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1.
Surface modification of silicone with polysaccharides for the development of antimicrobial urethral catheters
Matej Bračič, 2016, doktorska disertacija

Opis: In this work, alternative polysaccharide-based coatings were used to improve the antimicrobial and antifouling properties of silicone surfaces used for urethral catheters. The introduction of a catheter in the urethra is commonly connected with a high risk of microbial infections which often result in long-term health damage. Polysaccharide-based coatings like chitosan, carboxymethyl chitosan, and a synergistic formulation between hyaluronic acid and a natural lysine-based surfactant, were used to treat silicone surfaces to overcome the infection problems as an alternative to conventional approaches, which include the administration of antibiotics or coatings with metal ions. The polysaccharide-based macromolecular solutions and dispersions were firstly characterised by means of pH-titrations, dynamic light scattering and scanning electron microscopy in order to determine the size of particles in dispersions and their pH dependant charging behaviour. The knowledge gained from this was used to thoroughly study the interactions of the polysaccharide-based solutions and dispersions with the model silicone surfaces. The model surfaces were ultra-thin films prepared by dissolution of silicone in toluene and subsequent spin-coating on quartz crystals. The influence of pH, salt concentration, and various surface activation processes on the adsorption behaviour was evaluated by means of a very precise quartz crystal microbalance with dissipation. This knowledge was transferred to the application of the coatings on real systems i.e. casted silicone sheets and silicone tubes. The surface morphology, surface chemistry, as well as the mechanical and chemical stability of the coatings were further characterised on both model and real systems. For this purpose different microscopy and spectroscopy methods, pH-potentiometric titrations and methods for evaluation of mechanical properties were used. Finally the antimicrobial and antifouling properties were evaluated. The antimicrobial properties were tested against gram-positive and gram-negative bacteria as well as fungi, which are commonly found in infected urine, while the antifouling properties were tested by measuring the adhesion of bovine serum albumin, fibrinogen, and lysozyme biomolecules onto functionalised model films using the quartz crystal microbalance. The results showed that homogeneous and stable coatings can be achieved by adsorption from dispersions of the polysaccharide-based nanoparticles of 200-300 nm in size, which are formed by precipitation; i.e. careful pH adjustments of chitosan to pH = 6.5, carboxymethyl chitosan to pH = 7, and by mixing the hyaluronic acid and natural lysine-based surfactant solutions at concentrations of 2.5 x 10-4 mol/L and 1.25 x 10- 3 mol/L for the hyaluronic acid and 5.0 x 10-4 mol/L and 1.2 x 10-3 mol/L for the surfactant, respectively . The mass of the coatings on model silicone films can be increased by a 3-step adsorption, which directly influences the antimicrobial properties of the coatings that are improved with increasing coating mass, reaching values of up to 90 % in reduction of microorganism growth. It was also shown that the hyaluronic acid-natural surfactant formulation is superior to the chitosan coatings. The same conclusions were drawn from the antifouling evaluation where the zwitterionic nature of the formulation between natural based lysine surfactant and HA successfully suppressed the adhesion of biomolecules on silicone surfaces, while the chitosan coatings only moderately prevented the adhesion of proteins. One can conclude that the polysaccharide-based coatings can be successfully introduced to silicone surfaces from dispersion and as such successfully prevent biomolecule adhesion and reduce the growth of pathogen microorganisms which can be found in the urine during urethral infections.
Ključne besede: Urethral catheters, Antimicrobial coatings, Silicone, Polysaccharides, Natural surfactants
Objavljeno: 24.10.2016; Ogledov: 1276; Prenosov: 196
.pdf Celotno besedilo (5,86 MB)

2.
Rheological studies of concentrated guar gum
Marija Oblonšek, Sonja Šostar-Turk, Romano Lapasin, 2003, izvirni znanstveni članek

Opis: Polymers and surfactants are essential ingredients of the printing paste. Polysaccharides are used commercially to thicken, suspend or stabilise aqueoussystems. Also they are used to produce gels and to act as flocculates, binders, lubricants, to serve as modifiers of film properties, and have a function as adjusters of rheological parameters. Surfactants, on the other hand, perform numerous functions acting as dispersants, wetting agents, emulsifiers and antifoaming agents. The rheological properties of polysaccharide thickeners (guar gums with different substitution levels and different producers) at different concentrations and temperatures and, second,the effects produced by the addition of nonionic surfactants (polyoxyethylene stearyl alcohols with different numbers of EO groups) have been studied under linear and nonlinear shear conditions. Experimental data have been correlated with the different modelsČ flow curves with the Cross, Carreau and Meter-Bird model, and mechanical spectra with the generalized Maxwell model and Friedrich-Braun model. The surface tensions of aqueous systems containing polysaccharide andžor surfactants have been determined overextended concentration ranges in order to detect the CMC conditions and toprovide a better understanding about the polysaccharide-surfactant interactions.
Ključne besede: textile printing, printing pastes, polysaccharides, thickeners, rheology, viscoelasticity, surfactants, guar gum
Objavljeno: 01.06.2012; Ogledov: 1666; Prenosov: 69
URL Povezava na celotno besedilo

3.
An effect of sodium dodecylsulfate on the corrosion of copper in sulphuric acid media
Regina Fuchs-Godec, Valter Doleček, 2004, izvirni znanstveni članek

Opis: The effect of sodium dodecylsulfate (SDS) on copper corrosion in a solution of 0.5 M H2SO4 + x M SDS was studied using electrochemical polarisation measurements. The critical micelle concentration (CMC) of SDS in 0.5 M H2SO4 is 8 * 10-4 M, and the experimental concentrations of SDS were in the range below and above the CMC. It was found that SDS is a good anodic inhibitor at lower anodic overpotentials, i.e. very close to the rest potential. Adsorptionof the inhibitor obeys the Langmuir isotherm. Plots of log [▫$theta$▫/(1-▫$theta$▫)] versus log ▫$c_{inh}$▫ yielded straight lines with a slope change at the CMC. Accordingly, the CMC could be determined from these electrochemical measurements. The values of ▫$Delta$▫▫$G_{ads}$▫ calculated from the Langmuir plots are negative, suggesting that the inhibitive action of SDS in 0.5 M H2SO4 results from the electrostatic adsorption of C12H25SO4- ions onto the positively charged copper surface.
Ključne besede: electrochemistry, corrosion inhibitors, surfactants, potentiodynamic polarisation, corrosion kinetic parameters, copper, Langmuir isotherm, critical micelle concentration, sulphuric acid
Objavljeno: 01.06.2012; Ogledov: 1233; Prenosov: 89
URL Povezava na celotno besedilo

4.
Inhibitory effect of non-ionic surfactants of the TRITON-X series on the corrosion of carbon steel in sulphuric acid
Regina Fuchs-Godec, 2007, izvirni znanstveni članek

Opis: The corrosion inhibition characteristics of non-ionic surfactants of the TRITON-X series, known as TRITON-X-100 and TRITON-X-405, on stainless steel (SS) type X4Cr13 in sulphuric acid were investigated by potentiodynamic polarisation measurements. It was found that these surfactants act as good inhibitors of the corrosion of stainless steel in 2 mol L-1 H2SO4 solution, but the inhibition efficiency strongly depends on the electrode potential. Thepolarisation data showed that the non-ionic surfactants used in this study acted as mixed-type inhibitors and adsorb on the stainless steel surface, in agreement with the Flory-Huggins adsorption isotherm. Calculated Gads values are -57.79 kJ mol-1 for TRITON-X-100, and -87.5 kJ mol-1 for TRITON-X-405. From the molecular structure it can be supposed that these surfactants adsorb on the metal surface through two lone pairs of electrons on the oxygen atoms of the hydrophilic head group, suggesting a chemisorption mechanism.
Ključne besede: electrochemistry, corrosion inhibitors, non-ionic surfactants, Flory-Huggins isotherm, critical micelle concentration, sulphuric acid
Objavljeno: 01.06.2012; Ogledov: 1427; Prenosov: 85
URL Povezava na celotno besedilo

5.
Inhibition properties of TRITON-X-100 on ferritic stainless steel in sulphuricacid at increasing temperature
Regina Fuchs-Godec, Gregor Žerjav, 2009, izvirni znanstveni članek

Opis: The inhibiting action of a non-ionic surfactant of the TRITON-X series (TRITON-X-100) on stainless steel type X4Cr13 in 1.0 M H2SO4 solution at five different temperatures was investigated by the potentiodynamic polarisation measurements. The inhibition efficiency has been calculated in the presence and in the absence of the inhibitor. The experimental data suggest that the inhibition efficiency increases with increasing concentration of the TRITON-X-100, and decreases with the increasing temperature. Adsorption of the non-ionic surfactant used here obeys the Flory- Huggins isotherm. The thermodynamic parameters, such as, the heat of adsorption, adsorption entropy, and the adsorption free energy, have been calculated by employing thermodynamic equations. Kinetic parameters, also been evaluated.
Ključne besede: non-ionic surfactants, corrosion inhibitors, sulphuric acid, Flory-Huggins adsorption isotherm
Objavljeno: 31.05.2012; Ogledov: 1408; Prenosov: 64
.pdf Celotno besedilo (332,60 KB)
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6.
The adsorption, CMC determination and corrosion inhibition of some N-alkyl quaternary ammonium salts on carbon steel surface in 2 M H2SO4
Regina Fuchs-Godec, 2006, izvirni znanstveni članek

Opis: Electrochemical measurements were performed to investigate the effectiveness of cationic surfactants of the N-alkyl quaternary ammonium salt type, i.e. myristyltrimethylammonium chloride (MTACl), cetyldimethylbenzylammonium chloride (CDBACl), and trioctylmethylammonium chloride (TOMACl), as corrosion inhibitors for type X4Cr13 ferritic stainless steel in 2 M H2SO4 solution. Potentiodynamic polarization measurements showed that these surfactants hinder both anodic and cathodic processes, i.e. act as mixed-type inhibitors. It was found that the adsorption of the N-alkyl ammonium ion in 2 M H2SO4 solution follows the Langmuir adsorption isotherm. Plots of log ▫$[/theta$▫/(1-▫$/theta$▫)] versus log▫$c_{inh}$▫ yielded straight lines with a slope, which changed drasticallyat the critical micelle concentration (CMC) of the surfactants studied. Accordingly, the CMC could be accurately determined from these measurements. The calculated values of the free energy of adsorption ▫$/Delta$▫▫$G_{ads}$▫ are, in cases when the charge on the metal surface is negative with respect to the PZC, relatively high what is characteristically for the chemisorption. On the other hand, for positive metal surfaces it is assumed that ▫$SO_4^{2-}$▫ anions are adsorbed first, so the cationic species would be limited by the surface concentration of anions. Accordingly ▫$/Delta$▫▫$G_{ads}$▫ values were lower in this case and the adsorption is due to merely electrostatic attraction, which is characteristically of physisorption.
Ključne besede: electrochemistry, corrosion inhibitors, cationic surfactants, Langmuir isotherm, corrosion kinetic parameters, critical micelle concentration, sulphuric acid
Objavljeno: 30.05.2012; Ogledov: 2039; Prenosov: 88
URL Povezava na celotno besedilo

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