Browsing by Author "Ekim, Sunay Dilara"

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Open Access
Control of contact charging on polymers with organic charge-transfer complexes and quantum dots
(2022-08) Ekim, Sunay Dilara
Contact charging, also known as triboelectrification, occurs when two insulator materials are contacted and separated. The mechanism of polymer triboelectrification and the following charge dissipation are still ‘mysteries’ in the current scientific research. However, generation and transfer of contact charges on surfaces could be harmful to many industries. It causes substantial economic losses in, e.g., space industry where satellites are damaged, in pharmaceuticals where charging of powder drugs is a severe problem for process and manufacturing, and in microelectronics where MEMs devices suffer from triboelectric charging. So far, the common approach to this problem is to render surfaces conductive with high loading of conductive additives, which is not ideal for most of the industrial applications. This thesis presents some efforts to open and explore new light-controlled discharging mechanisms for contact-charges on polymers, without an increase in surface conductivity of the polymer surface. The antistatic behavior of the polymer surfaces are achieved by doping of organic charge-transfer complexes (CTC)s or quantum dots (CdSe, CdSe/ZnSe). In the first part of the study, the CTCs formed from pyrene and its derivatives, and TCNQ doped into the polydimethylsiloxane (PDMS) were found to affect a faster discharge compared to the discharging on undoped polymers, as monitored by Faraday cup measurements. In a second setup, solutions of CTCs dropped into the vials of contact charged polymer beads in hexane affected a similar faster discharge of the beads, which was monitored by the fall time of the beads. In both solid samples and with the beads in hexane, the time required for the polymer discharge mediated by each CTC was related to the CTCs degree of charge transfer. Additionally, when the samples were excited by a UV source, the charge decays were faster in comparison to the non-illuminated samples. Theoretical calculations confirmed that HOMO-LUMO gap decreases upon excitation, which enhances the dissipation of tribocharges. It was also found that hydrogen bonds between donor and acceptor moieties alter the CTC morphology in PDMS, which yields differences in charging and discharging behavior. The formed CTC-composites were characterized by UV-Vis, AFM, XRD, and SEM. In the second part of this thesis, CdSe, CdSe/ZnSe quantum dots (QD) were doped in the polymers to test the polymer discharging performance of these materials. The formed QD-composites were characterized by UV-Vis, TRF, XRD, SEM, and TEM. This new set of materials bring in their unique properties to the polymer composites, i.e., bandgaps which are tunable, and quantum confinement effects in the nanocrystals. These properties unlatch new doors to the charge dissipation, one of which was explored by changing spatial delocalization of holes and electrons in semiconductors with band-gap engineering. In this study, the faster discharging on polymers doped with CTCs and QDs affected by a control of their properties, like degree of charge transfer (for CTC) and hole-electron localizations (QD) were displayed. It was shown that light-controlled remote discharging maybe expanded to other types of materials, and it can be fine-tuned by materials’ properties. The results point towards other possible but yet unexplored discharging mechanisms with unconventional additives, which do not simply increase the polymers’ surface conductivity. Finally, we believe that these findings can be useful where materials are needed to be antistatic, but not conductive, such as in the electronic coatings.
Open Access
Core-shell quantum dot-embedded polymers for antistatic applications
(American Chemical Society, 2023-12-07) Ekim, Sunay Dilara; Aydın, Firdevs; Kaya, Görkem Eylül; Baytekin, H. Tarık; Asil, Demet; Baytekin, Bilge
Electrical charges develop on the surfaces of two insulator materials when they are in contact and separated. The retention of charges on insulator polymers causes material losses and hazards in industries using these polymers. Here, we show that a set of core-shell quantum dots embedded into a common polymer can destabilize the charges on the polymer. The locations of the charge carriers in the nanostructure, or the “type” of the dots, affect their discharging ability, which can also be manipulated or reverted remotely by light. The mechanism of antistatic action is presumed to contain interaction with polymer mechanospecies. The quantum dot embedding renders the polymers antistatic without changing their conductivity. Such antistatic additives, by which the polymers remain insulating, can be used to prevent static charges, e.g., in electronic coatings and in other antistatic applications.
Open Access
Online lubricant degradation monitoring using contact charging of polymers
(Elsevier, 2022-05-15) Baytekin, Bilge; Baytekin, H. T.; Karluk, Azimet Akber; Ekim, Sunay Dilara
Lubrication of machine parts is necessary to prevent friction and wear in machine operation. However, oxidation of lubricants upon operation changes their chemical and physical properties and causes lubrication performance to deteriorate. Besides, one liter of wasted/used lubricant oil can contaminate a million liters of water. Current methods for the timely detection of oil deterioration lack practicality. Here we show simple, a triboelectrification-based method for oil degradation monitoring, in which the oxidation can be monitored by the changes in the contact charging (and separation) signals of oil-dipped cellulose and a common polymer tapped to each other. The commercial and base oil samples are oxidized at 100–200 °C for up to 80 h, simultaneously monitored by ATR-FTIR and the triboelectric method. The results show that a 40–90% decrease in the triboelectric open-circuit potentials in the presence of oxidized oil can directly indicate the start of oil oxidation without other accompanying analyses.
Open Access
Organic charge transfer cocrystals as additives for dissipation of contact charges on polymers
(American Chemical Society, 2022-12-06) Ekim, Sunay Dilara; Kaya, Görkem Eylül; Daştemir, M.; Yildirim, E.; Baytekin, H. T.; Baytekin, Bilge
Common polymers can accumulate surface charges through contact, a phenomenon known since ancient times. This charge accumulation can have detrimental consequences in industry. It causes accidents and yields enormous economic losses. Many empirical methods have been developed to prevent the problems caused by charge accumulation. However, a general chemical approach is still missing in the literature since the charge accumulation and discharging mechanisms have not been completely clarified. The current practice to achieve charge mitigation is to increase materials conductivity by high doping of conductive additives. A recent study showed that using photoexcitation of some organic dyes, charge decay can be started remotely, and the minute amount of additive does not change the material's conductivity. Here, we show the contact charging and charge decay behavior of polydimethylsiloxane doped with a series of organic charge transfer cocrystals (CTC) of TCNQ acceptor and substituted pyrene donors (CTC-PDMS). The results show that the CTC-PDMS are antistatic, and the discharging propensity of the composites follows the calculated charge transfer degree of the complexes. On the other hand, the CTC-PDMS are still insulators, as shown by their high surface resistivities. Kelvin probe force microscopy images of the contact-charged and discharged samples show a quick potential decay in CTC domains upon illumination. Combined with the fast overall decay observed, the antistatic behavior in these insulators can be attributed to an electron transfer between the mechanoions in the polymer and the CTC frontier orbitals. We believe our results will help with the general understanding of the molecular mechanism of contact charging and discharging and help develop insulator antistatics.