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Polyelectrolyte multilayers are nanofilms with vast applications in numerous areas such as medicine and food industry. Recently, they have been getting a lot of attention as potential food coatings for the prevention of fruit decay during transportation and storage, and therefore the coatings need to be biocompatible. In this study, we fabricated thin films made of biocompatible polyelectrolytes, positively charged polysaccharide chitosan, and negatively charged carboxymethyl cellulose on a model silica surface. Typically, to enhance the properties of the prepared nanofilms, the first layer (precursor layer) of poly(ethyleneimine) is used. However, for the construction of completely biocompatible coatings, this could be problematic due to potential toxicity. This study offers an option for a viable candidate as a replacement precursor layer: chitosan itself was adsorbed from a more concentrated solution. In the case of chitosan/carboxymethyl cellulose films, using chitosan over poly(ethyleneimine) as a precursor layer has shown a twofold increase in film thickness, as well as an increase in film roughness. In addition, these properties can be tuned by the presence of a biocompatible background salt (e.g., sodium chloride) in the deposition solution that has proven to change the film thickness and surface roughness depending on the salt concentration. Such a straightforward way of tuning the properties of these films combined with their biocompatibility makes this precursor material a prime candidate for use as a potential food coating.

The study is carried out with the aim of establishing in which measure the outcomes of polyelectrolyte multilayer formation can be predicted on the basis of the results of complexation studies in solution and vice versa. For this purpose, the correlation between the process of complex and multilayer formation involving three pairs of vinylic polyions in solutions of binary 1:1 sodium salts (NaX ; X = F, Cl, Br, I, NO3, ClO4) was explored by means of dynamic and electrophoretic light scattering, potentiometry, microcalorimetry, spectrophotometry and quartz crystal microbalance. The gradual reactant mixing in solution at lower salt concentrations resulted in Fuoss-Sadek sequence of events (primary complexes → secondary complexes→1:1 flocculate)., whereby the obtained nano-complexes could be overcharged. At high salt concentration and excess polycation present, metastable nano-complexes and precipitates containing surplus of positively charged monomers were formed. The amount of extrinsically compensated charge was in accord with the polycation affinities toward counteranions, established by monitoring the electrolyte-induced aggregation of positively charged nano-complexes. Perfect analogy with respect to counteranion influence on the amount of adsorbed polycation was noticed for corresponding multilayers. Aside from providing the deeper understanding of interpolyelectrolyte neutralization, the gained insights can also be used to steer the polyelectrolyte multilayer composition and properties.

In this study, the high-resolution ultrasonic spectroscopy (HR-US) technique was applied to examine interpolyelectrolyte neutralization. The mentioned method was tested on the example of complexation between poly(allylammonium) cations and poly(acrylate) anions in aqueous solutions at pH = 7. It was confirmed by HR-US that the type of titration (stepwise or abrupt), the direction of titration, and the type of background salt affect the outcome of interpolyelectrolyte neutralization. The obtained results were explained on the basis of ultrasonic velocity and attenuation changes in the context of suspension compressibility, a parameter that is extremely sensitive to molecular organization and intermolecular interactions. Moreover, the results of HR-US measurements proved to be consistent with previous results obtained by more traditional methods such as dynamic light scattering, microcalorimetry, and electrokinetics. This research demonstrates that HR-US is a convenient and reliable method that can be employed for the investigation of interpolyelectrolyte neutralization and polyelectrolyte-related processes.

Thin films made of weak polyelectrolytes poly(allylamine hydrochloride) (PAH) and poly(acrylic acid) (PAA) have been fabricated on silicon wafers using the layer-by-layer (LbL) method. To study the influence of counteranion type on the growth and properties of PAH/PAA multilayers, the nature of the supporting sodium salt was varied from cosmotropic to chaotropic anions (F$^–$, Cl$^–$, and ClO$_4$$^–$). Results of ellipsometry and AFM measurements indicate that the film thickness and surface roughness systematically increase on the order F$^–$ < Cl$^–$ < ClO$_4$$^–$. Furthermore, we found that the hydrophobicity of the PAH/PAA multilayer also follows the described trend when a polycation is the terminating layer. However, the heating of PAH/PAA multilayers to 60 °C during the LbL assembly suppressed the influence of background anions on the multilayer formation and properties. On the basis of the obtained results, it could be concluded that thermal annealing induces changes at the polymer–air interface in the sense of reorientation and migration of polymer chains.

Polyelectrolyte multilayers are coatings formed by the alternate deposition of polycations and polyanions on a charged surface. In this study we examined how the type of substrate affects a multilayer prepared from poly(allylamine hydrochloride) and poly(acrylic acid). Silicon and titanium wafers were used as substrates. Their properties were systematically studied using ellipsometry, tensiometry, atomic force microscopy and streaming potential measurements. Multilayers were built up at pH = 7 with tetramethylammonium chloride as the background salt. The growth of films was monitored by ellipsometry, while the morphology and surface roughness were determined by atomic force microscopy. It was found that the thickness of multilayers containing 10 layers on silicon is 10 nm, whereas the thickness of the same film on titanium is three times higher. It was shown that multilayers formed on silicon display a grain-like structure, which was not the case for a film formed on titanium. Such morphological properties are also reflected in the surface roughness. Finally, it was shown that, in addition to the electrostatic interactions, the hydrophobicity of the substrate also plays an important role in the polyelectrolyte multilayer formation process and influences its thickness and properties.

Bacterial adhesion can be controlled by different material surface properties, such as surface charge, on which we concentrate in our study. We use a silica surface on which poly(allylamine hydrochloride)/sodium poly(4-styrenesulfonate) (PAH/PSS) polyelectrolyte multilayers were formed. The corresponding surface roughness and hydrophobicity were determined by atomic force microscopy and tensiometry. The surface charge was examined by the zeta potential measurements of silica particles covered with polyelectrolyte multilayers, whereby ionic strength and polyelectrolyte concentrations significantly influenced the build-up process. For adhesion experiments, we used the bacterium Pseudomonas aeruginosa. The extent of adhered bacteria on the surface was determined by scanning electron microscopy. The results showed that the extent of adhered bacteria mostly depends on the type of terminating polyelectrolyte layer, since relatively low differences in surface roughness and hydrophobicity were obtained. In the case of polyelectrolyte multilayers terminating with a positively charged layer, bacterial adhesion was more pronounced than in the case when the polyelectrolyte layer was negatively charged.

We have shown that asphaltene self-association induces temperature gradients and convection currents and it is necessary to suppress these effects to obtain accurate data by DOSY NMR techniques. An interesting finding of this investigation is that aggregation process has been found to be affected by the magnetic field. The obtained results have shown for the first time a significant increase in diffusion coefficients of aggregates upon the increase in the magnetic field strength indicating higher molecular mobility of the present species and possible degradation of aggregates. We have shown that changes in diffusion coefficients are not a consequence of relaxation or viscosity effects. It is not yet clear what the reason for such behavior is and whether this effect is intrinsic. Traces of paramagnetic metals present in asphaltene samples may play a role in this process but this hypothesis is yet to be explored. Furthermore, this study has revealed a similar concentration range in which the Middle East crude oil asphaltenes aggregate being in agreement with previous results. Aggregates form different molecular weight species with different composition and number of monomer units. Ongoing experiments will throw more light on the magnetic field dependent asphaltene aggregation. This may have an impact on developing strategies for resolving asphaltene precipitation issues.

Dental restorations need to reproduce the aspect of the natural teeth of the patient, and must be non-toxic, biocompatible, and have good mechanical properties so that they can last for longer. The aim of this study was to determine the extent of bacterial adhesion of Streptococcus mutans on four different dental material surfaces, i.e., two glass–ionomer cements (Fuji conventional and Fuji hybrid) and two ceramic composites (Micro hybrid composite and Nano hybrid composite). To understand the bacterial adhesion on these four different dental materials, various surface properties were measured: roughness, contact angle, CIE color parameters and zeta potential. We found that the greatest adhesion extent was obtained for the Nano hybrid composite surface. The pronounced adhesion is the interplay between the relatively high roughness and hydrophilicity of the Nano hybrid composite surface. Color changes upon immersing ceramic composites in red wine and black tea proved that both beverages adhered to them. Black tea adhered more intensively than wine, and showed a higher inhibitory effect on the growth of Streptococcus mutans and Staphylococcus aureus.

In modern-day research, nanoparticles (size < 100 nm) are an indispensable tool for various applications, especially in the field of biomedicine. Although enormous efforts have been made to understand the properties and specificities of nanoparticles, many questions are still not answered and the new ones arise. In this review we summarize current trends in the nanoparticle’s synthesis and characterization and interpret the stability of nanoparticles in various media from aqueous solutions to biological milieu important for the in vitro and in vivo studies. To get more detailed insight into nanoparticle’s charging properties and interactions of nanoparticles with interfaces the theoretical models are presented. Finally, the overview of nanoparticle’s applications is given and the future prospects are discussed.

In this study, the surface properties of Ti/TiO2 substrate before and after the adsorption of polyelectrolytes were investigated. As model polyelectrolytes, strongly charged polycation poly(diallyldimethylammonium) (PDADMA) and strongly charged polyanion poly(4-styrenesulfonate) (PSS) were used. Initially, the bare titanium substrate was characterized by means of ellipsometry, atomic force microscopy (AFM), cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and measurements of inner surface potential using crystal electrode (CrE). It was shown that the substrate surface is very smooth with the roughness of 3.5 nm and oxide layer thickness of 3.8 nm. After the adsorption of PDADMA and PSS, polyelectrolyte-coated titanium surface was examined using the above-mentioned methods under the same conditions. It was found that both PDADMA cations and PSS anions form a stable polymeric nanofilm on Ti/TiO2 surface that partially covers the surface, without significant impact on the surface roughness. The corrosion protection effectiveness values indicate that the corrosion properties were greatly enhanced upon polyion adsorption and polyelectrolyte coating formation on the flat TiO2 surface. The obtained results were additionally confirmed by inner surface potential measurements. According to the methods employed, PDADMA nanofilm modification offers enhanced corrosion protection to the underlying titanium material in sodium chloride electrolyte solution.

International audience; Ceria (CeO$_2$) nanoparticles are known to be very often used in various applications from biomedicine to fuel cells. To optimize the applications, detailed information about the physicochemical properties such as size, shape, and charge of nanoparticles should be available. Therefore, in our study we performed a systematic study of ceria nanoparticles ranging from synthesis to comprehensive experimental and theoretical characterization. We synthesized ceria nanoparticles using two synthesis paths which led to the formation of two types of ceria nanoparticles. The structure and charging properties of both types of ceria nanoparticles were studied by using X-ray powder diffraction (XRD), high-resolution transmission electron microscopy (HR-TEM), particle charge detector (PCD) for surface charge density, and a ZetaPlus instrument for electrophoretic mobility measurements. The results suggested that in the case where hydrolysis of Ce(NO$_3$)$_3$ at room temperature was applied nanoparticles with morphology close to a spherical, more exactly truncated octahedron were synthesized. On the other hand, nanoparticles obtained by hydrothermal synthesis had characteristic cube-like morphology. Finally, for more complete understanding and interpretation of the studied system, we prepared a theoretical model based on the classical density functional theory for electrolyte solutions coupled with the surface charge regulation via the law of mass action. Even without using fitting parameters, the theory adequately describes the experimental data. All the results obtained in our study could serve as a basis for obtaining tuned and engineered ceria nanoparticles with optimized physicochemical properties which could lead to the improved applications of the nanotechnology in the biomedical research.

The objective of this study was to investigate interactions of zein (Z) and zein/rosin (Z/R) nanoparticles with gum arabic (GA), at different pH. Nanoparticles were firstly prepared by antisolvent precipitation of biopolymers from aqueous ethanol solutions. Nanoparticles suspensions were then dialyzed against water in order to remove ethanol and other impurities, and water suspensions of zein and zein/rosin nanoparticles were obtained. It was shown that composition of nanoparticles affects their surface charge density. Zeta potential of nanoparticles was positive without GA and changed to negative after addition of GA, at all pH tested. SEM analysis proved both Z and Z/R nanoparticles to be spherical and in size around 200 nm. The effect of addition of GA on particle size was determined using dynamic light scattering method. It was found that addition of GA increases size of nanoparticles at pH = 4 and pH = 5.5, from 150 – 220 nm to 250 – 320 nm. However, at pH = 3 it causes aggregation process, and diameter of particles increases up to few micrometres. Isothermal titration calorimetry was used to measure enthalpy changes in reaction between Z or Z/R nanoparticles and GA. Results showed that reaction between GA and Z or Z/R NPs is exothermic at each pH tested, except for Z NPs at pH = 3, where it was endothermic. At presented pHs, Z/R NPs were less charged compared to Z NPs, and their surface get saturated with GA molecules more rapidly. Z NPs showed greater enthalpy change in reaction with GA, compared to Z/R NPs.

We investigated ceria nanoparticle/strongly charged polyelectrolyte solution interface on the example of adsorption of a strong polyelectrolyte poly(sodium 4- styrenesulfonate), PSS, on cerium oxide nanoparticles in order to quantitatively characterize the above-mentioned interface. The obtained results could enable a better prediction of nanoparticles behavior in polyelectrolyte solution which could lead to improved applications of ceria nanoparticles. We initially both synthetized and characterized ceria nanoparticles. For the characterization X-ray powder diffraction (XRD), bright-field scanning transmission electron microscopy (BF- STEM), dynamic light scattering (DLS) and electrophoretic mobility measurements were used. Results revealed that nanoparticles are spherical with primary ceria nanoparticles diameter (nanocrystallite size) of approximately 3.5 nm. Results of high- resolution transmission electron microscopy (HRTEM), DLS and electrophoretic mobility measurements after adsorption of PSS showed that polyelectrolyte-coated nanoparticles were obtained. The comparison of average hydrodynamic diameters of uncoated and PSS- coated ceria nanoparticles leads to the assumed thickness of the polyelectrolyte layer of δ ≈ 9 nm. Finally, for the quantitative interpretation of polyelectrolyte adsorption on ceria nanoparticles the application of the modified Ohshima model was examined. In that respect, the adsorption parameters such as charge density of the polyelectrolyte layer electrophoretic softness and adsorption density were determined. It was thus shown that Ohshima model could be applied for studying ceria nanoparticle/strongly charged polyelectrolyte solution interface and that the obtained results could serve as a basis for further tailored applications of polyelectrolytes as stabilizing agents for nanoparticles.

This work is focused on a practical procedure by which pure and well-formed COD crystals were obtained. The effect of different type of stirring on the precipitation process and properties of COD crystals is studied. Mechanical and magnetic stirring are two common stirring types for precipitation of calcium oxalate and method using ultrasonic irradiation is newly described. The precipitation processes are systematically investigated varying solution stoichiometry (defined as a ratio of concentrations of the constituent ions in solution, (Ca+/(C2O42−) and concentration of additive (citrate). The differences of the structure, morphology and crystals properties between precipitates were investigated by SEM, FT-IR, TG and PXRD. In the ultrasonically stirred systems, COD was the only precipitated phase regardless of solution stoichiometry. Pure and well formed COD crystals with well-formed planes were obtained in the system with c(Ca2+)/c(C2O42−) = 3.86 and c(citrate) = 0.009 mol dm−3. The results demonstrate that ultrasonically assisted precipitation could be a new way in synthesis of COD crystals having different potential applications (in the fields of medicine and biotechnology).

Bacterial adhesion on material surfaces can be reduced by different type of coatings. In our study a silica surface on which polyelectrolyte multilayers were formed, with various proteins being the terminating layer, was used as a material surface. We examined three different types of proteins: bovine serum albumin (BSA), lysozyme and glucanase. Adhesion experiments were performed with two bacterial strains: Escherichia coli and Pseudomonas aeruginosa. In order to characterize the surface prior to bacterial adhesion, surface roughness and hydrophobicity were determined by profilometry, atomic force microscopy (AFM) and tensiometry, whereas the surface charge was estimated by zeta potential measurements of silica particles covered with polyelectrolyte multilayers and proteins. The extent of adhered bacteria was examined using scanning electron microscopy (SEM). It was confirmed that in the case where lysozyme was the outermost layer the lysis takes place, whereas in the case of BSA and glucanase specific protein-bacteria interactions are dominant. We showed that the adhesion strongly depends on the protein specificity and the surface physical properties do not play the key role in the adhesion process.

The application of catheters to the urinary tract is associated with nosocomial infections. Such infections are one of the most common types of infections in hospitals and health care facilities and can lead to numerous medical complications. Therefore, the understanding of the properties of urinary catheter surfaces and their potential modifications are crucial in order to reduce bacterial adhesion and subsequent biofilm formation. In our study, we consider standard polyvinyl chloride (PVC) catheter surfaces and compare their properties with the properties of the same surfaces coated with poly(diallyldimethylammonium chloride)/poly(sodium 4-styrenesulfonate) (PDADMA/PSS) polyelectrolyte multilayers. Uncoated and coated surfaces were characterized by means of roughness, hydrophobicity, and zeta potential measurements. Finally, bacterial adhesion extent of uropathogenic Escherichia coli on bare and polyelectrolyte multilayer coated surfaces was measured. The obtained results show that on non-treated surfaces, biofilm is formed which was not the case for multilayer coated surfaces. The PSS-terminated multilayer shows the lowest bacterial adhesion and could be helpful in prevention of biofilm formation. The analysis of the properties of the uncoated and coated surfaces reveals that the most significant difference is related to the charge (i.e., zeta potential) of the examined surfaces, while roughness and hydrophobicity of the examined surfaces are similar. Therefore, it could be concluded that the surface charge plays the crucial role in the bacterial adhesion on uncoated and coated PVC catheter surfaces.

Industrija proizvodnje videoigara postala je iznimno važna i jaka industrija na globalnoj razini. Međutim, iako su mnogi svjesni ove činjenice, manje je onih koji znaju da i industrija proizvodnje videoigara u Hrvatskoj raste i ostvaruje značajne uspjehe na svjetskoj razini. U ovom radu bit će dan osvrt na stanje industrije proizvodnje videoigara u Hrvatskoj i svijetu, kao i osvrt na obrazovnu podršku ovoj industriji u kojoj se svake godine traže novi zaposlenici koji će omogućiti nastavak sve brže ekspanzije niza hrvatskih pouzeća koja se bave razvojem videoigara.

The interfacial properties of the system cerium(IV) oxide/poly(sodium 4-styrenesulfonate) (NaPSS) aqueous solution were studied in a broad pH region by means of inner surface potential, zeta potential and adsorption measurements. Surface potential data were obtained using a single crystal electrode, while zeta potential and adsorption data were obtained using synthetized CeO2 nanoparticles. In order to examine the adsorption of NaPSS on cerium(IV) oxide in detail, surface and electrokinetic potentials of ceria particles were measured in the absence and in the presence of NaPSS. The results of surface potential measurements showed that negatively charged NaPSS molecules exhibit high adsorption affinity towards the CeO2 surface. Titration with NaPSS in the acidic region, where the ceria surface is originally positively charged, suggested that adsorption of negatively charged NaPSS molecules compensates positive charge at the surface and adsorption proceeds until the reversal of surface charge produces a critical value of the potential affecting the state of adsorbed NaPSS molecules. Adsorption of NaPSS on cerium(IV) oxide in the examined pH range was additionally confirmed by zeta potential and adsorption measurements in sodium chloride aqueous solution. From the measured pH dependence of the electrokinetic potential of CeO2 nanoparticles, isoelectric point was determined to be pHiep ≈ 5.4, while the electrokinetic potential in the presence of NaPSS was found to be negative in the whole investigated pH region. Finally, adsorption measurements were carried out which enabled the determination of the maximum surface concentration of the adsorbed polyelectrolyte as Γmax ≈ 1 μmol m−2.

The 25th Croatian Meeting of Chemists and Chemical Engineers with international participation (25HSKIKI), organized jointly by the Croatian Chemical Society and Croatian Society of Chemical Engineers, was held from 19-22 April 2017 in Valamar Diamant Hotel in Poreč, Croatia. The Meeting was organized under the auspices of Ministry of Science and Education and Ministry of Environment and Energy of the Republic of Croatia, University of Zagreb, Croatian Engineering Association, and Croatian Chamber of Economy. For the first time, the Meeting was endorsed by IUPAC and supported by more than 20 chemical and pharmaceutical companies.

Brewers’ spent grain (BSG), a lignocellulosic waste material, was evaluated as a low-cost adsorbent for the removal of synthetic dyes methylene blue (MB) and Congo red (CR) from aqueous solutions in a batch process. Characterisation of the BSG was performed by chemical analysis, FTIR and SEM. The effects of contact time, initial dye concentration, adsorbent particle size, adsorbent concentration and pH on the adsorption process were investigated. High removal of both dyes ranging from 70 to over 90 % was achieved. It was shown that in both cases (MB and CR adsorption) the process could be interpreted in terms of Langmuir and Freundlich adsorption isotherms. The kinetics of the adsorption process was well described by the pseudo-second-order model. The results indicated the potential use of BSG as a low-cost adsorbent for MB and CR dye removal from aqueous solutions. This work is licensed under a Creative Commons Attribution 4.0 International License.

Complexation between polyallylammonium cation and polystyrenesulfonate anion was investigated in aqueous solutions of binary 1:1 sodium electrolytes (NaX, X = F, Cl, Br, I, NO3, ClO4) by means of microcalorimetry, dynamic light scattering, electrokinetics and spectrophotometry. At lower molar ratios of monomer units charged polyelectrolyte complexes were formed. At molar ratios close to equivalence and at lower salt concentrations (c(NAX) / mol dm-3 ≤ 0.1) flocculation occurred. The obtained precipitates contained approximately equimolar amounts of oppositely charged monomer units. At c(NAX) / mol dm-3 ≥ 0.5 (X = NO3, ClO4) and in the case when the polycation was present in excess, the amount of positively charged monomer units in the precipitate was higher than that of negatively charged monomers (asymmetric neutralisation). In addition, the aggregation of positively charged complexes in concentrated solutions of all investigated electrolytes was noticed. The onset of aggregation was strongly anion specific. However, the aggregation of negatively charged complexes did not occur even at NaX concentration as high as 3 mol dm-3. The composition of the insoluble products obtained at equimolar ratio of monomer units and higher concentrations of NaNO3 and NaClO4 was dependent on the order of polymer addition, indicating non-equilibrium interpolyelectrolyte neutralisation at all ionic conditions. At 25 °C and c(NaClO4) = 1 mol dm-3 equilibrium was not reached after two months. By contrast, the supernatants showed no traces of free polyanion chains after being heated for a week at 60 °C. The pairing of monomer units was found to be predominantly entropically driven, irrespectively of the type of reaction products formed (polyelectrolyte complexes, precipitates), and electrolyte type. The results obtained indicate that the overcharging is not an enthalpically demanding process. The calorimetric measurements also suggest that strong influence of counteranions on the composition of reaction product must be related with differences in ion distribution around polycation. However, despite rather similar energetics for complex and precipitate formation in the presence of various sodium salts a clear correlation of formation enthalpies with corresponding anion hydration enthalpies (Hofmeister series) was observed. Somewhat surprisingly, the titration calorimetry experiments have also revealed that the increase in electrolyte concentration affects the enthalpy of interpolyelectrolyte neutralisation negligibly. Apart from providing a deeper insight into the process of interpolyelectrolyte neutralisation the described findings can be used as a platform for further modification of corresponding multilayers, simply by changing the ionic conditions during their preparation. This could be of considerable importance due to their promising use in biotechnology and biomedicine.

Complexation of α- and β-anomers of adamantyl galactosides and adamantyl mannosides, having different configuration of the chiral linker connecting the sugar and the adamantamine (AMA) subunits, with β-cyclodextrin (β-CD) was investigated by means of NMR spectroscopy, microcalorimetric titrations and computational studies. The synthesis of adamantyl galactosides is also reported. The experimental investigations are consistent with the formation of 1:1 complexes in which the hydrophilic part of the guest protruded out of the secondary rim. The β-cyclodextrin was shown to be a rather efficient binder for the examined guests in water, primarily as a consequence of the enthalpically favourable inclusion of the adamantyl moiety within the hydrophobic cavity of the host. The structures of AMA derivatives complexes were modelled by combination of molecular and quantum mechanics - B3LYP/6-31G(d) in implicitly modelled water (PCM). The differences in the stability of primary and secondary complexes were observed. The main reasons for that could be more pronounced dehydration of the hydrophilic part of the guest upon complete adamantane inclusion in the complexes of primary type and the different hydrogen bonding pattern at the primary and secondary CD rims.

The formation of polyelectrolyte multilayers on silica surfaces was investigated in the presence of binary 1:1 sodium salts (NaCl, NaBr and NaNO3) at various salt concentrations. The build-up of multilayers was monitored using electrophoretic light scattering and quartz crystal microbalance with dissipation monitoring techniques. As cationic polyelectrolyte poly(diallyldimethylammonium chloride) was used and as anionic poly(sodium 4-styrene sulfonate). The counterion specific formation of multilayers was observed at higher electrolyte concentrations and the more pronounced influence was observed in the case of nitrate and bromide than in the case of chloride salt. These results confirm that solely by adjusting the appropriate ionic strength and by choosing the electrolyte type, polyelectrolyte multilayers with various properties and structure can be obtained. This work is licensed under a Creative Commons Attribution 4.0 International License.

Dispersion of particles in liquid medium may remain stable for long time but may also undergo aggregation, and consequently sedimentation. Stability takes place if the particles repeal each other due to their electric charge or the protection layer of adsorbed long chain molecules. Dispersions of nanoparticles (nanodispersions), in absence of protection layer, are as a rule less stable with respect to ordinary colloid dispersions as a consequence of their low charge. The theoretical model for interaction of nanoparticles takes into account the common ionic cloud, but not the partial overlap as in the case of relatively larger ordinary colloid particles. The model based on the extended Bronsted concept for ionic interactions is described. The charge distribution among nanoparticles is also taken into account. It was shown that nanodisperions may be electrically stabilized only at low ionic strength if they are sufficiently charged.

This article summarizes methods for determining proton surface charge at mineral/water inter- faces. It covers conventional experimental procedures and discusses problems with the techniques. Also it involves recommendations for obtaining reasonable and comparable results. The term "comparable re- sults" refers to comparison between results for the same solid as obtained in different laboratories. The most important parameters for the surface titrations are discussed. We also propose a reference titration procedure that would allow direct, unbiased comparisons of experimental data. The article finally includes a check-list for researchers and reviewers which should allow limiting the amount of titration data that are not useful for future uses. (doi: 10.5562/cca2062)

The interfacial properties of the system titanium(IV) oxide/poly(4-styrenesulfonate) (PSS) over a broad pH region in the presence of different alkali metal chlorides of different concentrations were investigated by means of electrokinetic, adsorption and surface potential measurements. Adsorption and electrokinetic data were obtained with colloid TiO2 particles, while surface potential data were obtained using a single crystal rutile electrode with the 001 plane exposed to the liquid medium. The electrokinetic and surface potentials of TiO2 were measured in the absence and presence of PSS. Since the presence of PSS did not significantly affect surface potentials, it was concluded that negative PSS molecules adsorbed at the surface by forming an outer-sphere surface complex rather than inner-sphere complex. The adsorption decreases significantly with pH, while the electrokinetic potential in the presence of PSS is negative in the whole investigated pH region. Amount of adsorbed PSS molecules is limited by the electrostatic repulsion which suppresses further adsorption, i.e. above critical potential of −50 millivolts. In the acidic region, where the surface is originally positively charged the amount of adsorbed PSS molecules is high since negative PSS molecules should at first compensate original positive charge and in the second step reverse the charge to reach the critical potential. In the basic region the surface charge is already negative so that small amount of adsorbed PSS molecules creates critical potential that prevents further adsorption.

The method of stagnation point optical reflectometry was applied for investigation of adsorption of bovine serum albumin (BSA) on previously formed poly(allylamine hydrochloride)/poly(sodium 4-styrenesulphonate) (PAH/PSS) multilayer with PAH being a terminal layer. The solid substrate was silica in the form of silicon wafers carrying an oxide layer. In order to interpret the adsorption of BSA, the build-up mechanism of PAH/PSS multilayers was examined with special emphasis on the effect of electrolyte concentration, pH of solution, and the anchoring (precursor) layer on that process. Additionally, the effect of BSA concentration and of the anchoring layer on BSA adsorption was investigated. It was shown that in all investigated systems the adsorption of BSA depends on conditions under which the multilayer was formed (ionic strength, pH and presence of an anchoring layer), as well as on BSA concentration. It follows that adsorption of BSA could be controlled not only by choosing suitable BSA concentration, but also by modifying the preformed multilayer.

The reaction between polyallylammonium cation and polystyrenesulfonate anion was investigated in alkali-metal chloride (MCl, M = Li, Na, K, Rb, Cs), sodium perchlorate and tetraethylammonium chloride solutions by means of microcalorimetry, potentiometry, DLS and spectrophotometry. The influence of ionic strength, temperature and addition order on the course of interpolyelectrolyte neutralisation was examined. At lower molar ratios of positively to negatively charged monomers and at 25 °C primary polyelectrolyte complexes were formed. Close to equivalence their flocculation occurred. The complexation was predominantly entropically driven, however a correlation between obtained reaction and cation hydration enthalpies was noticed. The composition of the precipitates at equimolar monomer ratio in chloride salt solutions did not significantly depend on the addition order up to 1.0 mol dm −3 salt concentration. In contrast, the ratio of oppositely charged monomers in precipitates prepared in NaClO 4 ( c/ mol dm −3 ≥ 0.5) was affected by the addition order in a wide temperature range. The increase in electrolyte concentration and the decrease in temperature led to more pronounced asymmetric neutralisation. The equilibrium establishment in NaClO 4 (aq) proceeded extremely slowly. Even at high perchlorate concentrations the final reaction product was virtually insoluble polysalt.

Complexation between poly(acrylate) (PA) and poly(allylammonium) (PAH) macroions at pH = 7.0 was studied by means of electrokinetics, microcalorimetry and DLS. At low polyelectrolyte concentrations and no electrolyte present strong overcharging of primary nanocomplexes occurred. In contrast, the increase in polyelectrolyte concentration led to flocculation taking place near the equivalence. The nanocomplex charge reversal was also achieved in the high polymer concentration regime by the abrupt instead of stepwise titrant addition. The procedure was successfully used in the case of several other polyion pairs. The presence of electrolyte affected the PAH-PA interpolyelectrolyte neutralization considerably, leading to ion- specific aggregation and extrinsic charge compensation. The complexation energetics was weakly influenced by ionic conditions. To the best of our knowledge, the reported results are the first direct evidence for primary complex overcharging. Their rationalization explains why interpolyelectrolyte neutralization in solution and at surfaces usually results with formation of neutral and charged products respectively.

Electrostatically driven coassembly of poly(acrylic acid)-block-poly(acrylamide), PAA-b-PAAm, and poly(2-methylvinylpyridinium iodide), P2MVP, leads to formation of micelles in aqueous solutions. Light scattering and small angle neutron scattering experiments have been performed to study the effect of concentration and length of the corona block (N-PAAm = 97, 208, and 417) on micellar characteristics. Small angle neutron scattering curves were analyzed by generalized indirect Fourier transformation and model fitting. All scattering curves could be well described with a combination of a form factor for polydisperse spheres in combination with a hard sphere structure factor for the highest concentrations. Micellar aggregation numbers, shape, and internal structure are relatively independent of concentration for C-p < 23.12 g L-1. The Guinier radius, average micellar radius, hydrodynamic radius, and polydispersity were found to increase with increasing N-PAAm. Micellar mass and aggregation number were found to decrease with increasing N-PAAm.

It is known that the build-up of polyelectrolyte multilayers can be followed in situ by means of stagnation point optical reflectometry. Application of optical reflectometry to characterization of multilayers obtained by exposing a suitable substrate to solutions of a cationic homopolymer and an oppositely charged protein was investigated. In all experiments, bovine serum albumin (BSA) was used as the negatively charged component. The weak polyelectrolyte poly(dimethylaminoethyl)methacrylate (PAMA) or the strong polyelectrolyte poly(2-vinyl-n-methylpyridinium iodide) (PVP+) was used as the cationic homopolymer. Silica in the form of silicon wafers carrying an oxide layer was used as the solid substrate and potassium chloride or phosphate buffer were used as the supporting electrolyte. The influence of ionic strength, pH, type of cationic homopolymer (strong or weak), and protein concentration were investigated. It was shown that stagnation point optical reflectometry can be a useful method for characterization of the formation of multilayers containing polyelectrolyte and protein layers.

According to the surface complexation model (SCM), charging of a metal oxide surface in aqueous environment is due to interactions of active surface groups with ions from the bulk of the solution. Several models for mechanism of surface reactions were proposed. Interfacial equilibrium is determined by corresponding equilibrium constants, but also with the structure of the electrical interfacial layer (EIL). Therefore, evaluation of equilibrium parameters is not a simple task. Traditionally, the measurements of pH dependency of surface charge density was used for that purpose. This article shows that introduction of electrokinetic data produces more reliable results, especially in the case of specific adsorption. If surface charge density and/or adsorption data are not available, one may still deduce interfacial equilibrium constants from electrokinetic results combined with measurements of the surface potential.

Charging of water layer at gas/water interface is analyzed experimentally and theoretically. Experimental data on the surface tension and on the surface potential in the acidic range are presented. Literature electrokinetic data indicate the isoelectric point of gas/water interface at pH 3.8. In the acidic region surface potential vs pH have a slope to be 55 % of the Nernstian. The surface tension exhibit minimum at pH 3.8. Thermodynamic model, based on distribution of ions between bulk and interface, is developed. The interpretation of surface and electrokinetic potential data provided equilibrium constants for distribution of ions between bulk and interface and the ionization equilibrium constant of interfacial water. Significantly higher ionization of interfacial water with respect to the bulk phase was observed. The affinity of hydrogen and hydroxide ions to be accumulated at the interface is higher with respect to the bulk of the solution which is more pronounced for hydroxide ions. The minimum of surface tension at the isoelectric point, is presented and analyzed. The thermodynamic concept, in accordance with the Gibbs isotherm, takes into account the variation of the composition at the interface. Effect of electrolytes on the surface tension, i.e. Jones-Ray effect, is also discussed.

It is well-known that mixing of aqueous solutions of oppositely charged proteins and polyelectrolytes leads to the formation of aggregates often called protein–polyelectrolyte complexes. In this study, we investigated the interactions between aqueous solutions of lysozyme and sodium poly(styrenesulfonate) (PSS) as the model system for investigating protein–polyelectrolyte complexation processes. The experimental methods used in this study were isothermal titration microcalorimetry, electrophoretic mobility ( i.e. zeta potential determination) and particle size ( i.e. hydrodynamic radius) measurements. The effect of pH, reactant (protein and polyelectrolyte) concentration and titration direction (addition order) on lysozyme–PSS complexation was investigated at θ = 25 °C and at ionic strength I c = 10 −2 mol dm −3 . At all three examined pH values (pH = 3.1, 4.6 and 7.5) at low charge ratios a stable colloidal suspension was obtained in which charged colloid particles, whose sign of charge corresponds to that of the titrand, were present. On the other hand, at higher charge ratios large particles (floccules) appeared (with the hydrodynamic radius in the range 2–7 μm). These floccules were also charged and, at first, their charge sign was equal to that of the titrand (| ζ | = 30–50 mV). However, upon further addition of the titrant the charge of the floccules reversed as a result of the surplus of titrant molecules in the corona. The change in pH leads to the significant change in charge ratios at which the onset of flocculation is observed. In all examined cases the charge ratio at which zeta potential starts to change corresponds to the onset of flocculation determined by DLS. The reaction heat effects were determined and it was shown that in all examined cases complexation resulted in measurable negative enthalpy changes.

The layer-by-layer deposition method to prepare multilayers of polyelectrolytes of alternating charge has been followed in situ by means of optical reflectometry experiments. It turns out that in solutions containing both polyelectrolyte and appropriate salts up to a certain concentration, the regular build up of multilayers is modified and becomes an adsorption/redissolution process. We explain this by taking into account (i) that during the regular multilayer formation process the macromolecules cannot equilibrate, (ii) that the added salt plasticizes the multilayer to a state where the molecules are sufficiently mobile to enable them to equilibrate between the layer and the surrounding solution, and (iii) that the presence of excess polyelectrolyte brings the system to a one-phase region of the polyelectrolyte complex phase diagram, implying that polyelectrolyte complexes must dissolve under these conditions.

The silica particle interactions in the presence of spermidine were systematically investigated both from experimental and theoretical points of view. The hydrodynamic radii and the corresponding polydispersity indices of the colloidal silica particles were determined by dynamic light scattering (DLS) as a function of spermidine concentration. Whereas the effective size of the silica particles increases with increasing spermidine concentration (pointing to the particle aggregation), the polydispersity index first increases reaches a maximum and then further decreases with the increasing spermidine concentration. From the mobility measurements it was concluded that the increase in spermidine concentration causes less negative values of zeta potential, meaning that the adsorption of spermidine leads to the less negative silica surface. Moreover, Monte Carlo (MC) simulations also confirmed that the addition of spermidine reduces the repulsion between silica particles. The MC concentration profiles of spermidine close to the charged silica particle are in a very good agreement with the results obtained by theory. An important motivation for our study is the effectiveness of multivalent ions to coagulate colloidal suspensions ; e.g., the multivalent ions are exploited in the water purification process.

Adsorption of lead ionic species at the goethite aqueous interface, as well as the electrokinetic properties of the system, were measured as a function of pH. The interpretation was based on the Surface Complexation Model assuming that association of lead species with negatively charged surface sites takes place. The electrostatic potential affecting the state of the surface species was obtained from the electrokinetic potential by Gouy-Chapman theory introducing the electrokinetic slipping plane as an adjustable parameter. It was found that singly charged lead species (PbOH+) are bound to negatively charged surface sites with the equilibrium adsorption constant logKa = 14 ą 0.2. The capacitance of the Helmholtz layer was found to be C1 = 0.4 ą 0.1 F m-2. These findings were confirmed by employing the standard triple layer model (TLM).

The adsorption of salicylic acid on hematite particles and their electrokinetic mobilities were measured as a function of the pH. The equilibrium in the systems was interpreted by the refined adsorption isotherm which considers the dissociation of the acid in the bulk of the solution and the electrostatic interactions between the surface and the adsorbed ions. The latter was taken into account through the surface potential which was obtained from the electrokinetics using the Gouy–Chapman theory and introducing the concept of slipping plane separation. It was concluded that singly charged anions are the adsorbable species, which occupy a surface area of 87±15 A 2 and that the adsorption equilibrium constant is log K °=3.5±0.1. The slipping plane separation from the surface was found to be 15 A.

Wood fly ash is an industrial by-product of the combustion of different wood materials and is mostly disposed of as waste on landfills. In our preliminary experiments, wood ash exhibited antibacterial activity against urban wastewater bacteria and we focused on wood fly ash as a potential substrate for wastewater disinfection. The addition of ash at a concentration of 10 g L-1 (1 %) caused an instant increase of pH in urban wastewater and landfill leachate. High pH (10.1–12.7) inactivated bacterial populations in the wastewater and the removal of faecal coliforms and intestinal enterococci after 6 h of contact was 100 % (below the detection limit, Leteći pepeo iz drvne industrije je nusproizvod koji nastaje spaljivanjem različitog drvnog materijala i većinom završi na odlagalištima otpada. Budući da je u preliminarnim ispitivanjima leteći pepeo pokazao antibakterijsko djelovanje prema bakterijama iz otpadne vode, pokusi su usmjereni istraživanju pepela kao potencijalnog supstrata za dezinfekciju otpadne vode. Dodatak pepela u koncentraciji od 10 g L-1 (1 %) uzrokovao je trenutno povećanje vrijednosti pH komunalne i procjedne otpadne vode s odlagališta otpada. Visoki pH (10,1–12,7) uništio je bakterije u otpadnoj vodi te je korištenjem najučinkovitijega pepela (dobivenog spaljivanjem bukve) postignuto 100-postotno uklanjanje (odnosno manje od mogućnosti detekcije

The (de)protonation equilibrium of the poly(allylammonium) cation (PAH) in an aqueous solution of various binary 1 : 1 electrolytes of different concentrations (0.1 ≤ c(NaX)/mol dm−3 ≤ 1.0 ; X = Cl−, Br−, I−, NO3−) was investigated potentiometrically at 25 °C. The mixed (Kap*) and concentration apparent equilibrium deprotonation constants (Kap) were calculated from the experimentally collected data and concentration profiles of dissociated and undissociated functional groups were obtained. The standard pK value of monomers was estimated by extrapolating the pKap values determined at various concentrations of added electrolyte to the degree of dissociation α = 1. The dependence of pKap on the degree of dissociation could be well described by the two parameter model according to Mandel. The variation of pKap* with monomer dissociation degree was found to be in satisfactory agreement with the cylinder Stern model, based on the Poisson–Boltzmann (PB) equation, and a constant Stern capacitance. Generally, the derived apparent constants showed a pronounced dependence on the concentration of binary electrolytes and a weak dependence on the type of anion counterbalancing the polyion charge. The influence of the PAH chain length (polymers containing on average 150 and 700 monomers were examined) on the protonation equilibrium of PAH could not be observed.

The interfacial properties of the system hematite/dicarboxylic acid were investigated in the presence of sodium perchlorate by means of adsorption, zeta potential and surface potential measurements. Maleic and fumaric acid were used as dicarboxylic acids. No significant difference in the surface potential values of hematite with and without the presence of dicarboxylic acids was observed. On the other hand, the zeta potential and the corresponding isoelectric point values obtained after adsorption of fumaric and maleic acids on hematite differ significantly from the zeta potential values of pure hematite. The parameters characterizing the electrical interfacial layer were determined on the basis of simultaneous interpretation of experimental data showing that there are some differences in adsorption behavior of two investigated dicarboxylic acids. The obtained equilibrium constant for adsorption of fumaric acid (logK° = 4.9 ± 0.2) is higher than the same constant obtained for adsorption of maleic acid (logK° = 4.0 ± 0.1) and the value of C1 was in both cases determined as 2.2 ± 0.3 F m–2. (doi: 10.5562/cca2176)

The immobilization of desired bacteria onto material was usually performed in synthetic media. The aim of this study was to test the immobilization of phosphate (P)-accumulating bacteria Acinetobacter junii onto natural zeolitized tuff (NZ) in the raw or sterilized municipal wastewater containing the common bacteria Escherichia coli and Enterococcus faecalis and the performance of immobilized A. junii in the same type of wastewater. In the sterilized wastewater which contained the mixture of A. junii, E. coli and E. faecalis, the A. junii was selectively immobilized onto NZ in significantly higher numbers than E. coli and E. faecalis. The A. junii added in the form of bioparticles to the wastewater containing E. coli and E. faecalis, multiplied and removed P from wastewater. The P removal form wastewater was a function of biomass of P-accumulating bacteria and not the amount of NZ or bioparticles used. The performance of A. junii was significantly better in membrane filtered than in autoclaved wastewater. The experiments that were performed in raw non sterilized wastewater showed that A. junii can be successfully immobilized onto NZ in competition with natively present heterotrophic bacteria, retain its metabolic activity and successfully remove P from such water, which makes this technology feasible from biotechnological aspect.