Dynamics and Scission of Rodlike Cationic Surfactant Micelles in Shear Flow

Abstract

Flow-induced configuration dynamics and scission of rodlike micelles are studied for the first time using molecular dynamics simulations in presence of explicit solvent and salt. Predicted dependence of tumbling frequency and orientation distribution on shear rate S agrees with mesoscopic theories. However, micelle stretching increases the distance between the cationic head groups and adsorbed counter ions, which reduces electrostatic screening and increases the overall energy Φ linearly with micelle length. Micelle scission occurs when Φ exceeds a threshold value, independent of S.

Nonmonotonic Scission and Branching Free Energies as Functions of Hydrotrope Concentration for Charged Micelles

“…Furthermore, we also compute the branching free energy of CTAC micelles as a function of hydrotrope concentration and use this and the scission free energy to explain the origin of the ubiquitous large peak in the viscosity of this micellar solution with increasing hydrotrope concentration. All CG simulations were performed using the MARTINI [28] force field which has been used extensively [4,[23][24][25] [29,30] to model these surfactant systems, and has been shown to reproduce many experimental observations including the sphere-to-rod transition and shearinduced micelle stretching energy. Details of the simulation protocol are given in the Supporting Information (SI) [31], which includes Refs.…”

Anomalous diffusion and stress relaxation in surfactant micelles

“…Further, depending upon the surfactant and salt concentrations, which in turn determine the microstructure, we observe normal, subdiffusive and superdiffusive motion of surfactants. Specifically, superdiffusive behavior is associated with branch sliding, breakage and recombination of micelle fragments as well as constraint release in entangled systems.Over the past decades, the structure, dynamics and mechanical properties of self-assembled aggregates of cationic surfactants have been studied extensively [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20]. Self-assembly of cationic surfactant solutions can be controlled by manipulating the solvent-mediated electrostatic interactions among the surfactant molecules by altering the counter ion concentration.…”

“…Over the past decades, the structure, dynamics and mechanical properties of self-assembled aggregates of cationic surfactants have been studied extensively [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20]. Self-assembly of cationic surfactant solutions can be controlled by manipulating the solvent-mediated electrostatic interactions among the surfactant molecules by altering the counter ion concentration.…”

“…For times shorter than the reptation time (t ≤ τ r ), superdiffusive behavior was often observed while subdiffusive behavior was more common for τ >> τ r . On the other hand, normal CGMD simulations of a model [6][7][8] of CTAC-NaSal solution in water are conducted using the LAMMPS [24] molecular dynamics package. This model utilizes the MARTINI force field [25] for representing the interactions among the branch shown in the movie moves approximately ∼ 10 nm in 50 ns.…”

Scission energy and topology of micelles controlled by the molecular structure of additives

“…1(a–c)) as it has been widely used to study these surfactant systems and is capable of reproducing many experimental properties including sphere-to-rod transition, shear induced micelle stretching energy and nonmonotonic zero-shear viscosity of micellar solutions. 44–47,54,55,57–63 First, we built a linear micelle containing 250 SDS surfactants which spans the simulation box along the Z direction as shown in Fig. 1(d).…”