Solute particle near a nanopore: influence of size and surface properties on the solvent-mediated forces

Abstract

Nanoscopic pores are used in various systems to attract nanoparticles. In general the behaviour is a result of two types of interactions: the material specific affinity and the solvent-mediated influence also called the depletion force. The latter is more universal but also much more complex to understand since it requires modeling both the nanoparticle and the solvent. Here, we employed classical density functional theory to determine the forces acting on a nanoparticle near a nanoscopic pore as a function of its hydrophobicity and its size. A simple capillary model is constructed to predict those depletion forces for various surface properties. For a nanoscopic pore, complexity arises from both the specific geometry and the fact that hydrophobic pores are not necessarily filled with liquid. Taking all of these effects into account and including electrostatic effects, we establish a phase diagram describing the entrance and the rejection of the nanoparticle from the pore.

Lattice induced crystallization of nanodroplets: the role of finite-size effects and substrate properties in controlling polymorphism

“…Even if long interactions such as electrostatic ones are not present in this model, hydrophobicity can be well tuned simply by changing the ratio ε s/m /ε. 31,44 N denotes the initial number of particles in the liquid droplet. Periodic boundary conditions were applied.…”

Solvent-mediated interactions between nanostructures: From water to Lennard-Jones liquid

“…Accuracy of the DFT treatment is discussed in this review 54 . From there, droplet equilibration results were taken from our previous work 18 . For solvent-mediated interactions, we used the same system as with molecular dynamics simulation of water except that there is no equilibration protocol and the free energy is obtained directly through DFT.…”

“…The density and the temperature are respectively ρ LJ = 0.7 σ −3 LJ and k B T = 0.8 LJ which is located between the triple point and the critical temperature. This corresponds to the liquid density for a chemical potential supersaturation equal to ∆µ = 0.27k B T 18 . While the value of ∆µ influences quantitatively the solvent-mediated forces 17 , the supersaturation is chosen in this work to match the ratio of pressure between water coexistence pressure and atmospheric pressure (P coex = 1/20P atm ).…”

“…Once the model is chosen, solvent-mediated forces can be computed using various types of numerical methods. Monte-Carlo and molecular dynamics simulations are widely employed especially for water modeling while classical density functional theory (DFT) in which molecules are treated as a density field can grant access directly to liquid density profiles and the corresponding free energy 18,54 . DFT is less numerically expensive and avoids using free energy calculation techniques such as thermodynamic integration, transition path sampling and umbrella sampling.…”

“…Numerous studies have examined solvent-mediated forces in terms of range, strength and sign using both numerical [10][11][12][13][14][15][16][17][18][19] and experimental techniques [20][21][22][23][24][25][26][27][28][29][30] . In particular, it was found that the sign of solventmediated forces is controlled by the equilibrium contact angle [15][16][17][18]21 . On the one hand, when the solids are solvophilic, solvent molecules are attached to the solid surface.…”