| Summary: | 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 <inline-formula><math display="inline"><semantics><mi>γ</mi></semantics></math></inline-formula> of an LC with conventional methods, such as pendant drops, can be challenging, however, especially when we need to know <inline-formula><math display="inline"><semantics><mi>γ</mi></semantics></math></inline-formula> for different LC aligning conditions, as is the case when we seek <inline-formula><math display="inline"><semantics><mrow><mo>Δ</mo><mi>γ</mi></mrow></semantics></math></inline-formula>, the interfacial tension anisotropy. Here, we present measurements of <inline-formula><math display="inline"><semantics><mrow><mo>Δ</mo><mi>γ</mi></mrow></semantics></math></inline-formula> 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 <inline-formula><math display="inline"><semantics><mi>γ</mi></semantics></math></inline-formula> for different concentrations of stabilizer. By fitting the Szyszkowski equation to the data, we can extrapolate to zero-stabilizer concentration, obtaining the <inline-formula><math display="inline"><semantics><mi>γ</mi></semantics></math></inline-formula> of 5CB to pure water for each alignment. For normal alignment, we find <inline-formula><math display="inline"><semantics><mrow><msub><mi>γ</mi><mo>⊥</mo></msub><mo>=</mo><mn>31.9</mn><mo>±</mo><mn>0.8</mn></mrow></semantics></math></inline-formula> mN·m<sup>−1</sup>, on the order of 1 mN·m<sup>−1</sup> greater than <inline-formula><math display="inline"><semantics><mrow><msub><mi>γ</mi><mrow><mo>|</mo><mo>|</mo></mrow></msub><mo>=</mo><mn>30.8</mn><mo>±</mo><mn>5</mn></mrow></semantics></math></inline-formula> mN·m<inline-formula><math display="inline"><semantics><msup><mrow></mrow><mrow><mo>−</mo><mn>1</mn></mrow></msup></semantics></math></inline-formula> 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.
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