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ABSTRACT: Chitosan has more and more been suggested as a material for use as adsorbent in the treatment of effluents as well as in the synthesis of drug-loaded nanoparticles for controlled release. In both cases, a good understanding of the process of adsorption, both kinetically and in terms of equilibrium, has an importance of its own. In this manuscript we study the interaction between sodium cromoglycate, a drug used in asthma treatment, and chitosan. Equilibrium experiments showed that Sips (or Freundlich-Langmuir) isotherm described well the resultant data and adsorption possibly occurred as in multilayers. A model based on ordinary reaction-rate theory, compounded of two processes, each one with a correlated velocity constant, described the kinetics of sorption. Kinetic and equilibrium data suggested the possibility of surface rearrangement, favored by the increase of temperature.
Colloids and surfaces. B, Biointerfaces 03/2013; 109C:52-58. · 2.60 Impact Factor
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ABSTRACT: Adsorption phenomena occurring at the solid/liquid interface of chitosan particles are of extreme importance in the kinetics of drug release/upload as well as in effluent treatment by adsorption. In this work, equilibrium and kinetic aspects of protonated tetracycline adsorption on chitosan are explored using classic solution depletion method and zeta potential measurements. Equilibrium experiments showed that for solutions with tetracycline initial concentration of ca. 1.2 g L(-1), corresponding to a pH around 3, chitosan structure disrupted, as indicated by an increase in magnitude of tetracycline sorption. Adsorption and zeta potential isotherms before disruption suggested that the process of adsorption had a Langmuir character up to a point at which subsurface was exposed to adsorption; at this point, a second mode of sorption began: zeta potential tended to an equilibrium value, following Sips isotherm and tetracycline sorption had a linear dependence on its continuous phase concentration. The kinetics of tetracycline sorption suggested that sorption of tetracycline was divided between the sorption of protonated and non-protonated tetracycline; tetracycline in its non-protonated form seemed to rule the sorption of tetracycline.
Colloids and surfaces. B, Biointerfaces 05/2012; 100:222-8. · 2.60 Impact Factor
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ABSTRACT: Chitosan nanoparticles have been used in several systems destined to controlled release of active agents. In this manuscript the process of formation of chitosan nanoparticles, obtained employing the coacervation method with sodium sulfate is analyzed using zeta potential and small angle X-ray scattering (SAXS) measurements. Dispersions were obtained at pH=1 and pH=3 and presented a behavior, in terms of surface charging, that was independent of pH. However, SAXS results indicated a dependence of size-related behavior on pH. The difference in terms of behavior was explained through the influence of enthalpic and entropically driven components.
Colloids and surfaces. B, Biointerfaces 10/2011; 90:254-8. · 2.60 Impact Factor
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ABSTRACT: Solutions of chitin in Li(+)/N,N-dimethylacetamide systems were studied via viscometry, using LiCl concentrations of 3% and 5% (m/v) and chitin concentrations ranging from 0.075 to 0.375 gL(-1). The reduced viscosity number versus concentration plot showed a minimum that was related to the formation of Li(+)-OC complex moieties along chitin macromolecular chains. Viscosity behavior was affected by temperature according to the Eyring model: concentration dependence of flow enthalpy of activation was correlated to polymer-polymer interactions and flow entropy of activation to the stiffness of the complexed chitosan macromolecular chain.
Carbohydrate research 01/2011; 346(5):614-8. · 2.03 Impact Factor
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ABSTRACT: An anionic surfactant, synthesized with ricinoleic acid from castor oil, was obtained and its behavior in terms of microemulsion formation (via pseudo-ternary diagram analysis) and liquid-gas surface tension (both for microemulsions and pure surfactant-water systems) was determined as a function of temperature and NaCl concentration in the aqueous phase. Microemulsions were formed by using butanol as co-surfactant and kerosene as the oil phase. Concerning the pseudoternary diagrams, the increase in NaCl concentration resulted in a decrease in the Winsor IV region, which was correlated to a possible occurrence of nonmicellar aggregates, induced by the high concentration of NaCl in the aqueous phase. Surface tension measurements also indicated that at the very high NaCl concentrations used there could be the formation of surfactant aggregates. The oil phase in microemulsionated systems decreased surface tension (but increased CMC): Possible interactions between isolated surfactant molecules and molecules from the oil phase were used to explain these results.
Journal of Dispersion Science and Technology 07/2010; 31(7):980-985. · 0.56 Impact Factor
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ABSTRACT: Experiments to monitor and characterize the kinetics of adsorption of tetracycline on chitosan particles are reported in this work. The same pseudo-order kinetics that has been widely used for describing the adsorption in systems related to wastewater purification and drug loading was used to treat the present data. As some unexpected results came out from the experiments, it was necessary a detailed deduction for this sort of kinetics to be carried out, so that approximations related to short and long times were obtained. Firstly it was shown that an apparently linear t/q(t) versus t relationship did not imply a pseudo-second-order sorption kinetics, differently of what has been repeatedly reported in the literature. It was found that this misinterpretation could be avoided by using non-linear regression. Finally, the adsorption of tetracycline on chitosan particles was analyzed, using the insights obtained from theoretical analysis, and the parameters generated were used to analyze to adsorption kinetics and to propose an adsorption mechanism.
Journal of Colloid and Interface Science 08/2009; 340(2):182-91. · 3.07 Impact Factor
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ABSTRACT: Two surfactants were synthesized by reacting hydrogen halides (hydrogen chloride and hydrogen bromide) with 1-dodecylamine. The resultant cationic surfactants, 1-dodecylammonium chloride (DDAC) and 1-dodecylammonium bromide (DDAB), were characterized by NMR spectrometry and FTIR spectroscopy and data related to their adsorption at the fluid liquid/gas interface were obtained employing bubble surface tensiometry, in pure water and in HCl 0.1 M. Data did not fit well to Langmuir isotherm but Frumkin isotherm did adequately describe to process of adsorption. Adsorption isotherms, as well as data related to critical micelle concentration, CMC, indicated that in HCl 0.1 M, the presence of electrolytes and a common ion to DDAC decreased chloride solvation, changing surface packing and adsorption profile for this surfactant.
Journal of Dispersion Science and Technology 08/2009; 30(7):1046-1049. · 0.56 Impact Factor
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ABSTRACT: Chitosan is a polysaccharide used in a broad range of applications. Many of its unique properties come from the presence of amino groups in its structure. A proper quantification of these amino groups is very important, in order to specify if a given chitosan sample can be used in a particular application. In this work, a comparison between the determination of chitosan degree of deacetylation by conductometry and CHN elemental analysis was carried out, using a rigorous error analysis. Accurate expressions relating CHN composition, conductometric titration, and degree of deacetylation, in conjunction with their associated errors, were developed and reported in this note. Error analysis showed conductometric analysis as an inexpensive and secure method for the determination of the degree of deacetylation of chitosan.
Carbohydrate research 08/2009; 344(18):2591-5. · 2.03 Impact Factor
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ABSTRACT: Inverse emulsions consisting of chitosan solution as the dispersed phase and cyclohexane as the continuous phase were obtained, using cetyl trimethylammonium bromide (CTAB) as surfactant. The obtained dispersions clearly presented pseudoplastic character, which was evidenced by an intense drop in apparent viscosity as shear rate was increased. This pseudoplastic behavior was related to the formation of chitosan loops from the micelles to the continuous phase, promoting intermicellar interactions. Apparent shear modulus determination supported the presence of temporary cross‐linking and results from creep experiments were analyzed using Burger's model, in order to separate viscous and elastic intermicellar interactions.
Soft Materials 07/2009; 7(3):185-197. · 1.15 Impact Factor
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ABSTRACT: In this work chitosan membranes modified by contact with poly(acrylic acid) (PAA) aqueous solution at two different temperatures (25 degrees C and 60 degrees C) were obtained. The pure chitosan (CS) membranes, as well as those treated with PAA (CSPAA_25 and CSPAA_60) were characterized by FTIR-ATR, water sorption capacity, thermal analysis (TG/DTG), and scanning electron microscopy (SEM). In addition, in vitro permeation experiments were carried out using metronidazol and sodium sulfamerazine aqueous solutions at 0.1% and 0.2% as model drugs. FTIR-ATR results showed the presence of absorption bands of NH3+ and COO(-) indicating the formation of a polyelectrolyte complex between chitosan and poly(acrylic acid). The results also indicated that PAA penetrates deeper into the membrane at higher temperature (60 degrees C), forming a thicker complex layer. Polyelectrolyte complex formation as well as the influence of treatment temperature was confirmed by lower hydrophilicity, higher thermal stability, and lower permeability of the treated membranes. The results show that the methodology used is a simple and very efficient way to drastically change some membrane properties, especially their permeability.
Carbohydrate research 07/2009; 344(13):1709-15. · 2.03 Impact Factor
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ABSTRACT: Chitosan can be used as adsorbent in the treatment of effluents from the textile industry, especially for negatively charged dyes, due to its cationic polyelectrolyte nature. In this work, the sorption of a model dye, methyl orange, on chitosan hydrobeads is analyzed in terms of equilibrium and kinetic approaches. Equilibrium studies showed that dye adsorption had a mixed Freundlich-Langmuir behavior that had its Langmuir character increased as the pH was increased. In terms of adsorption kinetics, it was found to be of nth-pseudo-order, with fractional n increasing from approximately 2 to approximately 2.5 as pH and initial dye concentration in the continuous phase were increased. The increase in the apparent pseudo-order was related to changes in mathematical approximation for the solution of the sorption rate equation, which were the result of the decrease in the ratio (number of active sites for adsorption)/(number of adsorbate molecules).
Carbohydrate Research 10/2008; 343(14):2489-93. · 2.33 Impact Factor
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ABSTRACT: Polyelectrolyte complex (PEC) membranes were obtained by mixing solutions of two polymers of opposite charges, chitosan (Chi) and poly(acrylic acid) PAA. Three membranes were obtained: one made of pure chitosan and two membranes with chitosan mixed with PAA at a ratio of 95:5 (one prepared using PAA solution in 3.5% formic acid, named ChiPAA3.5, and another one using a PAA solution in 10% formic acid, named ChiPAA10). The membranes were characterized by swelling experiments, FT-IR spectroscopy, scanning electron microscopy (SEM), atomic force microscopy (AFM), mechanical properties and permeability studies in relation to a drug model (sodium sulphamerazine). The calculation of degree of ionization showed that the lower the formic acid concentration was, the higher the PAA dissociation degree. Polyelectrolyte complex formation was characterized by FT-IR. Water uptake results showed that PEC membranes were more hydrophilic than pure chitosan, ChiPAA3.5 being the most. Morphological analysis by SEM and AFM showed that PAA addition changed the membranes morphology, especially for ChiPAA3.5. Mechanical properties indicated that PEC membranes were more rigid than pure chitosan membranes and that the morphology has an influence on tensile strength values. Permeability values decreased with complex formation and were lower for ChiPAA10 than ChiPAA3.5. However, as drug concentration was increased, the difference between the two complex membranes disappeared. The results were discussed considering the drug-membrane interactions. Diffusion coefficient values indicated that ChiPAA3.5 had a higher drug retention capacity than ChiPAA10.
Journal of Biomaterials Science Polymer Edition 02/2008; 19(2):143-60. · 1.69 Impact Factor
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ABSTRACT: Particulate systems composed of polyelectrolyte complexes (PEC) based on chitosan and poly(methacrylic acid) were obtained via template polymerization. The resultant particles were characterized as having regions with different charge densities: chitosan predominating in the core and poly(methacrylic acid) at the surface, the particles being negatively charged, as a consequence. Albumin was adsorbed on these particles (after cross-linking with glutardialdehyde), and pH was controlled to obtain two conditions: (i) adsorption of positively charged albumin and (ii) adsorption of albumin at its isoelectric point. Adsorption isotherms and zeta-potential measurements showed that albumin adsorption was controlled by hydrogen bonding/van der Waals interactions and that brush-like structures may enhance the adsorption of albumin on these particles. It was also found that shearing can induce desorption of albumin from the PEC surface, depending on the continuous phase albumin concentration.
Langmuir 08/2007; 23(14):7687-94. · 4.19 Impact Factor
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ABSTRACT: Layer-by-layer (LbL) films have been produced with poly(o-ethoxyaniline) (POEA), chitosan and chitosan-poly(methacrylic acid) (CS-PMAA) nanoparticles. Because the adsorption of LbL films depends on ionic interactions and H-bonding, optimized conditions had to be established for the growth of multilayer films. Unusually thick films were obtained for POEA and CS-PMAA, thus demonstrating the importance of using chitosan in the form of nanoparticles. These nanostructured films were deposited on chromium electrodes to form a sensor array (electronic tongue) based on impedance spectroscopy. This system was used to detect copper ions in aqueous solutions
IEEE Transactions on Dielectrics and Electrical Insulation 11/2006; · 1.09 Impact Factor
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ABSTRACT: Chitosan/poly(methacrylic acid) complexes, CS/PMAA, were prepared via dropwise addition of a solution of PMAA to a solution of chitosan in acetic acid 2 wt %. The increase in molecular weight of PMAA inhibited the formation of insoluble complexes, while the increase in ionic strength first favored the formation of the complex followed by inhibiting it at higher concentrations. These observations were related to a description of polyelectrolyte complexation that was strongly dependent on macromolecular dimensions, both in terms of molecular weight and of coil expansion/contraction driven by polyelectrolyte effect.
Biomacromolecules 05/2006; 7(4):1245-52. · 5.48 Impact Factor
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ABSTRACT: Pure chitosan, glutaraldehyde crosslinked chitosan, and a blend of chitosan with poly(ethylene oxide) (PEO) membranes were prepared. The three membranes were characterized in terms of their swelling capacities as well as their permeabilities to a drug model (sulfamerazine sodium salt). For the permeation experiments, the variables analyzed were the type of membrane and the initial drug concentration in the liquid phase (from 0.1% to 1.5%). Permeability coefficients were calculated using UV spectroscopy. The results showed that for the three analyzed membranes, the permeability did not change with time (over the studied time interval). An increase in the permeability for CHI/PEO membranes compared to those made of pure chitosan was also observed, possibly due to microporous region formation and/or crystallinity reduction. For the crosslinked membrane, an even higher increase in the permeability coefficient was observed. In this case, the increase was attributed to free volume variation.
Carbohydrate Research 01/2006; 340(17):2630-6. · 2.33 Impact Factor
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ABSTRACT: Layer-by-layer (LbL) films have been produced with poly(o-ethoxyaniline) (POEA), chitosan and chitosan-poly(methacrylic acid) (CS-PMAA) nanoparticles. Because the adsorption of LbL films depends on ionic interactions and H-bonding, optimized conditions had to be established for the growth of multilayer films. Unusually thick films were obtained for POEA and CS-PMAA, thus demonstrating the importance of using chitosan in the form of nanoparticles
Electrets, 2005. ISE-12. 2005 12th International Symposium on; 10/2005
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A. L. P. Fernandes,
W. A. Morais,
A. I. B. Santos,
A. M. L. de Araújo,
D. E. S. dos Santos,
D. S. dos Santos,
F. J. Pavinatto,
O. N. Oliveira,
T. N. C. Dantas,
M. R. Pereira, J. L. C. Fonseca
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ABSTRACT: Chitosan nanoparticles were obtained via ionic crosslinking by using the sulfate ion. Chitosan molecular weight was varied by oxidative degradation of the chitosan β-glycoside bond, the molecular weight being indirectly monitored as the chitosan solution reduced viscosity at a fixed polymer concentration. The dependence between some physical properties of the resultant dispersions (turbidity, viscosity, zeta potential, and sedimentation column profile) and reduced viscosity was established. Atomic force microscopy images have shown the resultant particles formed to be clusters of chitosan nanoparticles with a diameter of ca. 70nm, the interaction between these particles being characterized by FTIR spectroscopy as the result of sulfate bridging. At the end of the paper, the potential of these dispersions for the incorporation of anionic drugs via adsorption was evaluated using a model compound. The resultant dispersions were capable of adsorbing more than 25% of mass of chitosan, being the partition coefficient higher than 3,500.
Colloid and Polymer Science 01/2005; 284(1):1-9. · 2.33 Impact Factor
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ABSTRACT: The stabilities of alumina dispersions were studied as a function of poly- and low molecular weight electrolyte concentration, using viscometry of the dispersing phase, and zeta potential measurements. The relation of polyelectrolyte adsorption to polymer concentration (at different low molecular weight electrolyte concentrations) was found to depend upon the dimensions of the polymer (which were a priori known to decrease with increasing poly- and low molecular weight electrolyte concentration). The occurrence of flocculation and bridging in the destabilization mechanism of the alumina dispersions was also characterized.
Colloid and Polymer Science 12/2004; 283(4):413-420. · 2.33 Impact Factor
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ABSTRACT: Rheological properties of concentrated alumina suspensions using a charged copolymer as the dispersant have been studied. The non-Newtonian behavior of these fluids was characterized and correlated to potential measurements and sedimentation column data, obtained with these dispersions. As a result, a clear relationship between dispersion stability and pseudoplastic/dilatant rheological behavior was established.
Colloid and Polymer Science 03/2004; 282(6):596-601. · 2.33 Impact Factor
