Surface Characterization of Polymer Blends using Contact Resonance Amplitude Imaging

We have used Contact Resonance Amplitude Imaging to study surface distribution of polymers in PMMA/SBS polymer blends.

Introduction

Atomic force microscopy has been widely applied to acquire high resolution 3D surface topography at micro- and nanometer scale. As the AFM technology has evolved, different modes have been developed so that a wide array of data types can be collected in order to gain different information on the examined sample. Here we introduce a mechanical mode called Contact Resonance Amplitude Imaging.

Contact resonance techniques are a class of dynamic contact AFM methods where a piezoelectric actuator is used for CR excitation. CR methods deliberately operate in the vicinity of a resonance. The high frequency of the dynamic excitation (kilohertz to megahertz) used in CR methods also allow for improved sensitivity to small changes in mechanical properties compared to quasi-static approaches, due to time averaging of the cantilever vibration response. Near-resonance operation exploits the fact that the CR frequency and amplitude depends on the sample’s elastic modulus due to tip–sample interaction forces. In Contact Resonance Amplitude Imaging, qualitative modulus information can be obtained by monitoring the relatively large shifts in signal amplitude that occur near resonance. In the resulting “CR Amplitude Image” the signal intensity corresponds to the amplitude of the cantilever vibration at the excitation frequency. In turn, the variation in cantilever vibration amplitude throughout the sample depends on the relative elastic stiffness or modulus of various sample components.

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