Researcher:
Ijaz, Aatif

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Aatif

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Ijaz

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Ijaz, Aatif

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2018 - 201922020 - 20224

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Now showing 1 - 6 of 6
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    Formation of mesoporous silica particles with hierarchical morphology
    (Elsevier, 2020) Ow-Yang, Cleva W.; N/A; N/A; Department of Chemistry; Department of Chemistry; Ijaz, Aatif; Yağcı, Mustafa Barış; Demirel, Adem Levent; Miko, Annamaria; Researcher; Researcher; Faculty Member; Teaching Faculty; Department of Chemistry; Koç University Surface Science and Technology Center (KUYTAM) / Koç Üniversitesi Yüzey Teknolojileri Araştırmaları Merkezi (KUYTAM); N/A; N/A; College of Sciences; College of Sciences; N/A; N/A; 6568; 163509
    The transformation of mesoporous silica morphology from monoliths to spherical particles was investigated at room temperature in Pluronic F127/TEOS system as a function of HCl acid catalyst concentration to understand and control the mechanism. It is shown that the specific surface area and the size of mesoporous spherical silica particles can simply be adjusted by the catalyst concentration without using any additives or post-treatment. Above 3 M acid concentration, novel monodisperse micron sized spherical silica with hierarchical order of two levels was obtained. These silica spheres were formed of densely packed distorted hexagonal platelets of 20-30 nm in diameter. Within these platelets mesoporous channels were oriented along a single direction, however the platelets were randomly oriented in the spherical particles. Controlling the agglomeration of mesoporous silica primary particles by the concentration of the acid catalyst to obtain micron-sized spherical particles is novel. This approach allows the synthesis of particles whose sizes can be controlled in the range of similar to 1-4 mu m and specific surface area in the range of similar to 200-500 m(2)/g. The morphology of the particles transforms from spherical shape to mesoporous monoliths at acid concentrations below 1 M due to slow hydrolysis and condensation. These results are important in understanding the role of catalyst concentration on the formation mechanism of different morphologies of mesoporous silica.
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    Refillable anti-icing SBS composite films
    (Elsevier, 2021) N/A; N/A; Department of Chemistry; Department of Chemistry; Department of Chemistry; Department of Chemistry; Ijaz, Aatif; Topçu, Gökhan; Qureshi, Mohammad Haroon; Miko, Annamaria; Demirel, Adem Levent; Researcher; Researcher; PhD Student; Teaching Faculty; Faculty Member; Department of Chemistry; Koç University Surface Science and Technology Center (KUYTAM) / Koç Üniversitesi Yüzey Teknolojileri Araştırmaları Merkezi (KUYTAM); Koç University Research Center for Translational Medicine (KUTTAM) / Koç Üniversitesi Translasyonel Tıp Araştırma Merkezi (KUTTAM); N/A; College of Sciences; Graduate School of Sciences and Engineering; College of Sciences; College of Sciences; N/A; N/A; N/A; 163509; 6568
    The lifetime of release-based anti-icing systems can be improved by refilling after the complete release of active agents. A novel swelling mediated consecutive filling of Diatomaceous Earth (DE) loaded Styrene-Butadiene-Styrene (SBS) composite films with PEG for anti-icing applications is reported. The degree of swelling and the diffusion of active agents into the composite was controlled by adjusting the composition of a binary mixture consisting of a non-solvent (acetone) and a good solvent (diethyl ether (DiEt)). Rhodamine 6G was used as a probe to show the extent of diffusion of dissolved molecules into SBS. The reversible loading of PEG-600 as anti-icing agent up to 19% by weight into DE/SBS composites and the complete release in the binary mixture having 30 vol. % DiEt was successfully achieved in consecutive cycles. After the 5th loading cycle, these composite films exhibited similar water contact angles (∼ 64°) and freezing delay times within error bars as those of the 1st loading cycle. At −15 °C, the average freezing delay time of the water droplets on DE/SBS composites filled with PEG in 30 vol. % DiEt was increased by a factor of three to 120 s. The successful refilling of the composites with reversible loading/release cycles and without any deterioration in the anti-icing properties at least up to 5 cycles is a significant contribution to the lifetime of release based functional coatings.
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    Tuning grain size, morphology, hardness and magnetic property of electrodeposited nickel with a single multifunctional additive
    (Elsevier, 2021) Kiss, Laszlo Ferenc; Varga, Lajos Karoly; N/A; Department of Chemistry; Department of Chemistry; Ijaz, Aatif; Miko, Annamaria; Demirel, Adem Levent; Researcher; Teaching Faculty; Faculty Member; Department of Chemistry; Koç University Surface Science and Technology Center (KUYTAM) / Koç Üniversitesi Yüzey Teknolojileri Araştırmaları Merkezi (KUYTAM); N/A; College of Sciences; College of Sciences; N/A; 163509; 6568
    The room temperature electrodeposition of high purity, nanocrystalline Ni films prepared in the presence of poly(2-ethyl-2-oxazoline) (PEOX) as a new multipurpose polymeric additive in Watts bath is presented. The grain size, morphology, hardness and magnetic property of the nickel films were simply tuned by adjusting the concentration of PEOX. Increasing PEOX concentration contributed to grain refinement down to 12.5 nm grain size and crystalline orientation towards (220) planes. The control over the crystalline grain size and the orientation by PEOX concentration allows the preparation of tailor made nickel layers with adjustable physical and chemical properties. The effect of PEOX on the structure is attributed to the high affinity of tertiary amide groups in PEOX for metal surfaces, whereas the incorporation of the macromolecular additive into the nickel layers was prevented. These findings are especially important in emerging applications where smooth, high purity nanocrystalline layers are required. PEOX as a multifunctional additive eliminates the need to use multiple electrolyte additives to obtain a set of desirable properties.
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    Anti-icing agent releasing diatomaceous earth/SBS composites
    (Royal Soc Chemistry, 2018) N/A; N/A; Department of Chemistry; Department of Chemistry; Ijaz, Aatif; Miko, Annamaria; Demirel, Adem Levent; Researcher; Teaching Faculty; Faculty Member; Department of Chemistry; Koç University Surface Science and Technology Center (KUYTAM) / Koç Üniversitesi Yüzey Teknolojileri Araştırmaları Merkezi (KUYTAM); N/A; College of Sciences; College of Sciences; N/A; 163509; 6568
    Diatomaceous earth (DE) loaded SBS based composites were developed for anti-icing applications. 30% by weight DE containing SBS composites were filled by keeping the composites in anti-icing agent (EG or PEG) solutions in diethyl ether/acetone binary mixtures. The dissolved anti-icing agents penetrated into the swollen DE/SBS matrix in the binary mixture. DE particles served as the anti-icing agent carrier in the hydrophobic SBS matrix. The amount of anti-icing agent retained in the composite was increased by increasing the concentration of the anti-icing agent in the binary mixture, which resulted in longer freezing times of water droplets on the composite. The effective anti-icing mechanism was shown to be the release of the anti-icing agent upon contact with water and subsequent decrease of the water freezing temperature. The release of PEG in the inner DE pores was achieved by cutting the composite films into smaller pieces and increasing the water/composite interfacial area. This shows that the developed composites maintain their anti-icing activity for longer times in the presence of scratches and wear. Scratches and wear allow the anti-icing agent filled pores of DE particles buried in the SBS matrix to be exposed to the top surface with the possibility of new anti-icing agents being released when in contact with water.
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    PublicationOpen Access
    Self-assembled poly(2-ethyl-2-oxazoline)/malonic acid hollow fibers in aqueous solutions
    (Elsevier, 2019) Department of Chemistry; Department of Chemical and Biological Engineering; Miko, Annamaria; Altıntaş, Zerrin; Ijaz, Aatif; Demirel, Adem Levent; Adatoz, Elda Beruhil; Teaching Faculty; Researcher; Researcher; Faculty Member; Department of Chemistry; Department of Chemical and Biological Engineering; College of Sciences; Graduate School of Sciences and Engineering; 163509; N/A; N/A; 6568; N/A
    Well-defined poly(2-ethyl-2-oxazoline) (PEOX)/Malonic Acid (MA) fibers having hollow tubular morphology were shown to form in aqueous solutions at 25 degrees C by complexation induced self-assembly between PEOX and MA. The fibers had diameter of similar to 1-3 mu m and a wall thickness of -40 nm. Different interactions between PEOX and MA were identified for complexation as a function of pH. At pI-12, when both ends of MA were protonated, H-bonded complexation was the driving interaction in the fiber formation. IR data showed both PEOX -C=0 band and MA -COOH band in dried fibers formed at pH2. The downshift in the -C=0 stretching of PEOX by as much as 15 cm(-1) confirmed the H-bonded complexation. The interaction enthalpy of PEOX and MA was determined by isothermal titration Calorimetry (ITC) as -49.39 kJ/mol which is consistent with H-bonding. Thermogravimetric analysis (TGA) of the fibers showed two distinct decomposition temperatures one between 100 and 150 degrees C corresponding to MA and the other one at 350-450 degrees C corresponding to PEOX which also indicated the presence of both components in the fibers. At pH4, when one end of MA was protonated and the other end was ionized, electrostatic complexation between carboxylate (-COO-) group of MA and the amide group of PEOX was the driving interaction in the fiber formation. At pH7, when both ends of MA were ionized, fiber formation was significantly hindered. The results are important in understanding the role of different interactions in the hollow fiber formation mechanism as a function of pH. pHresponsive hollow fibers have great potential to be used in biomedical applications for drug delivery and release purposes.
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    PublicationOpen Access
    Low ice adhesion anti-icing coatings based on PEG release from mesoporous silica particle loaded SBS
    (Royal Society of Chemistry (RSC), 2022) Department of Chemistry; Ijaz, Aatif; Miko, Annamaria; Demirel, Adem Levent; Researcher; Teaching Faculty; Faculty Member; Department of Chemistry; College of Sciences; N/A; 163509; 6568
    Release-based extremely low ice adhesion strength and durable anti-icing coatings were designed and realized by loading mesoporous silica particles (MSP) into the SBS polymer matrix and filling poly(ethylene glycol) (PEG) as the anti-icing agent into MSP/SBS composites. This approach allows the formation of a thin lubricating liquid layer of PEG and water at the ice/composite interface at sub-zero temperatures and results in ice adhesion strength as low as 3 kPa. The high specific surface area of MSP (428 m(2) g(-1)) as the anti-icing agent carrier significantly contributed to the retainment of PEG in the composites. The freezing time of water droplets on the composites increased and the ice adhesion strength decreased with the amount of PEG retained in the composites. After 15 icing/deicing cycles, the ice adhesion strength was measured to be similar to 5 kPa indicating a rather slow release (and removal with ice) of PEG at -10 degrees C from surface-exposed pores of MSP. The importance of PEG at the ice/composite interface was confirmed by ice adhesion strength measurements of frozen PEG-containing aqueous solutions on unfilled MSP/SBS composites. These results clearly show that PEG filled MSP/SBS composites demonstrate a passive anti-icing mechanism based on sustained release of PEG with extremely low ice adhesion strength and significant potential for longer-term use in sub-zero temperature and harsh environments.