Kocaman, Ceren
Precise control over membrane performance by tuning fabrication parameters is highly desirable. We developed ultrafiltration membranes by depositing cellulose nanocrystals (CNCs) of 180 nm length and 8 nm diameter on porous support via tangential flow filtration, then irreversibly coagulated the deposited layer permeating highly concentrated AlCl3 solution. At a high enough shear rate on the support surface, CNCs aligned in the flow direction, showing a nematic order. The shear rates for transition to the nematic phase determined from rheology analysis, polarized optical microscopy, and membrane performance were consistent with one another, at ca. 10 sˆ–1. Permeating and AlCl3 solution through the shear-aligned CNC deposit stabilized the CNC layer by screening repulsive electrostatic interactions, and a stable CNC layer was obtained. On changing the surface shear rate from 10 to 50 sˆ–1, the order parameter of CNCs increased from 0.17 to 0.7, and the rejection for Blue Dextran (5 kDa) increased from 82 to 92.7% and that for β-lactoglobulin (18 kDa) increased from 89.6 to 93.7%. By varying electrostatic interactions between nanocrystals during deposition, membrane performance was also tuned via changing ionic strength and pH of CNC suspensions. Increasing NaCl concentration of CNC suspensions from 0 to 25 mM increased Blue Dextran (5 kDa) rejection from 92.7% to 97% at high tangential flow rate and from 82% to 97% at low tangential flowrate. For membranes fabricated at high tangential flow rate, β-lactoglobulin (18 kDa) rejections increased from 93.7% to 98% when NaCl concentration increased from 0 to 25 mM. Increasing pH of CNC suspensions also increased probe molecule rejections, implying a smaller overall interparticle distance between CNCs in the deposited layer. CNC membranes’ pure water permeances were comparable to commercial membranes of similar separation properties. Polarized optical microscopy analyses showed that the alignment of CNCs and their aggregates, or tactoids, affect CNC deposits’ morphology. In all cases, CNC membrane structures and performances were tuned by easy-to-apply parameters. Hence, a simple and scalable method for controlling the rejection properties of ultrafiltration membranes is developed, which uses aqueous CNC suspensions to form the selective layer.


Tuning electrostatic interactions for controlled structure and rejection of cellulose nanocrystal membranes
Kocaman, Ceren; Büküşoğlu, Emre; Çulfaz Emecen, Pınar Zeynep (2022-11-05)
© 2022 Elsevier B.V.Precise control over membrane performance by tuning fabrication parameters is highly desirable. We developed ultrafiltration membranes by depositing cellulose nanocrystals (CNCs) on a porous support via tangential flow filtration, followed by irreversibly coagulating the deposited layer by permeating highly concentrated AlCl3 solution. By varying electrostatic interactions between nanocrystals during deposition, via varying ionic strength and pH of CNC suspensions, membrane performance w...
Investigating the Relationship between Shot-Peening Severity and Fatigue Life of AISI 4140 Steel by Magnetic Barkhausen Method
Çalışkan, Salim; Gür, Cemil Hakan (null; 2018-06-15)
Shot peening process results in compressive residual stresses on the surface which improves the fatigue performance of the components. Fatigue life of several aircraft parts is improved by shot peening. Thus, development of easy, rapid and reliable non-destructive methods for estimation of residual stress, and thus fatigue performance of the components will be very useful for aircraft industry. Recently the magnetic Barkhausen noise (MBN) method has gained importance for non-destructive characterization of ...
Investigating Dynamics of Machine Tool Spindles under Operational Conditions
Özşahin, Orkun; Özgüven, Hasan Nevzat (2011-05-13)
Chatter is one of the major problems in machining and can be avoided by stability diagrams which are generated using frequency response functions (FRF) at the tool tip. During cutting operations, discrepancies between the stability diagrams obtained by using FRFs measured at the idle state and the actual stability of the process are frequently observed. These deviations can be attributed to the changes of machine dynamics under cutting conditions. In this paper, the effects of the cutting process on the spi...
Simulation of glow discharge plasmas by using parallel particle in cell / monte carlo collision method : the effects of number of super particles used in the simulations
Erden, Emrah; Çetinkaya, Tahsin Ali; Rafatov, İsmail; Department of Mechanical Engineering (2013)
Mechanical amplification is achieved using a multi-flexure-hinge based compliant mechanism, due to limited displacement range of piezoactuator. In the design stage of mechanism, a comparison matrix analysis is performed to decide the best alternative among the possible compliant mechanism candidates. The mechanical design parameters of the displacement amplifier is determined optimally using the analytical equation derived using Pseudo Rigid Body Model, and the static analysis is performed using finite elem...
Syntheses and Optoelectronic Properties of Quinoxaline Polymers: The Effect of Donor Unit
Sendur, Merve; Balan, Abidin; Baran, Derya; Toppare, Levent Kamil (Wiley, 2011-09-15)
Tuning the bandgap of electrochromic polymers is one of the important research topics in electrochromism. To understand clearly the effect of donor unit in donor-acceptor-donor-type polymers, 2,3-bis(4-tert-butylphenyl)-5,8-di(thiophen-2-yl)quinoxaline and 2,3-bis(4-tert-butylphenyl)-5-(2,3-dihydrothieno[3,4-b][1,4]dioxin-5-yl)-8-(thiophen-2-yl)quinoxaline were synthesized and polymerized potentiodynamically. Their electrochemical and spectroelectrochemical studies were performed, and the results were compa...
Citation Formats
C. Kocaman, “PROCESSING CELLULOSE NANOCRYSTAL SUSPENSIONS FOR ALIGNED DEPOSITION,” M.S. - Master of Science, Middle East Technical University, 2022.