Adsorption Kinetics Of Polymers Research Articles

Single-particle electrophoresis for studying the adsorption of cationic polymers onto anionic particles.

Understanding the adsorption of polymers onto particles is crucial for many technological and biomedical applications. Even though polymer adsorption on particles is a dynamic process, most experimental techniques can only study the adsorption indirectly, in equilibrium and on the ensemble level. New analysis methods are required to overcome these limitations. We investigated the use of single-particle electrophoresis to study the adsorption kinetics of cationic polymers onto anionic particles and compared the resulting data to a theoretical model. In this approach, the electrophoretic mobility of single polystyrene (PS) particles, exposed to different concentrations of poly(2-guanidinoethyl methacrylate), was measured as a function of time. The polymer adsorption leads to an electrophoretic mobility change of the PS particle over time, from the initial negative value to a positive value at equilibrium. By fitting the kinetics data to the Langmuir model, the adsorption rate, desorption rate and equilibrium constant were determined. Finally, the adsorption kinetics of several other polymers was investigated. This showed that the presented technique enables direct analysis and comparison of the kinetics of polymer adsorption on the single-particlelevel.

Study on the kinetics of adsorption of poly(ethylene oxide) onto a silica particle using optical tweezers and microfluidics

The kinetics of poly(ethylene oxide) (PEO) adsorption onto the surface of a trapped silica particle in a controlled flow and solution environment was studied using optical tweezers and microfluidics. The polymer layer thickness, δH, was monitored directly by exploiting the balance of the trapping force and the hydrodynamic drag force of the flowing solution past the particle. The effects of polymer concentration, volumetric flow rate, pH, particle size, and molecular weight were evaluated as parameters. In all conditions, the time-series evolution of the δH was observed to increase with time scale up to ≈ 50 s and approached a plateau due to the saturation of PEO on the surface. As for the PEO concentration dependence, the plateau of the δH was found to increase with PEO concentration, affected by the surface diffusion and reconformation of the preferentially adsorbed polymer at the interface, in agreement with the previous studies. The effect of pH was found to be influenced by the volumetric flow rate. At a low flow rate, the plateau of the δH was observed to be independent of pH. In contrast, at a high flow rate, the plateau of the δH was observed to decrease at high pH. This is attributed to the decrease in the attractive interaction between the silica surface and the polymer, in addition to the influence of fluid force. Furthermore, the plateau of the δH was found to increase with particle size, corresponding to the increase in the number of colliding polymers. Finally, this study presents a novel perspective in understanding polymer adsorption kinetics by directly evaluating the layer thickness on a single particle viewpoint that is not accessible to the bulk measurements.

Adsorption Kinetics of Polystyrene and Poly(9-anthracenyl methyl methacrylate) onto SiO2 Surface Measured by Chip Nano-Calorimetry.

The alternating current (AC) chip nano-calorimetry is a powerful tool to investigate the physical properties of polymer thin films. In this paper, we report on the adsorption kinetics of polymers in which an AC chip nano-calorimetry was used for the first time. This technique allows for the real-time measurement of the adsorption kinetics of polymer chains onto the SiO2 surface. We used polystyrene (PS) and poly(9-anthracenyl methyl methacrylate) (PAMMA), which have different chemical natures and side group sizes. It was confirmed that the observed adsorption kinetics for PS were consistent with previously reported results obtained by dielectric spectroscopy. For PAMMA, we found characteristic adsorption kinetics, which shows a clear kink at the crossover between the early and later stages, while PS exhibits a lesser tendency of showing the kink as demonstrated by previously reported results.

Exploiting the Spatial Homogeneity of Adlayer Breakdown on Microelectrodes to Develop a Kinetic Model for S-NDR Copper Electrodeposition

Copper electrodeposition is a major component in integrated circuit manufacturing, ranging across lengthscales from nanoscale damascene plating to 100s of microns for thorugh-silicon-vias used in 3D interconnect packaging.1 Critical to this process is electrodeposition of void-free copper structures in high aspect ratio cavities, which is achieved with various additives that enable superconformal bottom-up filling. This physicochemical phenomenon is driven by an S-shaped negative-differential resistance (S-NDR), which promotes spatial bifurcation of the electrode surface into active and passive deposition regions. 2 Electrode bifurcation is dependent on additive adsorption/desorption kinetics, chemical species transport, and electrode geometry. Prior studies have demonstrated that the active/passive bifurcation is dependent on electrode size and that reduced electrode dimensions will permit a homogeneous reaction across the electrode.3 In this work, microelectrodes are used to experimentally probe the critical breakdown behavior in acid copper-sulfate electrolytes in the presence of micromolar concentrations of chloride and a single polymeric additive. In-situ optical microscopy indicates that the entirety of the microelectrode surface (either 12.5 or 25 μm in diameter) is either active or passive during cyclic voltammetry measurements, permitting current to be normalized to the geometric electrode area. Experimental electrolyte parameter sweeps cover chloride concentration, polymer concentration, copper concentration, and polymer adsorption kinetics (i.e. polymer type). These measurements are compared to static macroscopic electrodes and rotating disk electrodes at dimensions known to exhibit active/passive bifurcation. Experimental measurements are fit to finite element method computations using a two-additive model tracking the adsorption and rate-dependent desorption for chloride and polymer species. This work is an extension of previous computational models for describing S-NDR behavior in single additive systems.4-5 Kinetic constants for copper electrodeposition as well as adsorption and desorption dependent rate constants for chloride and polymer are fit to experimental cyclic voltammograms. Electrochemical kinetic constructs using microelectrodes and a 2-additive adsorption/consumption model provide a more accurate representation of critical breakdown phenomenon in S-NDR electrochemical systems. References T.P. Moffat, J.E. Bonevich, W.H. Huber, A. Stanishevsky, D.R. Kelly, G.R. Stafford, and D. Josell, “Superconformal Electrodeposition of Copper in 500-90 nm Features”, J. Electrochem. Soc., 147 (2000) 4524.T.P. Moffat and D. Josell, “Extreme Bottom-Up Superfilling of Through-Silicon-Vias by Damascene Processing: Suppressor Disruption, Positive Feedback and Turing Patterns”, J. Electrochem. Soc., 159 (2012) D208.S. Bozdech, K. Krischer, DA. Crespo-Yapur, E. Savinova, and A. Bonnefont, “1/f2 noise in bistable electrocatalytic reactions on mesoscale electrodes”, Faraday Discuss., 193 (2016) 187.D. Wheeler, T.P. Moffat, and D. Josell, “Spatial-temporal modeling of extreme bottom-up filling of through-silicon vias”, J. Electrochem. Soc., 160 (2013) D3260.D. Josell and T.P. Moffat, “Superconformal bottom-up nickel electrodeposition in high aspect ratio through silicon vias”, J. Electrochem. Soc., 163 (2016) D322.

Serum Protein-Resistant Behavior of Multisite-Bound Poly(ethylene glycol) Chains on Iron Oxide Surfaces.

Recent surveys have shown that the number of nanoparticle-based formulations actually used at a clinical level is significantly lower than that expected a decade ago. One reason for this is that the physicochemical properties of nanoparticles fall short for handling the complexity of biological environments and preventing nonspecific protein adsorption. In this study, we address the issue of the interactions of plasma proteins with polymer-coated surfaces. With this aim, we use a noncovalent grafting-to method to functionalize iron oxide sub-10 nm nanoparticles and iron oxide flat substrates and compare their protein responses. The functionalized copolymers consist of alternating poly(ethylene glycol) (PEG) chains and phosphonic acid grafted on the same backbone. Quartz crystal microbalance with dissipation was used to monitor polymer adsorption kinetics and evaluate the resistance to protein adsorption. On flat substrates, functionalized PEG copolymers adsorb and form a brush in moderate or highly stretched regimes, with densities between 0.15 and 1.5 nm–2. PEG layers using phosphonic acid as linkers exhibit excellent protein resistance. In contrast, layers prepared with carboxylic acid as the grafting agent exhibit mitigated protein responses and layer destructuration. The present study establishes a correlation between the long-term stability of PEG-coated particles in biofluids and the protein resistance of surfaces coated with the same polymers.

Effect of cationic polyacrylamide on precipitated calcium carbonate flocculation: Kinetics, charge density and ionic strength

We quantified the adsorption kinetics of cationic polyacrylamide (CPAM) of three charge densities but constant molecular weight and their effects on the dynamics of a polydisperse calcium carbonate (CC) flocculation at various ionic strengths. The adsorption kinetics of CPAM onto PCC can be explained by the balance of the electrostatic and van der Waals interactions, hydrogen bonding and steric hindrance between the adsorbed and dissolved CPAM molecules and CC. While the amount of adsorbed CPAM onto CC increased as a function of the CPAM charge density in the absence of salt, this relationship reversed at increased ionic strength (I=0.1). Decreasing charge on CPAM molecules allows more amide groups available for hydrogen bonding although reducing electrostatic attraction of CC. So the lower-charge CPAM benefits from the additional hydrogen bonding at higher ionic strength when the contribution of electrostatic attraction is reduced because of charge screening by salt. Discrepancies in quantity between the adsorbed and the polymer predicted from the monolayer surface coverage theory for flocculation rate were apparent. The polymer adsorption kinetics and its conformation were important variables in determining particle flocculation in this study, more than the quantity of adsorbed polymer.

Effect of Cationic Polyacrylamide Adsorption Kinetics and Ionic Strength on Precipitated Calcium Carbonate Flocculation

The effect of polymer adsorption kinetics and ionic strength on the dynamics of particle flocculation was quantified using a model system consisting of precipitated calcium carbonate (PCC) and cationic polyacrylamide (CPAM) at a low shear rate. All early flocculations detectable by a photodispersion analyzer (PDA) happened in nonequilibrium polymer adsorption regimes. We observed discrepancies in flocculation rates with the surface coverage theory, which is based on a simple monolayer adsorption model, in both early and late flocculation stages. For instance, the same amount of adsorbed CPAM reached at different polymer doses demonstrated different flocculating capabilities. This highlighted the importance of polymer adsorption kinetics upon flocculation. The transient conformation of the adsorbed CPAM during the kinetic process sometimes even superceded the adsorbed amount in the determination of PCC flocculation. Both antagonistic and synergetic effects of increased ionic strength on the CPAM-induced PCC aggregation were observed during early flocculation. However, late-stage PCC flocculation shared some similarities, irrespective of polymer dose and ionic strength. Despite the decreased amount of adsorbed polymer from the increased ionic strength, the combination of CPAM and salt, at certain concentrations, demonstrated a synergy to promote PCC aggregation more efficiently than the same amount of the respective components.

Polysilazane-Induced Aggregation of Hydrophobic Silver Colloids

Adsorbing polymers such as polysilazanes induce irreversible coagulation of hydrophobic silver colloids in nonpolar solvents. This is accompanied by broadening of the surface plasmon resonance (SPR) peak. A method to analyze the coagulation kinetics based on von Smoluchowski's theory utilizing the SPR change is described. The approach allows evaluating extinction spectra of aggregates of small sizes. A model for polymer adsorption kinetics in combination with a modified bridging efficiency model explains the observed coagulation inhibition over time in terms of macromolecules adsorption, spreading, and mutual repulsion.

The Influence of Anchoring-Group Structure on the Lubricating Properties of Brush-Forming Graft Copolymers in an Aqueous Medium

We have compared the lubricating properties of two different PEG-grafted, polycationic, brush-forming copolymers to gain a deeper understanding of the role of the polyionic backbone in the lubricating behavior of such materials, when used as additives in aqueous lubricant systems. Previously, poly(l-lysine)-graft-poly(ethylene glycol) (PLL-g-PEG) has been shown to adsorb onto oxide surfaces from aqueous solution and substantially lower frictional forces. Poly(allylamine)-graft-poly(ethylene glycol) (PAAm-g-PEG), which also has a polycationic backbone, has been synthesized in several different architectures, and its performance investigated via adsorption tests, rolling- and sliding-contact tribometry, and the surface forces apparatus. These tests show a clear reduction of friction forces with PAAm-g-PEG compared to water alone. However, when compared with PLL-g-PEG, while PAAm-g-PEG copolymers did not adsorb to the same extent or exhibit as high a lubricity in sliding geometry, they showed a similar lubricating effect under rolling conditions. The difference in the chemical structure of the backbones, especially the flexibility of the anchoring groups, appears to significantly influence both the extent and kinetics of polymer adsorption, which in turn influences lubrication behavior.

Adsorption Kinetics of NIPAM-Based Polymers at the Air−Water Interface As Studied by Pendant Drop and Bubble Tensiometry

The adsorption of N-isopropylacrylamide (NIPAM) based thermoresponsive polymers at the air-water interface was investigated by using drop and bubble shape tensiometry. The molecular weight dependence of polymer adsorption rate was studied by using narrowly distributed polymer fractions (polydispersity < 1.2) that were prepared by solvent:nonsolvent fractionation. The time-dependent surface tension profiles were fitted to the Hua-Rosen equation and the t values obtained were applied for interpretation of the kinetic data. It was found that the rate of polymer adsorption increased as the molecular weight of the polymer decreased. The relationship between polymer surface concentration and surface tension was determined by applying the pendant drop as a Langmuir-type film balance. From this relationship, the kinetics of polymer adsorption determined experimentally was compared with the adsorption rates predicted by a diffusion-controlled adsorption model based on the Ward-Tordai equation. The predicted adsorption rates were in good agreement with what was found experimentally. The dependence of the adsorption rate on the molecular weight of polymers can be satisfactorily described within the diffusion-controlled model.

The role of polymer adsorption kinetics in flocculation

The adsorption of polymeric flocculants on the surfaces of suspended solid particles is a non-equilibrium process. It is postulated that the process is controlled by an irreversible attachment between polymer molecules and solid particles. The frequency of such collisions determines the kinetics of adsorption and the distribution of adsorbed polymer on individual particle surfaces. A simplified model is presented in which polymer–particle collision frequencies determine the distribution of adsorbed polymer, and therefore, the adhesion efficiency of the particle–particle collisions that lead to flocculation. The implications of the model with regard to the effects of process variables, such as polymer molecular weight, particle size distribution, solids concentration and mixing conditions, are discussed at length. The critical importance of initial dispersion stability on polymer dosage requirements and overall process performance is demonstrated. The model provides considerable insight into the mechanisms involved in the use of progressive polymer addition to control adsorption and enhance flocculation efficiency.

Adsorption kinetics of polymers in membranes: change of layer thickness with solvency

In order to monitor changes in the adsorbed layer thickness of polymers adsorbed within the pores of membranes, an apparatus has been developed that monitors the differential pressure generated by fluid flowing through the membrane. The membranes used were commercially available “Whatman Anodisc” alumina filters and had uniformly sized pores of approximately 0.2 μm diameter. The apparatus consisted of an HPLC pump, a pressure transducer and a system of PTFE pipework, which was connected to a pair of membrane holders. Identical membranes were placed in each holder, one of which acted as an inlet filter for the other. This ensured that no contaminants affected the experimental results. The mean pore radius of each membrane was derived by flowing pure solvent through and applying Poiseuille's equation, which relates pore radius to the pressure difference across the membrane. The kinetics of adsorption of polystyrene from toluene were followed by monitoring the pressure increase that occurred as the adsorbed layer restricted the pores in the membrane. Once adsorbed, the polymer was bound irreversibly at the pore wall and the equilibrium thickness of the polymer layer was determined. By purging the apparatus with a poor solvent for the polymer, the degree of layer collapse was assessed. Toluene was then brought back into contact with the polystyrene layer, and the rate and extent of reswelling determined.

Mathematical Model of Kinetics of Polymer Adsorption and Replacement Adsorption onto a Solid Surface

A mathematical model of polymer adsorption from solution onto a planar surface is suggested. The kinetic model takes into account the adsorption and desorption rates as well as the rates of bond formation and dissociation between the macromolecule and the surface. The correspondence of this kinetic model to experimental data for polystyrene adsorption onto a chromium surface from cyclohexane and replacement adsorption of protic polystyrene by deutero-polystyrene is shown. Some values of the rate constant ratios are found.

Adsorption and spreading of polymers at plane interfaces; theory and molecular dynamics simulations

Nonequilibrium processes play a key role in the adsorption kinetics of macromolecules. It is expected that the competition between transport of polymer towards an interface and its subsequent spreading has a significant influence on the adsorbed amount. An increase of the transport rate can lead to an increase of the adsorbed amount, especially when the polymer has too little time to spread at the interface. In this study we present both molecular dynamics simulations and analytical calculations to describe some aspects of the adsorption kinetics. From MD simulations on a poly(ethylene oxide) chain in vacuum near a graphite surface, we conclude that the spreading process can, in first approximation, be described by either a simple exponential function or by first-order reaction kinetics. Combining these spreading models with the transport equations for two different geometries (stagnation-point flow and overflowing cylinder) we are able to derive analytical equations for the adsorption kinetics of polymers at solid-liquid and at liquid-fluid interfaces.

Polymer Adsorption Kinetics: Effects of Supply Rate

The saturation adsorbed amount of polymers on solid surfaces is mostly found to be independent of the polymer transport rate, or flux J, to the surface. In most cases this is because the experimental rate of transport strongly deviates from the relaxation rate in the polymer layer. We studied the adsorption of savinase on SiO2 from aqueous solution and found that the transport rate is an important parameter in the adsorption kinetics. The adsorption process can be viewed as an attachment to, followed by spreading of a polymer molecule over the surface. In this way the adsorbed amount strongly depends on J if the time for transport to the surface is in the same range as the spreading time. Using an analytical growing disk model for the polymer adsorption, we are able to, at least qualitatively, describe the adsorption kinetics.

Polyelectrolyte Complexation At Oxide-Water Interfaces : Influence on Colloidal Stability

The present study aimed at the colloidal stability at short terms of aluminium oxide particles in aqueous suspensions containing polyacrylic acid and complexing aluminium ions resulting from the oxide dissolution at initial pH 5. Carboxylic acid groups were found to strongly interact with aluminium ions and form a oxide-polymer complex. The kinetics of polymer adsorption was obtained by determining the concentrations of complexed polyacid or polyacid free of aluminium ion which are non adsorbed and remain in the supernatant as a function of time. The adsorption mechanism was found to depend on the carboxylic acid to aluminium ion ratio. For low value of this ratio, the polyelectrolyte rapidly adsorbed in the form of a polyion highly complexed with the initially solubilized aluminium ions. For high value of the ratio, the adsorption was long delayed and the polyacid underwent an aluminium-hydrogen ion exchange, the extent of which depended on the oxide dissolution rate as evidenced by increase of the pH of the suspension.

Dynamics of initial stage flocculation of polystyrene latex spheres with polyelectrolytes

Abstract An end-over-end rotation apparatus was created in order to obtain reproducible mixing suitable for the study of the kinetics of flocculation. The validity was verified by measuring the rate of coagulation of monodispersed polystyrene latex particles with simple electrolytes by means of a Coulter Counter. The method was applied to the analysis of the initial behavior of flocculation induced by the addition of excess polyelectrolyte flocculant with a nominal molecular weight of 4.5 million. In contrast to coagulation with a simple electrolyte, the rate of flocculation in the initial stage was remarkably enhanced and then decreased abruptly after certain mixing steps. The degree of the initial stage of enhancement and the duration of this stage were found to be dependent on the concentration of the polyelectrolyte. Ascribing the enhancement to the increase in the effective collision radius of the colloidal particles due to the attached polymer layer, the thickness of this layer, δHe, was calculated. Analyses showed that δHe increases as polymer concentration increases up to a layer thickness of 500 nm, which correlates with the size of the polymer in the solution. However, an analysis of the collision process between particles and polyelectrolytes implied that the kinetics of polymer adsorption in the initial stage are limited by transportation until near saturation. Taking into account the data on electrophoretic mobility, we concluded that our results are consistent with the picture of kinetically-controlled polymer adsorption proposed by De Witt and van de Ven [J.A. De Witt and T.G.M. van de Ven, Langmuir, 8 (1992) 788].

Mathematical Model of Kinetics of Polymer Adsorption onto a Solid Surface in the Diffusional Field

A mathematical model of polymer adsorption kinetics from a solution onto a solid/liquid interface in the diffusional field is suggested. The kinetic model takes into account the influence on adsorption and desorption rates of polymer molecular mass, hydrodynamic regime, and surface coverage of the polymer. The correspondence of the kinetic model to experimental data on polyethylene oxide adsorption onto a silica surface from water in stagnation point flow is shown. The surface area blocked by a macromolecule and the fraction of solvent in a saturated adsorbed layer have been calculated. Values are found for the rate constants of adsorption and desorption as well as for the constants of adsorption equilibrium for poly(ethylene oxide) with molecular mass from 7.1 × 10 3 to 847 × 10 3.

Effect of soluble aluminum ions on polyelectrolyte-alumina interaction. Kinetics of polymer adsorption and colloid stabilization

We investigated the adsorption of high-molecular-weight polyacrylamide, hydrolyzed polyacrylamide and polyacrylic acid onto partially soluble colloidal alumina in aqueous suspensions containing 10 −3 N KCl and 3× 10 −4 N AlCl 3. The polymer solution and the colloidal suspension were mixed at pH 5.0, and the electrophoretic mobility and pH were recorded as a function of time. The polymer-aluminium ion interaction resulted in polymer ionization and complexation between carboxylic acid groups and aluminium ions characterized by a maximal degree of complexation close to 0.6. When the polymer was added to the oxide suspension, we also determined the concentration of the different species by potentiometric titration, and characterized the polyelectrolyte adsorption kinetics on the colloidal alumina by determining the variation with time of the amount of free and complexed polymer segments in the supernatant liquid phase. Two different situations were investigated depending on the ratio of carboxylic acid to dissolved aluminium ions. For a low value of the ratio, the polymer was quickly adsorbed in a form which was highly complexed by aluminium ions pre-existing in the solution. For a high value of the ratio, the adsorption was very slow. Before adsorption, the polyacid also underwent an aluminium-hydrogen ion-exchange, the extent of which depended on the rate of oxide dissolution: it appeared that adsorption increased very strongly with complexation. From an investigation of the colloidal stability of the system and the zeta-potential of the colloid-polymer complex as a function of the amount of polymer added to the solution, the domain of electrosteric stabilization was determined and the instability near the point of zero charge was attributed to the electrostatic attraction between the positively and negatively charged groups.

Competitive Adsorption Kinetics of Polymers Differing in Length Only

Optical reflectometry was used to monitor adsorbed amounts of homopolymer as a function of time, and an impinging jet flow cell was used to control mass-transfer rates between the solution and the adsorbing surface. For poly(ethylene oxide) (PEO) adsorbing from water onto silica we found that exchange of short adsorbed polymers against longer ones in solution takes place at constant coverage, the total adsorbed amount being equal to the saturated level of the short component. This result agrees fully with predictions for an adsorbed layer of mixed composition which is in full equilibrium with its immediate surroundings