Coarse-Grained Molecular Dynamics Simulations of the Breakage and Recombination Behaviors of Surfactant Micelles

Abstract

Surfactant molecules can form micellar network structures that can be applied for turbulent drag reduction through their breakage and recombination behaviors. One of the mechanisms of turbulent drag reduction by surfactants is the "viscoelastic theory" as proposed by DeGennes. However, evaluating the rupture and coalescence properties of network micelles is challenging. Here, we study the breakage and recombination behaviors of an individual rodlike micelle using Martini coarse-grained force field molecular dynamics simulations. The flexibility of an individual micelle can be measured by its breakage energy. Micelle recombination behaviors can be attributed to three mechanisms: the coalescence energy, zeta potential, or hydrophobic driving effect of the surfactant micelles. Thus, an excellent micelle that is beneficial for turbulent drag reduction is difficult to rupture but easy to recombine. The breakage behavior should be considered prior to the recombination behavior, because the breakage energy of an individual micelle is approximately 1−2 magnitudes greater than its coalescence energy under various conditions. Organic counterion salts, such as salicylate sodium, favor micelle recombination because of their electrostatic screen effect and uneven distribution on the surfactant micelle surface. Furthermore, this work brings a novel approach to understanding the breakage and recombination behaviors of surfactant micelles, providing an essential and scientific guidance to the effective use of surfactants in turbulent drag reduction. It also provides direct evidence to support the viscoelastic theory.

Protobiotic Systems Chemistry Analyzed by Molecular Dynamics

“…By tracking these micelles along the experiment timeline, compositional vectors for each micellar state could be defined. Since micellar fission occurs in the 10 nanosecond time range, it is compatible with molecular dynamics [80,81,82], hence fission events could be discerned and analyzed as described [75,82]. Likewise, fusion events, despite being relatively rare, could be analyzed [83].…”

Interfacial Interaction Enhanced Rheological Behavior in PAM/CTAC/Salt Aqueous Solution—A Coarse-Grained Molecular Dynamics Study

“…, which can be found in many studies [50][51][52]. ij σ and ij ε are defined by the MARTINI force field [45].…”

“…where σ ij represents the effective distance of approach between two beads and ε ij is the depth of the potential well. The potential is truncated and shifted at a cutoff distance r = 1.2 nm, which can be found in many studies [50][51][52]. σ ij and ε ij are defined by the MARTINI force field [45].…”

“…The representative morphology was selected from the simulation results. From the figure, the spherical micelle had the smallest size; two or more spherical micelles coalesced and then formed a wormlike micelle; two wormlike micelles or one spherical micelle and one wormlike micelle coalesced and then a branch node exists and branched micelle forms, the branched micelle had the largest size [51]. Thus, if the concentration of CTAC is low, only small sized spherical micelles and wormlike micelles form; if the concentration increases, large wormlike micelles, and branched micelles will form.…”

Protobiotic Systems Chemistry Analyzed by Molecular Dynamics

“…This could be achieved by calculating local centers of mass [30] or more commonly, clustering molecular components together and assigning them to the same aggregate based on spatial distances, often by setting a limiting threshold [72,81]. By tracking these micelles along the experiment timeline, fission events could be discerned as described [77,82] and compositional vectors for each micellar state could be defined. Likewise, fusion events, despite being relatively rare, could be analyzed [83].…”