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The transient viscoelastic measurement of TMV superlattice with a novel AFM-based method

Haoran Wang (North Dakota State University), Xinnan Wang (NDSU)

Joint Session: Mechanics of cell sheets, multicellular assemblies and tissues and Mechanics and Physics of Biological Cells

Mon 4:20 - 5:40

Barus-Holley 141

Superlattice can be formed by mixing tobacco mosaic virus and Ba ions under certain conditions. This work introduced a novel method to perform the transient viscoelastic experiment on TMV superlattice by using AFM. By contrary to previous AFM-based dynamic methods for viscoelasticity measurement, the experiment proposed here is able to extract the viscosity and elasticity of the sample, respectively, instead of storage and loss moduli which are frequency-dependent properties. Accordingly, the results obtained from this experiment are applicable to a more general situation. Furthermore, the adhesion between the AFM tip and the sample surface is also taken into account in this method and thus more accurate results can be obtained. Besides, the experiment is set up based on a basic AFM, without the need for sinusoidal displacement generating unit and thus is more convenient and cheaper to operate. The experiment was proposed based on a model of viscoelastic contact mechanics which evolved from elastic contact mechanics model. The derivation followed the approach of functional equation that has been justified to be an effective method to extend the elastic solution to viscoelastic solution. The elastic moduli and viscosity of superlattice formed by TMV was measured to be E1=3 GPa, E2=0.0213 GPa, and =~12.4 MPa.s, respectively, corresponding to the parameters in the standard solid model. It means the TMV superlattice is quite rigid at the initial contact and tends to undergo a large deformation under a constant pressure. Further analysis revealed the shear thinning effect in the TMV superlattice. Finally, the transmission from the transient viscoelastic properties to the dynamic viscoelastic properties is demonstrated, which demonstrates the novel method's good versatility.