Determining forces acting on a nanoparticle in the vicinity of a cylindrical nanoscopic pore is of great scientific and industrial importance for a wide range of systems. Among them: filtering membranes, such as carbon nanotube-mixed matrices1, chaperonins, cylindrical proteins that use their shape to assist the folding of other smaller proteins2, or porous solids made of cylindrical cavities employed as nucleants for selective crystallization3. In all these cases, understanding the solute behavior close to the pore entrance plays a major role in the success of the desired application.
When studying this type of system, one major difficulty consists on modeling the depletion force accounting for the indirect role of solvent molecules. Depletion forces were studied in numerous simple cases such as the interaction between two big spheres4, two surfaces5 or a big sphere and a surface6. However, in these studies, solids and solvents were modeled as purely repulsive systems, and the role of solvophobicity was not examined.
In this work, we investigate how wetting properties can influence the rejection or entrance of a nanoparticle inside the pore. State-of-the-art methods of finite-temperature density functional theory were employed to compute three-dimensional density profiles and free energies. We applied the model first to a nanoparticle interacting with a flat surface and inside an infinite cylinder, and then we focused on a system made of a nanoparticle in the vicinity of a cylindrical pore. Our work contributes to the general understanding of solute infiltration within cylindrical pores by providing a qualitative picture guiding the design of pores in terms of size and solvophobicity. In addition, the quantitative figures obtained in this work enables a coarse-graining of the depletion forces thus avoiding the direct simulation of solvent molecules. This should ultimately lead to simplifications in the multi-scale modelling of solvent/nanoparticle/pore systems.
References:
[1] E. Gibbins, M. D’Antonio, D. Nair, L. S. White, L. M. F. dos Santos, I. F. Vankelecom, and A. G. Livingston, Desalination 147, 307 (2002).
[2] H. S. Rye, A. M. Roseman, S. Chen, K. Furtak, W. A. Fenton, H. R. Saibil, and A. L. Horwich, Cell 97, 325 (1999).
[3] U. V. Shah, D. R. Williams, and J. Y. Heng, Crystal Growth and Design 12, 1362 (2012).
[4] S. Asakura and F. Oosawa, The Journal of Chemical Physics 22, 1255 (1954).
[5] K. Nygård, S. Sarman, K. Hyltegren, S. Chodankar, E. Perret, J. Buitenhuis, J. F. van der Veen, and R. Kjellander, Physical Review X 6, 011014 (2016).
[6] R. Roth, B. Götzelmann, and S. Dietrich, Physical Review Letters 83, 448 (1999).
Acknowledgments:
The authors would like to thank the European Union’s Horizon 2020research and innovation programme for funding this work within the AMECRYS project http://www.amecrys-project.) undergrant agreement no. 712965.
Advances in molecular simulation , Interfacial and confined phenomena
