Influence of the Nanoparticle Surface Functionalization on the Interphase Measured by Atomic and Electric Force Microscopy

The macroscopic material properties of nanocomposites can be modified significantly by an interphase at the boundary layer between the nanoparticles and the polymer. This study investigates the extent of the interphase by means of atomic force microscopy (AFM) and electric force microscopy (EFM). For this purpose, nanocomposites based on silicone rubber containing hydrophilic and hydrophobic nanoparticles are produced. Moreover, nanoparticles functionalized with grafted polymer chains with different molecular weights are used. First, reference values for the diameter of the filler particles are gained from transmission electron microscopy (TEM) images of the nanocomposites and from AFM and EFM images of the pure particles. Then, the diameter of the nanoparticles in the polymer is determined from EFM measurements. All nanoparticles in the polymer have an increased diameter in comparison to the pure nanoparticles, which is attributed to the interphase. For the functionalized nanoparticles the interphase thickness increases with rising molecular weight of the grafted polymer chains.