Large amplitude oscillatory shear (LAOS) fingerprinting of the nonlinear response of polymers and other complex soft matter has proven an excellent tool in the characterization of such materials. The major methods of quantitative characterization of nonlinearity using LAOS are the use of Lissajous-Bowditch (LB) curves and Fourier transform rheology (FTR). Another LAOS-based tool, mechanical spectral hole burning (MSHB), has been developed in our labs to investigate the heterogeneous dynamics of polymer melts and solutions and offers the possibility of a complementary method to the LB and FTR analyses for the fingerprinting of the nonlinear response of polymers and other complex fluids. Here, we present results from an investigation of the MSHB, LB loop, and FTR behaviors of polybutadiene and polystyrene solutions. The goal of the study was to examine similarities and differences in how these methods "fingerprint" the nonlinear response of the different polymer solutions. We find that the vertical holes in the MSHB experiments vary in intensity with the square of the sine wave pump magnitude. This is also true for the third harmonics obtained in the FTR, but the origins are possibly different for the two signatures. We have analyzed the fingerprinting categories as a function of strain amplitude and frequency from the LB loops and higher harmonics of FTR and add an additional feature to the fingerprints that are related to MSHB signatures, which are found to complement the other two methods and add new information to the fingerprinting diagrams.
- Fourier transform rheology (FTR)
- Mechanical spectral hole burning (MSHB)
- Polymer solution