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In multiphasic materials the solvent is assumed to be neutral, whereas the solid and solutes may carry charge. The mixture is isothermal and all constituents are considered to be intrinsically incompressible. Since the viscosity of the fluid constituents (solvent and solutes) is considered negligible relative to the frictional interactions among constituents, the stress tensor $\sigma$ for the mixture includes only a contribution from the fluid pressure $p$ and the stress $\boldsymbol{\sigma}^{e}$ in the solid, $$\begin{equation} \boldsymbol{\sigma}=-p\mathbf{I}+\boldsymbol{\sigma}^{e}\,.\label{eq121} \end{equation}$$ The mechano-chemical potential of the solvent is given by $$\begin{equation} \tilde{\mu}^{w}=\mu_{0}^{w}\left(\theta\right)+\frac{1}{\rho_{T}^{w}}\left(p-p_{0}-R\theta\Phi\sum\limits _{\alpha}c^{\alpha}\right)\,,\label{eq122} \end{equation}$$ where $\mu_{0}^{w}\left(\theta\right)$ is the solvent chemical potential in the solvent standard state, $\theta$ is the absolute temperature, $\rho_{T}^{w}$ is the true density of the solvent (which is invariant since the solvent is assumed intrinsically incompressible), $p$ is the fluid pressure, $p_{0}$ is the corresponding pressure in the standard state, $R$ is the universal gas constant, $\Phi$ is the non-dimensional osmotic coefficient, and $c^{\alpha}$ is the solution volume-based concentration of solute $\alpha$ . The summation is taken over all solutes in the mixture. The mechano-electrochemical potential of each solute is similarly given by $$\begin{equation} \tilde{\mu}^{\alpha}=\mu_{0}^{\alpha}\left(\theta\right)+\frac{R\theta}{M^{\alpha}}\left(\frac{z^{\alpha}F_{c}}{R\theta}\left(\psi-\psi_{0}\right)+\ln\frac{\gamma^{\alpha}c^{\alpha}}{\kappa^{\alpha}c_{0}^{\alpha}}\right),\label{eq123} \end{equation}$$ where $M^{\alpha}$ is the molar mass of the solute, $\gamma^{\alpha}$ is its activity coefficient, $\kappa^{\alpha}$ is its solubility, $z^{\alpha}$ is its charge number, and $c_{0}^{\alpha}$ is its concentration in the solute standard state; $F_{c}$ is Faraday's constant, $\psi$ is the electrical potential of the mixture, and $\psi_{0}$ is the corresponding potential in the standard state.