Effect of particle-size dynamics on properties of dense spongy-particle systems: Approach towards equilibrium

Abstract

Hütter, M. (2017). Effect of particle-size dynamics on properties of dense spongy-particle systems: Approach towards equilibrium. Physical Review E, 96(1), [012604]. DOI: 10.1103/PhysRevE.96.012604 General rights Copyright and moral rights for the publications made accessible in the public portal are retained by the authors and/or other copyright owners and it is a condition of accessing publications that users recognise and abide by the legal requirements associated with these rights.• Users may download and print one copy of any publication from the public portal for the purpose of private study or research.• You may not further distribute the material or use it for any profit-making activity or commercial gain • You may freely distribute the URL identifying the publication in the public portal ? Take down policyIf you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediately and investigate your claim. Open-porous deformable particles, often envisaged as sponges, are ubiquitous in biological and industrial systems (e.g. casein micelles in dairy products and microgels in cosmetics). The rich behavior of these suspensions is owing to the elasticity of the supporting network of the particle, and the viscosity of permeating solvent. Therefore, the rate-dependent size change of these particles depends on their structure, i.e. the permeability. This work aims at investigating the effect of the particle-size dynamics and the underlying particle structure, i.e. the particle permeability, on the transient and long-time behavior of suspensions of spongy particles in the absence of applied deformation, using the dynamic two-scale model developed by Hütter et al. [Faraday Discuss., 158, 407-424 (2012)]. In the high-density limit, the transient behavior is found to be accelerated by the particle-size dynamics, even at average size-changes as small as 1%. The accelerated dynamics is evidenced by (i) the higher short-time diffusion coefficient as compared to elastic-particle systems and (ii) the accelerated formation of the stable FCC crystal structure. Furthermore, after long times, the particle-size dynamics of spongy particles is shown to result in lower stationary values of the energy and normal stresses as compared to elastic-particle systems. This dependence of the long-time behavior of these systems on the permeability, that essentially is a transport coefficient and hence must not affect the equilibrium properties, confirms that full equilibration has not been reached.

Stress relaxation of dense spongy-particle systems

“…The size-dynamics of different particles are assumed to be hydrodynamically uncoupled. The position-and size-dynamics in dimensionless form are, respectively, (see [7] for more detail),…”

“…However, the definition of S * given by Eq. (9a) is convenient for scaling the evolution equations (7).…”

“…The overall properties of suspensions of permeable particles are tailored through variations of the elastic properties of the particle and their internal structure [5,6]. The elasticity of the particle allows it to impinge in response to steric effects [7,8] or applied deformation [9][10][11][12][13], which gives rise to its elastic softness. The internal structure of the particle, i.e.…”

“…Particle systems generally undergo a transition from a liquid-like to a solid-like behavior as system density increases [20]. Concentrated suspensions have been found to undergo slow dynamics [7,21,22] and their properties vary in time. The microstructure, during this solidification process, is not fully equilibrated and part of the stress introduced during preparation persists in the system.…”

“…Aging, in general, also occurs in the absence of load. For instance, the evolution of the properties of dense permeable particle systems is studied in [7] as they are brought from a high-energy state to a long-lived glassy state under no applied deformation. In the case of prior deformation, the residual or internal stresses are the stresses remaining in a material after load removal and that relax slowly as time evolves, being a signal of an ongoing aging process.…”