Self-assembly of model short triblock amphiphiles in dilute solution

Abstract

In this work, a molecular theory is used to study the self-assembly of short diblock and triblock amphiphiles, with head-tail and head-linker-tail structures, respectively. The theory was used to systematically explore the effects of the molecular architecture and the affinity of the solvent for the linker and tail blocks on the relative stability of the different nanostructures formed by the amphiphiles in dilute solution, which include spherical micelles, cylindrical fibers and planar lamellas. Moreover, the theory predicts that each of these nanostructures can adopt two different types of internal organization: (i) normal nanostructures with a core composed of tail segments and a corona composed of head segments, and (ii) nanostructures with a core formed by linker segments and a corona formed by tail and head segments. The theory predicts the occurrence of a transition from micelle to fiber to lamella when increasing the length of the tail or the linker blocks, which is in qualitative agreement with the geometric packing theory and with experiments in the literature. The theory also predicts a transition from micelle to fiber to lamella as the affinity of the solvent for the tail or linker block is decreased. This result is also in qualitative agreement with experiments in the literature but cannot be explained in terms of the geometric packing theory. The molecular theory provides an explanation for this result in terms of the competition between solvophobic attractions among segments in the core and steric repulsions between segments in the corona for the different types of self-assembled nanostructures.

Acid-Base Equilibrium and Dielectric Environment Regulate Charge in Supramolecular Nanofibers

“…The possibility of molecular reorganization depends also on the strength of the β -sheet hydrogen bonds of the peptides. Only by a large structural transition, which involves enthalpic and entropic penalties, from a cylindrical nanofiber to a spherical micelle can the electrostatic penalty be reduced ( Israelachvili, 2011 ; Zaldivar et al, 2018 ; Zaldivar et al, 2019 ). This occurs experimentally for pH above 8.…”

“…Very noteworthy are the recent theoretical investigations by Zaldivar et al, who applied the same Molecular Theory approach to self-assemble of peptide amphiphiles and demonstrated the structural transitions between bilayer, cylindrical, and spherical structured nanofibers can occur as a function of pH ( Zaldivar et al, 2018 ; Zaldivar et al, 2019 ). Observe they opted to represent the peptide amphiphiles with much more coarse-graining.…”

“…Likewise, a similar approach was used to investigate the effect of solution conditions on the charge regulation of bacteriophage capsids ( Nap et al, 2014a ) and the absorption of acidic ligands to quantum dots ( Westmoreland et al, 2019 ). Also noteworthy is a recent study by Tagliazucchi et al in which the molecular theory was used to study the self-assembly of neutral and chargeable peptide amphiphiles ( Zaldivar et al, 2018 ; Zaldivar et al, 2019 ). However, ion-condensation and effects related to the electrostatic solvation free energy were not considered.…”

Molecular Basis for the Morphological Transitions of Surfactant Wormlike Micelles Triggered by Encapsulated Nonpolar Molecules

“…10,11,14,15,18 ■ THEORETICAL METHODS General Model. Our theory is based on our previous studies on the self-assembly of neutral triblock surfactants 37 and lysineterminated peptide amphiphiles. 38 It is derived from a MOLT previously developed by Szleifer and co-workers.…”

“…Morphology of the Aggregates and Thermodynamic Stability. As in our previous studies, 37,38 we assessed the morphology of the aggregates by considering three possible ideal shapes: spheres, infinitely long cylinders (wormlike micelles), and infinitely extended planar lamellas. These three ideal morphologies can be described using only one spatial coordinate, r, which represents the radial distance for spheres and cylinders and the distance to the central plane for lamellas.…”