Abstract
Two structural studies of the following two liquid crystals systems: [(C12EO4 + 1% SDS)/H2O, ca. 25–85 wt.% surfactant] and [(C12EO8 + 1% SDS)/H2O, ca. 40–71 wt.% surfactant] have been investigated. Both previous systems contain similar amount of Sodium Dodecyl Sulphate, SDS. It has been found that there are two mesophases at 25°C: the lamellar Lα and the hexagonal H1. Their structural parameters were determined using small angle X-ray scattering (SAXS) patterns. The mesophases study of the Lα and H1 regions allows the evolution description of the surfactant chains conformation.
The geometrical parameters of the Lα and H1 mesophases such as the thickness of hydrocarbon core of the lamellar mesophase and the diameter of rods forming the hexagonal structure were calculated. In the lamellar, Lα and the hexagonal, H1 mesophases, the surface area per molecule and the thickness of the hydrocarbon core exhibited a little sensitivity change toward concentration. The thickness of the ethoxy groups was estimated in Lα and H1 mesophases as a function of surfactant concentration in (C12EO4 + 1% SDS)/H2O and (C12EO8 + 1% SDS)/H2O systems at 25°C, respectively.
Kurzfassung
Die Strukturen der beiden flüssigkristallinen Systeme [(C12EO4 + 1% SDS)/H2O, ca. 25–85 wt.% Tensid] und [(C12EO8 + 1% SDS)/H2O, ca. 40–71 wt.% Tensid] wurden untersucht. Beide enthielten ähnliche Mengen an Natriumdodecylsulfat (SDS). Es konnte gezeigt werden, dass die Systeme bei 25°C zwei Mesophasen ausbilden: die lamellare Lα- und die hexagonale H1-Phase. Die strukturellen Parameter wurden mittels Kleinwinkelröntgenstreuung (SAXS) bestimmt. Die Untersuchung der Mesophasen in der Lα- und der H1-Region ermöglicht die Beschreibung der Tensidkettenkonformation.
Die geometrischen Parameter der Lα- und der H1-Mesophase, wie die Dicke des Kohlenwasserstoffkerns der lamellaren Mesophase oder der Durchmesser in der hexagonalen Mesophase gebildeten Stäbchen, wurden berechnet. In der lamellaren Lα- und der hexagonalen H1-Mesophase zeigten der Oberflächenplatzbedarf pro Molekül und die Dicke des Kohlenwasserstoffkerns eine geringe Abhängigkeit gegenüber der Konzentration. Die Dicke der Ethoxy-Gruppen in der Lα- und H1-Mesophase wurde als Funktion der Tensidkonzentration in den (C12EO4 + 1% SDS)/H2O und (C12EO8 + 1% SDS)/H2O-Systemen bei 25°C berechnet.
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