Browsing by Author "Naji, Mayssam"

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Open Access
Describing droplet motion on surface-textured ratchet tracks with an inverted double pendulum model
(American Chemical Society, 2021-04-27) Naji, Mayssam; Yelekli Kirici, Ecem; Javili, Ali; Erdem, Emine Yegan
We describe the motion of a droplet on a textured ratchet track using a nonlinear resonator model. A textured ratchet track is composed of a semicircular pillar array that induces a net surface tension local gradient on a droplet placed on it. When a vertical vibration is applied, hysteresis is overcome, and the droplet moves toward the local lower energy barrier; however, due to the repetitive structure of texture, it keeps moving until the end of the track. The droplet motion depends on the amplitude and frequency of the vertical oscillation, and this dependence is nonlinear. Therefore, finding a fully analytic solution to represent this motion is not trivial. Consequently, the droplet motion remains poorly understood. In this study, we elaborate on the utility of a double pendulum as a basis for modeling the droplet motion on surfaces inducing asymmetric force. Similar to the droplet motion, resonators, such as a double pendulum, are simple, yet nonlinear systems. Moreover, an inverted double pendulum motion has key characteristics such as the two-phase motion and the double peak motion, which are also observed in the droplet motion. We use various data-processing methods to highlight the similarity between these two systems both qualitatively and quantitatively. After establishing this comparison, we propose a model that utilizes an inverted double pendulum mounted on a moving cart to successfully simulate the motion of a droplet on a ratchet track. This methodology will lead to the development of an accurate droplet-motion modeling approach, and we believe that it will be useful to understand droplet dynamics more deeply.
Open Access
Modeling of droplet motion on textured surfaces
(2021-09) Naji, Mayssam
We describe the motion of a droplet on a textured ratchet track using a non-linear resonator model. A textured ratchet track is composed of semi-circular pillar array that induces a net surface tension gradient on a droplet placed on it. When a vertical vibration is applied, hysteresis is overcome, and the droplet moves towards the local lower energy barrier; however, due to the repetitive structure of texture, it keeps moving until the end of the track. The droplet motion depends on the amplitude and frequency of the vertical oscillation, and this dependence is nonlinear. Therefore, ﬁnding a fully analytical solution to represent this motion is not trivial. Consequently, the droplet motion still remains as a topic that needs further investigation. In this study we elaborate on the utility of double-pendulum as a basis for modeling the droplet motion on surfaces. Similar to the droplet motion, resonators, such as double pendulum, are simple, yet non-linear systems. Moreover, inverted double pendulum motion has key characteristics such as two phase motion and double peak motion, which are also observed in the droplet motion on textured ratchets. In this thesis, data processing models are developed to highlight the similarity between these two systems both qualitatively and quantitatively. After establishing this comparison, a model is proposed that utilizes an inverted double pendulum mounted on a moving cart to successfully simulate the motion of a droplet on a ratchet track. This methodology will lead to developing an accurate droplet-motion modeling approach which will be useful to understand droplet dynamics in more depth.
Restricted
The Pakistani Embassy in Ankara in the late 1990 's
(Bilkent University, 2017) Naji, Mayssam; Saeed, Muhammad Ramish; Abbas, Reem; Butt, Unas Sikandar; Waheed, Wajahat
Open Access
Size and shape analysis of silica (SiO2) and gold (Au) nanoparticles
(Taylor & Francis Inc., 2023-06-26) Bilgili, Devrim; Naji, Mayssam; Erdem, E. Yegan
In nanotechnology, the size and shape control of nanoparticles is crucial as their properties are highly dependent on their morphology. This obliges researchers to work on obtaining uniform size and shape distribution in synthesized particles so that their electrical, optical, and magnetic properties remain uniform within the same batch. This brings the problem of how to quantify the shape and size of nanoparticles in the most accurate way. The most common way to determine size distribution is using UV-vis spectrometry; however, this method disregards the existence of agglomerated particles and may sometimes give an incorrect measurement. Therefore a technique that can obtain this data directly from the transmission electron microscopy (TEM) images of particles would be more reliable as it would capture data for every single particle in the batch. In a classical statistical sense, our interest is the shape and size distribution of nanoparticles. In this paper, we quantify the size and shape of nanoparticles using the statistical techniques applied on TEM images of particles: Functional Data and Shape Analysis. By using this shape theory we obtain the geodesic distances not only between the particles but also among the frames. We further cluster the nanoparticles in terms of their similarities. We want to emphasize the importance of the deformation and how it is done of one nanoparticle onto another.
Embargo
Textured surfaces for oil droplet transport
(Elsevier BV, 2023-08-22) Yelekli Kirici, Ecem; Naji, Mayssam; Çanakçı, Ahmet Selim; Erdem, Emine Yegân
Droplet-based microfluidic systems bring the advantage of handling samples in discrete forms and these systems can be built as a surface-based platform, eliminating the need of a carrier fluid. Droplet transport on surfaces can be achieved by creating local energy gradients by using electrowetting, thermocapillary forces, chemical gradients and surface texture. These methods are developed for aqueous droplets; while controlled transportation of oil droplets remains as a challenge due to their low surface tension. One of the major challenges in achieving controlled oil droplet manipulation is to obtain oil repellent -oleophobic- surfaces. In this work, pillar arrays with mushroom shaped profiles were designed, fabricated, and tested to study oil wetting on textured surfaces. Contact angles higher than 170° were achieved for hexadecane droplets in Fakir state. Based on these findings, surface texture ratchet tracks that are composed of an array of arc shaped pillars were built to generate local energy gradients to manipulate oil droplets in a continuous fashion. Motion of hexadecane droplets at a speed of 7 mm/s was achieved. The results of this study are crucial for applications of oil droplet transport such as in biochemistry, smart surface development, wearable device design as well as microsystem packaging.