Nihan Kaya

Phase Transitions, Order Parameters and Threshold Voltages in Liquid Crystal Systems Doped with Disperse Orange Dye and Carbon Nanoparticles

At the first part of this work, three different textile dyes (disperse orange 11, 13 and 37) were separately doped (1% w/w) to the nematic liquid crystal (E7). Single‐walled nanotube and fullerene C60 in a small amount (0.05% w/w) were mixed to these solutions at the second stage. Order parameters, threshold voltages, textures and clearing temperatures for all of mixtures were determined. Co‐use of dyes and nanoparticles as dopant was resulted in notable increases in order parameters. While threshold voltages required for the change of order parameter decreased, an important change in the texture and clearing temperature of the liquid crystal was not observed.

Alignment and Reorientation in Nematic Liquid Crystals Doped with Red Dye and Carbon Nanotube

Four different dyes (Methyl red, Disperse red 1, 13 and 60) were separately doped to each of four different nematic liquid crystals (E7, E8, E63 and ZLI-1132). Their solubilities, textures, phase transition temperatures and order parameters were determined. At the second stage, single-walled nanotubes in a small amount were separately added to each of these solutions, and the experiments were repeated as similar to previous ones. The solubility of dyes was sufficient for using in experiments. When adding dyes and nanotubes, an appreciable change in textures of liquid crystals was not observed. The phase transition temperatures stayed within the limitations required. The changes observed in order parameters depending on the voltage were very small. The highest value of order parameter (0.77) was attained when co-using red 60 dye and nanotube as dopants in the liquid crystal E63.

Orientation in Nematic Liquid Crystals Doped with Orange Dyes and Effect of Carbon Nanoparticles

Some properties of nematic liquid crystal E7 doped with two disperse orange dyes used together and effect of addition of carbon nanoparticles (single walled carbon nanotube or fullerene C60) on them were studied. Two dyes (disperse orange 11 and 13) having high solubility and order parameter were used as co-dopants. A notable increase in order parameter was obtained comparing to that of liquid crystal doped with single dye. When carbon nanoparticles were used as dopant, a decrease in order parameter was observed at low temperatures while it increased at high temperatures. When applied voltage changed, the order parameter abruptly increased in its threshold value and saturated in higher voltages as expected. An appreciable change in textures was not observed with addition of dopants. This addition gave rise to an increase in nematic-isotropic phase transition temperatures compared with that of pure liquid crystal.

Phase Transitions and Molecular Orientation in Nematic Liquid Crystals Doped with Blue-red Dye Mixtures and Carbon Nanotubes

Phase transitions and molecular orientation in nematic liquid crystals (E7, E8, E63 and ZLI-1132) doped with blue dye (disperse blue 1, 3, 14 or 134) and blue 14 + red dye (disperse red 1, 60 or methyl red) mixtures were studied. At the second stage, effects of single-walled carbon nanotubes (SWCNTs) added to them were determined. When blue-red dye mixtures were doped into the liquid crystals, an increase in order parameter was observed compared to those of single dyes and a value of 0.70 was attained. The addition of carbon nanotubes resulted in very higher values of order parameter (Smax = 0.79). To determine the threshold value of order parameter for saturation, the experiments were repeated in various DC voltages. The threshold voltage was significantly reduced with addition of CNTs. With addition of dopants, an appreciable change in textures was not observed. Shifts in phase transition temperatures were in limitations required.

Catalytic air oxidation of manganese in synthetic waters

An attempt was made to study the oxidation of manganese by air in synthetic waters. A series of batch experments were performed at differnet values of concentration, temperature and pH. Unoxidized manganese in the solution was determined by formaldoxime spectrometric method. Results of these studies indicated that the air oxidation of manganese soluble in water can be effectively performed in basic media and that oxidation yield increasedwith an increase in pH and concentration. The yield was very high in the presence of manganese dioxide, sepiolite or clinoptilolite in solution and, the oxidation was almost completed especially at high values of pH and concentration. The reaction was found to be first order with respect to Mn2+ with a very low activation energy. A yield of 62% was obtained for the air oxidation of wastewater taken from the treatment plant of Corum Municipality.

A comprehensive study on adsorption behavior of some azo dyes from aqueous solution onto different adsorbents

One of the major environmental problems is the existence of dye materials in water sources. This pollutant must be removed from water by appropriate methods. Although most of these methods are efficient for the treatment of waters contaminated with dye pollutants, they are very costly and commercially unattractive. Adsorption is one of the most popular methods for the removal of dye pollutants from water especially if the sorbent is inexpensive. Sorbents are classified as natural sorbents, commercial sorbents, and the sorbents obtained from industrial and agricultural wastes. Although commercial activated carbon is widely used in wastewater treatment applications, it is very expensive. In this study, usability of inexpensive materials - sepiolite as a natural adsorbent, and walnut shell and hazelnut shell as agricultural wastes - was investigated instead of commercial activated carbon to remove some azo dyes (methyl red, methyl orange and methyl yellow) from aqueous solution. Batch experiments were carried out to determine the effect of different adsorption parameters such as pH, initial dye concentration, contact time, adsorbent dose and temperature. The equilibrium of adsorptions was modeled using Langmuir and Freundlich isotherm models. This comprehensive study showed that these alternative adsorbents had sufficient binding capacity to remove these azo dyes from water.

Alümina aerojellerin fiziksel özellikleri üzerine yaşlandırma ve kurutma süresinin etkisi

Dusuk yogunluga, yuksek gozeneklilige ve cok iyi yalitim kabiliyetine sahip olan aerojeller son yillarda giderek onem kazanmis ve bircok alanda kullanim yeri bulmustur. Dayanikli ve cevre dostu malzemeler olmalari sebebiyle gunumuzde yapilan calismalar aerojeller uzerine yogunlasmis olup, ozellikle gozenek yapilari ve yuzey alanlarinin gelistirilebilmesi icin etkili yollar arastirilmaktadir. Bu calismada, oldukca viskoz aluminyum tri-sek-butoksitin kontrollu hidrolizi ve sol-jel yontemi ile hazirlanan alumina aerojellerin aseton banyosunda yaslandirilma ve super kritik sartlarda kurutma surelerinin, jelin yapisal ve fiziksel ozelliklerine etkisinin incelenmesi amaclanmistir. Hazirlanan aerojeller, metanol banyosunda en az 24 saat dinlendirildikten sonra 7 gun ve 30 gun olmak uzere iki farkli zaman periyodunda aseton banyosunda yaslandirilmis ve bu sure icerisinde aseton banyosu en az dort kez degistirilmistir. Elde edilen alumina aerojeller super kritik kosullarda 2 saat ve 4 saat boyunca farkli surelerde kurutulmustur. Bu islem icin super kritik CO 2 sicakligi 45 o C ve basinci 100 bar’dir. Aseton banyosundaki yaslandirma suresi ve kurutma suresi degistirilerek gerceklestirilen sistematik calisma ile farkli kosullarda hazirlanan aerojellerin karakterizasyonu, FT-IR, SEM ve cok noktali BET analizleri ile gerceklestirilmistir . Deneysel sonuclar gostermektedir ki, gerek yaslandirma suresi gerekse kurutma suresi arttikca, numunelerin yogunlugu azalmistir. Kurutma suresinden ziyade yaslandirma suresinin yuzey alaninin artmasinda daha etkili olmasi sonucu en yuksek yuzey alani degeri 30 gun yaslandirma islemi sonucu 825,614 m 2 /g olarak bulunmustur. Yuzey alaninin artmasiyla birlikte gozenek boyut ve dagiliminda da iyilesmeler meydana gelmistir. Farkli yaslandirma ve kurutma sartlarinda elde edilen urunun kimyasal yapisinda herhangi bir degisim olmamistir.

Y-H TİPİ SIVI KRİSTAL SİSTEMLERE KARBON NANOTÜP İLAVESİNİN MOLEKÜLER YÖNLENME VE FAZ GEÇİŞİ ÜZERİNE ETKİLERİ

Ozellikle goruntu teknolojisindeki uygulamalari ile sivi kristaller son yillarda buyuk ilgi odagi haline gelmistir.Yolcu-Hanci (Y-H) tipi sivi kristal gostergeler genis gorus acisi, dusuk maliyet, mukemmel renk tonu ve yuksekparlakliklari sebebiyle yaygin bir sekilde kullanilmaktadirlar. Bu calismanin amaci, Y-H tipi sistemlerde farklimolekuler yapida boyalar ile tek duvarli karbon nanotup kullanarak molekuler yonlenmeyi gelistirmek venematik-izotropik faz gecis sicakligi uzerine etkilerini incelemektir. Bu amacla farkli kimyasal yapidaki ucboyarmadde, farkli bilesimdeki iki nematik sivi kristale ayri ayri eklenerek duzen parametreleri ve faz gecissicakliklari belirlenmistir. Bir sonraki asamada bu karisimlarin her birine iki farkli oranda tek duvarli karbonnanotup ilave edilmis ve deneyler tekrarlanmistir. Sonuc olarak sivi kristal icin duzen parametresi, boyaya bagliolarak farkli degerler almakla birlikte en yuksek degerini antrakinon yapili boyada bulmus; karbon nanotupilavesi farkli etkilere sebep olmustur. Katkili sivi kristallerin nematik-izotropik faz gecis sicakligindaki degisim,katkisiz hale kiyasla kabul edilebilir sinirlar icerisinde kaldigindan, sivi kristal fazin kararliligi uzerine olumsuzetkilerinin olmadigi sonucuna varilmistir.