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Abstract It is well-known that orientational order of nematic liquid crystals (NLCs) is converted during phase transition from the long-range order (LRO) in the nematic phase to the short-range order (SRO) in the isotropic state. Finding the initial temperature range of SRO in the isotropic state can be a challenging issue because most of the physical constants disappear after this phase transition. For the first time, to resolve this issue, we introduced a new method based on the electro-optic Kerr (EOK) effect in NLC mixtures. In this method, the coherence length (ξ), which was qualitatively estimated by employing the pre-transitional temperature (T ⁎) according to the de Gennes phenomenological theory, and the refractive index (n) were correlated with the Kerr constant (B) at the same temperature in the isotropic phase. Because molecular interaction in the NLCs is one of the essential factors in the investigation of the orientational ordering, we used n and ξ as described intra- and intermolecular interactions, respectively. In other words, n attributes to the polarization and dipole moment as an important parameter of the intramolecular interaction and ξ demonstrates the intermolecular interaction and domains of SRO interaction in the isotropic phase. Finally, the initial temperature range of SRO in the isotropic phase was found from the temperature dependence with B of the normalized values of influential coefficients n and ξ at the similar temperatures. Our proposed method appropriately can provide a suitable approach to distinguish the preservation of the anisotropy effect in the isotropic phase of NLCs. Graphical abstract Unlabelled Image Highlights • Initial temperature range of SRO defined in isotropic phase of NLC by electro-optical Kerr effect. • The ξ and refractive index (n) were correlated with B at the same temperature in the isotropic phase. • The proposed approach distinguishes preservation of anisotropy effect in isotropic phase of NLC. [ABSTRACT FROM AUTHOR]

It is well known that a relatively large Kerr effect in the isotropic phase of nematic liquid crystals (NLCs) is related to the existence of short-range ordering (SRO). Thus, the conversion of the long-range ordering (LRO) behavior in the nematic phase to the SRO in the isotropic phase of NLCs can characterize the nonlinear electro-optic Kerr effect. To show conversion from LRO to SRO, we employ an empirical solvent polarity scale (E T N ). Interestingly, E T N originates from the solvatochromic polarity (SP) parameters, which demonstrates the quantitative value for describing the molecular interaction in each temperature point, even in the isotropic phase of NLCs. Our results show that the higher E T N value leads to a larger Kerr constant (B) owing to the larger short-range molecular interaction between rigid rod-like NLCs. To demonstrate a linear relationship of the B value with the E T N and SP parameters, a new correlation is introduced for the first time. Our investigations and newly introduced parameters strongly indicate that short-range molecular interactions still exist in the isotropic phase of NLCs, even when the macroscopically observable LRO behaviors disappear. • Characterization of short-range molecular interaction by empirical solvent polarity scale. to analyze Kerr effect of NLC. • To show conversion long-range ordering to short-range ordering, we employed an empirical solvent polarity scale (E T N ). • E T N with quantitative value describes the molecular interaction in isotropic phase. • The higher E T N value leads to a larger B value due to the larger short-range molecular interaction between rod-like NLCs. [ABSTRACT FROM AUTHOR]