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    Öğe
    Comparison of experimental measurements and machine learning predictions of dielectric constant of liquid crystals
    (Indian Acad Sciences, 2022) Taşer, Pelin Yıldırım; Önsal, Gülnur; Uğurlu, Onur
    In this study, we investigated the dielectric properties of the phthalocyanine (Pc)-doped nematic liquid crystal (NLC) composite structures. 4-Pentyl-4 & PRIME;-cyanobiphenyl (5CB) NLC was dispersed with 1 and 3% wt/wt Pc to investigate the doping concentration effect. Dielectric measurements of the samples were carried out using the dielectric spectroscopy method. Moreover, the real and imaginary components of the dielectric constant values were estimated based on the input parameters (frequency, voltage value and dispersion rate) using two different traditional regression algorithms (k-Nearest Neighbor and Decision Tree Regression) and five different ensemble-based regression algorithms (Extreme Gradient Boosting, Random Forest, Extra Tree Regression, Voting and Bagging using k-Nearest Neighbor as a base learner). According to the obtained results, the Extra Tree Regression algorithm had the best prediction performance on real and imaginary components of the dielectric constant values. Moreover, it is seen from the obtained results that the ensemble-based regression algorithms are more successful than the traditional ones.
  • Küçük Resim
    Öğe
    Improvement of the dielectric and electro-optic properties of phthalocyanine- and quantum dot-doped nematic liquid crystals under UV illumination
    (Springer, 2022) Önsal, Gülnur
    In this study, dielectric and electro-optic properties of 4-pentyl-4 '-cyanobiphenyl (5CB) nematic liquid crystal (LC) and different concentrations of nickel (II) phthalocyanine (Ni(II)Pc) and cadmium selenide sulfide/zinc sulfide (CdSeS/ZnS) quantum dot (QD)-doped LC have been investigated in dark and ultraviolet (UV) illumination. Some important dielectric parameters such as the real and imaginary part of the complex dielectric constant (epsilon ' and epsilon ''), relaxation frequency (f(R)), and relaxation time (tau) have been determined. The output of the study shows that Ni(II)Pc and CdSeS/ZnS contribution and UV illumination improved the dielectric properties. Optical band gap (E-gap) values of all samples have been obtained using the UV spectroscopy technique. The E-gap value decreased after dispersion of Ni(II)Pc and CdSeS/ZnS in the pure LC. The results may be beneficial for the design of new optoelectronic devices.
  • Küçük Resim
    Öğe
    Investıgatıon of dıelectrıc propertıes of MBBA-5CB nematıc lıquıd crystal structures
    (2022) Önsal, Gülnur
    The dielectric anisotropy (????) is the response of the LC molecules to an applied electric field. In this study, the dielectric properties of 4-pentyl-4'-cyanobiphenyl (5CB) and N-(4-methoxybenzylidene)-4-butylaniline (MBBA) nematic liquid crystals with positive and negative dielectric anisotropy were investigated in detail. In addition, a structure with zero dielectric anisotropy was obtained by mixing MBBA and 5CB liquid crystals in certain rate (1:0.02). The behavior of the samples under 0V and 20V voltages was investigated in detail. Dielectric measurements were made with dielectric spectroscopy technique, which is a powerful method to investigate the molecular interaction mechanisms of liquid crystal materials, at a frequency of 1 kHz-10 MHz and a voltage of 0-20 V at room temperature. Some important parameters such as dielectric anisotropy (????), relaxation frequency (????), relaxation time (??) were determined for the samples. When electric field is applied to nematic liquid crystals, it is seen that, depending on the voltage, the relaxation frequency decreases, and the relaxation time increases.
  • [ X ]
    Öğe
    Ni(II)Pc ve CdSeS/ZnS Kuantum Nokta Katkılı Sıvı Kristal Yapıların Dielektrik Sabitinin Makine Öğrenmesi Algoritmaları ile Tahminlenmesi
    (2023) Aksoy, Mustafa; Önsal, Gülnur; Ugurlu, Onur
    Bu çalışmada, Ni(II)Pc (nikel(II)ftalosiyanin) ve CdSeS/ZnS (cadmium selenide sulfide/zinc sulfide) kuantum nokta katkılı 5CB (4-pentyl-4′-cyanobiphenyl) nematik sıvı kristal kompozit yapıların dielektrik özellikleri ile birlikte bu özelliklerin makine öğrenmesi algoritmaları ile tahminlenmesi rapor edilmektedir. Konsantrasyon oranının dielektrik özelliklere etkilerini saptamak için 5CB nematik sıvı kristal yapıya ağırlıkça %2 ve %5 oranında Ni(II)Pc ve CdSeS/ZnS kuantum nokta katkılanmıştır. Numunelerin dielektrik ölçümleri, dielektrik spektroskopi yöntemi kullanılarak gerçekleştirilmiştir. Ayrıca, dielektrik sabitinin reel (ε^') ve sanal bileşenlerinin (ε^'') tahmini için k-En Yakın Komşu, Karar Ağacı, Rastgele Orman algoritmaları kullanmış ve algoritmaların tahmin performansları karşılaştırmalı olarak incelenmiştir. Algoritmalarda girdi parametreleri frekans, voltaj ve katkı oranı; çıktı parametreleri ise, dielektrik sabitinin reel (ε^') ve sanal bileşenleri (ε^'') olarak belirlenmiştir. Elde edilen sonuçlara göre dielektrik sabitinin en iyi tahmin performansına Rastgele Orman algoritması ile ulaşılmıştır.