Research Project: İleri Malzemeler ve Üretim Teknikleri Kullanarak Yeni Çip İçinde Lab Optofluidik Dalga Klavuzlarının ve Akış Manipülasyon Yöntemlerinin Geliştirilmesi
Loading...
Contributors
Funders
ID
TB.00137
Authors
Kiraz, Alper
Faculty Member
Publications
Versatile liquid-core optofluidic waveguides fabricated in hydrophobic silica aerogels by femtosecond-laser ablation
(Elsevier, 2015) Erkey, Can; Kiraz, Alper; Özbakır, Yaprak; Yalizay, Berna; Morova, Yagiz; Dincer, Koray; Jonas, Alexandr; Akturk, Selcuk; Department of Physics; Department of Chemical and Biological Engineering; Yes; College of Engineering; College of Sciences
We report on the fabrication and characterization of versatile light waveguides exploiting filaments of a polar liquid confined within hydrophobic silica aerogels. Aerogels are highly porous materials with extremely low refractive index which makes them suitable as rigid cladding of liquid-core optofluidic waveguides based on total internal reflection of light. In this article, we introduce a new microfabrication technique that allows direct and precise processing of monolithic silica aerogels by ablation with femtosecond laser pulses. Using fast scanning of the focused laser ablation beam synchronized with the motion of the processed aerogel sample, we created high-quality straight microchannels of similar to 5 mm length with controlled cross-sections inside monolithic aerogels. After the ablation, we filled the channels with high-refractive index ethylene glycol, forming multimode liquid core - solid cladding optofluidic waveguides. Subsequently, we carried out light-guiding experiments to measure overall optical attenuation of these waveguides. The characterization of waveguide transmission yielded values of propagation losses lower than 10 dB cm(-1), demonstrating that the liquid-core waveguides with laser-ablated aerogel cladding represent an attractive alternative in optofluidic applications targeting controlled routing of light along arbitrary three-dimensional paths.
Passive sorting of emulsion droplets with different interfacial properties using laser-patterned surfaces
(Springer, 2019) Kiraz, Alper; Morova, Berna; Muradoğlu, Metin; Rashid, Muhammed Zeeshan; Erten, Ahmet; Jonáš, Alexandr; Department of Mechanical Engineering; Department of Physics; Department of Electrical and Electronics Engineering; Yes; College of Engineering; College of Sciences
We demonstrate passive sorting of emulsion microdroplets based on differences in their interfacial tension and contact angle. The sorted droplets are flowing inside a microfluidic channel featuring a shallow guiding track (depth similar to 0.6 mu m) defined by femtosecond laser micromachining in polydimethylsiloxane coating deposited on glass. Under these flow conditions, the droplets experience a confinement force that pulls them into the track; this force depends on the interfacial tension and the difference between the contact angles inside and outside the ablated track. The interplay between the confinement force, fluid drag, and wall friction then determines the trajectory of the droplet along the guiding track. We investigate experimentally the droplet trajectory as a function of droplet velocity and angle between the track and the channel axis and demonstrate precise control of droplet direction by adjusting the track angle. Moreover, we show that droplets of liquids with different interfacial tensions and contact angles travel different distances along the guiding track at a constant flow rate, which can be used for droplet sorting. We develop a theoretical model that incorporates the droplet position with respect to the ablated track, interfacial tension, and contact angles to predict the droplet trajectory under given experimental conditions. Thus, the dynamic behavior of the droplets leading to different guiding scenarios can be studied without the need of computationally expensive fluid dynamics simulations. The presented study paves the way for designing and optimizing new systems for advanced manipulation of droplets of different content using potentially reconfigurable guiding tracks.
Guiding of emulsion droplets in microfluidic chips along shallow tracks defined by laser ablation
(Springer, 2017) Erten, Ahmet Can; Kiraz, Alper; Rashid, Muhammed Zeeshan; Coşkun, Umut Can; Morova, Yağız; Morova, Berna; Bozkurt, Asuman Aşıkoğlu; Jonáš, Alexandr; Aktürk, Selçuk; Department of Physics; Department of Electrical and Electronics Engineering; Yes; College of Sciences; College of Engineering
We demonstrate controlled guiding of nanoliter emulsion droplets of polar liquids suspended in oil along shallow hydrophilic tracks fabricated at the base of microchannels located within microfluidic chips. The tracks for droplet guiding are generated by exposing the glass surface of polydimethylsiloxane (PDMS)-coated microscope slides via femtosecond laser ablation. The difference in wettability of glass and PDMS surfaces together with the shallow steplike transverse topographical profile of the ablated tracks allows polar droplets wetting preferentially the glass surface to follow the track. In this study, we investigate guiding of droplets of two different polar liquids (water/ethylene glycol) with and without surfactant suspended in an oil medium along surface tracks of different depths of 1, 1.5, and 2 mu m. The results of experiments are also verified with computational fluid dynamics simulations. Guiding of droplets along the tracks as a function of the droplet composition and size and the surface profile depth is evaluated by analyzing the trajectories of moving droplets with respect to the track central axis, and conditions for stable guiding are identified. The experiments and numerical simulations indicate that while the track topography plays a role in droplet guiding using 1.5-and 2-mu m deep tracks, for the case of the smallest track depth of 1 ae m, droplet guiding is mainly caused by surface energy modification along the track rather than the presence of a topographical step on the surface. Our results can be exploited to sort passively different microdroplets mixed in the same microfluidic chip, based on their inherent wetting properties, and they can also pave the way for guiding of droplets along reconfigurable tracks defined by surface energy modifications obtained using other external control mechanisms such as electric field or light.
