Biomedical subjects

HT Davis

Publications and source records attributed to HT Davis.

10 recordsLinked to original sources

PubMed1999

Simulation of Flow in Bidisperse Sphere Packings.

Simulation methods were used to construct bidisperse, random sphere packings and to calculate fluid velocities in the pore spaces under a uniform pressure gradient. Based on these calculations, the Kozeny-Carman (KC) relation was found to hold for monodisperse and bidisperse sphere packings (r(1)/r(2) = 2.6) over a range of compositions and Reynolds numbers, using the same KC parameter value (C = 5). These results are consistent with a stronger observation about the similarity of the pore-size and flow distributions. Pore-size distributions were Gaussian for all the simulated packings, and for all bidisperse mixtures and Reynolds numbers examined, the normalized longitudinal velocity distribution collapses onto an exponential distribution when scaled by the mean velocity. Copyright 1999 Academic Press.

Journal Article↗

PubMed1999

Role of Silicone Surfactant in Flexible Polyurethane Foam.

Grafted copolymers which consist of a polydimethylsiloxane backbone and polyethylene oxide-co-propylene oxide pendant groups are used as surfactants to stabilize the foam cells in the flexible polyurethane foaming process. The mechanical properties of the cured polyurethane foam such as air permeability and foam cell size are affected significantly by the structure of the silicone surfactant used in the formulation. It is shown that silicone surfactant has an important impact on both the bubble generation and the cell window stabilization stage. A series of silicone surfactants with different structures was tested. Surfactants with higher silicone content will provide lower surface tension and thus help increase the number of air bubbles introduced during mixing. These air bubbles serve as the starting point for foam cell growth. As a result, the cured polyurethane foam made with higher silicone content surfactant has a smaller bubble size. It is also shown that silicone surfactant can reduce the cell window drainage rate due to the surface tension gradient along the cell window. The Gibbs film elasticity, the dynamic film elasticity, and the film drainage rate were measured for the first time versus surfactant composition. Surfactants with longer siloxane backbones are shown to give higher film elasticity. Using the vertical film drainage and foam column tests, it is shown that surfactants with higher film elasticity will yield slower drainage rate and better foam cell stability. Copyright 1999 Academic Press.

Journal Article↗

PubMed1999

Giant wormlike rubber micelles

A low molecular weight poly(ethyleneoxide)-poly(butadiene) (PEO-PB) diblock copolymer containing 50 weight percent PEO forms gigantic wormlike micelles at low concentrations (<5 percent by weight) in water. Subsequent generation of free radicals with a conventional water-based redox reaction leads to chemical cross-linking of the PB cores without disruption of the cylindrical morphology, as evidenced by cryotransmission electron microscopy and small-angle neutron scattering experiments. These wormlike rubber micelles exhibit unusual viscoelastic properties in water.

Journal Article↗

PubMed1996