Temperature Dependence of the Rheology of Soft Matter on a MHz-oscillating Solid-liquid Interface

The temperature dependence of the resonant length, molecular weight, and rheology (shear viscosity and shear modulus) of chemisorbed soft matter on a solid-liquid interface oscillating at a megahertz frequency was studied using a quartz crystal microbalance. As a form of chemisorbed soft matter, self-assembled monolayers (SAMs) formed from six types of mercapto oligo(ethylene oxide) methyl ethers were used. A systematic analysis using the Voigt model showed that the variation in effective hydrated thickness (sensed mass), which is related to the resonant length, was classified into three types based on the molecular weight. As a result, a 2.2-nm change in the resonant length occurred in the studied temperature range from 10 to 35℃. Moreover, the variation in the effective hydrated thickness was dependent on the shear viscosity and shear modulus of the SAMs. A further investigation revealed that the relationships η₁∝M_n^0.13 and μ₁∝M_n^0.30 could be estimated regardless of the temperature, where η₁ and μ₁ are the shear viscosity and shear modulus of the SAM, and M_n is the molecular weight of mercapto oligo(ethylene oxide) methyl ether. As a result, we revealed that the experimental results followed the polymer formula irrespective of temperature.

A fast method for solving a linear model of one-dimensional blood flow in a viscoelastic arterial tree

For the purpose of optimization of the whole arterial tree, a fast method for solving of one-dimensional model of blood flow is required. A semi-analytic transmission line method for solving a linearized one-dimensional model of blood flow in an arterial tree with viscoelastic walls is proposed. The transmission line method that solves the linearized model in the frequency domain and the method of characteristics that solves either linearized or non-linear one-dimensional models in the time domain are compared regarding accuracy and computational time. For this purpose, the benchmark problem of a 37-artery network with available experimental data is used. In the case of the linearized model, the results from the transmission line method and the method of characteristics are practically the same. The difference between the transmission line method solution of the linearized model and the method of characteristics solution of the non-linear model is much smaller than the error of either method of characteristics or transmission line method numerical solutions with respect to the experimental data. For typical applications, the transmission line method is at least two orders of magnitude faster than the method of characteristics.

Quantification of the Mass and Viscoelasticity of Interfacial Films on Tin Anodes Using EQCM-D

Electrochemical quartz crystal microbalance coupled with dissipation (EQCM-D) is employed to investigate the solid electrolyte interphase (SEI) formation and Li insertion/deinsertion into thin film electrodes of tin. Based on the frequency change we find that the initial SEI formation process is rapid before Li insertion but varies significantly with increasing concentration of the additive fluoroethylene carbonate (FEC) in the electrolyte. The extent of dissipation, which represents the film rigidity, increases with cycle number, reflecting film thickening and softening. Dissipation values are almost twice as large in the baseline electrolyte (1.2 M LiPF6 in 3:7 wt % ethylene carbonate:ethyl methyl carbonate), indicating the film in baseline electrolyte is roughly twice as soft as in the FEC-containing cells. More importantly, we detail how quantitative data about mass, thickness, shear elastic modulus, and shear viscosity in a time-resolved manner can be obtained from the EQCM-D response. These parameters were extracted from the frequency and dissipation results at multiple harmonics using the Sauerbrey and Voigt viscoelastic models. From these modeled results we show the dynamic mass changes for each half cycle. We also demonstrate that different amounts of FEC additive influence the SEI formation behavior and result in differences in the estimated mass, shear modulus and viscosity. After three cycles, the film in baseline electrolyte exhibits a 1.2 times larger mass change compared with the film in the FEC-containing electrolyte. The shear elastic modulus of films formed in the presence of FEC is larger than in the baseline electrolyte at early stages of lithiation. Also with lithiation is a marked increase in film viscosity, which together point to a much stiffer and more homogeneous SEI formed in the presence of FEC.

Viscoelastic properties of collagen-adhesive composites under water-saturated and dry conditions

To investigate the time- and rate-dependent mechanical properties of collagen-adhesive composites, creep and monotonic experiments are performed under dry and wet conditions. The composites are prepared by infiltration of dentin adhesive into a demineralized bovine dentin. Experimental results show that for small stress level under dry conditions, both the composite and the neat adhesive have similar behavior. On the other hand, in wet conditions, the composites are significantly soft and weak compared to the neat adhesives. The behavior in the wet condition is found to be affected by the hydrophilicity of both the adhesive and the collagen. As the adhesive-collagen composites are a part of the complex construct that forms the adhesive-dentin interface, their presence will affect the overall performance of the restoration. We find that Kelvin-Voigt model with at least four elements is required to fit the creep compliance data, indicating that the adhesive-collagen composites are complex polymers with several characteristic time scales whose mechanical behavior will be significantly affected by loading rates and frequencies. Such mechanical properties have not been investigated widely for these types of materials. The derived model provides an additional advantage that it can be exploited to extract other viscoelastic properties which are, generally, time consuming to obtain experimentally. The calibrated model is utilized to obtain stress relaxation function, frequency-dependent storage and loss modulus, and rate-dependent elastic modulus.