ABSTRACT
We demonstrate the accurate nanoscale mapping of near-surface loss and storage moduli on a polystyrene-polypropylene blend with contact resonance force microscopy (CR-FM). These viscoelastic properties are extracted from spatially resolved maps of the contact resonance frequency and quality factor of the AFM cantilever. We consider two methods of data acquisition: (i) discrete stepping between mapping points and (ii) continuous scanning. For point mapping and low-speed scanning, the values of the relative loss and storage modulus are in good agreement with the time-temperature superposition of low-frequency dynamic mechanical analysis measurements to the high frequencies probed by CR-FM.
ABSTRACT
The objective of this study was to determine the viscoelastic properties present within the intermediate zone of the porcine temporomandibular joint (TMJ) disc using nanoindentation. A 50-microm conospherical indenter tip using a displacement-controlled ramp function with a 600 nm/s loading and unloading rate, a 3000-nm peak displacement with a holding period of 30 s was used to indent the samples. Experimental load-relaxation tests were performed on the TMJ disc to determine the response in three different directions; the mediolateral, anteroposterior, and articular surface directions. The experimental data were analyzed using a generalized Maxwell model to obtain values for short- and long-time relaxation modulus and of material time constants. The short time relaxation modulus E ( I ) values were 180.92, 64.99, and 487.77 kPa for testing done on the articular surface, mediolateral, and anteroposterior directions, respectively. Corresponding values for the long-time relaxation modulus E (infinity) were 45.9, 14.97, and 133.5 kPa. The method confirmed anisotropy present within the central intermediate zone of the porcine TMJ disc due to the directional orientation of the collagen fibers.
