InterPore2026

Forced Phase Separation in Nano-Pore Network

19 May 2026, 12:05

15m

Oral Presentation (MS05) Physics of multiphase flow in diverse porous media MS05

Speaker

Shuye Ling (Peking University)

Description

It is generally believed that whether a multicomponent system is miscible depends on the mixing energy. However, when droplets or bubbles are confined in nanoporous media with characteristic length scale R_0, its interfacial energy starts to reshape phase behavior because interfacial energy $(\propto R_0^2)$ may become comparable to or even dominant over mixing energy $(\propto R_0^3)$. Whether interfacial energy may change the miscibility of such mixtures confined in porous media as discrete fluid is still unexplored.
Here we investigate a simple scenario: mixture of two miscible or partially miscible components (A and B) are confined as blobs in a two identical and water-saturated pores. (Fig. (a)) The solubility of A and B in water is negligible so we only consider the phase behaviors of A-B system. The interfacial tensions between component A and water, component B and water are denoted as $\gamma_A$ and $\gamma_B$, respectively. For a mixed droplet with a mole fraction x of component A, we assume the interfacial tension between the droplet and water to be $\gamma=x\gamma_A+(1-x) \gamma_B$. For each single droplet, the interfacial energy F_interface is described by Xu’s model 1, and the mixing energy F_mix is described by the Flory-Huggins model [2-4]. For the two-pore system, the problem of determining the optimal phase equilibrium state is transformed into minimizing the function $F_{system}=F_{interface,1}+F_{interface,2}+ F_{mix,1}+ F_{mix,2}$. We define the dimensionless parameter $\epsilon=(M\gamma_A)/(\rho R_0 RT) $to characterize the ratio of interfacial energy to mixing energy.
We compute the minimum energy state of such two-pore systems. For systems dominated by mixing energy $(\epsilon≪1)$, the energy-optimal state may consist of two identical droplets or two droplets with different component ratios, depending on the Flory-Huggins coefficient $\beta$. However, further increasing ϵ results in very different physical picture. For a typical two-pore system with total dispersed phase saturation 0.7 and overall mole fraction of component A 0.4, we plot the absolute difference in mole fraction of component A between the two droplets $|x_{A1}-x_{A2} |$ as a function of $\beta$ and $\epsilon$ (Fig. (b)). Our new findings are as follows:

1. When $\beta$ is small and $\epsilon$ is small, the lowest-energy
   state of the system consists of two identical droplets.

2. As $\beta$ and $\epsilon$ increase beyond a certain threshold, the
   droplets corresponding to the lowest-energy state exhibit partial
   phase separation.

3. With further increase in $\beta$ and $\epsilon$, the droplets in the
   lowest-energy state can undergo complete phase separation, forming
   two pure-component droplets. Strikingly, absolute phase separation
   emerges in porous media for two components that can be miscible in
   open space.

In summary, we reveal a new mechanism for phase separation of miscible components: in porous media with high specific surface area, mixing can be replaced by interfacial energy dominated phase separation. This offers a fresh perspective for understanding phenomena such as protocell organelle formation in submarine hydrothermal vents and component distribution in petroleum reservoirs over geological scales.