Dusko Cakara - Academia.edu (original) (raw)

Papers by Dusko Cakara

Variable angle spectroscopic ellipsometry (VASE) measurements were employed to study the optical ... more Variable angle spectroscopic ellipsometry (VASE) measurements were employed to study the optical properties of HgI 2. The bulk crystal HgI 2 surface was subjected to a 10% KI etching prior to the VASE measurements. SE measurements were performed at room temperature, in air with several different angles of incidence. The uniaxial anisotropic nature of the HgI 2 crystal was treated in the VASE analysis. Anisotropic dielectric functions of single crystal HgI 2 , e 1 (wo) and e 1 (a), for optical electric field vector oriented parallel and perpendicular to the c axis, respectively, were obtained in the range of-2.0-5.0 eV. Surface aging effects of the HgI 2 crystal, after the 10% KI etching, were characterized by VASE.

Carbohydrate Polymers, Aug 1, 2009

The protonation of cotton fabric with irreversibly adsorbed medical chitosan (CO–CT) was measured... more The protonation of cotton fabric with irreversibly adsorbed medical chitosan (CO–CT) was measured in aquatic medium at 0.1M ionic strength by means of potentiometric titrations, and compared with the results obtained for pure cotton and chitosan. For CO–CT, the charging isotherm exhibits a charge reversal around pH≈6.0, which is identified as the point of zero charge (PZC). The pure chitosan and the acid fraction that is present in cotton, protonate according to the one-pK model, with pKCT=6.3 and pKCO=4.7, respectively. At pH>PZC, the charge of the acid fraction in CO–CT is negative and constant, and the proton binding is attributed purely to the adsorbed chitosan. On the other hand, the cotton-bound acid exhibits a more complex protonation mechanism in CO–CT than in the pure fabric, which is evidenced as an excess positive charge at pHPZC and a deviation from the one-pK behavior.

2022 45th Jubilee International Convention on Information, Communication and Electronic Technology (MIPRO), May 23, 2022

Surfaces and Interfaces, Aug 1, 2022

Textile Research Journal, May 10, 2011

The main purpose of this research was to qualitatively and quantitatively identify chitosan-based... more The main purpose of this research was to qualitatively and quantitatively identify chitosan-based viscose fibre functional group surfaces as modified by two chemically-similar phenolics, namely fisetin and quercetin. Potentiometric titration was used to determine fibre-dissociable weak acids as a consequence of the presence of chitosan and deposited flavonoids. In addition, a conventional spectrophotometric method using C.I. Acid Orange 7 dye was used for determining the amino groups only. Finally, the antioxidant and antimicrobial properties of the fibres were evaluated, respectively. It has been clearly shown that the introduction of flavonoid onto the fibres introduces a significant amount of anionic phenolic hydroxyl groups, leading to fibre antioxidant activity and a decrease in fibre antimicrobial efficiency.

Journal of Colloid and Interface Science, Dec 1, 2005

Colloidal silica is known to be stable at high salt concentrations and low pH, where silica is ba... more Colloidal silica is known to be stable at high salt concentrations and low pH, where silica is basically uncharged. This observation is in qualitative disagreement with the theory of Derjaguin, Landau, Verwey, and Overbeek (DLVO), which predicts rapid aggregation (or coagulation) under these conditions. This study reports a very different behaviour for Stöber-type silica heated at 800 • C, as these particles follow DLVO theory quantitatively. Unheated samples behave approximatively according to DLVO theory, but they show systematic deviations, in particular, featuring higher stability at low pH. The heat treatment also substantially modifies the charging properties, as heated particles show titratable surface charge densities in the range expected for the water-silica interface, while much higher charge densities are observed for the unheated samples. The electrophoretic mobilities, on the other hand, are hardly influenced by the heat treatment. We suspect that the suspension stability of the unheated particles is influenced by the presence of a hairy-layer of polysilicilic acid chains on the surface.

Colloids and Surfaces A: Physicochemical and Engineering Aspects, Feb 1, 2007

The charging behavior of carboxyl latex surface in the presence of poly(diallyl dimethyl ammonium... more The charging behavior of carboxyl latex surface in the presence of poly(diallyl dimethyl ammonium chloride) (DADMAC) was investigated by means of potentiometric titrations and electrophoretic mobility. The titration curves at different ionic strengths show a common crossing point, which coincides with the point of zero mobility, and can be identified with the point of zero charge (PZC). This characteristic behavior is due to the adsorption of the strong cationic polyelectrolyte on the weak acid particle surface, leading to an additional positive charge, and a corresponding shift of the surface potential. These features can be quantified in terms of modified Stern model and the standard electrokinetic model. This model predicts the PZC very well, while the magnitude of the charge and its ionic strength dependence are reproduced only semi-quantitatively.

Journal of Physical Chemistry B, Mar 20, 2012

Journal of Colloid and Interface Science, Dec 1, 2000

An ice electrode was constructed in order to measure dependency of the surface potential on pH. T... more An ice electrode was constructed in order to measure dependency of the surface potential on pH. The electrode had a Plexiglas body with a platinum plate on the bottom, which was cooled by passing the cooling liquid through a tube mounted inside the electrode. The temperature inside the electrode was −7 • C, while the electrolyte solution was kept at 0.02 • C, so that an ice layer was formed on the platinum plate. In the acidic region fast equilibration of electrode was observed. The slope dφ 0 /dpH was found to be between −40 and −46 mV. The maximum of the slope was observed at pH 4.4, which coincides with the isoelectric point of ice-water interface. In the basic region the equilibration was slow and more pronounced deviation from the Nernstian behavior was observed. The results were explained on the basis of the surface complexation model, assuming an amphotheric nature of surface OH groups. In the basic region the surface bears high negative charge so that binding of sodium ions at the interface influenced the results.

Applied Surface Science, Dec 1, 2022

Colloids and Surfaces A: Physicochemical and Engineering Aspects, May 1, 2009

Potentiometric titrations and electrophoresis techniques were used to study the charging behavior... more Potentiometric titrations and electrophoresis techniques were used to study the charging behavior of aqueous silica particle suspensions in the presence of poly(N,N-diallyldimethylammonium chloride) (DADMAC). The main finding is that the particles undergo charge reversal with increasing pH, which can be directly seen by electrophoresis and as a common crossing point in the titration curves at different salt levels. These features resemble the charging behavior of an amphoteric oxide surface. With increasing polymer dose, the charge reversal point shifts towards higher pH. These trends are well reproduced by a modified Stern model. The main effect of the adsorbed cationic polyelectrolyte is to further deprotonate the surface silanol groups, and thereby to induce additional negative charge on the surface.

Wheat (Triticum aestivum L.) yield is infl uenced by many independent factors including precipita... more Wheat (Triticum aestivum L.) yield is infl uenced by many independent factors including precipitation, fertilization, soil nutrients, and crop variety. Due to high correlations of these factors, it is diffi cult to analyze their relative importance on wheat yield. Th is study quantifi ed the eff ects of independent factors on wheat yield and identifi ed the most important control factors through a long-term experiment on the Loess Plateau, China. Th e experiment consisted of 17 treatments, including fi ve different levels of N and P fertilizer. Partial least squares regression (PLSR) was used to evaluate the factors on wheat yield in four variety groups-Qinmai4 (1985-1986), Changwu131 (1987-1996), Changwu134 (1997-2015), and 31-yr planting across the three varieties (1985-2015). Variable importance in projection (VIP) value revealed that N fertilizer had the greatest eff ect on wheat yield in all four groups (VIP = 1.266-2.313). Th e second most important factors were climate factors for Qinmai4 (VIP = 1.060), precipitation (February, annual, and fallow season) for Changwu131 (W 1 = 0.335-0.351, VIP = 1.381-1.474), and soil nutrients (total nitrogen [TN], soil organic matter [SOM], and available potassium [AK]) for Changwu134 (W 1 =-0.231-0.514, VIP = 1.084-2.317). When tested across varieties, TN and SOM were the second most important factors for 31-yr planting (W 2 = 0.455 and 0.313; VIP = 1.908 and 1.370, respectively). Th ese results indicate that PLSR can reveal the control factors on wheat yield in the study area and provide a reference tool for analyses in other crops or areas.

peutêtre utilisée pour déterminer le taux d'adsorption, et cela est en très bonne adéquation avec... more peutêtre utilisée pour déterminer le taux d'adsorption, et cela est en très bonne adéquation avec les mesures directes. La dépendance du point de charge nulle avec l'adsorption, pour deux masses molaires différentes, s'est montréeégale, ce qui ne souligne aucune influence de la masse molaire du polyélectrolyte sur le comportementélectrostatique de l'interface. xii A.