Theoretical and experimental study of the nanoparticle-driven blue phase stabilisation

• Published in: The European physical journal. E, Soft matter and biological physics Vol. 34; no. 2; p. 17
• Main Authors: Rožič, B., Tzitzios, V., Karatairi, E., Tkalec, U., Nounesis, G., Kutnjak, Z., Cordoyiannis, G., Rosso, R., Virga, E. G., Muševič, I., Kralj, S.
• Format: Journal Article
• Language: English
• Published: Berlin/Heidelberg Springer-Verlag 01-02-2011; EDP Sciences
• Subjects: Biological and Medical Physics; Biophysics; Complex Fluids and Microfluidics; Complex Systems; Condensed matter: structure, mechanical and thermal properties; Exact sciences and technology; Liquid crystals; Nanotechnology; Physics; Physics and Astronomy; Polymer Sciences; Regular Article; Soft and Granular Matter; Structure of solids and liquids; crystallography; Surfaces and Interfaces; Thin Films; Disclination Line; Cholesteric Phase; CdSe Nanoparticles; Aerosil; Oleyl Amine; Nanoparticles; Specific heat; Orientational order; Landau theory; Phase separation; Boundary conditions; Phase stability; Cholesteric crystals; Liquid crystals; Free energy; Defects
• ISSN: 1292-8941; 1292-895X
• DOI: 10.1140/epje/i2011-11017-8

.
We have studied theoretically and experimentally the effects of various types of nanoparticles (NPs) on the temperature stability range
T
BP
of liquid-crystalline (LC) blue phases. Using a mesoscopic Landau-de Gennes type approach we obtain that the
defect core replacement
(DCR) mechanism yields in the diluted regime
T
BP
(
x
)
1/(1 -
xb
) , where
x
stands for the concentration of NPs and
b
is a constant. Our calculations suggest that the DCR mechanism is efficient if a local NP environment resembles the core structure of disclinations, which represent the characteristic property of BP structures. These predictions are in line with high-resolution ac calorimetry and optical polarising microscopy experiments using the CE8 LC and CdSe or aerosil NPs. In mixtures with CdSe NPs of 3.5nm diameter and hydrophobic coating the BPIII stability range has been extended up to 20K. On the contrary, the effect of aerosil silica nanoparticles of 7.0nm diameter and hydrophilic coating is very weak.