RESUMO
A novel extrinsic method for the measurement of particle surface distribution in a carbon black-filled elastomer via nanoindentation is developed. This method is based on the measurement of the contact stiffness obtained from the continuous stiffness measurement mode. The proposed tip-particle model is held by two main hypotheses: the particles do not deform significantly during indentation so that only the elastomer matrix elastically deforms; particles are physically bounded with the surrounding matrix. Therefore, when the tip comes in contact with a particle, the latter becomes a hard extension of the tip, able to deform the elastomer matrix. Finally, the evolution of the measured contact stiffness is directly related to the increase of the contact area between the tip-particles set and the elastomer matrix. The proposed model is validated through a numerical and an experimental study. Moreover, an evaluation of the measurements bias allows to correct the particle surface distribution. A good agreement is found between the distribution measured from transmission electron microscopy observations and nanoindentation measurements.
RESUMO
Scanning force microscopy (SFM) in contact mode and in liquid medium has been employed to study immunospecies layers adsorbed on a silicon wafer. The silicon wafer has been grafted with a cyanosilane monolayer in order to create a surface with strong adhesive properties which prevent proteins being swept by the scan of the SFM tip. The force curves reveal that the adhesive force has been increased by a factor six without roughness modification (< 1 nm). After the incubation of the surface in a monoclonal antibody (mouse anti-human alpha-fetoprotein IgG) solution, SFM surface images suggest an homogeneous layer composed by ellipsoidal objects (40-60 nm in diameter, 6-13 nm in height). The substrate was moreover incubated in an antigenic solution (human alpha-fetoprotein): SFM images reveal that proteins have been added onto the antibody layer.