact angle is precisely defined so that it can be related back to the microscopic behavior through detailed theory. Our results indicate that the parameters describing the inner region have a detectable dependence on spreading velocity when this velocity exceeds a critical value. This dependence is not scaled (i.e., the data are not collapsed) by Ca, which suggests that an additional time scale must be present in the model of the inner region.

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PubMed1996

Microscopic and Macroscopic Dynamic Interface Shapes and the Interpretation of Dynamic Contact Angles.

We have studied shapes of dynamic fluid interfaces at distances </=1700 µm from the moving contact line at capillary numbers (Ca) ranging from 10(-3) to 10(-1). Near the moving contact line where viscous deformation is important, an analysis valid to O(1) in Ca describes the shape of the fluid interface. Static capillarity should describe the interface shape far from the contact line. We have quantitatively determined the extent of the regions described by the analysis with viscous deformation and by a static shape as a function of Ca. We observe a third portion of the interface between the two regions cited above, which is not described by either the analysis with viscous deformation or a static shape. In this third region the interface shape is controlled by viscous and gravitational forces of comparable magnitude. We detect significant viscous deformation even far from the contact line at Ca approximately > 0.01. Our measured dynamic contact angle parameter extracted by fitting the analysis with viscous deformation to the shape near the moving contact line coincides with the contact angle of the static-like shape far from the contact line. We measure and explain the discrepancy between this dynamic contact angle parameter and the apparent contact angles based on meniscus or apex heights. Our observations of viscous effects at large distances from the contact line have implications for dynamic contact angle measurements in capillary tubes.

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