Mervenur KILIÇ, Mustafa CAN, Nejmettin AVCI, Atilla Eren MAMUK

Kolesterik Sıvı Kristal - Polimer Liflerinin Elektro-eğirme Yöntemi ile Üretilmesi ve İncelenmesi

Sıvı kristallerin ekran teknolojisi, sensör, esnek devre elamanları, ışık modülatörleri gibi uygulamalarda kullanılabildiği bilinmektedir. Kolesterik mezofaz sıvı kristaller ışığın seçici geçirgenlik özelliği ile ön plana çıkmaktalardır. Bu çalışmada, ilk defa tek-iğneli elektro-eğirme kullanılarak kolesterik sıvı kristaller-polimer kompozit liflerinin üretilmiş ve incelenmiştir. Bu bağlamda ilk olarak, mavi, yeşil ve kırmızı renkte ışığı yansıtabilecek sırasıyla 470 nm, 550 nm ve 640 nm spiral adım uzunluklarına sahip kolesterik sıvı kristaller hazırlanmıştır. Konak nematik mezofaz olarak E-7 ve yüksek burma gücüne sahip R-5011 kiral katkı maddesi kullanılmıştır. Bu kolesteriklerin yaklaşık istenilen adım uzunluklarına sahip oldukları UV-VIS spektrofotometre ölçümleri ile gösterilmiştir. Ayrıca, hazırlanan kolesteriklerin karakteristik bir tekstür olan oily-streak desenlere sahip olduğu görülmektedir. Bu kolesterikler poliakrilonitril ile karıştırılarak dimetilformamid içerisinde çözdürülmüştür. Bu çözeltiler tek-iğneli elektro-eğirme sistemi ile 16 kV, 18 kV, 20 kV, 22 kV ve 24 kV uygulama voltajları altında eğirilerek sıvı kristal polimer kompozit lifleri haline getirilmişlerdir. Eğirilen liflere katkılanan kolesterik sıvı kristallerin varlığı optik ve yapısal analizler geçekleştirilerek belirlenmiştir. Polarize optik mikroskop ile yapılan görüntülemelerde çapraz polarizörler arasındaki lifler boyunca parlamalar gözlenmiştir. Bu parlamalar lif boyunca sıvı kristallerin yerleştiğini göstermektedir. Ayrıca, yapısal analiz sonucu her bir lifte üretim parametreleri ve katkı maddelerine göre lif yapısının değişimi üzerine çalışma yapılmıştır. Tüm kolesterik örnekleri için düşük uygulama voltajlarında eğirilen lifler boyunca uzanan küresel boncuk yapılar tespit edilmişken daha yüksek uygulama voltajlarında eğirilen liflerde boncuk yapılar oldukça seyrek gözlenmiştir. Kızılötesi spektroskopisi analizleri sonucu liflerin sıvı kristallerin sergilediği titreşim pikleri ile aynı dalga sayılarında pikler vermesi lif yapılarında sıvı kristallerin varlığını göstermiştir.

Anahtar Kelimeler:

Kolesterik sıvı kristaller, elektro-eğirme, lif

Production and Investigation of Cholesteric Liquid Crystal-Polymer Fibers by Electrospinning Method

It is well-known that liquid crystals are widely used in applications such as display technology, sensor, elastic circuit component, and light-modulator. Cholesteric liquid crystals come into prominence with their selective transmittance of light. In the study, cholesteric liquid crystals - polymer fiber composites are produced and investigated using single-needle electrospinning for the first time. In this sense, in the beginning, cholesteric liquid crystals with 470 nm, 550 nm, and 640 nm spiral pitches which can reflect blue, green, and red lights, respectively are prepared. It is used E-7 as host nematic mesophase and R 5011 with high twisting power as a chiral dopant material. It was shown by UV-VIS spectrophotometer measurements that the cholesterics have approximately the desired spiral pitch lengths. It is also observed that the the cholesterics have oily-streak patterns, which is a characteristic texture for cholesterics. In addition, the cholesterics are mixed with polyacrylonitrile and the mixture is solved into dimethylformamide. Moreover, liquid crystal-polymer composite fibers are produced by spinning the solutions using single-needle electrospinning under spinning voltages of 16 kV, 18 kV, 20 kV, 22 kV and 24 kV. The existence of liquid crystals inside the fiber is proved by carrying out optical and structural analyses. In the imaging with a polarized optical microscope, irradiances were observed along the fibers between the cross polarizers. These irradiances indicated that liquid crystals have settled along the fiber. Also, it studies on a variance of the fiber structure depending on liquid crystal dopant and production parameters with structural analyses. For the all cholesteric samples, spherical bead structures were detected along the spun fibers at low spinning voltages, while in the fibers at higher spinning voltages the bead structures were observed very rarely. Infrared spectroscopy analysis of the fibers showed the presence of liquid crystals in the fiber structures with peaks at the same wave numbers as the vibration peaks exhibited by liquid crystals.

Keywords:

Cholesteric liquid crystals, electrospinning, fiber,

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