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Spontaneous size selection in cholesteric and nematic emulsions.
T Tixier1, M Heppenstall-Butler, E M Terentjev
1Cavendish Laboratory, University of Cambridge, Madingley Road, Cambridge CB3 0HE, UK.
Langmuir : the ACS Journal of Surfaces and Colloids
|February 24, 2006
Summary
Liquid crystal emulsions spontaneously form narrow droplet size distributions. Droplets smaller than a critical radius coalesce freely, while larger, topologically charged droplets are stable, freezing the size distribution.
Area of Science:
- Colloid and Surface Science
- Soft Matter Physics
- Materials Science
Background:
- Liquid crystal emulsions exhibit complex behaviors influenced by interfacial properties.
- Spontaneous size selection is a key phenomenon in emulsion formation.
- Topological defects within droplets can significantly alter emulsion stability.
Purpose of the Study:
- To investigate the mechanism of spontaneous size selection in lyotropic cholesteric (W/O) and thermotropic nematic (O/W) liquid crystal emulsions.
- To characterize the droplet size distribution and identify factors controlling it.
- To understand the role of topological defects and interfacial anchoring in emulsion stability.
Main Methods:
- Dynamic light scattering (DLS) for droplet size characterization.
- Analysis of droplet coalescence based on topological charge.
- Determination of critical radius (R) based on Frank elastic (K) and surface anchoring (W) constants.
Main Results:
- A narrow, monomodal droplet size distribution is achieved spontaneously without filtration.
- Droplets smaller than the critical radius (R < K/W) lack topological charge and coalesce freely, depleting smaller sizes.
- Larger droplets (R > K/W) possess a +1 topological charge, creating an energy barrier that prevents coalescence and "freezes" the size distribution.
Conclusions:
- Spontaneous size selection in liquid crystal emulsions is governed by a balance between droplet size, topological charge, and interfacial anchoring energy.
- The critical radius (R = K/W) acts as a threshold for droplet stability and coalescence.
- The findings provide insights into controlling emulsion properties through interfacial engineering and understanding self-assembly processes in soft matter.