20 research outputs found
Premicellar aggregation of amphiphilic molecules: Aggregate lifetime and polydispersity
A recently introduced thermodynamic model of amphiphilic molecules in
solution has yielded, under certain realistic conditions, a significant
presence of metastable aggregates well below the critical micelle concentration
-- a phenomenon that has been reported also experimentally. The theory is
extended in two directions pertaining to the experimental and technological
relevance of such premicellar aggregates. (a) Combining the thermodynamic model
with reaction rate theory, we calculate the lifetime of the metastable
aggregates. (b) Aggregation number fluctuations are examined. We demonstrate
that, over most of the metastable concentration range, the premicellar
aggregates should have macroscopic lifetimes and small polydispersity.Comment: 7 pages, 2 figure
Free energy approach to micellization and aggregation: Equilibrium, metastability, and kinetics
Differential capacity and chronocoulometry studies of a quaternary ammonium surfactant adsorbed on Au(111)
The biphasic effect of ABA triblock copolymers on the self-assembly of surfactants: insight from dissipative particle dynamics
Nonclassical Hydrophobic Effect in Micellization: Molecular Arrangement of Non-Amphiphilic Structures
Micellization brought about by nonclassical hydrophobic effect invokes enthalpy as the driving force. Thus, the underlying molecular phenomena differ from the entropically dominated hydrophobic effect. In quest for a molecular-scale understanding, we report on the molecular arrangement of nonamphiphilic structures of an anionic boron cluster compound, COSAN. We synergistically combine experimental (NMR and calorimetry) and theoretical (molecular dynamics and quantum chemical calculations) approaches. The experimental data support the mechanism of closed association of COSAN, where the self-assembly is driven by the enthalpy contribution to the free energy. Molecular dynamics simulations in explicit solvent show that water molecules form a patchy network around COSAN molecules, giving rise to the strong hydrophobic self-association. In the second solvation shell, water forms a slightly hydrophilic âspotâ close to the C-H segments of the cluster. The simulations further show a counterintuitive short-range [COSAN]ââââ[COSAN]â attraction and Na+âââ[COSAN]â repulsion. Quantum chemical calculations reveal a major role of solvation in stabilizing the contact pairs. Further, the calculations show the parallel/X-shape geometrical arrangements of COSAN dimers as the most preferred. Lastly, dihydrogen bonding are found to influence the structure of micelles. In summary, we provide a molecular view of nonclassical micellization that can be extended to other amphiphiles like boranes