Interparticle Interactions in Colloidal Systems: Toward a Comprehensive Mesoscale Model

Abstract

Intermolecular interactions control the collective behavior of colloidal clusters. The overwhelming majority of literature focuses on cohesive attributes of intermolecular forces as they govern the jamming process. However, the overlooked sliding component plays a critical role in the slow relaxation dynamics of colloidal aggregates and the emergence of discontinuous shear thickening in dense suspensions. Here, we use crystalline calcium-silicate-hydrate (C-S-H) as a model system to explore synergistic cohesive and sliding interactions. We use the free energy perturbation approach to reconstruct potential of mean force profile between two finite-sized nanolayers in an aqueous environment. We show that sliding free energy barriers decay exponentially as the separation distance increases. The characteristic length scale of the decay is related to the interface corrugation. We introduce a simple yet effective mechanism to capture the sliding behavior of colloids with surface roughness. Moreover, we develop a global free energy landscape model by juxtaposing cohesive and sliding interactions. This model enables us to measure the height of energy barriers, which is essential to elucidate deformation mechanism and dynamics of colloidal aggregates. For cohesive colloids, our approach predicts a sublinear relation between applied normal and shear stress at the onset of sliding that is in contrast to Amontons' laws of friction. We demonstrate that the sublinear trend is due to the adhesion and nature of soft contact at the nanoscale. The proposed framework provides a new route to draw a more realistic picture of intermolecular interactions in nanoparticulate systems such as geomaterials, cementitious systems, complex colloidal assemblies, and dense suspensions.

Nanolayered attributes of calcium‐silicate‐hydrate gels

“…For the end‐to‐end interaction, we did not observe significant oscillations and there is only one stable state of the interaction. Also, the PMF shows a wide curvature similar to that obtained for Tobermorite previously …”

“…Also, the PMF shows a wide curvature similar to that obtained for Tobermorite previously. 57 From the PMF, we calculate molecular level elastic modulus along the basal spacing as:…”

“…As a result of strong ionic correlation forces, 41,42,57,92 C-S-H nanolayers adhere strongly together and form colloidal nanosized clusters. 79,93 Due to the absence of foreign surface for heterogeneous nucleation of C-S-H layers in our simulations, the texture of our mesoscale models resembles those of inner products, and it is distinct from that of fibrillar outer products that precipitate on the surface of cement clinkers.…”

“…The distribution skews toward denser local packing densities as a result of an increase in overall packing fraction [Color figure can be viewed at wileyonlinelibrary.com] simulations. 41,42,57 These MPFs are dominated by layers' face-to-face interactions as a result of attractive ionic correlation effects that cannot be described via the mean-field theories such as the celebrated DLVO theory. The features of these free energy curves in the face-to-face direction govern the behaviors of the gel at the mesoscale.…”

Mesoscale simulation of aggregation of imogolite nanotubes from potential of mean force interactions

“…Further investigations are taken in the direction of altering the surface chemistry of the tubes, tuning the salinity of the solution, and adjusting the temperature and pressure of the systems to find the optimal stacking condition. We also plan to refine the representation of the computed PMF curve by either combining LJ and Yukawa potentials [31] or Fourier series [32]. We will also plan to study the mechanical properties of the tube assembly [33] as a function of their length.…”