Effect Of Preferential Adsorption Research Articles

Adsorption-active polydisperse brush with tunable molecular mass distribution.

Recently, a novel class of responsive uncharged polymer brushes has been proposed [Klushin et al., J. Chem. Phys. 154(7), 074904 (2021)] where the brush-forming chains have an affinity to the substrate. For sufficiently strong surface interactions, a fraction of chains condenses into a near-surface layer, while the remaining ones form the outer brush with a reduced grafting density. The dense layer and the more tenuous outer brush can be seen as coexisting microphases. The effective grafting density of the outer brush is controlled by the adsorption strength and can be changed reversibly as a response to changes in environmental parameters. In this paper, we use numerical self-consistent field calculations to study this phenomenon in polydisperse brushes. Our results reveal an unexpected effect: Although all chains are chemically identical, shorter chains are adsorbed preferentially. Hence, with the increase in the surface affinity parameter, a reduction in the surface grafting density of the residual brush is accompanied by a change in the shape of its molecular mass distribution (MMD). In particular, an originally bidisperse brush can be effectively transformed into a nearly monodisperse one containing only the longer chain fraction. We introduce a method of assigning different chain conformations to one or the other microphase, based on analyzing tail length distributions. In a polydisperse brush with a uniform MMD, short chains are relegated to the adsorbed phase, leading to a narrower effective MMD in the residual brush. Preferential adsorption is not absolute, and longer chains are also partially involved in adsorption. As a result, not only the width of the distribution decreases but also its shape evolves away from the initial uniform distribution. We believe that the effect of preferential adsorption stems from a fundamental property of a polydisperse brush, which is characterized by a spectrum of chemical potential values for monomers belonging to chains of different lengths. Hence, preferential adsorption is also expected in polyelectrolyte brushes; moreover, brush polydispersity would affect coexistence with any other condensed phase, not necessarily related to adsorption.

Self-Assembly of a Thermally Responsive Double-Hydrophilic Copolymer in Ethanol-Water Mixtures: The Effect of Preferential Adsorption and Co-Nonsolvency.

Lower alcohols can induce a combined collapse-swelling de-mixing transition (lower critical solution temperature (LCST)-type co-nonsolvency) in aqueous solutions of poly( N-isopropylacrylamide) (PNIPAM) by interacting with the polymer's amide groups. This interaction results in an increase of the total surface area of hydrophobic sites and destabilizes the chains. Here, we make use of this phenomenon to drive the counterintuitive self-assembly of a PNIPAM-containing double-hydrophilic graft copolymer in water-ethanol mixtures at T ≪ LCST. Rheological frequency sweeps are used to quantify the distinct solvation states of PNIPAM at various temperatures and ethanol concentrations. The energy stored through elastic deformation at the de-mixing transition is simply related to the solvent binding. We find that the storage modulus decreases progressively, but nonlinearly with ethanol concentration, which evidences a preferential solvation pattern. Analogously, through a combination of dynamic light scattering and transmission electron microscope analyses, we demonstrate that a low-temperature structure variation takes place by adding ethanol following a similar solvent-content morphology dependent model.

Is “dark water” really dark?

We consider features of experimental studies performed by microwave spectroscopy methods and showing the collisional pressure broadening of molecular lines by hydrogen at very low temperatures. It is shown that the effect of preferential adsorption of orthohydrogen by the walls of the gas cell of a spectrometer can influence significantly the measurement results and lead to an erroneous interpretation of the data given by astrophysical studies of the interstellar space.

Competitive adsorption of trace elements in calcareous soils as affected by sewage sludge, poultry manure, and municipal waste compost

The competitive adsorption of trace elements is a key issue in assessing the mobility of trace elements in calcareous soils and can be affected by disposal of sewage sludge, municipal waste, and poultry manure. The effect of municipal sewage sludge, poultry manure, and municipal waste compost on the sorption of cadmium (Cd), copper (Cu), zinc (Zn), and nickel (Ni) in surface samples of three calcareous soils was studied. As the applied concentrations increased, Cu and Cd adsorption increased, while Zn and Ni adsorption decreased in all treatments. Based on the distribution coefficient (K d) values and proportion of increase or decrease in metal adsorption, the selectivity sequence in control and amended soils found was Cu ≫ Cd ≫ Ni > Zn and Cu ≫ Cd ≫ Zn > Ni, respectively. In general, among control and amended soils, control soils showed the highest K d for Cd, Cu, and Ni, while sludge, poultry manure, and composted waste-amended soils had lowest K d for Cd, Cu, and Ni, respectively. In the case of Zn, composted waste-amended and control soils had highest and lowest K d, respectively. The present experimental results indicated that the addition of organic amendments to these calcareous soils reduced the sorption of Cd, Cu, and Ni. Thus, the effects of preferential adsorption and organic matter should be considered in assessing the risk associated with applying sewage sludge, poultry manure, and composted material to calcareous soils.

Surface-modified zeolite-filled chitosan membranes for pervaporation dehydration of ethanol

Surface-modified zeolite-filled chitosan (CS) membranes were prepared by incorporating 3-mercaptopropyltrimethoxysilane (MPTMS)-modified H-ZSM-5 zeolite into chitosan for pervaporation dehydration of aqueous ethanol solution. The physicochemical characterization by XPS, FT-IR, XRD, DMA and SEM showed that –SO 3H group was readily grafted on the surface of H-ZSM-5 with the mediation of MPTMS and hydrogen peroxide, and the accompanying ion–ion interaction between –SO 3H group on surface-modified H-ZSM-5 and –NH 3 + group on chitosan substantially eliminated the nonselective voids at the chitosan–H-ZSM-5 interface of the filled membranes. The experimental results also revealed that H-ZSM-5 exhibited desirable size-selective and preferential adsorption effects for aqueous ethanol solution. As a result, modified H-ZSM-5 filled membranes showed higher swelling degree and permeation flux, and improved selectivity for aqueous ethanol solution. In comparison between chitosan control membrane (permeation flux 54.18 g/(m 2 h) and separation factor 158.02 for 90 wt.% aqueous ethanol solution at 80 °C), the modified H-ZSM-5 filled membrane with 8 wt.% filling content exhibited a remarkably improved pervaporation performance with permeation flux 278.54 g/(m 2 h) and separation factor 274.46 under the identical experimental condition.

Effect of Preferential Adsorption on the Synergism of a Homologous Cationic Surfactant Mixture

To evaluate the effect of preferential surface adsorption of bromide ions on the synergism of homologous cationic surfactant mixtures reported previously, the surface tension of the aqueous solutions of the hexadecyltrimethylammonium chloride (HTAC)-dodecyltrimethylammonium bromide (DTAB) system was measured as a function of the total molality of surfactants and the relative proportion of DTAB at 298.15 +/- 0.05 K under atmospheric pressure. The excess Gibbs energies calculated from them were -2.6 kJ mol(-)(1) in the mixed adsorbed film and -2.0 kJ mol(-)(1) in the mixed micelle, respectively. A useful analytical procedure to evaluate the composition of individual ions (hexadecyltrimethylammonium, dodecyltrimethylammonium, chloride, and bromide ions) in the adsorbed film and micelle was developed and applied.

Electrokinetic Measurements Reveal Interfacial Charge at Polymer Films Caused by Simple Electrolyte Ions

The interfacial charge on spin-coated films of poly(tetrafluoroethylene-co-2,2-bis(trifluoromethyl)-4,5-difluoro-1,3-dioxole) (Teflon AF) was studied by streaming potential and streaming current measurements in diluted aqueous solutions of potassium chloride, potassium hydroxide, and hydrochloric acid. ζ potential and surface conductivity were derived from electrokinetic data determined at varied concentrations of the electrolytes by means of the novel microslit electrokinetic setup (ref 1: J. Colloid Interface Sci. 1998, 208, 329). The results obtained revealed the high relevance of unsymmetrical (preferential) adsorption of ions as the origin of charge formation at unpolar polymer materials in aqueous environments. The preferential adsorption of hydroxide ions (OH-) was found to predominate as compared to the adsorption of hydronium ions (H3O+) at similar concentrations, i.e., in solutions of neutral pH. No effect of preferential adsorption was induced by chloride (Cl-) and potassium (K+) ions. For the...

Surface segregation in small supported particles

Surface segregation in small alloy particles on a support is investigated by means of Monte Carlo simulations as a function of the particle size. The results are compared with those in semi-infinite systems in the same approximation. Large differences in segregation behaviour are found, due to the limited supply of atoms for segregation and due to the effect of preferential adsorption of one component at the particle/support interface. The occurrence of certain ensembles of atoms on the surface which can be the sites for catalytic activity of the particles has also been studied and shows an unexpected particle size dependence. Again the bond strength between either component and the support may modify the observed trends.

Transition phenomena of polymers in mixed solvents in the vicinity of theta conditions: Effect of preferential adsorption

Viscosimetric measurements were obtained with the ternary systems polystyrene/dioxane/methanol, polystyrene/benzene/methanol and poly(methyl methacrylate)/dioxane/cyclohexane, changing the solvent mixture composition at constant temperature. The polystyrene and poly(methyl methacrylate) systems exhibit a transition phenomenon with solvent-mixture composition in which the polymer is just above the theta condition. In the case where two theta conditions occur ((θ-intra, θ-inter) the transition point is closely related to the intramolecular theta conditions. Moreover the intramolecular theta conditions vary with the molecular weight in the region of molecular weights where the preferential adsorption also varies. This variation induces a variation of the transition point with molecular weight which obeys a formula analogous to that giving the variation of the preferential adsorption with molecular weight.

Adsorption of poly(4‐tert‐butylphenyl methacrylate) on silica from THF/water

AbstractAdsorption studies of poly(4‐tert‐butylphenyl methacrylate) (PBPh) on silica from a binary solvent (THF/water) are reported. In order to investigate the influence of the composition of the binary solvent on the adsorption of the polymer on a special silica with hydrophobic surface, measurements of the adsorption isotherms were carried out using Aerosil R‐972. The adsorption isotherm of PBPh for the hydrophobic silica/THF solution interface exhibits higher values than the isotherms for hydrophobic silica/aqueous THF solution interfaces. The amount of adsorbed polymer decreases when the water content of the binary mixture increases. The results are discussed in relation to the effects of preferential adsorption of one of the solvents by the polymer.

Effects of poly(2-vinylpyridine) as a template for the radical polymerization of methacrylic acid—III. Influence of monomer concentration

The template polymerization of methacrylic acid along atactic poly (2-vinylpyridine) was studied calorimetrically at various monomer concentrations from 0.1 to 9.0 M in DMF; the concentration of the P2VP template was fixed at 0.4 base M. Azobisisobutyronitrile and bis( p- tert-butylcyclohexyl)peroxydicarbonate were used as initiators at concentrations of 0.1 and 0.01 M, respectively. The temperature was 30°. The results could be well described by a generalized kinetic model in which the effect of preferential adsorption of monomer by the template, this adsorption being assumed to be of the Langmuir type, has been taken into account, i.e. the model incorporates propagation along the template not only by picking-up monomer from the surrounding solution (mechanism II) but also by zipping-up pre-adsorbed monomer (mechanism I).

Collapse of one polymer coil in a mixture of solvents

Abstract We discuss the size of a polymer chain P dissolved in a mixture of two solvents A and B, which are both good solvents of P, but which are close to a consolute critical point Tc. As shown earlier by one of us preferential adsorption effects become very important in this situation, and upset the classical picture : in a certain region near the AB critical point, the chain is predicted to collapse(1). There is one complication however : when the polymer concentration inside the coil increases, the AB critical point inside the coil shifts and preferential adsorption is reduced. We conclude that, upon decreasing the temperature T (with the bulk A/B concentration fixed at the critical value) ***he P chain must collapse first at a certain temperature T*, but must return to its ideal dimensions when T reaches Tc. Similar conclusions should hold for gels ***ollen by a mixture of two solvents.

The application of light scattering to the investigation of preferential adsorption effects in quasi-ternary systems

Abstract

Adsorption of Elastomers on Carbon Black

Abstract During the past three years considerable progress has been made in the study of adsorption of high polymers on the surfaces of solids from solution. A number of experimental investigations have established that linear polymers are adsorbed at a number of segments along the molecular chain and that an apparent saturation value of the adsorption is reached with increasing concentration, leading to isotherms that exhibit considerable similarity with the classical Langmuir isotherm. Kolthoff and others have shown that poor solvents favor adsorption and that fractions of high molecular weight are adsorbed preferentially. Polymer of low molecular weight is adsorbed more rapidly, but is eventually replaced by fractions of higher molecular weight. Kolthoff and Gutmacher also observed some evidence of adsorption hysteresis in rubber-carbon black systems. Preferential adsorption effects have also been described by Goldfinger and others, who, in addition, furnished an estimate of the thickness of the adsorbed layer. Theoretical explanation for many of these effects has recently come from a detailed statistical mechanical treatment of polymer adsorption by Frisch, Simha, and Eirich.