You are invited to CHEM 591 – Graduate Student Seminars of Chemistry Department.
This week’s speakers are Mahnam Ebadi, Ezgi Kutbay and Hatice Arı.
Please see the seminar information and the abstracts below.
1.Chemical Structure – Charging Interrelation in the Electrification of Organic Powders with Fused Aromatic Ring Structure
Mahnam Ebadi
Advisor: Assoc. Prof. Bilge Baytekin
Time: April 22, 2025, 12:30, SBZ14
Abstract: The mechanism of static charge accumulation on the insulating surfaces via contact and the following charge dissipation remains a mystery since ancient times. Since many industries suffer from static electrification during production, handling, and usage of the products, scientists are trying to decipher the charging mechanisms, charge transfer modes, and any contributing factors. On the other hand, quantifying the materials based on their tendency to accept or donate electrons upon contact has often proved challenging. It ends up in contradictory, irreproducible findings, especially with insulating powders. In this study, we aim to provide a more comprehensive perspective to determine whether chemical structure is a deciding factor in the triboelectrification of insulating powders. In this regard, we focus on common aromatic powders to see how variations in the number and spatial arrangement of aromatic rings affect the charging behavior. Additionally, we study the impact of functional groups’ type, number, and positioning on the triboelectrification of these powders. However, to reach our goal, we must also determine to what degree other factors such as particle morphology, size, roughness, flowability, and grindability affect the charging behavior. Therefore, powders were characterized by analyzing their SEM micrographs and XRD diffractograms. Then, their tribocharging charging was studied by grinding them in an agate mortar and obtaining the generated voltage. The results show some correlations between the chemical structure and the sign and magnitude of the acquired charges.
2. Investigation of Ion-Dynamics in Ionic Liquid Devices using X-Ray Photoelectron Spectroscopy with AC Biasing
Ezgi Kutbay
Advisor: Prof. Şefik Süzer
Time: April 22, 12:30, SBZ14
Abstract: X-ray Photoelectron Spectroscopy (XPS) has long been used to investigate surface composition, chemical states, and electronic environments in materials. In this study, we utilize XPS specifically to extract local electrical potential profiles by monitoring shifts in core-level binding energies under applied DC and/or AC biases. To achieve this, a Square Wave (SQW) signal with varying frequencies was employed. A co-planar capacitor configuration was used, featuring a polyethylene membrane (PEM) coated with either the ionic liquid N,N-Diethyl-N- methyl-N-(2-methoxyethyl)ammonium bis(trifluoromethanesulfonyl)imide (DEME-TFSI) alone, or a 1:1 volume mixture of DEME-TFSI and N,N-Diethyl-2-methoxy-N- methylethanaminium tetrafluoroborate (DEME-BF4). The measurements were conducted in- operando, allowing simultaneous acquisition of XPS spectra and current data. Although ionic liquids offer advantages such as wide electrochemical windows and thermal stability, their high viscosity and cost can hinder ionic mobility and conductivity. A promising approach to address these limitations involves mixing different ILs to tailor their properties. For example, adjusting the ratio of DEME-TFSI and DEME-BF4 alters electrolyte characteristics. The pronounced size difference between the TFSI and BF4 anions provides an opportunity for detailed investigation via XPS. ILs exhibit complex charging and discharging dynamics, notably through the formation of an Electrical Double Layer (EDL) at the electrode interface. Key aspects of this behavior can be probed within suitable time windows using AC modulation. To separate the contributions from fast polarization and slower ionic migration, two frequencies—10 kHz and
0.1 Hz—were selected as representative high and low limits. Binding energy shifts were analyzed at various points on the device, both before and after inserting two identical resistors in series with the circuit. This allowed for quantification of the AC current and extraction of system resistance and capacitance under specific operating conditions. Overall, this non- invasive methodology demonstrates that XPS is a powerful tool for probing localized electrochemical processes. The technique offers valuable insights that can contribute to the development of next-generation energy harvesting and storage systems.
3. Spatiotemporal Formation of Calcium Phosphate Liesegang Patterns in Agarose-Gelatin Hydrogel Blends
Hatice Arı
Advisor: Assoc. Prof. Bilge Baytekin
Time: April 22, 12:30, SBZ14
Abstract: Biomineralization is a process in which organic materials shape the nucleation, growth, and orientation of inorganic minerals. One of the common biomineralization processes in nature is the mineralization of calcium phosphates. In a body, these minerals are mostly found in bone or dentin enamels. The biological formation of calcium phosphates is hard to study since they are accompanied by many other complex biological processes. However, the chemical understanding of their formation, such as the determining identity and the morphology of the product, can help in many (medical) applications, such as developing biocomposite ceramic materials, implants, and curing of some diseases. The best media to mimic these structures in an artificial medium are the polymer hydrogel media such as gelatin or agarose – they can serve as a protein of sugar scaffold for the nucleation and growth of the minerals.
Reaction diffusion systems artificially constructed in hydrogels can serve as an optimum platform to study formation of such mineral precipitates. In these systems two reactant ions are let to mix, react, and form a precipitate without a convection, only through the diffusion of one into the other. Such a system for calcium phosphate has been extensively studied for more than 50 years for its pattern characteristics. The formed reaction-diffusion precipitate patterns (Liesegang patterns) were not examined extensively for the morphology (or the identity) of the calcium phosphate product so far. In this study, we aim to create an artificial system of calcium phosphate Liesegang patterns in agarose-gelatin blends in varying proportions to mimic the biological media. The varying ratios of the two polymers help development of different precipitate morphologies. Interestingly, in some blends, different particle morphologies within an individual band appeared, whereas in some others, different morphologies in different generations of bands were detected. We believe that this work might offer new insights into understanding the evolutionary pathway of biomineralization process, developing bioinspired composite ceramic materials as much as it contributes to the fundamentals of precipitation and mineralization.