Multicritical behaviors and an induced twist grain boundary phase in a binary liquid crystalline mixture

Area of Science:

• Materials Science
• Condensed Matter Physics
• Physical Chemistry

Background:

• Chiral tolans are liquid crystal materials with complex phase behaviors.
• Theoretical models, such as Renn and Lubensky's, predict specific phase diagrams for these compounds.
• Understanding these phase diagrams is crucial for potential applications in display technologies and other fields.

Purpose of the Study:

• To experimentally determine the composition-temperature phase diagram of a mixture of n=9 and n=16 chiral tolans (nF(2)BTFO1M7).
• To compare the experimental findings with the theoretical predictions of the Renn and Lubensky model.
• To investigate the influence of composition on the mesophase behavior and identify phase transitions.

Main Methods:

• Synthesis and preparation of chiral tolans mixtures (n=9 and n=16).
• Optical microscopy for phase identification and characterization.
• Photothermal methods for determining transition temperatures.
• Analysis of the composition-temperature phase diagram.

Main Results:

• The experimental phase diagram for the nF(2)BTFO1M7 mixture was established.
• The pure compounds n=9 and n=16 exhibit distinct phase sequences: Cry-Sm-C*-Sm-A-TGB(A)-N*-BP-I and Cry-Sm-C*-N*-BP-I, respectively.
• Upon increasing the n=16 composition, the Sm-A and twist grain boundary phase A (TGB(A)) mesophases disappeared, and a TGB(C) phase emerged.
• Four out of five predicted multicritical points from the Renn and Lubensky model were experimentally identified.

Conclusions:

• The experimental phase diagram provides a validation of theoretical predictions for chiral liquid crystal mixtures.
• The study highlights the tunability of mesophase behavior through composition in chiral tolans.
• The identification of multiple multicritical points underscores the complexity and richness of the observed phase transitions.