Dynamical simulation of electrostatic striped colloidal particles

Abstract

The static and dynamic properties of striped colloidal particles are obtained using molecular dynamics computer simulations. Striped particles with n = 2 to n = 7 stripes of alternating electric charge are modeled at a high level of detail through a pointwise (PW) representation of the particle surface. We also consider the extent to which striped particles are similar to comparable isotropically attractive particles-such as depletion attracting colloids-by modeling striped particles with an isotropic pair interaction computed by coarse-graining (CG) over orientations at a pair level. Surprisingly, the CG models reproduce the static structure of the PW models for a range of volume fractions and interaction strengths consistent with the fluid region of the phase diagram for all n. As a corollary, different n-striped particle systems with comparable pair affinities (e.g., dimer equilibrium constant) have similar static structure. Stronger pair interactions lead to a collapsed structure in simulation as consistent with a glass-like phase. Different n-striped particle systems are found to have different phase boundaries and for certain n's no glass-like state is observed in any of our simulations. The CG model is found to have accelerated dynamics relative to the PW model for the same range of fluid conditions for which the models have identical static structure. This suggests striped electrostatic particles have slower dynamics than comparable isotropically attractive colloids. The slower dynamics result from a larger number of long-duration reversible bonds between pairs of striped particles than seen in isotropically attractive systems. We also found that higher n-striped particles systems generally have slower dynamics than lower n-striped systems with comparable pair affinities.

Molecular dynamics out of equilibrium: mechanics and measurables

“…The combination of hard core and soft interactions (including Coulomb forces) are used in more elaborated models like the CHARMM and AMBER force fields, the DLVO potential for spherically symmetrical colloidal particles or colloids with asymmetrically distributed surface charges …”

“…The combination of hard core and soft interactions (including Coulomb forces) are used in more elaborated models like the CHARMM 29,30 and AMBER 31,32 force fields, the DLVO potential for spherically symmetrical colloidal particles 33 or colloids with asymmetrically distributed surface charges. [34][35][36] In some cases, the pairwise additivity assumption breaks down. Typical corrections involve the minimal inclusion of 3-body and higher-order-body forces successively in the potential as needed to obtain agreement with experiment.…”

“…A nonlinear regime emerges if one considers a hierarchy of dynamical events at various length scales which are so strongly coupled that it is difficult to separate the microscopic reaction coordinate(s) and the characteristic nonstationary response of the environment. Emerging efforts target physical examples in which the time scales of the microscopic system and the complex environment are sufficiently coupled that it does not trivially reduce to adiabatic coupling, while also being sufficiently tractable that the models can be connected to an underlying molecular representation of the system and its environment. As it is difficult to speed up the environment to match the rates of the microscopic subsystem, a reasonable alternative is to slow down the microscopic subsystem.…”

A Cuban Campesino in Chemistry’s Academic Court

“…A selected snapshot of Hernandez’s research efforts shown (clockwise from top left) through journal covers spanning across transition state theory (reprinted with permission from ref , copyright 2010 Elsevier), Janus and striped particles (reprinted with permission from ref , copyright 2014 AIP Publishing), diffusion through complex environments (reprinted with permission from ref , copyright 2010 American Chemical Society), stochastic hard collisions (reprinted with permission from ref , copyright 2018 Elsevier), sustainable nanoparticles (reprinted with permission from ref , copyright 2016 American Chemical Society), and diversity equity (reprinted with permission from ref , copyright 2018 American Chemical Society).…”

Effective Surface Coverage of Coarse-Grained Soft Matter

“…The phase and spatial behavior observed in the assembly of a monomeric species into oligomeric clusters − drives the design of materials with unique functionalities. − At atomistic length scales, the structural complexity arising from assembly is often difficult to describe using analytical theory or to simulate on relevant time scales due to the large numbers of degrees of freedom that constitute such systems. To reduce this complexity, the atomistic degrees of freedom can be reduced to a coarse-grained (CG) description where a group of atomic degrees of freedom is mapped onto a single CG site. − At mesoscopic length scales, CG macromolecules can be modeled using repulsive potentials that are finite valued at the origin, i.e., bounded potentials. , The finite nature of bounded interactions allows for multiple macromolecules to overlap and occupy the same volume in configuration space. , Studies of mesoscopic systems with interactions dictated by bounded potentials include colloid suspensions, polymer–colloid mixtures, star polymers, and block copolymers. , …”