Biomedical subjects

D G Bucknall

Publications and source records attributed to D G Bucknall.

4 recordsLinked to original sources

PubMed2005

Droplet spreading on microstriped surfaces.

When a droplet of fluid is deposited on a surface with chemical and/or topological patterns, its static shape is highly dependent on the 2D distribution of the patterns. In the case of chemical stripes, three distinct spreading regimes have been observed as a function of wettability contrast between the two kind of stripes. For low wettability contrast, the droplet spreads with the same [corrected] velocity normal and parallel to the stripes [corrected] and the macroscopic contact angle is close to Cassie's contact angle. When the wettability contrast is intermediate/high, the resulting shape of the droplets is elongated. In the intermediate wettability contrast regime, an ideal situation shows stick and slip behavior of the contact line, during which the contact line jumps from one stripe to another. For a high wettability contrast, the confinement of the fluid between two chemical stripes leads to a 2D spreading.

Journal Article↗

PubMed2002

Film thickness effects on the distribution of high-molecular-weight heterotelechelic polymers.

High-molecular-weight heterotelechelic deuteriopolystyrene, NDPSF, possessing an amine functional group at one end of the chain and a fluorocarbon group at the other was tethered to a silicon substrate by its amine functional group. These layers were coated with an unfunctionalised polystyrene matrix, HPS, such that the total film thickness covered a range from 2.2 to 9 times the radius of gyration of NDPSF. The detailed distribution of the polymers after annealing for times much greater than the reptation period of either of the components, was obtained using neutron reflectometry. No evidence for bridging of the two interfaces was found for the thicker films, but the finite concentration of the NDPSF polymer observed for the thinnest films may be due to bridging since the energy gain of the fluorocarbon end is just greater than the loss due to configurational entropy losses. A linear increase in the ellipsometric thickness of the excess of NDPSF at the substrate was discovered and we attribute this to the NDPSF slowly being leached out of the layer initially at the substrate followed by diffusion into the bulk of the film. The concentration profiles obtained are consistent with hindered relaxation of the large NDPSF molecules, when they are tethered at the substrate or at the vacuum surface.

Journal Article↗

PubMed2001

Neutron reflection from a dimyristoylphosphatidylcholine monolayer adsorbed on a hydrophobised silicon support.

Neutron specular reflection has been used to study the structure of a monolayer of dimyristoylphosphatidylcholine (DMPC) deposited using the Langmuir-Blodgett technique onto a silicon oxide substrate. A self-assembled monolayer of octadecyltrichlorosilane with a deuterated alkyl chain (d-OTS) had been previously bonded onto this silicon oxide substrate which rendered it hydrophobic. In the system under study, the alkyl chains of the phospholipid were found to penetrate extensively into the d-OTS layer with the mixed chain region (d-OTS and DMPC) having a total thickness of 30.5 A. This mixed region was divided into two halves for analysis; the 'lower half' (nearest to the substrate surface) was found to comprise anchored d-OTS chains mixed with the lipid chains in the volume ratio approx. 0.60:0.35. The corresponding volume ratio in the 'upper half' of this region was determined to be approx. 0.50:0.40. The thicknesses of these regions were found to be 17.9 A (incorporating approx. 6% solvent) and 12.6 A (incorporating approx. 9% solvent) for the lower and upper halves respectively. The DMPC head groups were found to be confined to the most external layer (furthest away from the silicon substrate). This layer was found to have a thickness of 9.4 A and included a small fraction of the lipid alkyl chains with approx. 47% solvent.

Dimyristoylphosphatidylcholine↗

PubMed2000

Modulation of cytochrome C coupling to anionic lipid monolayers by a change of the phase state: a combined neutron and infrared reflection study.

The effect of monolayer domain formation on the electrostatic coupling of cytochrome c from the subphase to a monolayer at the air/water interface was studied using a combination of neutron reflection (NR) and infrared reflection absorption spectroscopy (IRRAS) techniques. The monolayers consisted of a binary mixture of the zwitterionic phosphatidylcholine and the anionic phosphatidylglycerol. For a monolayer of dipalmitoylphosphatidylcholine (DPPC) and dimyristoylphosphatidylglycerol (DMPG, 30 mol%), which exhibits a non-ideal mixing of the two lipid components, we observed a significantly higher protein coupling to the liquid-condensed phase compared to the liquid-expanded state. In contrast, this higher protein binding was not observed when the two lipids had identical chain lengths (nearly ideal mixing). Similarly, for an equimolar mixture of DPPC and DMPG, we did not observe significant differences in the protein binding for the two phase states. The results strongly suggest that the domain formation in a condensed monolayer under non-ideal lipid mixing conditions is crucial for the cytochrome c binding strength. Furthermore, this study demonstrates the significant advantages of gathering information on protein-monolayer coupling by the combined use of a dedicated IRRAS set-up with the NR technique.

1,2-Dipalmitoylphosphatidylcholine↗