Surface layer thickness, graft

We could not conclude at the moment whether the solvent dependent surface properties are to be explained only by the difference in the depth of graft layer. Another possibility is the change in polar group orientation in graft layer as suggested by Hoffman(18). This arguement will be settled by direct determination of the thickness of graft layer prepared under various conditions. Clarification of the surface layer thickness - sur-... 

Fig. 28 Cell density versus distance histogram at 3 days after incubation on item a non-grafted photoreactive copolymer surface, and graft-polymer-layer-thickness gradient surfaces of a polyDMAPAAmMel, b polyMA, c polyDMAAm. The number of cells per unit area (0.225 mm ) is plotted against the unit distance (500 jim) from the edge of the photomask...

Fig. 2. Schematic of a flat, tethered layer. L is the average layer thickness while d is the average spacing between chain graft points on the surface...

Recently, Quirk and Mathers [264] performed LASIP of isoprene on silicon wafers. A chlorodimethylsilane-functionalized diphenylefhene (DPE) was coupled onto the surface and lithiated with n-BuLi to form the initiating species. The living poly(isoprene) (PI) was end- functionalized with ethylene oxide. A brush thickness of 5 nm after two days of polymerization (9.5 nm after four days) was obtained in contrast to a polymer layer thickness of 1.9 nm by the grafting onto method using a telechelic silane functionahzed PI. 

Fig. 4 A Atomic force microscope (AFM) images, projected at 30° for viewing, of non-treated dithiocarbamated polymer film surface (a) and the PST(polystyrene)-grafted surface by UV irradiation through the lattice-patterned projection mask for 5 (fc), 10 (c), and 20 min (d). B Relationship between the average thickness of the PST-grafted layers and UV irradiation time...

Okano et al. [51] applied poly(IPAAm) to modifying the surface of commercial polystyrene1 culture dishes for bovine aortic endothelial cells as well as for rat hepatocytes. Graft polymerization of IPAAm onto the polystyrene dishes was carried out by using an electron beam. The thickness of the poly(IPAAm)-grafted layer in aqueous systems was 0.5 pm at 37 °C and 0.6 pm at 15 °C. After endothelial cells were cultured at 37 °C for 2 days, the temperature was decreased to 10 °C and the number of cells that were detached from the surface was counted. Okano et al. observed that 100% of cells were detached from the poly(IPAAm)grafted surface. 

When calculating the theoretical force curves shown in Fig. 9 we used the XPS results to obtain the value of s and twice the length of the polymer brush was set to 23 nm. The anchoring points for the grafted PEO-chains were set at a distance 1.5 nm away from the mica surface. This value was chosen to be equal to the undisturbed layer thickness of the adsorbed chitosan polymer without grafted side-chains. When the prefactor is set equal to 1, the lower curve in Fig. 9 is obtained, and when a prefactor equal to two is used the upper curve is obtained. 

The equilibrium thickness found in these experiments is in very good agreement with the equilibrium results [128,129]. The largest thickness at which surface forces come into play (hw ca. 80 nm) is about 15 times the unperturbed radius of gyration of the copolymer molecule. This figure is consistent with those reported for grafted polymer layers studied with SFA [242,243]. 

In aqueous solutions the carboxylate groups of the grafted mercapto components can act as anchors for PVFA-co-PVAm molecules. The adsorption from differently concentrated PVFA-co-PVAm solutions (0.3 pmol L-1 to 3000 pmol L-1) gave polyelectrolyte layer thicknesses between 0.9 and 2.7 nm (determined by ellipsometry and angle-resolved XPS). The values found are in good agreement with the layer thicknesses on bare silicon wafer surfaces [97]. The layer thicknesses of the pre-adsorbed mercapto compounds range from 0.5 to 0.9 nm. That means that at very low polyelectroyte concentrations in the stock solution no increase in layer thickness was ob-... 

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