Interphase characterization via the stiffness contrast of a scanning forcemicroscope in displacement modulation mode

The physical properties as well as the thickness of the interphase between polymer and reinforcing phase are generally expected to show a strong influ ence on the macroscopic mechanical properties of composite materials. In th is study the scanning force microscope (SFM) has been applied for detecting stiffness gradients near the interface between copper and epoxide, In disp lacement modulation mode the load exerted by the tip is modulated sinusoida lly by vibrating the normal position of the cantilever or the sample. The c orresponding amplitude of dynamic cantilever bending is related to local su rface stiffness, Thus, using the SFM, the local mechanical properties of th e surface under investigation can be probed. When scanning the tip across t he reinforcement/polymer interface, the polymeric interphasial zone can be identified with the observed stiffness gradient. For a commercial epoxide b ased on diglycidyl ether of bisphenol A (DGEBA) cured with an amine-contain ing hardener, a stiffness gradient was detected that could be fitted by a G aussian profile typical for diffusional processes. The width of the stiffne ss gradient was similar to 280 nm, The observation is discussed in terms of interface-induced segregation processes between resin and hardener, as wel l as heat conduction mechanisms that can occur during the exothermic curing reaction. Both mechanisms are diffusional in nature and, via the local net work structure, are expected to show some influence on the local stiffness of the cured epoxy, Copyright (C) 2000 John Wiley & Sons, Ltd.