Search

[Display omitted] • Our IR film is flexible, ultrathin, thermally-insulated, and transparent. • Our CLC polymer IR film shows high optical transmittance, and low haze. • It significantly reduces the greenhouse gas emissions. • It prevents energy consumption for cooling system and lighting in indoor spaces. • The proposed polymer IR film is a promising candidate for energy-efficient window. Transparent windows that insulate infrared (IR) light entering indoor spaces promise to reduce energy consumption. However, a long-standing challenge for an energy-efficient window is achieving compactness and flexibility simultaneously. In this paper, we report the fabrication of a transparent, flexible, ultrathin, and thermally-insulated IR reflector using a coatable chiral-nematic liquid crystal polymer and polyvinyl alcohol (PVA) as an alignment layer. PVA is transparent, biocompatible, thermostable, noncorrosive, and cost-effective. The fabricated IR reflector shows high optical transparency (∼91%) and low haze (≈9.8%) values in the visible spectrum of light. Moreover, it significantly reduces greenhouse gas emissions by preventing energy consumption for cooling systems and lighting in indoor spaces; specifically, it reduces electricity consumption in indoor spaces for lighting and cooling systems under hot weather conditions. To demonstrate the mechanical stability of the fabricated reflector, many mechanical, flexibility, and bending stability tests were conducted. The results show that our proposed IR reflector is a potential candidate for designing desirable shapes for many applications, such as anti-IR devices and energy-efficient windows, for achieving significant environmental and economic benefits. [ABSTRACT FROM AUTHOR]

We report experimental studies on optical (birefringence, Δn), dielectric (Δε) and bend-splay elastic anisotropies (ΔK = K 33 − K 11) of a few mixtures of two nematic liquid crystals, namely CCH-7 and CCN-47, made of highly polar molecules with identical cores and antagonistic orientation of permanent dipoles. In particular, the polar group (-CN) attached to the bicyclohexane core of CCH-7 is oriented along the longitudinal direction whereas, in CCN-47, it is oriented along the transverse direction. We show that apart from the significant contribution to the optical and dielectric anisotropies, the antagonistic orientation of strongly polar groups plays a crucial role in determining the bend-splay elastic anisotropy. The elastic properties are explained based on a model proposed by Priest, considering the effect of intermolecular association and the resulting length-to-width ratio of the molecules. • Binary mixtures of positive and negative dielectric anisotropy liquid crystals. • Antagonistic orientation of dipoles tends to cancels out their effect. • Antiparallel association increases effective length-to-width ratio of the molecules. • Orientation of dipole moments determines the elastic anisotropy of liquid crystals. [ABSTRACT FROM AUTHOR]

In this paper, we introduce technologies for fast switching of nematic liquid crystals (LCs) using three-terminal electrodes. Fast switching of LCs can be achieved by employing a vertical trigger pulse, by applying a vertical bias field, and by random alignment of LCs. [ABSTRACT FROM PUBLISHER]

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]

Abstract The temperature dependence of optical birefringence, order parameter, effective geometry parameter, and normalized polarizability was determined for nematic liquid crystal mixtures by measuring the refractive indices. The effects of the adjustable parameters obtained from temperature-dependent refractive indices were analyzed appropriately for the crossover temperature and order parameter values. Besides, a four-parameter power law expression method was used for the optical birefringence measurement to address inappropriate fits in the weak first-order phase transition region. From this method, the effective second order phase transition temperature T ⁎⁎ was determined by showing the slightly higher values than phase transition temperature. The value of the order parameter critical exponent λ obtained from this method showed a good agreement with the mean field theory by demonstrating closeness to the tricritical hypothesis (β = 0.25). As a consequence, the measurement of the temperature-dependent optical birefringence was successfully verified the pre-transitional phenomena accurately, and it can facilitate an insightful description of that region. Graphical abstract Unlabelled Image Highlights • Temperature dependence of high birefringence (∆ n) liquid crystals was analyzed. • The temperature dependent order parameter was sorted based on ∆ n values. • Lower (∆ n) o and β values were valuable factors for increasing T co at the same T NI. • A four-parameter power law expression shows the high critical exponent value. [ABSTRACT FROM AUTHOR]

• There is linear relationship between order parameter and pitch length. • PSCLCs indicate a iregular transmission features. • NLCs play important roles on the PSCLs optical behaviors. Polymer stabilized cholesteric liquid crystals (PSCLCs) with unique characteristics play important roles in optics and photonics. In this case, temperature induced effects can modify their function in various phenomena. In this work, optical responses of PSCLCs were studied at different temperatures and temperature dependent properties of prepared PSCLC were successfully equationalized. According to the experimental results, there are good linear relationship between calculated pitch lengths and temperature. Moreover, the experimental results indicate that nematic liquid crystal (NLC) temperature dependent characteristics play important roles on the PSCLCs pitch length. In this case, quantitatively investigation of relationship between pitch length and LC order parameter provide new method for calculation of pitch length. Therefore, the calculation of pitch length based on NLC order parameter can facilitate the studies on PSCLCs. [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]