Whispering gallery mode study of phase transition and shape change in liquid crystal droplets

Neogi, Arkalekha (author), Zaplotnik, Jaka (author), Ravnik, Miha (author), Muševič, Igor (author)

We demonstrate that the Whispering Gallery Mode (WGM) lasing spectroscopy is a versatile high resolution tool to study the structure of interfaces of liquid crystalline (LC) droplets immersed in an immiscible fluid, such as water. The eigenfrequencies of WGMs in spherical microcavities are very sensitive to the refractive index profile in the nanometer thin interfacial region. This makes it possible to detect interfacial phenomena and temperature change in LC droplets with interferometric accuracy. We use 10–30 µm diameter droplets of a nematic liquid crystal labeled with a fluorescent dye and floating in water as an optical microcavity that sustains the WGMs. At the isotropic–nematic transition we observe wetting of the droplet's interface by a nanometer-thin layer of paranematic LC. Just below this transition, we observe red-shift and strong fluctuations of WGM spectra just before spherical droplet elongates into a fiber. The experiments are modeled with Finite-Difference Time-domain (FDTD) analysis of WGMs in nematic droplet and we find very good qualitative agreement.

• Language: English
• Keywords: Whispering Gallery Mode spectroscopy, liquid crystals, liquid crystal droplets
• Work type: Article
• Typology: 1.01 - Original Scientific Article
• Organization: FMF - Faculty of Mathematics and Physics
• Publication status: Published
• Publication version: Version of Record
• Year: 2026
• Number of pages: Str. 604-615
• Numbering: Vol. 22, iss. 3
• PID: 20.500.12556/RUL-178234
• UDC: 538.9
• ISSN on article: 1744-6848
• DOI: 10.1039/D5SM01126D
• COBISS.SI-ID: 264538627
• Publication date in RUL: 21.01.2026

Record is a part of a journal

• Title: Soft matter
• Shortened title: Soft matter
• Publisher: Royal Society of Chemistry
• ISSN: 1744-6848
• COBISS.SI-ID: 23741223

Licences

• License: CC BY 4.0, Creative Commons Attribution 4.0 International
• Link: http://creativecommons.org/licenses/by/4.0/
• Description: This is the standard Creative Commons license that gives others maximum freedom to do what they want with the work as long as they credit the author.

Secondary language

• Language: Slovenian
• Keywords: WGM spektroskopija, tekoči kristali, tekočekristalne kapljice

Projects

• Funder: EC - European Commission
• Project number: 884928
• Name: Light-operated logic circuits from photonic soft-matter
• Acronym: LOGOS