Temperature Study of Nonionic Polymers Adsorption at the Alumina—Solution Interface

The temperature influence of the structures of polyvinyl alcohol (PVA) and polyethylene glycol (PEG) adsorption layers on the alumina surface was studied. The amount of polymer adsorbed, the surface and diffuse layer charge of Al₂O₃ particles in the absence and presence of the polymer, and the thickness of polymer adsorption layers were determined in the 5°–40°C temperature range. An increase of PVA and PEG adsorption with an increase of temperature was observed. It is caused by conformation changes of polymer macromolecules from the coil structure to more and more stretched conformation when the temperature increases. Such a behavior was confirmed by the parameters calculated from the experimental data ( R _h—hydrodynamic radius of a polymer coil in the solution, δ—thickness of the polymer adsorption layer, R _s—radius of a sphere equivalent to the volume that falls per a macromolecule in the adsorbed layer). From the comparison of the values of diffuse layer charge and surface charge, the main factor influencing the ζ potential changes was determined. The free energy of PVA and PEG adsorption was calculated using the ζ potential data.     

Hydrazinodeoxycellulose for collection of metal ions from aqueous solution

We measured ellipsometrically the adsorption of polystyrene and polymethylmethacrylate on high-vacuum-vapoured chromium-, platinum- and gold-mirrors from various solvents under variation of the molecular weight of polymers. For both polymers we find an increase in thickness and adsorbed amount with an increase in polymer-concentration of solution. The concentration of the adsorbed polystyrene-film decreases, the concentration of the adsorbed polymethylmethacrylate-film increase with the polymer concentration of solution. Molecules of high molecular weight produce bigger thicknesses and adsorbed amounts than molecules of low molecular weight. With increasing polarity of the adsorbent we find an increase of thickness and amount of the adsorbed layer and a decrease of concentration. An increasing polarity of the solvent results in a decrease of thickness and amount and in an increase of concentration of the adsorbed layer. In saturation the polystyrene-molecules adsorb in the conformation of statistical coils. For the polar PMMA-molecules we find a divergent behaviour of the adsorption as a result of the strong interactions between the polar polymer-segments.     

Kalorimetrische Untersuchungen zur Adsorption von Polyäthylenglykolen und niedermolekularen Substanzen an Siliziumdioxid

The adsorption enthalpies of polyethyleneglycols (PEG) with various molecular weights and of low molecular substances such as ethylglycol, ethanol and diethylether from carbon tetrachloride on aerosil, a finely divided silicium dioxide-powder, were measured with an isoperibolic calorimeter. In addition the adsorption isotherms were determined with an infrared spectrometer to correlate the adsorption enthalpies with the weight of adsorption. For assessment of the competitive interactions in the adsorption system the heats o f wetting, dilution and immersion were determined. From the adsorption enthalpies and isotherms it can be seen that the adsorbed polyethyleneglycols have a very flat conformation for all degrees of coverage. In low concentrated polymer solution every second monomer segment of the polyethyleneglycol chain in average is bound to aerosil through hydrogen bonding; in saturation each fourth. The flat conformation of adsorbed PEG is confirmed from ellipsometric measurements on chromiumoxide surfaces; the thickness of the adsorption film of PEG was smaller than 30 Å. The linear correlation between the extinction of hydrogen bonds and the adsorption enthalpy shows, that the adsorption enthalpy is a definite measure for the numbers of hydrogen bonds. The low molecular substances, ethylglycol, diethylether and ethanol, used for comparison, adsorb in flat conformation like polyethyleneglycol.     

A Quantitative study of polymeric dispersant adsorption onto oxide-coated titania pigments

Polyacrylic acid salts and similar copolymers are used extensively in the coatings industry to disperse oxide-coated titania pigments. The effect of polymer adsorption onto the pigment can vary widely depending on polymer composition, pigment surface treatment, and solution properties such as pH and ionic strength. This investigation examines the effect of molecular weight on the adsorbed layer thickness and stabilizing action of polyacrylic acid dispersants. In order to understand the stabilization mechanism, a DLVO model was used in which the surface treatment layer of the pigment and the adsorbed layer thickness of the dispersant were taken into account. It was found that only this level of detail could account for the degree of stability found in pigment suspensions. Layer thickness and adsorption isotherms indicate that the dispersant molecules do not adsorb completely flat to the pigment surface but with enough loops and tails to provide some electrosteric stabilization.     

Adsorption at the solution-solid interface: Alkyd resin on TiO2 pigment

Gel permeation chromatography results obtained from the adsorption of alkyd from different solutions on anatase TiO₂ surfaces are reported, and the influences of the solvent–resin interactions in the adsorption process are discussed, covering the thickness of the adsorbed layer, the type of molecular weight species adsorbed, and its dependence on the concentration of the solution. Resin–pigment interaction was found to be influenced by the type of solvents used.     

Adsorption of poly(dimethyl siloxanes) from solution on silica: 2

The adsorption energy (Δε_s), the change in energy on breaking a solvent-adsorbent bond and forming a segment-adsorbent bond, for poly(dimethyl siloxane) at the solution/silica interface has been measured under actual adsorption conditions. The effect of the adsorption energy on the extent of mass adsorption and on the conformation of the adsorbed polymer layer was evaluated. At low surface coverage, it is primarily the adsorption energy which determines the conformation of the adsorbed polymer layer as a function of the molecular weight. This effect is opposed by an entropy lowering, resulting from a restriction of the configuration of the adsorbed polymer molecules. At high surface coverage, lateral interactions between the adsorbed polymer molecules became an important factor causing a decrease in the fraction of directly adsorbed segments per molecule with increasing coverage.     

Possibilities of Colloidal Silica Separation from Water Suspension in the Polyethylene Glycol (PEG) Presence at Different Temperatures

The influence of polyethylene glycol (PEG) adsorption on the silica (SiO₂) suspension stability was examined in the range 15–35°C. For this purpose the following methods were applied: turbidimetry, spectrophotometry, and microelectrophoresis. They allow determination of silica suspension stability, its absorbance, and zeta potential of the solid particles in the absence and presence of the polymer. The obtained results indicate that both polymer adsorption and temperature influence the stabilization-flocculation properties of the systems under examination. The silica suspensions without the polymer are relatively stable in the whole range of the investigated temperatures (electroststic stabilization). The adsorption of polyethylene glycol with lower molecular weight (PEG 2000) practically does not change the stability properties of the suspension (steric stabilization), whereas the adsorption of PEG with the higher molecular weight (20000) causes its deterioration (bridging flocculation). The higher the temperature is the greater the effect of destabilization is obtained. Such behavior of the investigated system is the result of changes in the structure of the polymer adsorption layer with the increasing temperature.     

Investigations of flocculation possibilities of the water alumina suspension in the presence of nonionic polymer

The effect of solution pH and molecular weight of polyethylene glycol (PEG) and polyethylene oxide (PEO) on their adsorption as well as stability of the colloidal Al₂O₃ water suspension was studied. The following methods were applied: turbidimetry, spectrophotometry, viscosimetry, potentiometric titration and microelectrophoresis.It was shown that the increasing solution pH affects conformation of the adsorbed macromolecules which affects the stability properties of such systems. The polymer adsorption causes deterioration of the stability conditions of the investigated alumina systems in comparison to those without polymer at all investigated pH values. At pH 3 and 6 the effect of the suspension destabilization is significantly smaller than at pH 9. The most effective flocculent of Al₂O₃ water suspension is PEO of the molecular weight 218,000 at pH 9.     

Conformation and thermodynamics of adsorbed macromolecules at the liquid/solid interface

Calorimetric measurements and results of the adsorption of poly(ethylene glycols) on Aerosil out of solution are reported. With the aid of conformation models for the adsorbed macromolecules and by comparing with the results on low molecular weight model substances, the measured values and their dependence on coverage, molecular weight and solvent are discussed. The resulting structure of the polymer layer, characterized by the adsorbed amount, the number of adhesive segments, the adsorption enthalpy, the thickness and the concentration of the adsorbed layer is verified by i.r. spectroscopic and ellipsometric data.     

Investigation of the adsorption of tropocollagen type I on titanium and Ti6Al4V

The adsorption of tropocollagen type I on titanium and Ti6Al4V has been investigated using physicochemical (zeta potential measurements), biochemical (ELISA), and imaging methods (SEM, AFM). Zeta potential measurements on both materials showed isolectric points in the pH_iep range 4.3-4.8 if the metal surfaces were covered with amorphous oxide layers. Adsorption of both collagen molecules and fibrillar collagen led to a shift of about 0.5 pH units towards the alkaline region. From ELISA-based results it can be concluded that in the investigated concentration range of 0.01-0.5 mg/ml, the adsorption of collagen molecules leads to the formation of a rather uniform covering. The influence of pH and ionic strength on the adsorption behavior has been investigated. A model of the competitive adsorption of both tropocollagen molecules and in vitro reconstituted fibrils is presented. Based on this model, two methods are proposed for the improved adsorption of collagen fibrils: (i) adsorption from solutions that are essentially free from tropocollagen and oligomeric species; and (ii) use of already adsorbed tropocollagen as nucleation sites for further fibrillar growth.     

The effect of acids and bases on the dispersion and stabilization of ceramic particles in ethanol

The dispersion and stability of alumina, titania, and silicon carbide powders in ethanolic medium have been investigated. An operational pH-scale, pH*, based on an ethanol-based reference electrode, was used to systematize the suspension properties. The electrokinetic behavior was determined as a function of pH*. The isoelectric points in ethanol — pH¹_iep(SiC)=7.5; pH¹_iep(Al₂O₃)=4.4 and pH¹_iep(TiO₂)=4.2 — were discussed in relation to the dissociation constants of the charge determining reactions at the powder surfaces. We have evaluated the long-term stability of the ethanolic dispersions through settling studies which showed that the primary particle size could be retained for extended times providing that the surface potential and ionic strength were optimized.     

The effect of anionic polyelectrolytes on the properties of aqueous silicon nitride suspensions

The effect of anionic polyelectrolytes on the electrokinetic and rheological properties of concentrated Si3N4 suspensions was investigated experimentally. We found that polyelectrolyte adsorption and, thus, colloidal stability at pH>pHSi3N4iep is mainly governed by the surface charge density of the solid phase. Comparing anionic methacrylic acid comb copolymer modifications with grafted poly(ethylene oxide) chains (PMMA-PEO), with poly(acrylic acid) (PAA) showed that the grafted PEO chains have a minor influence on the colloidal stability. The common viscosity minimum for all the anionic polyelectrolytes around pH 7 suggests that the suspensions are electrosterically stabilized. The polyacrylic backbone attains an extended conformation perpendicular to the surface. The effect of excess addition of polyelectrolyte was also discussed; we attribute the significant increase in suspension viscosity to the increased ionic strength caused by the release of associated counterions of the polymer functional groups.     

The Influence of an Acid-base-equilibrium on the Adsorption Behaviour of a Weak Polyampholyte

A weak diblock polyampholyte PMAA-b-PDMAEMA, poly(methacrylic acid)-block-poly((dimethylamino)ethyl methacrylate), was investigated as a model system for the influence of an acid-base-equilibrium of a phthalic acid buffer system on the polyelectrolyte adsorption behaviour. The adsorption of polyampholyte from aqueous solution onto silicon surfaces is known to be strongly influenced by the parameters of the polymer solution and the properties of the polyampholyte itself like block ratio or molecular weight. In the case of the investigated polyampholytes, the main parameter with the most significant influence on the adsorption is the pH. The big influence of pH on adsorption results from the charges of the polymer chains and the substrate, which are determined by the pH. Therefore, it should be useful to investigate the influence of a buffer system on the polyampholyte adsorption. On the one hand the buffer system enables to determine the pH of the aqueous polyampholyte solution more precisely. On the other hand the concentrations of different phthalic species like the phthalic acid, the hydrogen phthalate and the phthalate are strongly influenced by pH. These different species were observed to have a strong influence on the adsorption behaviour of the polyampholyte, so the adsorption as function of pH was observed to be also determined by the acid-base-equilibrium of the buffer system. The adsorbed amount of polyampholyte dried after the adsorption process was determined using ellipsometry, while the surface topography of these adsorbed layers were characterized by atomic force microscopy (AFM). This revised version was published online in July 2006 with corrections to the Cover Date.     

Kinetics of poly(acrylic acid) adsorption at the liquid–glass interface

The kinetic behavior of the adsorption of weak polyacid, namely, poly(acrylic acid) on a smooth glass surface has been studied at 30°C. For the evaluation of various adsorption parameters—the adsorption coefficient, surface coverage (θ), and thickness of the adsorbed layer—a new simple kinetic model has been proposed. The effect of the factors such as pH, electrolyte concentration, and molecular weight on adsorption behavior has been studied. © 1994 John Wiley & Sons, Inc.     

Effect of the type of polymer functional groups on the structure of its film formed on the alumina surface – Suspension stability

The effects of polymer functional group and solution pH on stability of colloidal Al₂O₃ water suspension were studied. Both the nonionic polymers: polyethylene glycol (PEG), polyethylene oxide (PEO) and the ionic ones: polyacrylic acid (PAA), polyacrylamide (PAM), polyvinyl alcohol (PVA) were used in the experiments. The following methods were applied: turbidimetry (stability measurements), spectrophotometry (determination of polymer adsorption), viscosimetry (thickness of polymer adsorption layer), potentiometric titration (solid surface charge density) and microelectrophoresis (potential zeta). It was shown that anionic polyacrylic acid is both the most effective stabilizer (at pH 9) and flocculant (at pH 3) of the alumina suspension. Its carboxyl groups have the greatest affinity for the surface active sites (the largest adsorption) of all functional groups present in the other examined polymers. The latter, i.e. hydroxyl (PEG, PEO, and PVA) and acetate (PVA) show a much lower affinity for the Al₂O₃ surface (negligible adsorption) and minimally affect the stability of the alumina-solution system.     

Adsorption of poly(dimethyl siloxanes) from solution on silica: 1

The adsorption of a broad range of poly(dimethyl siloxanes) on silica, treated and untreated, has been studied. Three solvents, n-hexane, CCl₄, and benzene were employed. Adsorption was molecular weight dependent and more polymer adsorbed from n-C₆H₁₄ than from CCl₄. Only negative adsorption from C₆H₆ solution was observed. The results are rationalized on the basis of the polymer—solvent interaction values (χ), the solvent—adsorbent and the solute—adsorbent adsorption energies. It is concluded that the loss in configurational entropy on adsorption of the macromolecules is a major factor in determining the adsorption isotherms.     

Interfacial properties of polyelectrolyte–cellulose systems. II. Electrokinetic properties of cellulose fibers with adsorbed monolayers of cationic polyelectrolyte

Zeta potential measurements by the streaming current method were performed on pulp (DP) fibers with or without irreversibly adsorbed monolayers of cationic polyelectrolyte. Factors affecting the electrokinetic properties of these fibers, such as the amount of adsorbed polymer, the polymer molecular weight (M_n 50,000 and 200,000), ionic strength (10^?5 ～ 10^?2M KCl), and the pH of the streaming medium (KCl solution), were examined. As the amount of adsorbed polymer increased, the negative zeta potential of the fibers decreased until the polarity of the zeta potential was reversed to the positive side. A marked change in the value of zeta potential was not observed when the formation of the saturated monolayer was completed. The zeta potential also varied in proportion to an increase in the amount of polymer adsorbed. Experimental results are interpreted with reference to the origin of the surface charge, the amphoteric nature of the surface, the modes of adsorption, and the adsorbed polymer chain configuration. Possible effects of the adsorbed monolayer formation on the structural change of the electric double layer at the fiber surface are discussed. It is concluded that the formation of a monolayer of cationic polyelectrolytes on the negatively charged cellulose fibers under the condition of k₁ > k₂ (part I) provides a means to arbitrarily control the charge of the fibers until formation of a saturated monolayer.     

Studies on Solution Behavior of Aqueous Mixtures of Nonionic Polymer in Presence of Cationic Surfactants

The interactions of two gemini surfactants (16–s–16, s = 5, 6) and their conventional counterpart cetyltrimethylammonium bromide (CTAB) with polyethylene glycols (PEG 3000 and PEG 35000) have been investigated using conductivity, steady state fluorescence, viscosity and TEM techniques. The results indicate that there is no interaction between the PEG 3000/CTAB complex at lower polymer concentrations. However, a very weak interaction is observed at higher concentrations (0.5 and 1.0 wt% PEG 3000), while PEG 3000 and PEG 35000 interact with the gemini surfactants. Both critical aggregation concentration (CAC) and critical micelle concentration (CMC) increases with polymer concentration but are independent of the polymer molecular weight. From steady state fluorescence it is found that the addition of PEG results in no drastic decrease in the aggregation number (N) for all surfactants. This suggests that the atmosphere surrounding the polyion-bound micelles, with respect to the influence on the forces acting at the micelle surface, is equivalent to the counterion/water atmosphere surrounding free micelles. The relative viscosity (η _r) results show an enhancement in η _r for all the surfactants. The increase in η _r is quite significant with gemini surfactants. Polymer-surfactant interaction also depends on the polymer molecular weight. Also, the interaction seems to affect both inter polymer–polymer association as well as chain expansion. Additionally the surfactant induced changes in the polymer conformation depicted by TEM study at the micro structural level confirmed previously observed interactions determined by different analytical techniques.     

共聚高分子吸附的Monte Carlo模拟

用MonteCarlo方法对选择性溶剂中两嵌段共聚高分子在固液界面的吸附进行了模拟 ,获得了吸附等温线以及吸附层厚度、链附着率、表面覆盖率、链节浓度分布等表征吸附层结构的信息 ,同时模拟获得了固液界面区吸附构型大小及分布等表征高分子构型的微观信息 ,考察了吸附性链节A所受的对比排斥能、链组成以及体相浓度等因素对这些参数的影响 .     

Investigation of Methane and Carbon Dioxide Gases Permeability Through PEBAX/PEG/ZnO Nanoparticle Mixed Matrix Membrane

This paper presents a new kind of mixed matrix membrane using polyethylene glycol (PEG) as organic filler. In this mix, PEG and ZnO nanoparticles (as inorganic modifier) were added to a PEBAX polymer matrix at different concentration to study their effects on the morphology, permeability and selectivity of the membrane. To characterize the chemical structure of samples FTIR and for morphological characterization, XRD and SEM were employed. The permeability of pure gases CO₂ and CH₄ in PEBAX, and PEBAX/PEG/ZnO with different ZnO and PEG contents were determined by the constant pressure-variable volume method. Also influences of temperature and pressure on permeation properties of these membranes were studied. The results were indicative of an increase in gas permeability and enhancement which for neat PEBAX membrane, CO₂/CH₄ permeability of 44.6 and 2.193 Barrer and selectivity of 20.39 were obtained. The permeability of PEBAX/PEG (40 wt.%)/ZnO (4 wt.%) membrane was enhanced to 94.49 Barrer for CO₂ and 3.933 for CH₄. The selectivity of PEBAX/ZnO(4 wt.%) improved to 31.58 for the CO₂/CH₄ gas pair.