Colloids and Interfaces — Open Access Journal

Polyetheretherketone (PEEK) biomaterial is a polymer which has been widely used since the early 90s as a material for human bone implant preparations. Nowadays it is increasingly used due to its high biocompatibility and easily modeling, as well as better mechanical properties and price compared to counterparts made of titanium or platinum alloys. In this paper, air low-temperature and pressure plasma was used to enhance PEEK adhesive properties as well as surface sterilization. On the activated polymeric carrier, biologically-active substances have been deposited with the Langmuir-Blodgett technique. Thereafter, the surface was characterized using optical profilometry, and wettability was examined by contact angle measuring. Next, the contact angle hysteresis (CAH) model was used to calculate the surface free energy of the modified surface of PEEK. The variations of wettability and surface free energy were observed depending on the deposited monolayer type and its components. Full article

Surface-tension induced flows may have a significant impact on the surface topography of thin films or small printed structures derived from polymer solution processing. Despite a century of research on Marangoni convection, the community lacks quantitative experimental flow field data, especially from within drying solutions. We utilize multifocal micro particle tracking velocimetry (µPTV) to obtain these data and show a calibration routine based on point spread function (PSF) simulations as well as experimental data. The results account for a varying sample refractive index, beneficial cover-glass correction collar settings as well as a multifocal lens system. Finally, the calibration procedure is utilized exemplarily to reconstruct a three-dimensional, transient flow field within a poly(vinyl acetate)-methanol solution dried with inhomogeneous boundary conditions. Full article

The spreading of small liquid drops over thin and thick porous layers (dry or saturated with the same liquid) is discussed in the case of both complete wetting (silicone oils of different viscosities over nitrocellulose membranes and blood over a filter paper) and partial wetting (aqueous SDS (Sodium dodecyl sulfate) solutions of different concentrations and blood over partially wetted substrates). Filter paper and nitrocellulose membranes of different porosity and different average pore size were used as a model of thin porous layers, sponges, glass and metal filters were used as a model of thick porous substrates. Spreading of both Newtonian and non-Newtonian liquid are considered below. In the case of complete wetting, two spreading regimes were found (i) the fast spreading regime, when imbibition is not important and (ii) the second slow regime when imbibition dominates. As a result of these two competing processes, the radius of the drop goes through a maximum value over time. A system of two differential equations was derived in the case of complete wetting for both Newtonian and non-Newtonian liquids to describe the evolution with time of radii of both the drop base and the wetted region inside the porous layer. The deduced system of differential equations does not include any fitting parameter. Experiments were carried out by the spreading of silicone oil drops over various dry microfiltration membranes (permeable in both normal and tangential directions) and blood over dry filter paper. The time evolution of the radii of both the drop base and the wetted region inside the porous layer were monitored. All experimental data fell on two universal curves if appropriate scales are used with a plot of the dimensionless radii of the drop base and of the wetted region inside the porous layer on dimensionless time. The predicted theoretical relationships are two universal curves accounting quite satisfactorily for the experimental data. According to the theory prediction, (i) the dynamic contact angle dependence on the same dimensionless time as before should be a universal function and (ii) the dynamic contact angle should change rapidly over an initial short stage of spreading and should remain a constant value over the duration of the rest of the spreading process. The constancy of the contact angle on this stage has nothing to do with hysteresis of the contact angle: there is no hysteresis in the system under investigation in the case of complete wetting. These conclusions again are in good agreement with experimental observations in the case of complete wetting for both Newtonian and non-Newtonian liquids. Addition of surfactant to aqueous solutions, as expected, improve spreading over porous substrates and, in some cases, results in switching from partial to complete wetting. It was shown that for the spreading of surfactant solutions on thick porous substrates there is a minimum contact angle after which the droplet rapidly absorbs into the substrate. Unfortunately, a theory of spreading/imbibition over thick porous substrates is still to be developed. However, it was shown that the dimensionless time dependences of both contact angle and spreading radius of the droplet on thick porous material fall on to a universal curve in the case of complete wetting. Full article

We considered pattern formation, i.e. viscous fingering, in the ink splitting process between an elastic flexographic printing plate and the substrate. We observed an unexpected scaling behavior of the emerging pattern length scale (i.e., finger width) as a function of printing velocity, fluid viscosity, surface tension, and plate elasticity coefficients. Scaling exponents depended on the ratio of the capillary number of the fluid flow, and the elastocapillary number defined by plate elasticity and surface tension. The exponents significantly differed from rigid printing plates, which depend on the capillary number only. A dynamic model is proposed to predict the scaling exponents. The results indicate that flexo printing corresponded to a self-regulating dynamical equilibrium of viscous, capillary, and elastic forces. We argue that these forces stabilize the process conditions in a flexo printing unit over a wide range of printing velocities, ink viscosities, and mechanical process settings. Full article

The aim of the work was the development of cheap and effective adsorbents based on titanium silicates deposited on the products of thermochemical processing of rice husk to extract cesium and strontium radioisotopes from aqueous media. Synthesis of adsorbents was carried out using the cheapest and widely used titanium water-soluble reagent, titanium sulfate (an intermediate product of white rutile pigment production), as feedstock. After treatment with titanium sulfate and neutralization, hydrothermal treatment was carried out in various ways. The traditional method of processing in an autoclave was used, as well as the blowing at different temperatures by steam. The distribution coefficients and the adsorption capacity for cesium and strontium ions on these sorbents were studied. Along with the chemical composition of adsorbents obtained by those ways, the type and the temperature of hydrothermal treatment also affected the adsorption properties. It was found that the adsorbent obtained by hydrothermal treatment in an autoclave has the highest degree of cesium ions extraction (Kd = 27,500). The highest degree of strontium ions extraction (Kd = 2,095,000) has an adsorbent obtained by hydrothermal treatment with water vapor blowing. Full article

The aim of this article was to develop a simple, cheap, light, highly efficient sorption membrane and filtering device for the purification of naturally polluted water with application in outdoor conditions. Sorption membranes have been prepared from cellulose pulp using paper and pulp technology. The sorbents were introduced into paper pulp as a filler (as activated carbon) or were chemically grafted to cellulose fibers. The absorption ability of such membranes assembled in a filter device has been investigated. The removal of weighted small mechanical particles, microorganisms, dissolved organic contaminants and colloids, and the undesirable ion impurities by the filter was investigated. Using a 10 × 10 cm filter, purification and disinfection of 18 liters of natural polluted water from a lake was done. Purification of dirty water occurs with gravity from a tank (bucket). Full article

The studies of pyrolysis of caffeic acid (CA) and its surface complexes is important for the development of technologies of heterogeneous catalytic pyrolysis of plant- and wood- based renewable biomass components. In this work, the structure and thermal transformations of the surface complexes of CA on the surface of nanoceria were investigated using Fourier transform–infrared (FT–IR) spectroscopy, thermogravimetric analysis (TGA) and temperature-programmed desorption mass spectrometry (TPD MS). It was found that CA on the surface of cerium dioxide forms several types of complexes: bidentate carboxylates, monodentate carboxylates and complexes formed as a result of interaction with phenolic hydroxyl groups. This is due to the ability of nanosized cerium dioxide to generate basic hydroxyl groups that can deprotonate phenolic groups to form phenolates on the surface. The main pyrolysis products were identified. The possible ways of forming 3,4-dihydroxyphenylethylene, acetylene carboxylic acid, pyrocatechol and phenol from surface complexes of CA were suggested. It was established that on the nanoceria surface effectively occur the decarboxylation, decarbonylation, and dehydration reactions of the CA, which are the desirable processes in biomass conversion technologies. Full article

Nitric oxide (NO) generating surfaces are potentially promising for improving haemocompatibility of blood-contacting biomaterials. In the present report, Cu-modified poly(vinyl chloride) (PVC) and polyurethane (PU) were prepared via polydopamine (pDA)-assisted chelation. The copper content on the PVC and PU modified surfaces, assessed by inductively coupled plasma - optical emission spectrometry (ICP-OES), were about 3.86 and 6.04 nmol·cm⁻², respectively. The Fourier-transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS) data suggest that copper is attached to the polymer surface through complex formation with pDA. The cumulative leaching of copper from modified PVC and PU during the five day incubation in phosphate buffered saline (PBS), measured by inductively coupled plasma mass spectrometry (ICP-MS), was about 50.7 ppb and 48 ppb, respectively which is within its physiological level. Modified polymers were tested for their ability to catalytically generate NO by decomposing of endogenous S-nitrosothiol (GSNO). The obtained data show that Cu-modified PVC and PU exhibited the capacity to generate physiological levels of NO which could be a foundation for developing new biocompatible materials with NO-based therapeutics. Full article

In this study, multilayer organic light-emitting diodes (OLEDs) consisting of three solution-processed layers are fabricated using slot die coating, gravure printing, and inkjet printing, techniques that are commonly used in the industry. Different technique combinations are investigated to successively deposit a hole injection layer (poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) (PEDOT:PSS)), a cross-linkable hole transport layer (N,N′-bis(4-(6-((3-ethyloxetan-3-yl)methoxy)-hexyloxy)phenyl)-N,N′-bis(4-methoxyphenyl)biphenyl-4,4′-diamin (QUPD)), and a green emissive layer (TSG-M) on top of each other. In order to compare the application techniques, the ink formulations have to be adapted to the respective process requirements. First, the influence of the application technique on the layer homogeneity of the different materials is investigated. Large area thickness measurements of the layers based on imaging color reflectometry (ICR) are used to compare the application techniques regarding the layer homogeneity and reproducible film thickness. The total stack thickness of all solution-processed layers of 32 OLEDs could be reproduced homogeneously in a process window of 30 nm for the technique combination of slot die coating and inkjet printing. The best efficiency of 13.3 cd A⁻¹ is reached for a process combination of slot die coating and gravure printing. In order to enable a statistically significant evaluation, in total, 96 OLEDs were analyzed and the corresponding 288 layers were measured successively to determine the influence of layer homogeneity on device performance. Full article

Today, the drilling operators use the Colloidal Gas Aphron (CGA) fluids as a part of drilling fluids in their operations to reduce formation damages in low-pressure, mature or depleted reservoirs. In this paper, a Taguchi design of experiment (DOE) has been designed to analyse the effect of salinity, polymer and surfactant types and concentration on the stability of CGA fluids. Poly Anionic Cellulose (PacR) and Xanthan Gum (XG) polymers are employed as viscosifier; Hexadecyl Trimethyl Ammonium Bromide (HTAB) and Sodium Dodecyl Benzene Sulphonate (SDBS) have been also utilized as aphronizer. Moreover, bubble size distributions, rheological and filtration properties of aphronized fluids are investigated. According to the results, the polymer type has the highest effect, whereas the surfactant type has the lowest effect on the stability of CGA drilling fluid. It was also observed that increasing salinity in CGA fluid reduces the stability. Finally, it should be noted that the micro-bubbles generated with HTAB surfactant in an electrolyte system, are more stable than SDBS surfactant. Full article

In this work, adsorption of rhodamine B (RB) and acid yellow 17 (AY17) was investigated on ordered mesoporous carbon material obtained by soft-templating method with hydrochloric acid (ST-A). For comparison, the adsorption process on commercial activated carbon CWZ-22 was also carried out. The sorbents were characterized by nitrogen adsorption/desorption isotherms and scanning electron microscopy. Langmuir and Freundlich adsorption isotherm models were applied to simulate the equilibrium data of RB and AY17. Adsorption isotherm data could be better described by the Langmuir model than the Freundlich model. The adsorption kinetics of RB and AY17 on studied carbons could be well depicted by using pseudo-second-order kinetic modeling. The adsorption capacity increased with temperature increase in the range of 298–315 K. In the whole diffusion process, the intraparticle diffusion was involved, but not the whole rate-controlling step. The calculated thermodynamic parameters, including Gibbs free energy (∆G), enthalpy (∆H), and entropy (ΔS) suggested that adsorption processes of RB and AY17 on ST-A and CWZ-22 were endothermic and spontaneous. Full article

The impact of solid bodies on the free surface of liquid pools is involved in many practical applications—such as bullets and air-to-sea anti-torpedo defense systems, or the water entry of athletes in water sports—aimed at improving the performance through a control of cavity dynamics. This work reports an experimental investigation of the impact of a linear array of hydrophilic (H) and superhydrophobic (SH) spheres on a deep water pool. The array consisted of ten magnetic spheres, with different permutations of H and SH spheres. Using high speed shadowgraphy, we captured the underwater kinematics of the array for different permutations of H and SH spheres. In particular, we observed the evolution or absence of an air cavity attached to the array as a function of the position of the H and SH spheres. The position of the first SH sphere from the leading edge of the array (Z_SH) emerged as a key parameter that alters the characteristics of cavity evolution. The appearance and pinch-off characteristics of a wake cavity behind the trailing edge were governed by the wetting properties of the leading and trailing surfaces of the array. The position of the first SH surface, as well as the wetting characteristics of the leading and trailing surfaces, are potential control parameters to alter underwater cavity evolution during solid surface impact on deep water pools. Full article

The adsorption of nucleic acid components on the surface of nanocrystalline titanium dioxide (anatase, pH_pzc = 6.5) in NaCl solutions was investigated using potentiometric titrations and multibatch adsorption experiments over a wide range of pH and ionic strengths. The Basic Stern surface complexation model was applied to experimental data to obtain quantitative equilibrium reaction constants. Adsorption results suggest that there is a considerable difference in the binding of nucleobases, nucleosides, and nucleotides with an anatase surface. Full article

Sorptive properties of the Transcarpathian clinoptilolite towards Pr(III) were studied under dynamic conditions. The sorption capacity of clinoptilolite under optimal conditions (sorbent grain diameter of 0.20–0.31 mm; pH 9.0, temperature of preliminary precalcination of 350 °C, and flow rate of the Pr(III) salt solution with the concentration of 1.0 μg·mL⁻¹ through the sorbent of 5 mL·min⁻¹) was equal to 47.5 mg·g⁻¹. The best desorbent of Pr from the clinoptilolite was the 1 M solution of KCl acidified with HCl to a pH value of 3.0. The method of Pr(III) trace amounts preconcentration in a solid phase extraction mode with further determination of this REE via spectrophotometric technique was developed. The linearity of the proposed method was evaluated in the range of 2–100 ng·mL⁻¹ with detection limit of 0.7 ng·mL⁻¹. Full article

We consider the anomalously slow dewetting of colloidal particles adsorbed at a liquid/gas interface. The particles move in the vertical direction under the action of a regular capillary force and an irregular force caused by defects (roughness and chemical heterogeneity). The particle diffusion is modeled by a random walk over a potential minima with jump rates determined by the Arrhenius law. The averaged particle motion is found under the assumption of Gaussian distributions for characteristic properties of spatial heterogeneities. Full article

In this article we report the production of metal oxide (TiFe₂O₄, ZnFe₂O₄) nanoparticles by pulsed laser ablation technique in a liquid environment. We used nanosecond Nd: YAG laser systems working at 532 nm and 1064 nm of wavelength and the energy of the laser beam was kept constant at 80 mJ. Absorbance spectra, surface plasmon resonance, optical band-gap, and nanoparticle morphology were investigated using ultraviolet-visible (UV-Vis) spectroscopy, Fourier transform infrared spectroscopy (FTIR), and scanning electron microscopy (SEM). Changing the wavelength of the laser for growth, nanoparticles showed shift between the absorbance and surface plasmon resonance peaks in their UV-Vis spectra, which implies that the optical properties of the colloid nanoparticles depend on laser parameters. This was confirmed with the variation of the band gap energy. Furthermore, redshift for the absorbance peak was observed for samples as-grown at 532 nm around 150 nm as a function of time preparation. Conversely, for the samples as-grown at 1064 nm there was no shift in the absorbance spectra, which could be due to agglomeration and formation of larger particles. The characterization results showed appropriate plasmonic photo-catalysts properties of the particles, hence the photoactivation of the nanoparticles was examined on antibacterial effect using colonies of Staphylococcus aureus and Escherichia coli. Full article

In this study, we investigated the behaviour of rhamnolipid and Greenzyme in brine solutions relevant to hydrocarbon reservoir. Prior to this work, several studies only reported the behaviour of the biosurfactants dissolved in sodium chloride solutions of varied salinity. The results of this study are relevant to the application of the biosurfactants in enhanced oil recovery, during which the compounds are injected into reservoir saturated with formation water, typically of high salinity and complex composition. Surface tension and conductivity methods were used to determine the critical micelle concentrations of the biosurfactants, Gibbs surface excess concentrations and standard free energy at water-air interface. The results show that rhamnolipid and Greenzyme could reduce the surface tension of water from 72.1 ± 0.2 mN/m to 34.7 ± 0.4 mN/m and 47.1 ± 0.1 mN/m respectively. They were also found to be stable in high salinity and high temperature with rhamnolipid being sensitive to brine salinity, composition and pH while Greenzyme showed tolerance for high salinity. Furthermore, the Gibbs standard free energy of micellisation shows that rhamnolipid and Greenzyme have the tendency to spontaneously form micelles with rhamnolipid showing more surface adsorption. However from maximal Gibbs surface excess concentration calculations, Greenzyme monomers tend to favour aggregation more than that of rhamnolipid. Full article

There is a big gap between idealized colloid science and the needs of a printing ink formulator. This often leads to formulations based on intuition and experience rather than good science. By bringing together the most relevant colloid and interface science with the capabilities of modern apps, it is possible to bridge the gap between theory and reality to the benefit of both the colloid science community and those who need the science to improve their formulations. The process of making current science usable also exposes the limitations of available theories. This suggests a methodology for highlighting the grand challenges to the colloid science research community, including the challenge of making any new science more usable. Full article

We have studied theoretical and experimental methods of methanol adsorption in micropores of aluminum oxide agglomerates obtained by gas-dispersion synthesis. It is shown that the necessity to use strict equations based on the theory of volume filling of micropores, which implies a physical and formal analogy between the volume filling of micropores and capillary condensation, for qualitative and quantitative description of adsorption equilibrium in open slit-like micropores. The applicability of the proposed equations for the description of adsorption equilibrium in such systems is demonstrated on the example of experimental methanol adsorption/desorption isotherm on the aluminum oxide, which possesses a microporous structure. Full article