AI Article Synopsis
- A new quaternary mixture of DDTMABr, sodium bromide, 1-dodecanol, and water exhibits both biaxial and uniaxial nematic phases, indicating complex liquid-crystalline behavior.
- The study included constructing a partial phase diagram and examining how phase transitions occur based on DDTMABr concentration and temperature through optical birefringence methods.
- An unusual phenomenon during the transition from biaxial to uniaxial phases was observed, linked to the micelles' shape anisotropy, which was confirmed by small-angle X-ray scattering showing lower shape anisotropy compared to other systems.
Article Abstract
A novel quaternary lyotropic liquid-crystalline mixture of dodecyltrimethylammonium bromide (DDTMABr)/sodium bromide/1-dodecanol/water, presenting the biaxial nematic phase (NB ) in addition to two uniaxial discotic (ND) and calamitic (NC) nematic ones, was synthesized. The partial phase diagram of this new mixture was constructed as a function of the DDTMABr molar-fraction concentration. The phase transitions from uniaxial to biaxial nematic phases were studied by means of the temperature dependence of the optical birefringence. In a particular region of the phase diagram, anomalous behavior was observed in the crossover from N-B to N+b: the contrast of the conoscopic fringes, which allows the birefringence measurements, almost vanishes, and the sample loses its alignment. This behavior, which was not observed before in lyotropics, was interpreted as a decrease in the mean diamagnetic susceptibility anisotropy (Δχ) of the sample, which was related to the shape anisotropy of the micelles. Small-angle X-ray scattering measurements were performed to evaluate the micellar shape anisotropy; these revealed that this mixture presented a smaller shape anisotropy than those of other lyotropic micellar systems presenting the NB phase.
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| http://dx.doi.org/10.1002/cphc.201301003 | DOI Listing |
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