Biomedical subjects

H E H Meijer

Publications and source records attributed to H E H Meijer.

3 recordsLinked to original sources

PubMed2005

Film drainage and interfacial instabilities in polymeric systems with diffuse interfaces.

We report an experimental investigation on the effect of mutual diffusion in polymeric systems on film drainage between two captive drops. The main objective is to study the influence of diffuse interfaces on film drainage. This is done by using material combinations with different interfacial properties and interferometric visualization of the film between two interacting drops. For highly diffusive systems film drainage is observed to be, in contrast to immiscible systems, non-axisymmetric and unstable immediately after the film formation (at a few micrometers film thickness). Depending on whether the total thickness of the diffusion layers in the film is smaller or larger than the thickness of the film, Marangoni convection is found to enhance or delay film drainage. Enhanced film drainage is determined to be in order of 100 times faster than predicted by the current models, while delayed film drainage is observed after a drainage period where experimental and predicted results (assuming, a partially mobile interface) are in close agreement.

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PubMed2005

Rigidity percolation in dispersions with a structured viscoelastic matrix.

This paper deals with rigidity percolation in composite materials consisting of a dispersion of mineral particles in a microstructured viscoelastic matrix. The viscoelastic matrix in this specific case is a hydrocarbon refinery residue. In a set of model random composites the mean interparticle surface-to-surface distance was controlled, changing particle volume fraction phi and particle number density independently. This was achieved by mixing two sets of monodisperse particles with widely differing radii (0.35 microm and 17.5 microm) with the matrix. A scaling exponent of 3.9 +/- 0.6 for the storage modulus G' vs phi- phi(c) was observed above a threshold phi(c) , in good agreement with theoretical values for rigidity percolation. It is found that at the rigidity-percolation threshold the pore structure, as characterized by the mean surface-to-surface distance for the filler, rather than the filler volume fraction, is similar for different types of composites. This behavior is explained from the internal structure of the viscoelastic matrix, which consists of fractal solid aggregates dissolved in a viscous medium; the effective radius of these aggregates and the mean surface-to-surface distance together determine whether or not the aggregates are capable of providing rigidity to the composite. The explanation is further supported by a qualitative comparison with effective-medium calculations. These indicate that the observed breakdown of time-temperature superposition near phi(c) is due to the appearance of a time scale characteristic for the mechanical interplay between the viscous binder phase and the purely elastic solid particles.

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PubMed2003

Film drainage between two captive drops: PEO-water in silicon oil.

An experimental study of the deformation and drainage of a Newtonian liquid film trapped between two drops is performed for the cases of a constant and slightly rising interaction force. Series of polyethylene oxide (PEO) water solutions are used for the dispersed and polydimethylsiloxane (PDMS) for the continuous phase. The film evolution is observed by an interferometric technique. Experimental data for the film thinning rate and for the film profile allow quantitative comparison with the available drainage models.

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