Biomedical subjects

C W Extrand

Publications and source records attributed to C W Extrand.

6 recordsLinked to original sources

PubMed2006

Relation between contact angle and the cross-sectional area of small, sessile liquid drops.

In this theoretical study, the cross-sectional areas of small, sessile drops were calculated for solid surfaces with a wide range of wettability. These areas were then used to estimate obstruction of rectangular gas flow channels by sessile liquid drops. Our findings suggest that even a small improvement in wettability (i.e., a lower contact angle) will lead to a substantial decrease in blockage. This work has implications for small channels that contain two-phase flow, such as those found in fuel cells.

Journal Article↗

PubMed2006

Designing for optimum liquid repellency.

In the current state-of-the-art, most super repellent surfaces are not sufficiently robust to move out of the laboratory into the commercial realm. With the hope of creating super repellent surfaces that could be employed in a wider variety of commercial applications, means to improve the robustness of ultralyophobic surfaces have been explored theoretically. Suspension pressures and drop retention forces were examined in terms of asperity shape, size, and spacing. The findings from this study suggest a strategy for creating surfaces that maintain their liquid repellency even after exposure to large hydrostatic pressures associated with liquid columns or jets.

Journal Article↗

PubMed2005

Modeling of ultralyophobicity: suspension of liquid drops by a single asperity.

With the aim of understanding the underlying physical phenomenon associated with utlralyophobic (or super repellent) surfaces, model studies have been performed on single asperities of different size and shape. A small liquid drop was deposited on top of each model asperity, and liquid was sequentially added. If the advancing contact angle was sufficiently large, it was possible to suspend large drops atop asperities with an apparent contact angle approaching 180 degrees. If more and more liquid was added, eventually the suspended drops collapsed. Roughening the surface of the asperities further bolstered suspension. Using an analysis that accounts for both capillary forces and the influence of gravity, the critical suspension volume was correctly predicted for each liquid/asperity combination.

Microscopy, Electron, Scanning↗

PubMed2004

Criteria for ultralyophobic surfaces.

Very rough surfaces can suspend small liquid drops and produce very large contact angles. This behavior often is referred to as ultralyophobicity or super repellency. It is proposed that two criteria must be met to invoke ultralyophobicity: a contact line density criterion and asperity height criterion. The proposed criteria were tested using experimental data available in the literature and were found to correctly predict suspension of small water drops on model rough surfaces with a wide variety of asperity shapes, sizes, and spacing.

Journal Article↗

PubMed2004

Contact angles and their hysteresis as a measure of liquid-solid adhesion.

The wetting behavior of a series of aliphatic polyamides was examined. Polyamides and polyethylene were molded against glass to produce smooth surfaces. After cleaning, chemical composition of the surfaces was verified with X-ray photoelectron spectroscopy. Advancing and receding contact angles were measured from small sessile water drops. Contact angles decreased with amide content while contact angle hysteresis increased. Wetting free energies calculated from contact angles were equal to those from dewetting, suggesting that contact angle hysteresis did not arise from surface anomalies, but from hydrogen bonding between water and the amide groups in the polyamide surfaces.

Journal Article↗

PubMed2002

Water contact angles and hysteresis of polyamide surfaces.

The wetting behavior of a series of aliphatic polyamides (PAs) has been examined. PAs with varying amide content and polyethylene (PE) were molded against glass to produce surfaces with similar roughness. After cleaning, chemical composition of the surfaces was verified with X-ray photoelectron spectroscopy. Advancing and receding contact angles were measured from small sessile water drops. Contact angles decreased with amide content while hysteresis increased. Hysteresis arose primarily from molecular interactions between the contact liquid and the solid substrates, rather than moisture absorption, variations in crystallinity, surface deformation, roughness, reorientation of amide groups, or surface contamination. Free energies of hysteresis were calculated from contact angles. For PE, which is composed entirely of nonpolar methylene groups, free energies were equivalent to the strength of dispersive van der Waals bonds. For PAs, free energies corresponded to fractional contributions from the dispersive methylene groups and polar amide groups.

Glass↗