Abstract
We present a novel simulation technique derived from Brownian cluster dynamics used so far to study the isotropic colloidal aggregation. It now implements the classical Kern-Frenkel potential to describe patchy interactions between particles. This technique gives access to static properties, dynamics and kinetics of the system, even far from the equilibrium. Particle thermal motions are modeled using billions of independent small random translations and rotations, constrained by the excluded volume and the connectivity. This algorithm, applied to a single polymer chain leads to correct static and dynamic properties, in the framework where hydrodynamic interactions are ignored. By varying patch angles, various local chain flexibilities can be obtained. We have used this new algorithm to model step-growth polymerization under various solvent qualities. The polymerization reaction is modeled by an irreversible aggregation between patches while an isotropic finite square-well potential is superimposed to mimic the solvent quality. In bad solvent conditions, a competition between a phase separation (due to the isotropic interaction) and polymerization (due to patches) occurs. Surprisingly, an arrested network with a very peculiar structure appears. It is made of strands and nodes. Strands gather few stretched chains that dip into entangled globular nodes. These nodes act as reticulation points between the strands. The system is kinetically driven and we observe a trapped arrested structure. That demonstrates one of the strengths of this new simulation technique. It can give valuable insights about mechanisms that could be involved in the formation of stranded gels.
Highlights
The structure and dynamics of a wide range of complex liquids is determined by the aggregation of small particles in solution such as colloids,1–4 proteins,5–7 micelles8,9 or oil droplets.10 Depending on the concentration, the range and strength of the attraction, stable cluster dispersions, transient gels, glasses, phase separated systems can be formed
To mimic the particle Brownian motion resulting from the random collisions with the solvent molecules, a random force, and a friction term are introduced in the equations of motion; leading to either dissipative particle dynamics (DPD) if hydrodynamic interactions are taken into account or Brownian dynamics (BD) if not
PRELIMINARY RESULTS ON STEP-GROWTH POLYMERIZATION: FORMATION OF OUT OF EQUILIBRIUM ARRESTED STRANDED GELS
Summary
The structure and dynamics of a wide range of complex liquids is determined by the aggregation of small particles in solution such as colloids, proteins, micelles or oil droplets. Depending on the concentration, the range and strength of the attraction, stable cluster dispersions, transient gels, glasses, phase separated systems can be formed (see, for example, recent reviews). In order to better understand these processes computer simulations have been done on model systems They are important tools in colloidal physics giving relevant insights about the structure and dynamical properties, even far from the equilibrium. Newtonian dynamic simulations are numerically solving the equations of motion for a set of particles. Nowadays BD techniques can deal with a set of 104 particles integrating the equations of the motion over a physical time up to few seconds for micrometric colloidal particles in water at 20 ◦C. This approach is very useful to investigate systems that rapidly reach their equilibrium. This is generally the case in the one phase domain of the phase diagram
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