CONTACT-ANGLE MICROSCOPY ON A CARBOSILANE DENDRIMER WITH HYDROXYL END-GROUPS - METHOD FOR MESOSCOPIC CHARACTERIZATION OF THE SURFACE-STRUCTURE

A carbosilane dendrimer containing hydroxyl terminal groups, which sho wed two types of wetting in dependence of the substrate used, was stud ied by tapping force microscopy. Due to the preferential adsorption of the hydroxyl groups, the dendrimer displayed autophobic spreading on mice, whereas a substrate which was first coated with a semifluorinate d polymer was only partially wetted. In both cases, submicrometer-size d droplets were deposited on the surface. Microscopic contact angles w ere measured and compared with macroscopic values obtained by a standa rd sessile drop technique. The comparison showed lower values for the microscopic angle which were explained by deformation of the droplets caused by the tapping tip. The oscillatory motions of the tip intermit tently touching a viscoelastic sample were calculated using a simple m odel of the tapping mode. The indentation of the tip into the sample a nd the induced phase shift relative to the oscillations in air were de termined from the model, showing a good agreement with experimental re sults. Compared to traditional methods, this approach offers advantage s such as (i) three-dimensional visualization of the whole droplet, (i i) submicrometer resolution of the structure near the three-phase boun dary, and (iii) accurate determination of small contact angles.