Contact Angle Microscopy on a Carbosilane Dendrimer with Hydroxyl End Groups:  Method for Mesoscopic Characterization of the Surface Structure

Abstract

A carbosilane dendrimer containing hydroxyl terminal groups, which showed two types of wetting in dependence of the substrate used, was studied by tapping force microscopy. Due to the preferential adsorption of the hydroxyl groups, the dendrimer displayed autophobic spreading on mica, whereas a substrate which was first coated with a semifluorinated polymer was only partially wetted. In both cases, submicrometer-sized droplets were deposited on the surface. Microscopic contact angles were measured and compared with macroscopic values obtained by a standard 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 intermittently touching a viscoelastic sample were calculated using a simple model of the tapping mode. The indentation of the tip into the sample and the induced phase shift relative to the oscillations in air were determined from the model, showing a good agreement with experimental results. Compared to traditional methods, this approach offers advantages such as (i) three-dimensional visualization of the whole droplet, (ii) submicrometer resolution of the structure near the three-phase boundary, and (iii) accurate determination of small contact angles.

Dendronized Polymers: Synthesis, Characterization, Assembly at Interfaces, and Manipulation

“…Examples include synthetic and biological polymers [58±60] as well as spherical dendrimers. [61,62] Of particular interest for rather soft organic materials is the operation in the ªinter-mittent contactº or ªtappingº mode, [57] which minimizes wear during imaging.…”

Synthesis of a Carbosilane Dendrimer with Fluorocarbon Substituents at the Silicon Atoms in the Surface Layer of the Molecular Structure

“…One of the basic methods of modifying the surface of dendrimers and, hence, controlling their properties involves chemical transformations with the use of numerous functional groups. The introduction of fluorinated moieties into the surface layer of the dendrimer molecular structure endows such systems with some specific properties: a low surface energy, a combination of hydrophobic and oleophobic interactions, an affinity for supercritical ëé 2 , and other features [1,2] determined by the structure of the fluorine atom and the electronic structure of the fluorine-carbon bond [3,4].…”

Scanning Polarization Force Microscopy: a Technique for Studies of Wetting Phenomena At the Nanometer Scale

“…This behavior is not surprising in this case due to the large surface energy of cleaved mica. Values of 300-600 mJ/m 2 have been reported for the surface energy of freshly cleaved mica (Sheiko et al, 1997), compared with 53 mJ/m 2 for the surface tension of sulfuric acid.…”