TY - JOUR
T1 - Phase inversion characteristics observed upon water dilution of a bidiscontinuous phase
AU - Goldmünz, Eliezer
AU - Aserin, Abraham
AU - Garti, Nissim
N1 - Publisher Copyright:
© 2019
PY - 2020/2/5
Y1 - 2020/2/5
N2 - This study presents a directly aggregated pseudo-ternary system. The three apexes of the investigated system represent a surfactant phase [Tween 80:propylene glycol (9:1 wt ratio)], an oil phase [isopropyl myristate:benzyl alcohol (7.5:2.5 wt ratio)], and water. Within the pseudo-ternary system, water dilution line, termed N91 (90 wt% surfactant phase and 10 wt% oil phase), was found to represent transparent and thermodynamically stable compositions from concentrate to high water dilution (>95 wt% water). Despite that the system was found to be directly aggregated, dilution line N91 exhibited classical L2→L1 phase inversion characteristics (at 39 wt% water). To explain this phenomenon, a novel structural interpretation regarding the observed inversion as an obstruction of the bidiscontinuous phase, consisting of oil and water-segregated domains, is proposed. The evaluation of dilution line N91 was based on electrical conductivity, SAXS, SD-NMR, rheometry, DSC and cryo-TEM. The structural transitions along water dilution line N91 were found to be as follows: 'pseudo L1' (pseudo direct surfactant-oil aggregates) → bi-discontinuous structure (of which partial is a hexagonal H1 mesophase) → L1. We concluded that the high concentration of low CPP (critical packing parameter) surfactant plays a major role in determining the system's geometry throughout the water dilution line. As a result, the proposed interpretation of the structural inversion observed along dilution line N91 differs from the classical U-type inversion interpretation (L2 →bicontinuous →L1).
AB - This study presents a directly aggregated pseudo-ternary system. The three apexes of the investigated system represent a surfactant phase [Tween 80:propylene glycol (9:1 wt ratio)], an oil phase [isopropyl myristate:benzyl alcohol (7.5:2.5 wt ratio)], and water. Within the pseudo-ternary system, water dilution line, termed N91 (90 wt% surfactant phase and 10 wt% oil phase), was found to represent transparent and thermodynamically stable compositions from concentrate to high water dilution (>95 wt% water). Despite that the system was found to be directly aggregated, dilution line N91 exhibited classical L2→L1 phase inversion characteristics (at 39 wt% water). To explain this phenomenon, a novel structural interpretation regarding the observed inversion as an obstruction of the bidiscontinuous phase, consisting of oil and water-segregated domains, is proposed. The evaluation of dilution line N91 was based on electrical conductivity, SAXS, SD-NMR, rheometry, DSC and cryo-TEM. The structural transitions along water dilution line N91 were found to be as follows: 'pseudo L1' (pseudo direct surfactant-oil aggregates) → bi-discontinuous structure (of which partial is a hexagonal H1 mesophase) → L1. We concluded that the high concentration of low CPP (critical packing parameter) surfactant plays a major role in determining the system's geometry throughout the water dilution line. As a result, the proposed interpretation of the structural inversion observed along dilution line N91 differs from the classical U-type inversion interpretation (L2 →bicontinuous →L1).
KW - Bidiscontinuous
KW - DSC
KW - Microemulsions
KW - Oil-in-water
KW - SAXS
KW - Tween-80
UR - http://www.scopus.com/inward/record.url?scp=85076039489&partnerID=8YFLogxK
U2 - 10.1016/j.colsurfa.2019.124213
DO - 10.1016/j.colsurfa.2019.124213
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AN - SCOPUS:85076039489
SN - 0927-7757
VL - 586
JO - Colloids and Surfaces A: Physicochemical and Engineering Aspects
JF - Colloids and Surfaces A: Physicochemical and Engineering Aspects
M1 - 124213
ER -