Browsing by Author "Orakdogen, Nermin"

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Open Access
Design of Weakly Cationic Alco-Cryogels Consisting of Poly (Alkylmethacrylates)-Based Sulfonated Terpolymer Network with Tunable Multiresponsive Assembly
(Elsevier Science Ltd., 2021) BEŞLİ, NUR SENA ÖKTEN; Orakdogen, Nermin
Cryogels with ion-, and solvent-responsiveness have been designed by cryogelation of 2-(diethylamino)ethyl methacrylate (DEAEMA) as weakly cationic monomer, hydroxyethyl methacrylate as neutral comonomer and 2- acrylamido-2-methyl-1 -propanesulfonic acid as anionic termonomer in ethanol-water mixture (50:50 v/v), which had been proved to offer a good miscibility of monomers. Influence of composition of terpolymer and polymerization temperature on the properties of terpolymer cryogels (Cgels) and hydrogels (Hgels) were evaluated by swelling kinetics, and response against rapid ionic strength change. Degree of swelling was extremely sensitive to salt concentration, cation/counterion type as well as the solvent type; acetone and monohydric alcohols with various hydrophobic alkyl groups; methanol, ethanol, and 2-propanol. Swelling of terpolymer networks in the form of Cgel and Hgel decreased with increase in the size of ions present in swelling medium and followed the order of swelling behavior CF- > Br- > I-. Terpolymer alcogels exhibited salting-out behavior in the presence of Cl- and Br(- )ions, while "salting-in" behavior was observed in KI solutions of high concentrations. Sensitivity sequence of terpolymer alcogels to mono- and di-valent cations with a common anion (SO42-) on swelling was Na+ > k(+) > Mg2+ > Zn2+. Variation of elastic moduli with swelling in salt solutions was investigated and for terpolymer hydrogels, possible contribution of ionic crosslinks to effective crosslinking density nu(e) was discussed. Increasing Na2SO4 concentration up to 0.1 M induced a 2-fold increase in the elastic modulus of terpolymer alcogels. With attention to the polarity of solvent, terpolymer gels exhibited an irregular swelling profile with a change in composition of solvent, showing the so called cosolvency phenomena. After two successive cycles of swelling and shrinking promoted by the change of ionic strength of KCl solution, the terpolymer gels were stable and dynamic swelling process was reversible. Swelling data agree well with second-order kinetic model and with increasing amount of DEAEMA in terpolymer feed, diffusion mechanism changed from non-Fickian type to Fickian diffusion. In ionic environments, the salt-sensitivity and excellent water absorption/retention capability give this intelligentized terpolymer gels wide potential applications.
Open Access
One-Shot Preparation of Polybasic Ternary Hybrid Cryogels Consisting of Halloysite Nanotubes and Tertiary Amine Functional Groups: An Efficient and Convenient Way by Freezing-Induced Gelation
(MDPI, 2021) BEŞLİ, NUR SENA ÖKTEN; Orakdogen, Nermin
A convenient method for the preparation of polybasic ternary hybrid cryogels consisting of Halloysite nanotubes (HNTs) and tertiary amine functional groups by freezing-induced gelation is proposed. Ternary hybrid gels were produced via one-shot radical terpolymerization of 2-hydroxyethyl methacrylate (HEMA), 2-acrylamido-2-methyl-1-propane sulfonic acid (AMPS), and DEAEMA in the presence of HNTs. The equilibrium swelling in various swelling media and the mechanical properties of the produced ternary hybrid gels were analyzed to investigate their network structure and determine their final performance. The swelling ratio of HNT-free gels was significantly higher than the ternary hybrid gels composed of high amount of HNTs. The addition of HNTs to terpolymer network did not suppress pH- and temperature-sensitive behavior. While DEAEMA groups were effective for pH-sensitive swelling, it was determined that both HEMA and DEAEMA groups were effective in temperature-sensitive swelling. Ternary hybrid gels simultaneously demonstrated both negative and positive temperature-responsive swelling behavior. The swelling ratio changed considerably according to swelling temperature. Both DEAEMA and HEMA monomers in terpolymer structure were dominant in temperature-sensitive swelling. Mechanical tests in compression of both as-prepared and swollen-state demonstrated that strength and modulus of hybrid cryogels significantly increased with addition of HNTs without significant loss of mechanical strength. Ultimately, the results of the current system can benefit characterization with analysis tools for the application of innovative materials.
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Sepiolite-Embedded Binary Nanocomposites of (Alkyl)Methacrylate-Based Responsive Polymers: Role of Silanol Groups of Fibrillar Nanoclay on Functional and Thermomechanical Properties
(Elsevier, 2021) BEŞLİ, NUR SENA ÖKTEN; Orakdogen, Nermin
Binary nanocomposites filled with fibrillar nanoclay sepiolite (SP) was manufactured using a hydrophilic terpolymer matrix containing 2-(diethylamino)ethyl methacrylate, hydroxyethyl methacrylate and 2-acrylamido-2-methyl-1-propanesulfonic acid. A direct correlation between dispersion of nanofillers, matrix-filler local interaction and improvement of macroscopical mechanical properties was obtained. Mechanical testing revealed that incorporation of SP nanofillers impart to terpolymer matrix a higher degree of reinforcement. Besides fibrous structure of SP, the interactions between silanol (-SiOH) groups present along fibers and terpolymer chains are responsible of extent of reinforcement of nanocomposites. The increase in modulus imparted by incorporation of -SiOH groups reflected a continuous increase in crosslinking density created by terpolymer-nanofiller interactions. Effective crosslink density of nanocomposites was expressed by a cubic polynomial function of SP loading. Swelling ratio of SP nanofiller containing nanocomposites was found to highly decrease at CSP > 3.50%(w/v), with regard to clay-free terpolymers reflecting strong interactions between pendant hydroxyl, carbonly, tertiary amino groups of terpolymer matrix and silanol groups of SP. Excellent pHresponsive swelling was observed in the range of pH 2.1?10.7 and the nanocomposites swelled in acidic conditions depending on the amount of protonated diethyl amino groups. Sensitivity sequence of terpolymer nanocomposites to mono- and di-valent cations with a common anion (Cl-) on swelling was Na+ > K+ > Mg2+. The control of quantity of SP fibers and polymerization temperature allows to manage mechanical properties by just tuning chemical architecture of terpolymer/clay nanocomposites. SP reinforcement of terpolymers can enrich various further characteristics such as targeted delivery of biomolecules or drugs.