Interfacial modification and structural transitions induced by guest molecules solubilized in U-type nonionic microemulsions

TY - JOUR

T1 - Interfacial modification and structural transitions induced by guest molecules solubilized in U-type nonionic microemulsions

AU - Garti, Nissim

AU - Amar, Idit

AU - Yaghmur, Anan

AU - Spernath, Aviram

AU - Aserin, Abraham

PY - 2003/5/1

Y1 - 2003/5/1

N2 - Alcohols and polyols are essential components (in addition to the surfactant, water, and oil) in the formation of U-type self-assembled nano-structures, (sometimes called L-phases or U-type microemulsions). These microemulsions are characterized by large isotropic regions ranging from the oil side of the phase diagram up to the aqueous corner. The isotropic oily solutions of reverse micelles ("the concentrates") can be diluted along some dilution lines with aqueous phase to the "direct micelles" corner via a bicontinuous mesophases (i.e., two structural transitions). This dilution takes place with no phase separations or occurrence of liquid crystalline phases. The structural transitions were determined by viscosity, conductivity, and pulsed gradient spin echo NMR (PGSE NMR), and are not visible to the eye. Two guest nutraceutical molecules (lutein and phytosterols) were solubilized, at their maximum solubilization capacity, in the reversed micellar solutions (L2 phase) and were further diluted with the aqueous phase to the aqueous micellar corner (L1 phase). Structural transitions (for the two types of molecule) from water-in-oil to bicontinuous microstructures were induced by the guest molecules. The transitions occurred at an earlier stage of dilution, at a lower water content (20 wt.% aqueous phase), than in the empty (blank) microemulsions (transitions at 30 wt.% aqueous phase). The transitions from the bicontinuous microstructure to the oil-in-water microemulsions were retarded by the solubilizates and occurred at later dilution stage at higher aqueous phase contents (50 wt.% aqueous region for empty microemulsion and >60 wt.% for solubilized microemulsion). As a result, the bicontinuous isotropic region, in the presence of the guest molecules, becomes much broader. It seems that the main reason for such "guest-induced structural transitions" is related to a significant flattening and enhanced rigidity of the interface. The guest molecules of the high molecular volume are occupying high volume fraction of the interface (when the solubilization is maximal).

AB - Alcohols and polyols are essential components (in addition to the surfactant, water, and oil) in the formation of U-type self-assembled nano-structures, (sometimes called L-phases or U-type microemulsions). These microemulsions are characterized by large isotropic regions ranging from the oil side of the phase diagram up to the aqueous corner. The isotropic oily solutions of reverse micelles ("the concentrates") can be diluted along some dilution lines with aqueous phase to the "direct micelles" corner via a bicontinuous mesophases (i.e., two structural transitions). This dilution takes place with no phase separations or occurrence of liquid crystalline phases. The structural transitions were determined by viscosity, conductivity, and pulsed gradient spin echo NMR (PGSE NMR), and are not visible to the eye. Two guest nutraceutical molecules (lutein and phytosterols) were solubilized, at their maximum solubilization capacity, in the reversed micellar solutions (L2 phase) and were further diluted with the aqueous phase to the aqueous micellar corner (L1 phase). Structural transitions (for the two types of molecule) from water-in-oil to bicontinuous microstructures were induced by the guest molecules. The transitions occurred at an earlier stage of dilution, at a lower water content (20 wt.% aqueous phase), than in the empty (blank) microemulsions (transitions at 30 wt.% aqueous phase). The transitions from the bicontinuous microstructure to the oil-in-water microemulsions were retarded by the solubilizates and occurred at later dilution stage at higher aqueous phase contents (50 wt.% aqueous region for empty microemulsion and >60 wt.% for solubilized microemulsion). As a result, the bicontinuous isotropic region, in the presence of the guest molecules, becomes much broader. It seems that the main reason for such "guest-induced structural transitions" is related to a significant flattening and enhanced rigidity of the interface. The guest molecules of the high molecular volume are occupying high volume fraction of the interface (when the solubilization is maximal).

KW - Food-grade

KW - Lutein

KW - Microemulsion

KW - Microstructure transition

KW - Non-ionic surfactant

KW - Phytosterols

UR - http://www.scopus.com/inward/record.url?scp=0042740551&partnerID=8YFLogxK

U2 - 10.1081/DIS-120021797

DO - 10.1081/DIS-120021797

M3 - Journal article

AN - SCOPUS:0042740551

SN - 0193-2691

VL - 24

SP - 397

EP - 410

JO - Journal of Dispersion Science and Technology

JF - Journal of Dispersion Science and Technology

IS - 3-4

ER -