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

Area of Science:

• Materials Science
• Condensed Matter Physics
• Soft Matter Physics

Background:

• Liquid-crystalline (LC) blue phases (BPs) exhibit unique structural properties.
• The temperature stability range of BPs is crucial for their applications.
• Nanoparticles (NPs) are explored as a means to modify LC properties.

Purpose of the Study:

• To investigate the effect of various nanoparticles on the temperature stability range of LC blue phases.
• To theoretically and experimentally determine the mechanism behind NP influence on BP stability.
• To identify nanoparticle characteristics that optimize BP temperature stability.

Main Methods:

• Mesoscopic Landau-de Gennes type theoretical approach.
• High-resolution ac calorimetry.
• Optical polarising microscopy.

Main Results:

• A theoretical model predicts that the defect core replacement (DCR) mechanism enhances BP stability, dependent on NP concentration (x) and a constant (b).
• The DCR mechanism is effective when the local NP environment mimics the disclination core structure of BPs.
• Experimentally, CdSe NPs (3.5nm, hydrophobic) extended the BPIII stability range by up to 20K.
• Aerosil NPs (7.0nm, hydrophilic) showed a negligible effect on BP stability.

Conclusions:

• The defect core replacement (DCR) mechanism is a key factor in enhancing the temperature stability of liquid-crystalline blue phases with nanoparticles.
• Hydrophobic CdSe nanoparticles effectively stabilize blue phases, while hydrophilic aerosil nanoparticles do not.
• Tailoring nanoparticle properties, such as surface chemistry and size, is critical for optimizing their impact on blue phase stability.