How Dimensionality Affects the Structural Anomaly in a Core-Softened Colloid

Abstract

The interaction between hard core–soft shell colloids are characterized by having two characteristic distances: one associated with the penetrable, soft corona and another one corresponding to the impenetrable core. Isotropic core-softened potentials with two characteristic length scales have long been applied to understand the properties of such colloids. Those potentials usually show water-like anomalies, and recent findings have indicated the existence of multiple anomalous regions in the 2D limit under compression, while in 3D, only one anomalous region is observed. In this direction, we perform molecular dynamics simulations to unveil the details about the structural behavior in the quasi-2D limit of a core-softened colloid. The fluid was confined between highly repulsive solvophobic walls, and the behavior at distinct wall separations and colloid densities was analyzed. Our results indicated a straight relation between the 2D- or 3D-like behavior and layer separation. We can relate that if the system behaves as independent 2D-layers, it will have a 2D-like behavior. However, for some separations, the layers are connected, with colloids hopping from one layer to another, thus having a 3D-like structural behavior. These findings fill the gap in the depiction of the anomalous behavior from 2D to 3D.

Core-softened colloid under extreme geometrical confinement

“…In our system, N = 1000 particles were confined between parallel, smooth walls, whose interaction potential is purely repulsive, given by R6 potential, as follow 19,23,85 where z is the distance between the particles and the walls, A = 4.0, B = 0.1875, z c / σ = 2.0 and U R6 c = A ( σ / z c ) 6 + B ( z c / σ ). The dashed black line of Fig.…”

“…18 Confinement can induce structural changes, such as the formation of ordered and disordered layers of particles. 14,19 Moreover, the presence of surfaces in close proximity can influence particle–surface interactions, resulting in adsorption or depletion effects. By adjusting the slit size, shape, and surface properties, it is possible to manipulate phase transitions and enhance colloidal stability, 12,17,20–23 impacting the rheological and mechanical properties of the system.…”

“…80,81 Additionally, the ramp-like model led to reentrant melting phases between the distinct crystals, which are related to a second and a third region of water-like anomalies, and later shown that these extra anomalous regions vanish as the system transitions from a 2D-like, layered regime under confinement to the 3D limit. 19 This, along with inspiration from experimental works, 5,66,79 led to another question: if confinement can induce anomalous regions, can it induce new crystalline morphologies in the system?…”