Structural and dynamic features of bis(2-ethylhexyl) phosphoric acid (HDEHP)–n-octylamine (NOA)mixtures as a function of the NOA mole fraction (XNOA) have been investigated by SAXS, WAXS, IR,dielectric spectroscopy and polarized optical microscopy. In the 0 ¡ XNOA , 0.5 range, mixtures aretransparent liquids, while the abrupt formation of a waxy solid characterized by an hexagonalbidimensional structure occurs at XNOA = 0.5. Such a composition-induced phase transition results fromthe synergetic effect of the progressive increase in number density of ordered HDEHP–NOA nanodomainswith XNOA. Mainly driven by an HDEHP to NOA proton transfer, the increase of structural order with XNOAarises from the progressive substitution of loosely hydrogen bonded HDEHP–HDEHP aggregates withstrongly bonded NOA–HDEHP ones. Analysis of SAXS patterns at temperatures in the 10–70 uC rangeemphasized that these local structures are scarcely impacted by an increase of thermal fluctuations. Effectsdue 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 inregulating the molecular organization in surfactant mixtures and can be used to design novel materialswith planned physico-chemical properties.
|Numero di pagine||8|
|Stato di pubblicazione||Published - 2013|
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