Liquid Crystals in Aqueous Micellar Solutions

Organic liquids which are nearly insoluble in water, such as alkanes, can be solubilized in aqueous phases containing surfactant micelles. The mechanism and kinetics of micellar solubilization has been extensively studied (see [A. A. Pena and C. A. Miller, Adv. Coll. Int. Sci. 123-126, 241 (2006)] for a recent review) for various combinations of organic liquids and surfactants.

We study the behavior of single liquid crystal drops which are immersed into aqueous phases containing an ionic surfactant at concentrations well above the critical  micelle concentration (cmc). We observe that a nematic order has only a small effect on the solubilization process whereas a smectic order strongly influences the occurring transient structures: Smectic drops form filament structures which resemble the myelin figures which appear when lyotropic lamellar phases are brought in contact with water. When nematic or isotropic drops are immersed in the surfactant solution, we observe a linear decrease of the drop size with time and the presence of convective flows and self-propelled motions of the droplets. Also, the transient formation of emulsions is observed: Tiny aqueous droplets appear in the nematic or isotropic drops and, at low temperatures, nematic drops expell tiny nematic droplets into the aqueous environment.

Fig 1: Micrograph (polarizers not completely crossed) of a MBBA drop floating in an aqueous C14TAB solution (c = 10 weight%), showing the spontaneous expulsion of tiny droplets into the aqueous phase. Bild vergrößern
Fig 1: Micrograph (polarizers not completely crossed) of a MBBA drop floating in an aqueous C14TAB solution (c = 10 weight%), showing the spontaneous expulsion of tiny droplets into the aqueous phase.
Fig 2: Micrograph (polarizers not completely crossed) of the interface between 8CB and an aqueous C14TAB solution (c = 1 weight%), showing the growth of myelin-like structures into the aqueous phase. Bild vergrößern
Fig 2: Micrograph (polarizers not completely crossed) of the interface between 8CB and an aqueous C14TAB solution (c = 1 weight%), showing the growth of myelin-like structures into the aqueous phase.

Find more information:

Solubilization of Thermotropic Liquid Crystal Compounds in Aqueous Surfactant Solutions
K. Peddireddy, P. Kumar, S. Thutupalli, S. Herminghaus, and Ch. Bahr, Langmuir 28, 12426 (2012).
DOI: 10.1021/la3015817

Myelin Structures Formed by Thermotropic Smectic Liquid Crystals
K. Peddireddy, P. Kumar, S. Thutupalli, S. Herminghaus, and Ch. Bahr, Langmuir 29, 15682 (2013).
DOI: 10.1021/la4038588

Lasing and waveguiding in smectic A liquid crystal optical fibers
K. Peddireddy, V. S. R. Jampani, S. Thutupalli, S. Herminghaus, Ch. Bahr, and I. Musevic, Opt. Express 21, 30233 (2013).
DOI: 10.1364/OE.21.030233

 
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