Using Topological Defects To Engineer Self-Healing Materials

Nematic liquid crystals, commonly found in television displays, could find wider applications as a controllable scaffold for nano-sized colloids.

AsianScientist (Jun. 23, 2015) – A group of researchers from Osaka University and the Advanced Industrial Science and Technology (AIST) has developed technology for controlling the number and shapes of topological defects in nematic liquid crystal film. Their results, published in Nature Communications, also demonstrated that objects measuring a few microns could be reversibly operated by a low voltage of 2V or less.

Nematic liquid crystal is an intermediate phase between solid and liquid made up of rod-like molecules and is a common material for displays. Topological defects in liquid crystals not only affect the optical and rheological (flow) properties of the host material, but can also act as scaffolds to trap nano or micro-sized colloidal objects.

Topological defects have drawn attention as one way of expanding possibilities of the use of nematic liquid crystals other than displays—creating a gel capable of repairing itself or producing a special light wave called an “optical vortex” for example.

However, it has been difficult to control the number and shape of topological defects. This is because the creation of complex defect shapes involves confining the liquid crystals in curved geometries or adding complex-shaped colloidal objects.

Through the use of topologically patterned substrates, the researchers demonstrated the controlled generation of three-dimensional defect lines with non-trivial shapes and even chirality in a flat slab of nematic liquid crystal. By using the defect lines as templates and exploiting the electrical response of liquid crystals, they constructed colloidal superstructures that could be reversibly reconfigured by voltages as low as 1.3 V.

Although liquid crystal has become synonymous with televisions, many materials also exist in the liquid crystalline state, such as functional high molecule materials used for bulletproof vests, organic semiconductors used for solar batteries and biological materials such as DNA.

Since this group’s technology for controlling the number and shapes of topological defects can be used for all types of materials, it could contribute to applications in a wide range of areas. Three-dimensional engineering of the defect shapes in liquid crystals is potentially useful in the fabrication of self-healing composites and in stabilizing artificial frustrated phases.

The article can be found at: Yoshida et al. (2015) Three-Dimensional Positioning And Control Of Colloidal Objects Utilizing Engineered Liquid Crystalline Defect Networks.

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Source: Osaka University.
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