Order parameter and crossover temperature from temperature-dependent refractive indices for low birefringence liquid crystals

Ranjkesh, Amid; Choi, Jun‐Chan; Park, Ji-Sub; Park, Minkyu; Kiani, Somaye; Zakerhamidi, M.S.

doi:10.1016/j.molliq.2017.01.036

Cited by 19 publications

(8 citation statements)

References 39 publications

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“…The plot can be correlated with the variation in the order parameters of a LC with temperature or solvent exposure. 65 Figure 8IIb shows that upon solvent removal from the setup, R N increases with the restoration of the nematic order of the droplet. Thus, by quantifying the intensity of transmitted light, the change in the phase of the 5CB droplets can be detected by this simple experiment.…”

Section: Resultsmentioning

confidence: 99%

“…Figure IIa shows that R N gradually decreases when the hexane vapor is exposed to the 5CB drop owing to progressively higher transmitted light exposure on the light-dependent resistor as the nematic to isotropic phase transition takes place in the drop. The plot can be correlated with the variation in the order parameters of a LC with temperature or solvent exposure Figure IIb shows that upon solvent removal from the setup, R N increases with the restoration of the nematic order of the droplet.…”

Section: Results and Discussionmentioning

confidence: 99%

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Self-Organized Liquid Crystal Droplets as Phototunable Softmasks

Thakur

Dasmahapatra

Bandyopadhyay

2021

ACS Appl. Mater. Interfaces

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A single-step self-organized pathway is harnessed to generate large-area and high-density liquid-crystal (LC) microdroplets via rapid spreading of an LC-laden volatile liquid film on an aqueous surfactant bath. The surfactant loading on the water bath and LC loading in the solvent fluid help in tuning the size, periodicity, and ordering of LC microdroplets. Remarkably, the experiments reveal a transition from a spinodal to heterogeneous nucleation pathway of dewetting when the surfactant loading is modulated from below to beyond the critical micellar concentration in the aqueous phase. In the process, a host of unprecedented drop formation modes, such as dewetting and contact-line instability, random ejection, and "fire cracker" toroid splitting, have been uncovered. Subsequently, the LC microdroplets on the air−water interface are employed as photomasks suitable for soft-photolithography applications. Such masks help in the decoration of a host of mesoscale three-dimensional features on the films of photoresists when photons are guided through the LC droplets. In such a scenario, phase transition of LC droplets under solvent vapor annealing is employed to control the movement of photons through drops and subsequently modulate the light exposure on the photoresist surface. Such a simple softphotolithography setup leads to an array of flattened droplets on a positive resist, while donut features are observed on the negative tone. Remarkably, the orientation of nematogens within 4-cyano-4′-pentylbiphenyl droplets and at the three-phase contact-line provides additional handles in controlling the transmission of photons, which facilitates such a unique pattern formation. A number of low-cost and simple strategies are also discussed to order such soft-photolithography patterns. Importantly, with a minor modification to the same experimental setup, we could also measure the variation in the order parameter of the LC droplet during its phase transitions from the nematic to isotropic state.

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Section: Resultsmentioning

confidence: 99%

Section: Results and Discussionmentioning

confidence: 99%

Self-Organized Liquid Crystal Droplets as Phototunable Softmasks

Thakur

Dasmahapatra

Bandyopadhyay

2021

ACS Appl. Mater. Interfaces

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“…For many of the LC compounds studied, β are approximately 0.25 and insensitive to materials [ 36 ]. Equation (6) is only valid for T sufficiently smaller than T NI [ 37 ]. In this study, T / T NI is less than 0.5 and thus S can be estimated by substituting T = 298 K, β = 0.25, and T NI into Equation (6).…”

Section: Resultsmentioning

confidence: 99%

A Comparative Study on Electro-Optic Effects of Organic N-Benzyl-2-Methyl-4-Nitroaniline and Morpholinium 2-Chloro-4-Nitrobenzoate Doped in Nematic Liquid Crystals E7

et al. 2020

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Improvements in electro-optical responses of LC devices by doping organic N-benzyl-2-methyl-4-nitroaniline (BNA) and Morpholinium 2-chloro-4-nitrobenzoate (M2C4N) in nematic liquid crystals (LCs) have been reported in this study. BNA and M2C4N-doped LC cells have the fall time that is fivefold and threefold faster than the pristine LC cell, respectively. The superior performance in fall time of BNA-doped LC cell is attributed to the significant decrements in the rotational viscosity and threshold voltage by 44% and 25%, respectively, and a strong additional restoring force resulted from the spontaneous polarization electric field of BNA. On the other hand, the dielectric anisotropy (Δε) of LC mixture is increased by 16% and 6%, respectively, with M2C4N and BNA dopants. M2C4N dopant induces a large dielectric anisotropy, because the phenyl-amine/hydroxyl in M2C4N induces a strong intermolecular interaction with LCs. Furthermore, BNA dopant causes a strong absorbance near the wavelength of 400 nm that filters the blue light. The results indicate that M2C4N doping can be used to develop a high Δε of LC mixture, and BNA doping is appropriate to fabricate a fast response and blue-light filtering LC device. Density Functional Theory calculation also confirms that BNA and M2C4N increase the dipole moment, polarization anisotropy, and hence Δε of LC mixture.

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“…This parameter controls all physical properties of LCs in addition to verifying their degree of intrinsic long-range order [ 18 – 21 (19–20, 20–21)]. There are various methods for determining the order parameter, with techniques based on optical anisotropy being the most popular due to their high accuracy 22 , 23 . Among these, the Vuks method is an extensively utilized method that concts the LC’s molecular polarizability to its macroscopic refractive indices and determines the order parameter at the microscopic level 24 .…”

Section: Introductionmentioning

confidence: 99%

“…The arrangement of molecules in LC naturally affects how light is transmitted. The order parameter of many nematic liquid crystals was recently determined using mentioned above optical approaches 12 , 22 , 29 – 31 .…”

Section: Introductionmentioning

confidence: 99%

Temperature-dependent optical properties of some mixtures nematic liquid crystal

Alipanah

Zakerhamidi

Ranjkesh

2022

Sci Rep

Self Cite

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The presence of optical anisotropy in liquid crystals (LCs) has caused these materials to have dual refractive indices: ordinary (no) and extra-ordinary (ne). Many fundamental information about LCs can be found by looking at these refractive indices. In this work, the refractive indices of four mixtures nematic liquid crystal (NLC) have been studied as a function of temperature, and the relevant functions were then calculated. Subsequently, the order parameter of mentioned LCs was determined using three methods: Vuks, Haller, and the effective geometry parameter method. It was concluded that the obtained values are not significantly different and exhibit the same temperature dependence. The obtained results were evaluated in relation to the approach utilized.

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Order parameter and crossover temperature from temperature-dependent refractive indices for low birefringence liquid crystals

Cited by 19 publications

References 39 publications

Self-Organized Liquid Crystal Droplets as Phototunable Softmasks

Self-Organized Liquid Crystal Droplets as Phototunable Softmasks

A Comparative Study on Electro-Optic Effects of Organic N-Benzyl-2-Methyl-4-Nitroaniline and Morpholinium 2-Chloro-4-Nitrobenzoate Doped in Nematic Liquid Crystals E7

Temperature-dependent optical properties of some mixtures nematic liquid crystal

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