NDLI: Measuring the Anisotropy in Interfacial Tension of Nematic Liquid Crystals

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Measuring the Anisotropy in Interfacial Tension of Nematic Liquid Crystals

Content Provider	MDPI
Author	Honaker, Lawrence Sharma, Anjali Schanen, Andy Lagerwall, Jan
Copyright Year	2021
Abstract	Liquid crystal (LC) phases typically show anisotropic alignment-dependent properties, such as viscosity and dielectric permittivity, so it stands to reason that LCs also have anisotropic interfacial tensions. Measuring the interfacial tension $γ$ of an LC with conventional methods, such as pendant drops, can be challenging, however, especially when we need to know $γ$ for different LC aligning conditions, as is the case when we seek $Δ γ$ , the interfacial tension anisotropy. Here, we present measurements of $Δ γ$ of the common synthetic nematic LC compound 5CB against water using a microfluidic droplet aspiration technique. To ensure tangential and normal alignment, respectively, we add poly(vinyl alcohol) (PVA) and sodium dodecylsulfate (SDS), respectively, as a stabilizer and measure $γ$ for different concentrations of stabilizer. By fitting the Szyszkowski equation to the data, we can extrapolate to zero-stabilizer concentration, obtaining the $γ$ of 5CB to pure water for each alignment. For normal alignment, we find $γ_{⊥} = 31.9 \pm 0.8$ mN·m⁻¹, on the order of 1 mN·m⁻¹ greater than $γ_{\| \|} = 30.8 \pm 5$ mN·m $^{- 1}$ for tangential alignment. This resonates with the empirical knowledge that 5CB aligns tangentially to an interface with pure water. The main uncertainty arises from the use of polymeric PVA as tangential-promoting stabilizer. Future improvements in accuracy may be expected if PVA can be replaced by a low molar mass stabilizer that ensures tangential alignment.
Starting Page	687
e-ISSN	20734352
DOI	10.3390/cryst11060687
Journal	Crystals
Issue Number	6
Volume Number	11
Language	English
Publisher	MDPI
Publisher Date	2021-06-15
Access Restriction	Open
Subject Keyword	Crystals Crystallography Liquid Crystal Interfacial Tension Surface Tension Alignment Anisotropy Pva Sds Microfluidics
Content Type	Text
Resource Type	Article

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