New Lyotropic Mixtures with Non-Chiral N-Acylamino Acid Surfactants Presenting the Biaxial Nematic Phase Investigated by Laser Conoscopy, Polarized Optical Microscopy and X-ray Diffraction

Abstract

Amino acid-based surfactants were used as the main surfactants to prepare new lyotropic mixtures presenting three nematic phases. One of them is biaxial (NB), and the two others are uniaxial, discotic (ND) and calamitic (NC). These surfactants were the non-chiral molecules, potassium N-dodecanoyl-dl-alaninate (dl-KDDA), potassium N-dodecanoyl-dl-serinate (dl-KDDS), disodium N-dodecanoyl-dl-aspartate (dl-NaDDAs) and potassium N-dodecanoyl-glycinate (KDDGly). Measurements of the optical birefringences and X-ray diffraction analysis were used to characterize the nematic phases and phase transitions. Mixtures with dl-KDDS exhibited the largest biaxial phase domain (~9 °C) with respect to the other mixtures in this study. The results obtained with the KDDGly mixture showed that the existence of hydrogen bonding between the head groups of the surfactant molecules seems to hinder the orientation of the micelles under the action of an external magnetic field.

Composition and Formation of Liquid Crystal Domains in Hydrocarbon Resources

“…The HA concentration in this case, 1 order of magnitude less than the critical micelle concentration, is too low for it to form liquid crystals on its own in water. The spontaneous aggregation of amphiphilic molecules/surfactants on the outer surfaces of hydrocarbon drops and liquid crystal formation on hydrocarbon drop surfaces in ternary water–surfactant–hydrocarbon mixtures has been reported previously. − We further demonstrate this by adding 1 μg of 5CB to the water (74 mL) + octacosane (10 mg) mixture. We obtain the same outcome with this positive control (Figure b).…”

“…Their cooperative self-assembly leads to the formation of anisotropic water + HA spheres in water above the critical micelle concentration . This lyotropic behavior is expected over a broad range of temperatures and is also observed for PEG-8 distearate (CAS Registry Number 9005-08-7), non-chiral N -acylamino acid, and sodium naphthenates − in water. The details of self-assembly are typically temperature-dependent .…”

“…Formation processes for liquid crystal layers at hydrocarbon–water interfaces using surface-active liquid-crystal-forming materials are more apparent. The formation of liquid crystal shells surrounding hydrocarbon drops dispersed in water − or surrounding water drops dispersed in hydrocarbon liquids , follow established fluid physics principles. For such liquid crystal shells to occur, the aqueous or hydrocarbon phase does not need to be saturated with the surface-active material.…”

“…Since then, numerous works concerning preparation, property measurement, property prediction, and applications have appeared and are exemplified here. − To construct aqueous core + liquid crystal shell domains dispersed in an aqueous phase, a less obvious case, the molecules forming the shell must be at or above their saturation concentration in the two aqueous phases. For surfactants, this means above the critical micelle concentration. − Stabilizers may also be included in the phases, and they impact the structure of the liquid crystal shells formed. The domain size and shell thickness are variables that can be controlled.…”

Effect of Dopant Structure on Birefringences and Symmetric Tensor Invariants of Lyotropic Nematic Phases

“…Properties of lyotropic nematic phases (LNPs) have been extensively investigated for several years to understand their formation mechanism and to find which factors affect obtaining the different nematic phases [1][2][3][4]. Their main property, which attracts the attention of the researchers, is that the local directors of their building blocks, so-called "micelles", exhibit average preferred alignment in a certain direction along the whole sample.…”