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Phase transition and dewetting of a 5CB liquid crystal thin film on a topographically patterned substrate

We report thermally induced nematic to isotropic (N–I) phase transition as well as dewetting of 5CB Liquid Crystal (LC) thin films coated on flat and topographically patterned substrates with grating geometry of different line width (l(P)) and periodicity (λ(P)). On a flat substrate, the nematic to...

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Autores principales: Dhara, Palash, Mukherjee, Rabibrata
Formato: Online Artículo Texto
Lenguaje:English
Publicado: The Royal Society of Chemistry 2019
Materias:
Acceso en línea:https://www.ncbi.nlm.nih.gov/pmc/articles/PMC9066433/
https://www.ncbi.nlm.nih.gov/pubmed/35518868
http://dx.doi.org/10.1039/c9ra02552a
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author Dhara, Palash
Mukherjee, Rabibrata
author_facet Dhara, Palash
Mukherjee, Rabibrata
author_sort Dhara, Palash
collection PubMed
description We report thermally induced nematic to isotropic (N–I) phase transition as well as dewetting of 5CB Liquid Crystal (LC) thin films coated on flat and topographically patterned substrates with grating geometry of different line width (l(P)) and periodicity (λ(P)). On a flat substrate, the nematic to isotropic (N–I) phase transition, which takes place within a temperature range between 31.1 °C and 34.4 °C is fully reversible, with re-appearance of identical Schlieren texture when the sample is cooled down during isotropic to nematic (I–N) transition. Upon further heating beyond N–I transition and annealing at T ≈ 65 °C, the film undergoes nucleated dewetting with formation and growth of holes, which eventually merge to form isolated droplets. The morphology of the dewetted structures remains unaltered when the film is cooled to room temperature from this stage, though the features undergo phase transition to the nematic state. In contrast on a topographically patterned substrate, the phase transition cycle is associated with a change of the texture of the film during cooling to the nematic stage. Interestingly the molecules exhibit homeotropic anchoring when λ(P) ≈ 1.5 μm and planar anchoring when λ(P) large (≈10 μm). When heated further to T ≈ 65 °C, the film dewets on topographically patterned substrates resulting in a collection of droplets, which are aligned to the substrate patterns when λ(P) is large (≈10 μm). In contrast the dewetted droplets are random and not correlated to the patterns when λ(P) is lower (≈1.5 μm).
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spelling pubmed-90664332022-05-04 Phase transition and dewetting of a 5CB liquid crystal thin film on a topographically patterned substrate Dhara, Palash Mukherjee, Rabibrata RSC Adv Chemistry We report thermally induced nematic to isotropic (N–I) phase transition as well as dewetting of 5CB Liquid Crystal (LC) thin films coated on flat and topographically patterned substrates with grating geometry of different line width (l(P)) and periodicity (λ(P)). On a flat substrate, the nematic to isotropic (N–I) phase transition, which takes place within a temperature range between 31.1 °C and 34.4 °C is fully reversible, with re-appearance of identical Schlieren texture when the sample is cooled down during isotropic to nematic (I–N) transition. Upon further heating beyond N–I transition and annealing at T ≈ 65 °C, the film undergoes nucleated dewetting with formation and growth of holes, which eventually merge to form isolated droplets. The morphology of the dewetted structures remains unaltered when the film is cooled to room temperature from this stage, though the features undergo phase transition to the nematic state. In contrast on a topographically patterned substrate, the phase transition cycle is associated with a change of the texture of the film during cooling to the nematic stage. Interestingly the molecules exhibit homeotropic anchoring when λ(P) ≈ 1.5 μm and planar anchoring when λ(P) large (≈10 μm). When heated further to T ≈ 65 °C, the film dewets on topographically patterned substrates resulting in a collection of droplets, which are aligned to the substrate patterns when λ(P) is large (≈10 μm). In contrast the dewetted droplets are random and not correlated to the patterns when λ(P) is lower (≈1.5 μm). The Royal Society of Chemistry 2019-07-12 /pmc/articles/PMC9066433/ /pubmed/35518868 http://dx.doi.org/10.1039/c9ra02552a Text en This journal is © The Royal Society of Chemistry https://creativecommons.org/licenses/by/3.0/
spellingShingle Chemistry
Dhara, Palash
Mukherjee, Rabibrata
Phase transition and dewetting of a 5CB liquid crystal thin film on a topographically patterned substrate
title Phase transition and dewetting of a 5CB liquid crystal thin film on a topographically patterned substrate
title_full Phase transition and dewetting of a 5CB liquid crystal thin film on a topographically patterned substrate
title_fullStr Phase transition and dewetting of a 5CB liquid crystal thin film on a topographically patterned substrate
title_full_unstemmed Phase transition and dewetting of a 5CB liquid crystal thin film on a topographically patterned substrate
title_short Phase transition and dewetting of a 5CB liquid crystal thin film on a topographically patterned substrate
title_sort phase transition and dewetting of a 5cb liquid crystal thin film on a topographically patterned substrate
topic Chemistry
url https://www.ncbi.nlm.nih.gov/pmc/articles/PMC9066433/
https://www.ncbi.nlm.nih.gov/pubmed/35518868
http://dx.doi.org/10.1039/c9ra02552a
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