Thickness Of Adsorbed Polymer Layer Research Articles

Design of robust Self-Compacting concrete based on analysis of component properties

This study aims at investigating the impacts of component properties on the robustness of flowable concretes such as Self-Compacting Concrete (SCC). We first reviewed the key parameters that identify various component properties. They are the adsorbed polymer layer thickness and adsorption–desorption kinetics of polymers, particle size and distribution of powders, packing properties of powders and aggregates. We then analyzed the SCC robustness index (in terms of yield stress) of the parameters at a given standard variation of each raw component content based on a recently proposed SCC robustness assessment method. The results suggest that when subjected to a standard variation of each raw component, the standard SP, water, and aggregate variations significantly impact SCC robustness. Based on the maps of the robustness index of each key parameter, a general frame of the influence of component properties on SCC robustness was proposed, which provides guidance for designing robust SCC with the raw materials at hand.

Unraveling the Polymer Chain-Adsorbed Constrained Interfacial Region on an Atomistically Thin Carbon Sheet.

Confinement of graphene and its functional derivatives in synthetic and biomacromolecules has been widely demonstrated recently to manifest in several multiscale phenomena in their mixtures. However, the intricate adsorbed interfacial region formed between polymer chains and a single layer of atomistically thin carbon sheet hitherto evaded an understanding of its nature and characteristics. Here, we reveal the structure of this constrained region and estimate the thickness of the adsorbed polymer layer on a single layer of an atomistically thin graphene oxide sheet using both direct experiments and molecular dynamics simulations. We use small-angle neutron scattering on a model multicomponent mixture formed by an adsorbing polymer, graphene oxide, and solvent for revealing the structure of the constrained interfacial region. We quantify the intricate adsorbed polymer layer thickness on a single layer of atomistically thin graphene oxide sheet by Euclidean approximation of the experimentally observed self-similar interfacial structure. The state of polymer chain random walk and influence of unadsorbed chains under experimental conditions are investigated and juxtaposed against the accuracy of this quantification. For long-chain polymers, the adsorbed layer thickness increases with increasing polymer molecular weight and shows a scaling relationship δ ∼ Rg0.22 with the polymer radius of gyration. For short-chain polymers, the thickness is nearly independent of molecular weight and shows a scaling relationship δ ∼ 0.6 Rg0.22. Coarse-grained molecular dynamics simulations performed on a model system similar to experiments qualitatively ratify the experimentally observed molecular weight-thickness relationship. Simulations show no discernible scaling relationship between radius of gyration and adsorbed layer thickness for low-molecular-weight polymers but show a consistent scaling δ ∼ Rg for high-molecular-weight polymers. A comparison between results from experiments and simulations indicates a discerning pathway in deciphering interface-governed multiscale phenomena in mixtures of adsorbing macromolecules with graphene and its functional derivatives.

Nanoparticle surface modification by amphiphilic polymers in aqueous media: Role of polar organic solvents

We investigate the role of three polar organic solvents (dimethyl formamide (DMF), dimethyl sulfoxide (DMSO), and glycerol) on the interfacial behavior of Pluronic P105 poly(ethylene oxide)–poly(propylene oxide)–poly(ethylene oxide) (PEO–PPO–PEO) block copolymers on protonated silica nanoparticles in an aqueous dispersion. The polymer adsorption and self-assembly have been assessed from critical surface micelle concentration (csmc, measured by pyrene fluorescence spectroscopy) and adsorbed layer thickness (measured by capillary viscometry) data. Above its csmc, PEO–PPO–PEO block copolymers form hydrophobic domains on the nanoparticle surface. Below a critical concentration in water (known as critical displacer concentration, cdc), organic solvents act as displacers (molecules that can displace adsorbed polymer from a solid surface). The critical displacer concentration is obtained from the csmc and the polymer adsorbed layer thickness data. The cdc is found to be dependent on both the amount of nanoparticles present in the system as well as the nature of the displacer. Below the cdc, the csmc increases and the adsorbed polymer layer thickness decreases with increasing organic solvent concentration. Interfacial free energy calculations suggest that DMF, DMSO, and glycerol can adsorb onto the silica particles by displacing adsorbed PEO. These calculations are consistent with the experimental results in that, as a displacer, glycerol is the most effective and DMF is the least effective. Above the cdc, the influence of glycerol or DMSO on csmc is opposite to that of DMF which is attributed to the cosolvent effect.

Multiscale Structure, Interfacial Cohesion, Adsorbed Layers, and Thermodynamics in Dense Polymer-Nanoparticle Mixtures

We establish the existence and size of adsorbed polymer layers in miscible dense nanocomposites and their consequences on microstructure and the bulk modulus. Using contrast-matching small-angle neutron scattering to characterize all partial collective structure factors of polymers, particles, and their interface, we demonstrate qualitative failure of the random phase approximation, accuracy of the polymer reference site interaction model theory, ability to deduce the adsorbed polymer layer thickness, and high sensitivity of the nanocomposite bulk modulus to interfacial cohesion.

Steric stabilization of suspensions, the adsorbed polymer layer thickness [proceedings

Steric stabilization of suspensions, the adsorbed polymer layer thickness [proceedings

A model for the collision efficiency of shear-induced agglomeration involving polymer bridging

An expression is derived in terms of key dimensionless groups, including a group for steric interaction, to determine the collision efficiency for shear-induced agglomeration of non-colloidal particulate suspensions. Agglomeration is assumed to take place due to bridging of polymer layers on colliding particles. The forces considered arise due to the van der Waals, double-layer, steric and hydrodynamic interactions. The expression for collision efficiency was determined a priori from physico-chemical parameters including the shear rate and it shows the dependence on flocculant concentration, molecular weight and shear rate. A cone and plate device was used to experimentally study the agglomeration of spherical glass beads dispersed in an aqueous glycerin solution. Non-ionic polyethylene oxide (PEO) was used as a flocculant. The collision efficiency was found to have a power law dependence on shear rate and be a strong function of adsorbed polymer layer thickness.

Temperature influence of nonionic polyethylene oxide and anionic polyacrylamide on flocculation and dewatering behavior of kaolinite dispersions

Nonionic polyethylene oxide (PEO) and anionic polyacrylamide (PAM) flocculation of kaolinite dispersions has been investigated at pH 7.5 in the temperature range 20–60 °C. The surface chemistry (zeta potential), particle interactions (shear yield stress), and dewatering behavior were also examined. An increase in the magnitude of zeta potential of kaolinite particles, in the absence of flocculant and at a fixed PEO and PAM concentration, with increasing temperature was observed. The zeta potential behavior of the flocculated particles indicated a decrease in the adsorbed polymer layer thickness, while at the same time, however, the adsorbed polymer density showed a significant increase with increasing temperature. These results suggest that polymer adsorption was accompanied by temperature-influenced conformation changes. The hydrodynamic diameter and supernatant solution viscosity of both polymers decreased with increasing temperature, consistent with a change in polymer–solvent interactions and conformation, prior to adsorption. The analysis of the free energy (Δ G ads) of adsorption showed a strong temperature dependence and the adsorption process to be more entropically than enthalpically driven. The polymer conformation change and increased negative charge at the kaolinite particle surface with increasing temperature resulted in decreased polymer bridging and flocculation performance. Consequently, the shear yield stress and the rate and the extent of dewatering (consolidation) of the pulp decreased significantly at higher temperatures (>40 °C). The temperature effect was more pronounced in the presence of PEO than PAM, with 40 and 20 °C indicated as the optima for enhanced performance of the latter and former flocculants, respectively. The results demonstrate that a temperature-induced conformation change, together with polymer structure type, plays an important role in flocculation and dewatering behavior of kaolinite dispersions.

Studies of rheological behavior of colloidal silica suspensions with interaction potential

Rheological measurements of both electrostatically and sterically stabilized silica suspensions are analyzed on the basis of the hard sphere approximation. For electrostatically stabilized suspensions, non-Newtonian viscosity is related to an effective pairwise interaction potential. It is shown that the shear rate dependence of viscosity can be predicted. For sterically stabilized suspensions, a structural model is used in order to obtain, in particular, low shear viscosity. From its dependence on particle volume fraction, the adsorbed polymer layer thickness can be deduced. In addition, the variations of shear modulus as a function of particle volume fraction are scaled with a power law.

Adsorbed polymer layer thickness determination at the solid—liquid interface by different techniques

Four techniques, (photon correlation spectroscopy (PCS), microelectrophoresis, sedimentation coefficient measurement and viscosimetry) were used to determine the thickness of a polyethylene glycol layer at the solid—liquid interface. A comparison of obtained results indicates that PCS is most recommended, then microelectrophoresis. The accuracies of the techniques for this particular application are compared, and the reasons for the differences are explained. The layer thicknesses are discussed in terms of their relationship to the radius of gyration of the polymer in bulk solution.

Theory of phase equilibria in polymer stabilized colloidal suspensions

The results of calculations describing the observed phase behaviour of polymer stabilized colloidal dispersions based on the Gibbs-Bogolyubov variational approach are presented. The effective pairwise additive macroparticle interaction is assumed to be a superposition of Yukawa potentials. Hardspheres are chosen as the reference system for the disordered phases, while an Einstein model is taken to be a suitable reference system for the ordered phases. In sterically stabilized colloidal dispersions, temperature variations in the range of the repulsive steric interaction between macroparticles are allowed. Additional insight into the temperature dependence of the adsorbed polymer layer thickness is obtained by comparing the results of the variational approach with those obtained using the phenomenological Flory-Huggins theory of phase separation. In order to describe the observed reversible depletion flocculation, the double Yukawa model potential permits changes in the depletion attraction with free polymer concentration.

Variation of effective adsorbed polymer layer thickness with molecular weight in good and poor solvents

Variation of effective adsorbed polymer layer thickness with molecular weight in good and poor solvents