Brownian motion near soft surfaces is a situation widely encountered in nanoscale and biological physics. However, a complete theoretical description is lacking to date. Here, we theoretically investigate the dynamics of a two-dimensional colloid in an arbitrary external potential and near a soft surface. The latter is minimally modelled by a Winkler’s foundation, and we restrict the study to the colloidal motion in the direction perpendicular to the surface. We start from deterministic hydrodynamic considerations, by invoking the already-established leading-order soft-lubrication forces acting on the particle. Importantly, a negative softness-induced and position-dependent added mass is identified. We then incorporate thermal fluctuations in the description. In particular, an effective Hamiltonian formulation is introduced and a temperature-dependent generalized potential is constructed in order to ensure equilibrium properties for the colloidal position. From these considerations and the Fokker–Planck equation, we then derive the relevant Langevin equation, which self-consistently allows to recover the deterministic equation of motion at zero temperature. Interestingly, besides an expected multiplicative-noise feature, the noise correlator appears to be modified by the surface softness. Moreover, a softness-induced temperature-dependent spurious drift term has to be incorporated within the Ito prescription. Finally, using numerical simulations with various initial conditions and parameter values, we statistically analyze the trajectories of the particle when placed within a harmonic trap and in presence of the soft surface. This allows us to: (i) quantify further the influence of surface softness, through the added mass, which enhances the velocity fluctuations; and (ii) show that intermediate-time diffusion is unaffected by softness, within the assumptions of the model.
Le mouvement brownien proche de surfaces déformables est une situation fréquemment rencontrée en physique à l’échelle nanométrique et en biologie. Cependant, une description théorique complète fait encore défaut à ce jour. Dans cet article, nous étudions théoriquement la dynamique d’un colloïde bidimensionnel soumis à un potentiel extérieur arbitraire, au voisinage d’une surface élastique. Cette dernière est modélisée de manière minimale par une réponse de type Winkler, et nous restreignons l’étude au mouvement du colloïde dans la direction perpendiculaire à la surface. Nous commençons par des considérations hydrodynamiques déterministes, en invoquant les forces de lubrification élastique, au premier ordre en déformabilité, déjà établies. Il est important de noter qu’une masse ajoutée, négative et dépendante de la position, induite par la déformation de la surface, est identifiée. Nous incorporons ensuite les fluctuations thermiques dans la description. En particulier, une formulation hamiltonienne effective est introduite et un potentiel généralisé dépendant de la température est construit afin d’assurer les propriétés d’équilibre pour la position du colloïde. À partir de ces considérations et de l’équation de Fokker–Planck, nous dérivons ensuite l’équation de Langevin pertinente, qui permet de retrouver de manière auto-consistante l’équation déterministe du mouvement à température nulle. Il est intéressant de noter qu’en plus du bruit multiplicatif attendu, le corrélateur du bruit semble être modifié par la déformabilité de la surface. De plus, un terme de dérive spurieuse dépendant de la température, induit par l’élasticité, doit être incorporé dans la prescription d’Ito. Enfin, en utilisant des simulations numériques avec diverses conditions initiales et valeurs de paramètres, nous analysons statistiquement les trajectoires de la particule lorsqu’elle est placée dans un piège harmonique en présence de la surface élastique. Cela nous permet de : (i) quantifier l’influence de l’élasticité de la surface, à travers la masse ajoutée, qui renforce les fluctuations de vitesse ; et (ii) montrer que la diffusion à temps intermédiaire est indépendante de l’élasticité, dans les hypothèses du modèle.
Revised:
Accepted:
Published online:
Mots-clés : Mouvement brownien, lubrification élastique, élasticité
Yilin Ye 1, 2; Yacine Amarouchene 1; Raphaël Sarfati 3; David S. Dean 1; Thomas Salez 1
CC-BY 4.0
@article{CRPHYS_2025__26_G1_619_0,
author = {Yilin Ye and Yacine Amarouchene and Rapha\"el Sarfati and David S. Dean and Thomas Salez},
title = {Brownian motion near a soft surface},
journal = {Comptes Rendus. Physique},
pages = {619--630},
year = {2025},
publisher = {Acad\'emie des sciences, Paris},
volume = {26},
doi = {10.5802/crphys.263},
language = {en},
}
TY - JOUR AU - Yilin Ye AU - Yacine Amarouchene AU - Raphaël Sarfati AU - David S. Dean AU - Thomas Salez TI - Brownian motion near a soft surface JO - Comptes Rendus. Physique PY - 2025 SP - 619 EP - 630 VL - 26 PB - Académie des sciences, Paris DO - 10.5802/crphys.263 LA - en ID - CRPHYS_2025__26_G1_619_0 ER -
Yilin Ye; Yacine Amarouchene; Raphaël Sarfati; David S. Dean; Thomas Salez. Brownian motion near a soft surface. Comptes Rendus. Physique, Volume 26 (2025), pp. 619-630. doi: 10.5802/crphys.263
[1] A brief account of microscopical observations made in the months of June, July and August, 1827, on the particles contained in the pollen of plants; and on the general existence of active molecules in organic and inorganic bodies, Philos. Mag., Volume 4 (1828) no. 21, pp. 161-173 | DOI
[2] Investigations on the theory of the Brownian movement, Dover Publications, 1956, 122 pages | Zbl
[3] Mouvement brownien et molécules, J. Phys. Théor. Appl., Volume 9 (1910) no. 1, pp. 5-39 | DOI
[4] Sur la théorie du mouvement brownien, C. R. Acad. Sci. Paris, Volume 146 (1908), pp. 530-533
[5] Irreversibility and generalized noise, Phys. Rev., Volume 83 (1951) no. 1, 34 | DOI
[6] Über die von der molekularkinetischen Theorie der Wärme geforderte Bewegung von in ruhenden Flüssigkeiten suspendierten Teilchen, Ann. Phys. (Berlin), Volume 322 (1905) no. 8, pp. 549-560 | DOI
[7] Markoff random processes and the statistical mechanics of time‐dependent phenomena. II. Irreversible processes in fluids, J. Chem. Phys., Volume 22 (1954) no. 3, pp. 398-413 | DOI
[8] Statistical-mechanical theory of irreversible processes. I. General theory and simple applications to magnetic and conduction problems, J. Phys. Soc. Japan, Volume 12 (1957) no. 6, pp. 570-586 | DOI
[9] Transport of soft matter in complex and confined environments (2025) | arXiv
[10] Confined Brownian motion, Phys. Rev. E, Volume 49 (1994) no. 6, 5158 | DOI
[11] Die Bewegung einer starren Kugel langs der Achse eines mit zaher Flussigkeit gefullten Rohres, Ark. Mat. Astron. Fys., Volume 17 (1923), pp. 1-28
[12] The slow motion of a sphere through a viscous fluid towards a plane surface, Chem. Eng. Sci., Volume 16 (1961) no. 3, pp. 242-251 | DOI
[13] Statistics of particle trajectories at short time intervals reveal fN-scale colloidal forces, Phys. Rev. Lett., Volume 99 (2007), 018303 | DOI
[14] Anisotropic and hindered diffusion of colloidal particles in a closed cylinder, Langmuir, Volume 26 (2010) no. 22, 16722 | DOI
[15] Test of the diffusing-diffusivity mechanism using near-wall colloidal dynamics, Phys. Rev. E, Volume 96 (2017) no. 4, 042604 | DOI
[16] Rolling and aging in temperature-ramp soft adhesion, Phys. Rev. E, Volume 97 (2018), 012609 | DOI
[17] Stochastic inference of surface-induced effects using Brownian motion, Phys. Rev. Res., Volume 3 (2021) no. 3, L032011, 6 pages | DOI
[18] Non-Gaussian diffusion near surfaces, Phys. Rev. Lett., Volume 130 (2023) no. 7, 077101 | DOI
[19] Numerical simulations of confined Brownian-yet-non-Gaussian motion, Eur. Phys. J. E, Volume 46 (2023) no. 4, 24, 11 pages | DOI
[20] Hydrodynamic coupling of two Brownian spheres to a planar surface, Phys. Rev. Lett., Volume 85 (2000), 3317 | DOI
[21] Effect of the wall on the velocity autocorrelation function and long-time tail of Brownian motion, J. Phys. Chem. B, Volume 109 (2005) no. 45, 21406 | DOI
[22] Broadband boundary effects on Brownian motion, Phys. Rev. E, Volume 92 (2015), 062106 | DOI
[23] Probing the nanohydrodynamics at liquid-solid interfaces using thermal motion, Phys. Rev. Lett., Volume 96 (2006), 046101 | DOI
[24] Brownian motion near a liquid-like membrane, Eur. Phys. J. E, Volume 20 (2006), pp. 379-385 | DOI
[25] Hydrodynamic mobility of an optically trapped colloidal particle near fluid-fluid interfaces, Phys. Rev. Lett., Volume 103 (2009), 248303 | DOI
[26] Microparticle Brownian motion near an air-water interface governed by direction-dependent boundary conditions, J. Colloid Interface Sci., Volume 629 (2023), pp. 917-927 | DOI
[27] Transport and dispersion across wiggling nanopores, Nat. Phys., Volume 14 (2018), pp. 1108-1113 | DOI
[28] Enhanced diffusive transport in fluctuating porous media, ACS Nano, Volume 15 (2021) no. 4, pp. 7392-7398 | DOI
[29] Particle mobility between two planar elastic membranes: Brownian motion and membrane deformation, Phys. Fluids, Volume 28 (2016) no. 7, 071903 | DOI
[30] Brownian motion of soft particles near a fluctuating lipid bilayer, J. Chem. Phys., Volume 159 (2023) no. 24, 244903 | DOI
[31] Correlations in suspensions confined between viscoelastic surfaces: noncontact microrheology, Phys. Rev. E, Volume 96 (2017), 022607 | DOI
[32] Enhanced diffusion over a periodic trap by hydrodynamic coupling to an elastic mode (2025) | arXiv
[33] Observation of Brownian elastohydrodynamic forces acting on confined soft colloids, Proc. Natl. Acad. Sci. USA, Volume 121 (2024) no. 42, e2411956121, 7 pages | DOI
[34] A mechanism for shear thickening of polymer-bearing surfaces: elasto-hydrodynamic coupling, Europhys. Lett., Volume 23 (1993) no. 2, 113 | DOI
[35] Optimal lift force on vesicles near a compressible substrate, Europhys. Lett., Volume 67 (2004) no. 4, 676 | DOI
[36] Soft lubrication, Phys. Rev. Lett., Volume 92 (2004) no. 24, 245509 | DOI
[37] Soft lubrication: the elastohydrodynamics of nonconforming and conforming contacts, Phys. Fluids, Volume 17 (2005) no. 9, 092101 | DOI
[38] Transient elastohydrodynamic drag on a particle moving near a deformable wall, Q. J. Mech. Appl. Math., Volume 59 (2006) no. 2, pp. 277-300 | DOI
[39] The elastohydrodynamic force on a sphere near a soft wall, Phys. Fluids, Volume 19 (2007) no. 10, 103106 | DOI
[40] Soft swimming: exploiting deformable interfaces for low Reynolds number locomotion, Phys. Rev. Lett., Volume 101 (2008) no. 4, 048102 | DOI
[41] Dynamic deformations and forces in soft matter, Soft Matter, Volume 5 (2009) no. 15, pp. 2858-2861 | DOI
[42] Asymptotic theory of the elastohydrodynamic adhesion and gliding motion of a solid particle over soft and sticky substrates at low Reynolds numbers, J. Fluid Mech., Volume 653 (2010), pp. 391-429 | DOI
[43] Similarity theory of lubricated Hertzian contacts, Phys. Fluids, Volume 25 (2013) no. 10, 101705 | DOI
[44] Elastohydrodynamics of a sliding, spinning and sedimenting cylinder near a soft wall, J. Fluid Mech., Volume 779 (2015), pp. 181-196 | DOI
[45] Lubrication of soft viscoelastic solids, J. Fluid Mech., Volume 799 (2016), pp. 433-447 | DOI
[46] Mobility of an axisymmetric particle near an elastic interface, J. Fluid Mech., Volume 811 (2017), pp. 210-233 | DOI
[47] Reciprocal theorem for the prediction of the normal force induced on a particle translating parallel to an elastic membrane, Phys. Rev. Fluids, Volume 3 (2018) no. 8, 084101 | DOI
[48] Regimes of soft lubrication, J. Fluid Mech., Volume 915 (2021), A49, 23 pages | DOI
[49] Lift forces on three-dimensional elastic and viscoelastic lubricated contacts, Phys. Rev. Fluids, Volume 6 (2021) no. 3, 034003 | DOI
[50] Soft-lubrication interactions between a rigid sphere and an elastic wall, J. Fluid Mech., Volume 933 (2022), A23 | DOI
[51] Effect of fluid viscoelasticity, shear stress, and interface tension on the lift force in lubricated contacts, J. Chem. Phys., Volume 159 (2023) no. 16, 164106 | DOI
[52] Similarity solutions in elastohydrodynamic bouncing, J. Fluid Mech., Volume 986 (2024), A13, 22 pages | DOI
[53] Capillary lubrication of a spherical particle near a fluid interface, J. Fluid Mech., Volume 1001 (2024), A58, 17 pages | DOI
[54] Singular viscoelastic perturbation to soft lubrication, Phys. Rev. Res., Volume 6 (2024), 043060, 6 pages | DOI
[55] Jump of an atomic force microscopy probe towards an elastic substrate in a liquid environment, J. Fluid Mech., Volume 1013 (2025), A49 | DOI
[56] Shear flow experiments in an assembly of gel beads and modelling of bingham behavior, Polym. Adv. Technol., Volume 3 (1992) no. 1, pp. 33-39 | DOI
[57] Dynamic interactions between microbubbles in water, Proc. Natl. Acad. Sci. USA, Volume 107 (2010) no. 25, pp. 11177-11182 | DOI
[58] Hydrodynamic interaction between a spherical particle and an elastic surface: a gentle probe for soft thin films, Phys. Rev. Lett., Volume 108 (2012) no. 26, 264501 | DOI
[59] Effect of surface elasticity on the rheology of nanometric liquids, Phys. Rev. Lett., Volume 111 (2013) no. 21, 215701 | DOI
[60] Hydrodynamic force between a sphere and a soft, elastic surface, Langmuir, Volume 30 (2014) no. 39, pp. 11619-11624 | DOI
[61] Experimental study and modeling of boundary lubricant polyelectrolyte films, Macromolecules, Volume 48 (2015) no. 7, pp. 2244-2253 | DOI
[62] Out-of-contact elastohydrodynamic deformation due to lubrication forces, Phys. Rev. Lett., Volume 115 (2015) no. 24, 248302 | DOI
[63] Self-sustained lift and low friction via soft lubrication, Proc. Natl. Acad. Sci. USA, Volume 113 (2016) no. 21, pp. 5847-5849 | DOI
[64] Noncontact viscoelastic imaging of living cells using a long-needle atomic force microscope with dual-frequency modulation, Phys. Rev. Appl., Volume 8 (2017) no. 4, 044010 | DOI
[65] Membrane-induced hydroelastic migration of a particle surfing its own wave, Nat. Phys., Volume 14 (2018) no. 12, pp. 1211-1215 | DOI
[66] Elastohydrodynamic lift at a soft wall, Phys. Rev. Lett., Volume 120 (2018) no. 19, 198001 | DOI
[67] Compliant surfaces under shear: elastohydrodynamic lift force, Langmuir, Volume 35 (2019) no. 48, pp. 15605-15613 | DOI
[68] Direct measurement of the elastohydrodynamic lift force at the nanoscale, Phys. Rev. Lett., Volume 124 (2020) no. 5, 054502 | DOI
[69] Direct measurement of the viscocapillary lift force near a liquid interface, Phys. Rev. Lett., Volume 134 (2025) no. 9, 094001 | DOI
[70] Elastic deformation during dynamic force measurements in viscous fluids, Curr. Opin. Colloid Interface Sci., Volume 27 (2017), pp. 43-49 | DOI
[71] Small-scale flow with deformable boundaries, J. Indian Inst. Sci., Volume 98 (2018) no. 2, pp. 159-183 | DOI
[72] Lift at low Reynolds number, Eur. Phys. J. E, Volume 46 (2023), 111 | DOI
[73] Fluid-elastic interactions near contact at low Reynolds number, Ann. Rev. Fluid Mech., Volume 56 (2024) no. 1, pp. 491-519 | DOI
[74] Validity of Winkler’s mattress model for thin elastomeric layers: beyond Poisson’s ratio, Proc. R. Soc. Lond., Ser. A, Volume 476 (2020) no. 2242, 20200551, 27 pages | DOI
[75] Highly resolved Brownian motion in space and in time, Ann. Rev. Fluid Mech., Volume 51 (2019) no. 1, pp. 403-428 | DOI
[76] Fluid-mediated force on a particle due to an oscillating plate and its effect on deposition measurements by a quartz crystal microbalance, Phys. Rev. Lett., Volume 125 (2020) no. 14, 144501 | DOI
[77] Unsteady drag force on an immersed sphere oscillating near a wall, J. Fluid Mech., Volume 977 (2023), A21 | DOI
[78] Stochastic differential equations: an introduction with applications, Universitext, Springer, 2013, xxxi+379 pages
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