Self-assembly in surfactant-based mixtures driven by acid–base reactions: bis(2-ethylhexyl) phosphoric acid–n-octylamine systems

Abstract

Structural and dynamic features of bis(2-ethylhexyl) phosphoric acid (HDEHP)-n-octylamine (NOA) mixtures as a function of the NOA mole fraction (X NOA ) have been investigated by SAXS, WAXS, IR, dielectric spectroscopy and polarized optical microscopy. In the 0 ¡ X NOA , 0.5 range, mixtures are transparent liquids, while the abrupt formation of a waxy solid characterized by an hexagonal bidimensional structure occurs at X NOA = 0.5. Such a composition-induced phase transition results from the synergetic effect of the progressive increase in number density of ordered HDEHP-NOA nanodomains with X NOA . Mainly driven by an HDEHP to NOA proton transfer, the increase of structural order with X NOA arises from the progressive substitution of loosely hydrogen bonded HDEHP-HDEHP aggregates with strongly bonded NOA-HDEHP ones. Analysis of SAXS patterns at temperatures in the 10-70 uC range emphasized that these local structures are scarcely impacted by an increase of thermal fluctuations. Effects due to the steric compatibility between HDEHP and NOA apolar moieties have been highlighted. Overall, the results allow us to emphasize the role of specific polar and apolar interactions joined to steric effects in regulating the molecular organization in surfactant mixtures and can be used to design novel materials with planned physico-chemical properties.

How self-assembly of amphiphilic molecules can generate complexity in the nanoscale

“…6A) [17,50]. It is interesting to note that the building of unidirectional structures causes an obvious increase in viscosity but also an unexpected reduction of the activation energy of the diffusion and longitudinal relaxation time as reported in the graph of Fig.…”

Dynamical Properties of Self-Assembled Surfactant-Based Mixtures: Triggering of One-Dimensional Anomalous Diffusion in Bis(2-ethylhexyl)phosphoric Acid/n-Octylamine Systems

“…7 Such composition-induced disorder−order transition becomes impressive in the X NOA = 0.5 sample, which appears macroscopically as a waxy solid and, consequently, the 1 H NMR spectrum is characterized by a single very broad signal, centered at 1.85 ppm.…”

Recent Developments on 1,3-Dipolar Cycloaddition Reactions by Catalysis in Green Solvents

“…In addition, it is worth noticing that it has been recently found that ionic liquids can be easily prepared by simply mixing two opportunely chosen amphiphilic liquids [18]. In this case, further additional properties can arise, like anysotropical self-assembly [19,20], response to an external magnetic field [21], enhanced proton conductivity [22], and enhanced capability of salt solubilization [23], which can open a wide scenario of new and promising applications.…”