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Ranjkesh, Amid,Choi, Jun-Chan,Park, Ji-Sub,Park, Min-Kyu,Kiani, Somaye,Zakerhamidi, Mohammad Sadegh,Kim, Hak-Rin Elsevier 2017 Journal of molecular liquids Vol.230 No.-
<P>The temperature dependencies of three low birefringence (Delta n) liquid crystals (LCs) at similar clearing temperatures (T-NI) were investigated to characterize the order parameter S(T) and crossover temperature (T-co). Three different methods were used to determine the S(T) property, including the Vuks model, the Haller approximation model, and a model based on the effective geometry parameter (alpha(eg)). In our low Delta n LCs with relatively analogous T-NI, three parameters (B, (Delta n)(o), and beta) that originated from the modified four-parameter model were analyzed to increase the T-co condition. A larger absolute value for the B parameter and a smaller beta parameter were also needed to reduce the temperature dependence of Delta n. In particular, a lower (Delta n)(o) value was found to be beneficial for increasing the Too value, which resulted in a higher T-co value for the low Delta n LCs, compared with that of a high An LC with a similar T-NI value. This led to a narrower temperature range between T-co and T-NI for the low Delta n LCs compared to that of the high Delta n LC, which could result in appropriate temperature properties for LCs for practical display applications, including a lower temperature dependence of Delta n and wider operational temperature regime. (C) 2017 Published by Elsevier B.V.</P>
Ranjkesh, Amid,Kiani, Somaye,Strzeż,ysz, Olga,Zakerhamidi, Mohammad Sadegh,Yoon, Tae-Hoon Elsevier 2018 Journal of molecular liquids Vol.268 No.-
<P><B>Abstract</B></P> <P>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 <I>T</I> <SUP>⁎⁎</SUP> was determined by showing the slightly higher values than phase transition temperature. The value of the order parameter critical exponent <I>λ</I> obtained from this method showed a good agreement with the mean field theory by demonstrating closeness to the tricritical hypothesis (<I>β</I> = 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.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Temperature dependence of high birefringence (∆<I>n</I>) liquid crystals was analyzed. </LI> <LI> The temperature dependent order parameter was sorted based on ∆<I>n</I> values. </LI> <LI> Lower (∆<I>n</I>)<SUB>o</SUB> and <I>β</I> values were valuable factors for increasing <I>T</I> <SUB>co</SUB> at the same <I>T</I> <SUB>NI</SUB>. </LI> <LI> A four-parameter power law expression shows the high critical exponent value. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>
Ranjkesh, Amid,Yoon, Tae-Hoon The Royal Society of Chemistry 2018 Journal of materials chemistry. C, Materials for o Vol.6 No.45
<P>Autonomous stimulus-responsive polymer-stabilized cholesteric liquid crystals (PSCLCs) are promising materials for various applications. In this work, a PSCLC cell whose wavelength of selective reflection changes autonomously according to the temperature or can be controlled by applying an electric field was fabricated by using ultraviolet (UV) light absorbers. The UV light absorbers in the PSCLC cell are used not only for preventing the degradation of the substrate but also for stabilizing the polymeric network by converting the harmful UV radiation into harmless heat. To achieve the optimum conditions, different types of UV light absorbers were examined at various concentrations and UV light intensities. The results revealed that the benzophenone-type UV absorbers provide an extensive blue-shift tuning of the Bragg reflection in the PSCLC. By determining the molar extinction coefficient (<I>ε</I>) values, which provide a measure of UV light absorption at a given wavelength, at three important wavelengths-the maximum absorption wavelength (<I>λ</I>max) of the UV absorbers, <I>λ</I>max of the photoinitiator (345 nm), and the UV lamp wavelength (365 nm)-the UV light intensity gradient throughout the cell was defined. Reduction of the <I>ε</I> value indicates a sharp drop in the UV light intensity within a PSCLC cell. This phenomenon leads to the diffusion of reactive mesogens towards the UV lamp side of the cell to achieve a tight pitch gradient and extensive blue-shift tuning of the selective reflection.</P>
Ranjkesh, Amid,Yoon, Tae-Hoon American Chemical Society 2019 ACS APPLIED MATERIALS & INTERFACES Vol.11 No.29
<P>Recently, single-substrate flexible liquid crystal (LC) devices have attracted considerable attention because they can provide desirable shapes, small weight, flexibility, and rollability. In this work, we fabricate a flexible single-substrate thermoresponsive cholesteric LC (CLC) film by a facile method called photoenforced stratification method. Our fabricated single-substrate CLC film consists of microscale polymer containers filled with a CLC solution. Our results showed that the temperature response of the fabricated single-substrate CLC film depends on the chiral material doped into the CLC solution. The single-substrate ultrathin CLC film exhibits very high flexibility and robustness without performance reduction. The fabricated flexible single-substrate CLC film may pave the way for the development of novel technologies for thermoresponsive devices with changeable shapes and designs.</P> [FIG OMISSION]</BR>
Linear dichroism and order parameters of nematics doped with azo dyes
Ranjkesh, Amid,Choi, Jun-Chan,Joo, Kyung-Il,Park, Hee-Won,Zakerhamidi, Mohammad Sadegh,Kim, Hak-Rin Informa UK (TaylorFrancis) 2017 Molecular Crystals and Liquid Crystals Vol.647 No.1
<P>We investigated solvent-solute effects using dye-doped nematic liquid crystals (NLCs) where three Sudan dyes of different concentrations were used as solutes doped into high- and low-polar NLCs as anisotropic solvents. The polarized spectroscopic absorption, dichroic ratio (R), and order parameter (S) were measured, which showed that the rod-like Sudan black B had a higher S and R due to a higher anisotropic solvent-solute effect produced by transition moment and global charge transfer along the molecular axis induced by high polar NLC. The order parameters measured by the Vuks method also showed a higher solvent-solute effect for the high-polar NLC.</P>
Production of novel activated carbon fibers from smoked cigarette wastes using NaOH
Zahra Ranjkesh,Komeil Nasouri 한국고분자학회 2023 Macromolecular Research Vol.31 No.7
This research reports the activated carbon fibers (ACFs) production from smoked cigarette wastes by a simple and facile technique. One-step carbonization/activation process with a NaOH activating agent has been considered for the first time. Cigarette waste-derived ACFs samples were synthesized using various NaOH concentrations and heating rates. The carbon yield, morphology, chemical composition, and surface area of the ACFs were analyzed and compared. Pre-treatment with NaOH activation agent improves the carbon yield, thermal stability, and surface area. The optimal microporous ACFs with 34.82 wt% of carbon yield and 1357 m2/g of surface area were synthesized by 10 g/L of NaOH pre-treatment and 2 ℃/min of heating rate. The ACFs samples synthesized with higher NaOH concentrations are mainly the mesoporous structure and lower surface area. This study presented a manageable approach for synthesizing high-performance ACFs with unique fibrous structures from smoked cigarette wastes. Main advantage of the designed procedure is establishing an environmentally friendly manufacturing of micro/ mesoporous ACFs.
Amirnia, Mehdi,Ranjkesh, Mohammad-Reza,Azimpouran, Mahzad,Karkon-Shayan, Farid,Alikhah, Hossein,Jafari-Asl, Mohammadali,Piri, Reza,Naghavi-Behzad, Mohammad Asian Pacific Journal of Cancer Prevention 2016 Asian Pacific journal of cancer prevention Vol.17 No.1
Background: Dermatoscopy can be applied to diagnose pigmented skin lesions. The aim of the present study was to compare dermatoscopic and histopathologic results in basal cell carcinoma (BCC) and melanocytic nevus of theface. Materials and Methods: In an analytical-descriptive study, 61 patients suspected of BCC or melanocytic nevi of face were randomly selected. The skin lesions of patients were evaluated with dermatoscopic method from February 2012 to February 2014 and results were compared with pathological features of samples. Results: In this study, mean age of patients was $49.5{\pm}18.9$. Some 25 (41%) were men and 36 (59%) were women. In 27 cases (44.3%) there was diagnosis of melanocytic nevus, in 28 cases (45.9%) diagnosis of BCC, and in 3 cases (4.9%) there was mixed diagnosis. The relationship between patients' gender and dermatoscopic diagnosis of the patients was statistically significant (P=0.001). For BCC the sensitivity and specificity of dermatoscopic method were 100% and 97% respectively and for melanocytic nevi 96.4% and 97%. Conclusions: Dermatoscopic study not only can be helpful in improving clinical diagnosis while guiding missed malignant lesions to pathologic evaluations, but also could be useful in evaluating further suspicious or recurrent cases.