Sevim İşçi

Rheology and structure of aqueous bentonite-polyvinyl alcohol dispersions

The influence of polymer on flow behaviour of Balikesir, Turkey bentonite dispersions (2%, w/w) was studied for non-ionic polymer, polyvinyl alcohol (PVA). In a range of 3.3 × 106 −3.3 × 105 mol/l, PVA was added to the bentonite dispersions in different concentrations and its behaviour was observed on rheology parameters. Thixotropy was detected by a hysteresis loop of the flow curves. The data were interpreted taking into account the interactions of colloidal clay particles, bentonitic clay concentrations, structure, and concentrations of added PVA. The particle size analysis was explained by surface orientation of PVA to the clay particles dispersed in aqueous solution. Zeta potential determination also emphasized that PVA molecules got attached on the face and edge surface of clay particles. The morphology of bentonite dispersions was analysed by scanning electron micrograph (SEM). FTIR studies carried out in parallel to rheology studies showed that hydrogen bonds were formed between surface of the clay, and absorbed PVA molecules and adsorbed water. The presence of PVA did not prevent extensive swelling of bentonite.

Effect of the adsorption of cetylpyridinium bromide on the flow behaviour of bentonite dispersions

Abstract The adsorption of the cationic surfactant, cetylpyridinium bromide (CPBr), and the rheological behaviours of the CPBr-coated bentonite dispersions (0.1% w/v) are investigated in the concentration range of 0.01–10 mmol/l CPBr. The adsorption capacity and the influence of the cationic surfactant on the flow behaviours change with the nature of the exchangeable cations, i.e. Na+ and Ca2+, of the bentonite samples.

Influence of Clay Surface Modification on Morphology and Rheology of Polyethylene Glycol/Montmorillonite Nanocomposites

The effects of surface modification of Na-montmorillonite (Na-MMT) on morphology and the rheological properties of polyethylene glycol/ organoclay nanocomposites are investigated. Dodecyltrimethylammonium bromide (DTABr) is used to modify the clay surface. Adsorption of DTABr on Na-MMT is monitored by zeta potential measurements. From zeta potential measurements, three DTABr concentrations, 1 × 10—3, 7.5 × 10— 3, and 5 × 10—2 mol/L, are chosen to fabricate the polyethylene glycol/organoclay composites. The morphology of three sets of organoclays (OMMT1, OMMT2, and OMMT3) is studied by X-ray diffraction (XRD) technique. The increase of basal spacing is found to be 0.2 nm as the DTABr concentration is increased to 7.5 × 10— 3 mol/L. The rheological properties of polyethylene glycol (PEG)/ organoclay nanocomposites are studied for three organoclays at different PEG concentrations. All nanocomposites show Bingham plastic flow behavior. The OMMT3 shows maximum viscoelastic properties in the polymer matrix. The morphology and electrokinetic properties of the PEG/organoclay nanocomposites are also investigated.

Synthesis and characterization of HDA/NaMMT organoclay

In this study, the rheologic and colloidal characterizations of sodium montmorillonite (NaMMT) were examined. Hexadecylamine (CH3(CH2)15NH2, HDA) was added to the bentonite water dispersion (2%, w/w) in different concentrations in the range 5.6 × 10−4−9.4 × 10−3 mmol/l. The rheological and electrokinetic behaviour of aqueous montmorillonite dispersions was investigated as a function of solid content and HDA concentration. The basal spacings of the HDA/NaMMT composites were studied by X-ray diffraction. The FTIR spectra were obtained from the modified bentonite products, which revealed the characteristic absorbances after treatment with HDA.

Characterization of Rheology, Electrokinetic Properties, and Surface Micromorphology of DTABr-MMT and CPBr-MMT Organoclays

In this study, the characterization of sodium-activated montmorillonite (NaMMT) dispersions (2 wt%) are examined in detail using rheological parameters, such as viscosity, yield value, apparent and plastic viscosity, and electrokinetic parameters, such as mobility and zeta potentials. Besides, the influence of solid content on viscosity is also evaluated. Dodecyltrimethylammonium bromide (DTABr) and cetylpyridinium bromide (CPBr) cationic surfactants are added to the NaMMT dispersions in different concentrations in the range of 10 3-5 10 2 mol/L. The rheological and electrokinetic properties, and the morphology of the organoclays (DTABr-NaMMT and CPBr-NaMMT) prepared with surfactants are compared in detail. Atomic force microscopy (AFM) techniques are used to characterize the morphology of NaMMT before and after intercalation of DTABr and CPBr surfactants. The intercalation of the surfactants in NaMMT dispersion has been studied by X-ray diffraction to examine whether the interlayer spacing swells or not. The basal spacings have been changed with the alkyl chain length of the surfactants. The morphology of bentonite dispersions is analyzed by scanning electron microscopy.

Colloidal properties and in vitro evaluation of Hydroxy ethyl cellulose coated iron oxide particles for targeted drug delivery

In this study, superparamagnetic iron oxide (Fe3O4) nanoparticles were prepared for the targeted drug delivery applications by controlling the colloidal properties with a cellulosic polymer that is Hydroxy ethyl cellulose (HEC). Fe3O4 particles were treated with HEC in a variable range of polymer concentration. Rheological, electrokinetic, magnetorheological and morphological properties of the dispersions were investigated to have stable and fully covered surfaces of Fe3O4 particles by coating with HEC and obtaining non-toxic biocompatible multifunctional magnetic particles. Fully coated HEC and iron-oxide particles were characterized thermally, magnetically and tested for toxicity in vitro. Then Doxorubicin hydrochloride (DOX), which is an anticancer drug widely used for cancer therapies, was loaded onto nanoparticles and their drug loading efficiency was determined. Finally, effects of DOX-loaded particles on the cancer cells were examined to report a nano drug system which can potentially open up new possibilities in the design of therapeutic agents. Results indicated that the synthesized nanoparticles in this study could be suitable to magnetically manipulated targeted delivery systems, imaging, magnetic hyperthermia treatments.

Influence of Cationic Polymers on the Rheological Behavior of Bentonite Clay Suspensions

In this study, the rheological behaviours of the bentonitic clay suspensions were determined as a function of the addition of three types of cationic polymers, namely polyethyleneimine (PEI), polydimethyldiallylammonium chloride (PDDA) and polybrene (PB). The addition of polymers at concentrations ranging between 10-10 g/l affect rheological properties and stabilities of bentonite dispersions. The results are interpreted according to the type of polymers and concentrations. Introduction Bentonite which is a kind of smectite group clay mineral is almost made up 80 % of montmorillonite and contains a crystal lattice with three layers. Bentonite clays are widely used in various industrial products and processes such as paints, coatings, ceramics, pesticides, pharmaceuticals, cosmetics, cement, and drilling fluids to modify the rheology and control the stability of systems. The adsorption of polymers modifies the surface properties, rheology and suspension stability of clays, which is of great technological importance. So far, the interaction of small electrolytes, cationic and anionic surfactants, and nonionic polymers with clay components has been widely investigated. However, the studies on polyelectrolyte and clay interaction are scarcer. Clay particles are capable of aggregating in three different arrangements, namely , face-to-face, edge-to-face, and edge-to-edge. The Bingham yield value (extrapolated shear stress) and plastic viscosity are a criterion of particle-particle interaction. In this study, the effect of the addition of PEI, PDDA and PB on the rheological and electrokinetic properties of the 2 % bentonitic clay dispersions have been investigated. The aim of the study is to investigate and to understand the role and mechanism of cationic polymer addition on the flow behaviour of bentonite.

The ionic polymers in the targeted drug delivery agents as the coating materials

E the toxicity of chemicals, drug candidates, natural compounds and nanomaterials requires predictive methods. Animal models are of limited predictivity and are too slow and costly for screening of the large and increasing numbers of compounds that need to be tested. Also, changes in legislation (e.g. animal bans for cosmetics testing) and other developments steeply increase the demand for alternative methods. However, many alternative methods are of unknown predictivity, and accepted alternative methods for predicting toxicity for human internal organs are not available. This problem is addressed by our work, which was initially focused on the kidney. Recently, we have developed the first animal-free platforms for the accurate prediction of nephrotoxicity in humans. These platforms include the only available predictive methods based on human induced pluripotent stem cell-derived renal cells and a predictive high-throughput platform. The high-throughput platform is currently applied in collaboration with the US Environmental Protection Agency to predict the human nephrotoxicity of ToxCast compounds. The test balanced accuracies of our predictive methods range between ~ 80%-90%, and these methods also reveal injury mechanisms and compound-induced cellular pathways. Based on a similar methodology we are now developing high-throughput platforms for predicting toxicity for other human organ systems, including liver and vasculature, and we are also establishing predictive organ-on-chip technologies for efficient repeated dose testing.Psychostimulant medications, such as Methylphenidate (MPH) have become main stay treatments for Attention Deficit Hyperactivity Disorder (ADHD) symptoms, such as hyperactivity, impulsivity and inattention in children. Such symptoms frequently also co-exist in children with Autistic Spectrum Disorders (ASD), thereby complicating a differential diagnosis. The presence of ADHD-like symptoms in children with ASD can have a significant detrimental impact on learning and social interaction, and can limit the outcome of behavioural interventions to address areas of core ASD difficulties. Therefore, it is of clinical relevance and potential benefit to address the issue of effectiveness and tolerability/safety of stimulants such as methylphenidate in children with co-morbid diagnoses of ASD + ADHD. This study performed a meta-analysis of three randomised controlled trials homogeneously measuring the effect of immediate release Methylphenidate (MPH) to reduce scores of hyperactivity in children with comorbid ADHD + ASD. The findings that IR-MPH produces an overall moderate significant benefit to reduce hyperactivity in ASD are discussed in relation to the risk/benefit question of medication use in this population.