Adsorption of polymers at the solution–solid interface. X. Reinforcement studies of nitrile rubbers by silicas

Vulcanizates of three acrylonitrile–butadiene copolymers were prepared by γ-ray irradiation. Two pyrogenic silicas of differing surface areas and with surface modifications were incorporated as fillers. Measurements of initial modulus, stress–strain hysteresis, tear energy, and swelling show little differences between the reinforcement effects of the various fillers, although the extent of filler reinforcement is related to the acrylonitrile content of the rubber. The considerable range of interaction energies implied by solution adsorption studies are not reflected in the reinforcement phenomena.     

Adsorption of polymers at the solution–solid interface. V. Styrene–methyl methacrylate copolymers on carbon

The adsorption of a series of block and random styrene–methyl methacrylate copolymers on an animal charcoal and on Graphon has been studied. On charcoal, adsorption decreases with increase of molecular weight because of the inability of larger coils to penetrate into the adsorbent. An analysis is presented which requires that coils undergo considerable distortion on adsorption in pores. The adsorption of random copolymers on Graphon is also in reverse order of molecular weight; this effect may be due to particle bridging leading to the formation of interparticle “pores.” The relative affinity of the styrene and methyl methacrylate residues is different on charcoal and Graphon, respectively; on both surfaces, however, relatively few of the more active residues are required for adsorption. Block and random copolymers are adsorbed to different extents which depend on the nature of the adsorbent surface.     

Adsorption of polymers at the solution–solid interface. XIV. Adsorption and steric stabilization with styrene–acrylonitrile copolymers

The adsorption of random copolymers of styrene and acrylonitrile of azeotropic composition from their trichloroethylene solutions onto precipitated silica exhibits a maximum at intermediate molecular weights. These copolymers are able to stabilize dispersions of some, but not all, grades of precipitated silica; here, too, a maximum effect is found at intermediate molecular weights. Copolymers are partially desorbed by ethyl cyanide, which destabilizes silica dispersions. Block copolymers of low acrylonitrile contents do not stabilize well but, when preadsorbed, affect the behavior of subsequently adsorbed random copolymers. In particular, high molecular weight random copolymers flocculate the pretreated silica; silica with grafted polyacrylonitrile chains may also be flocculated by these copolymers.     

Adsorption of polymers at the solution–solid interface. XIII. Adsorption and steric stabilization with styrene–2-vinylpyridine copolymers

Random and block copolymers of styrene and 2-vinylpyridine, covering the full range of composition, have been synthesized. The adsorption of these polymers from trichloroethylene solution on to precipitated silica has been studied and their ability to impart colloidal stability to the silica dispersions also investigated. Estimates of the layer thickness of adsorbed copolymers have been made. Polystyrene is not adsorbed from trichloroethylene and does not stabilize dispersions of precipitated silica. A random copolymer having 1% 2-vinylpyridine units is adsorbed but shows very little steric stabilization. Random copolymers of 2-vinylpyridine content greater than 10% and AB block copolymers of more than 6% 2-vinylpyridine behave very similarly in respect both of the quantity adsorbed and in their ability to stabilize silica suspensions. Layer thickness does not seem to depend on copolymer composition. Random copolymers with low to intermediate 2-vinylpyridine contents are better steric stabilizers in trichloroethylene than are the corresponding copolymers of methyl methacrylate with styrene: this is attributed in part to the longer sequences of adsorbable units in the vinylpyridine copolymers.     

Absorption of polymers at the solution–solid interface. XII. Stabilization of dispersed silica by absorbed styrene–methyl methacrylate copolymers

The ability of styrene–methyl methacrylate copolymers to stabilize silica dispersions has been investigated. Random, block, and graft copolymers covering the entire composition range have been employed in carbon tetrachloride, trichloroethylene, and benzene solutions. Equilibrium sediment volumes and dispersion turbidities provide adequate and concordant estimates of stabilization efficiency. Polystyrene is not adsorbed by precipitated silica from trichloroethylene or benzene and does not stabilize dispersions in these liquids; although adsorbed from carbon tetrachloride, there is no stabilization. Poly(methyl methacrylate) is an efficient dispersion stabilizer, and its performance is independent of molecular weight over a wide range. Random copolymers having styrene contents in excess of ca. 60% do not stabilize in trichloroethylene but do so in carbon tetrachloride, although well adsorbed in both cases. With this major exception, and that of a low-styrene graft copolymer in carbon tetrachloride, copolymers of all structures and compositions stabilize well, better than poly(methyl methacrylate) in the solvents examined. A substantial degree of surface coverage is necessary for optimum stabilization. Subsidiary solution adsorption and layer thickness measurements are also reported.     

Adsorption of toluene-soluble polymers at the toluene–water interface

The adsorption of several toluene-soluble polymers at the toluene–water interface has been investigated by using the duNouy ring method of measuring interfacial tension γT /W . Polystyrene and poly(ethylene-co-vinyl acetate) (11.1 mole-% vinyl acetate) have little affinity for this interface at 29°C, but poly(methyl methacrylate) (PMMA) (M?_n = 420,000) and ethyl cellulose (EC) (M?_n = 50,100; 49.1% ethoxyl) adsorb significantly at concentrations as low as 1.0 × 10^?4 g/100ml. A plot of interfacial tension lowering versus initial logarithm of initial bulk phase polymer concentration is linear from 1.0 × 10^?4 to 1.0 × 10^?1 g/100 ml for EC and 1.0 × 10^?4 to 1.0 × 10^?2 g/100 ml for PMMA. When the PMMA concentration increases to 1.15 × 10^?1 g/100 ml, its adsorption behavior changes markedly. Prolonged time effects occur and adsorption becomes dependent upon dissolved water content of the toluene prior to formation of the toluene/water interface. Such effects are not observed with the other solutions studied. Increasing temperatures have variable effects on values of γT /W for the polymer solutions studied. Experiments with various polymer mixtures indicate that the polymer lowering T /W the most is preferentially adsorbed at the toluene–water interface and rapidly displaces less strongly adsorbed polymers.     

Adsorption of polymers at the solution-solid interface. VIII. Competitive effects in the adsorption of polystyrenes on silica

The adsorption behavior on silica of some polystrenes of moderate molecular weight distribution, both singly and in mixtures, has been examined. The adsorption isotherms indicate that, in both a good solvent (trichloroethylene) and under theta conditions, the species of higher molecular weight is preferentially adsorbed at or near full surface coverage, but that the smaller adsorbate has an improved opportunity for adsorption at low surface coverage. The use of tritiated adsorbates substantiate the isotherm data in cyclohexane solution.     

Adsorption of polymers at the solution-solid interface

Summary The adsorption of ethylene-vinyl acetate copolymer which consists of two different adsorption energy segments from solution onto glass sphere was studied. The adsorption depends on molecular weight and the constant obtained by application ofUllman's equation is decreased with the increase of molecular weight. The molecular weight dependence of adsorption suggests that the polymer chain adsorbed at solution-solid interface consist of sequences and loop chains. The relation between maximum adsorption and area occupied with adsorbed polymer chain from various solution was discussed, and the solvent dependence of maximum adsorption was explained in the difference of polymer solubility.

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Zusammenfassung Die Adsorption von Äthylen-Vinylacetat-Copolymeren, die aus zwei unterschiedlichen Segmenten hinsichtlich der Adsorptionsenergie bestehen, aus der Lösung an Glaskugeln wurde untersucht. Die Adsorption hängt vom Molekulargewicht ab; und die Konstante , erhalten durch Anwendung derUllmanschen Gleichung, nimmt mit der Zunahme des Molekulargewichts ab. Die Molekulargewichts-Abhängigkeit der Adsorption läßt vermuten, daß die Polymerketten, in der Grenzfläche adsorbiert, aus Sequenzen und Schleifen bestehen. Die Beziehungen zwischen maximaler Adsorption und mit adsorbierter Polymerketten besetzter Fläche aus verschiedener Lösung wird diskutiert und die Lösungsmittel-Abhängigkeit der maximalen Adsorption wurde aus dem Unterschied der Polymer-Löslichkeit erklärt.

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With 7 figures and 3 tables     

Adsorption of polymers at the solution-solid interface. VI. Polyacids on nylon powder

The adsorption of some polyacids, principally poly(acrylic acid), on nylon powder has been studied. In aqueous solutions at low pH the adsorption behavior of poly(acrylic acid) is controlled by adsorbate coil dimensions rather than by electrostatic effects. Less adsorption takes place from methanol solutions but the process is much more rapid than from water. Above a critical value, increase of adsorbate molecular weight leads to a reduced adsorption, the effect being particularly evidenced by aqueous solutions. Model compounds (propionic and glutaric acids) are rapidly adsorbed from both methanol and water, but give low specific absorptions. Adsorption of poly(acrylic acids) and model compounds, is reduced, but not eliminated, by modification of the nylon adsorbent through acetylation or methoxymethylation. The adsorption of poly(acrylic acid) on nylon is not readily reversible; however, partial neutralization will release preadsorbed poly(acrylic acid) from nylon powder. The adsorption behavior of copolymers of acrylic acid with N-vinylpyrrolidone is reported, as are brief studies on some other homopolyacids. The results are generally interpreted on the basis of sorption of the macromolecules into a swollen, flexible adsorbent.     

Adsorption of interacting oligomers and polymers at an interface

We discuss in a qualitative way the physical background of a recently developed polymer adsorption theory, in which all the possible chain conformations for interacting chain molecules near an adsorbing interface are taken into account. Any conformation is described as a step-weighted random walk in a lattice. Each step is weighted according to a segmental weighting factor that contains the adsorption energy (for segments in contact with the surface), the entropy of mixing, and the attraction or repulsion between segments and solvent molecules. A suitable computing method is used to calculate the contribution of all chain conformations to the concentration profile, to the adsorbed amount, to the fraction of trains, loops and tails, to the layer thickness, etc. The theory is valid for any chain length and any concentration in the solution.Results for various chain lengths are given. Oligomers have a low affinity for the surface, whereas polymer adsorption isotherms are of the well known high affinity type. Three concentration regimes can be distinguished. In (extremely) dilute solutions the molecules on the surface adsorb as isolated chains (the Henry region).     

Selective adsorption behavior of polymer at the polymer–nanoparticle interface

Coarse‐grained molecular dynamics simulations are used to investigate the adsorption behavior of monodisperse and bidisperse polymer chains on the nanoparticle (NP) surface at various polymer–NP interactions, chain lengths, and stiffness. At a strong polymer–NP interaction, long chains preferentially occupy interfacial region and squeeze short chains out of the interfacial region. Semiflexible chains with proper stiffness wrap NPs dominantly in a helical fashion, whereas fully flexible chains constitute the surrounding matrix. As chain stiffness increases, the results of the preferential adsorption are the opposite. The chain‐length or chain‐stiffness‐induced selective adsorption behavior of polymer chains in the polymer–NP interfacial region relies on a delicate competition between entropic and enthalpic contributions to the total free energy. These results could provide insights into polymer–NP interfacial adsorption behavior and guide the design of high‐performance nanocomposites. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016 , 54, 1829–1837     

Adsorption of methylmethacrylate-vinylferrocene copolymers at the solution/solid interface

A series of methylmethacrylate–vinylferrocene random copolymers was synthesized and characterized. Their adsorption from toluene and chloroform was measured onto pyrogenic silicas. The level of adsorption depended on the solvent, the surface area of the adsorbent, and the copolymer composition. Thus, an inverse adsorption-solubility relationship for toluene and chloroform was observed. However, in solvents such as tetrahydrofuran, 2-butanone, and cyclobutanone, which have strong interaction with silica, this trend was not evident. The compositional dependence of the adsorption of these copolymers in toluene and chloroform is similar. Initially, adsorption tends to increase with the vinylferrocene content in the polymer, and at equimolar copolymer compositions the adsorption reaches a maximum which is followed by a decrease in the adsorption values at high vinylferrocene contents. Gel permeation chromatography(GPC) measurements allowed us to conclude that high molecular weight polymer was preferentially adsorbed.     

Adsorption of oligooxypropylenated amines at the aqueous solution—air interface: Homologous series of piperidine and morpholine derivatives

The surface tension isotherms for pure oligooxypropylenated piperidine and morpholine at the aqueous solution—air interface were determined and interpreted. The surface excess concentration, Γ, the surface area per molecule, A, and the standard free energy of adsorption, ΔG°, were calculated according to a new empirical adsorption equation. The standard free energy contribution for the oxypropylene group (PO) in morpholine derivatives,ΔG° (PO) = −3.34 kJ mol⁻¹, is substantially lower than that for the PO group located in the piperidine derivatives, i.e. ΔG° (PO)= −3.12 kJ mol⁻¹.     

Adsorption and surface-induced self-assembly of surfactants at the solid–aqueous interface

Increasing insight into the interfacial behaviour of surfactants has emerged during the past few years. Important advances in this area are largely due to the use of surface-specific techniques like ellipsometry, neutron reflectivity, fluorescence spectroscopy, and atomic force microscopy (AFM) for in situ studies of surfactant layer properties. This review covers recent developments in the area which have contributed to the current understanding of adsorption mechanisms and interfacial structures.     

A diffuse‐interface modeling for liquid solution–solid gel phase transition of physical hydrogel with nonlinear deformation

A diffuse‐interface model is presented in this paper for simulation of the evolution of phase transition between the liquid solution and solid gel states for physical hydrogel with nonlinear deformation. The present domain covers the gel and solution states as well as a diffuse interface between them. They are indicated by the crosslink density in such a way that the solution phase is identified as the state when the crosslink density is small, while the gel as the state if the crosslink density becomes large. In this work, a novel order parameter is thus defined as the crosslink density, which is homogeneous in each distinct phase and smoothly varies over the interface from one phase to another. In this model, the constitutive equations, imposed on the two distinct phases and the interface, are formulated by the second law of thermodynamics, which are in the same form as those derived by a different approach. The present constitutive equations include a novel Ginzburg–Landau type of free energy with a double‐well profile, which accounts for the effect of crosslink density. The present governing equations include the equilibrium of forces, the conservations of mass and energy, and an additional kinetic equation imposed for phase transition, in which nonlinear deformation is considered. The equilibrium state is investigated numerically, where two stable phases are observed in the free energy profile. As case studies, a spherically symmetrical solution‐gel phase transition is simulated numerically for analysis of the phase transition of physical hydrogel.     

Effect of surfactant structure on the adsorption of carboxybetaines at the air–water interface

In order to study the effect of charge on the adsorption of surfactants at the air–water interface, two carboxybetaines have been synthesized with different number of separation methylenes between their charged groups. After purification and structure confirmation, the equilibrium and dynamic surface tensions were measured as a function of surfactant concentration for both the cationic and neutral forms of the surfactant molecules. The effect of ionic strength on the adsorption process was also studied. The equilibrium surface tension values were interpreted according to the Langmuir model and the dynamic surface tension data, converted to surface concentration by the Langmuir parameters, are consistent with the assumption of diffusion control over the range of surfactant concentrations studied. The diffusion coefficients show a progressive decrease in the rate of adsorption when the number of methylene units between the betaine charged groups increase.     

Adsorption kinetics at the solid/solution interface: statistical rate theory at initial times of adsorption and close to equilibrium

The kinetics of solute adsorption at the solid/solution interface has been studied by statistical rate theory (SRT) at two limiting conditions, one at initial times of adsorption and the other close to equilibrium. A new kinetic equation has been derived for initial times of adsorption on the basis of SRT. For the first time a theoretical interpretation based on SRT has been provided for the modified pseudo-first-order (MPFO) kinetic equation which was proposed empirically by Yang and Al-Duri. It has been shown that the MPFO kinetic equation can be derived from the SRT equation when the system is close to equilibrium. On the basis of numerically generated points ( t, q) by the SRT equation, it has been shown that we can apply the new equation for initial times of adsorption in a larger time range in comparison to the previous q vs radical t linear equation. Also by numerical analysis of the generated kinetic data points, it is shown that application of the MPFO equation for modeling of whole kinetic data causes a large error for the data at initial times of adsorption. The results of numerical analysis are in perfect agreement with our theoretical derivation of the MPFO kinetic equation from the SRT equation. Finally, the results of the present theoretical study were confirmed by analysis of an experimental system.     

Adsorption kinetics of octylphenyl ethers of poly(ethylene glycol)s on the solution—air interface

We studied the dynamic surface tension of aqueous solutions of Triton X-100 and Triton X-405 by the maximum bubble pressure and the inclined plate methods in the lifetime range from 0.001 s up to 10 s. It is established that in the region of large and ultimately small surface pressure and time the adsorption follows diffusion kinetics, but in the region of intermediate values of lifetime and surface pressure both the surfactants decrease the surface tension faster than predicted by the existing diffusion theory. We offer a model that provides for the ability of poly(ethylene glycol) chains to adsorb on the water-air interface and to change the area that a molecule occupies on the surface. For this model we achieve full coincidence of the measured values and the values calculated according to the diffusion theory of the dynamic surface tension.

It is ascertained that the Triton X-405 molecule can exist in the surface layer in different states: with the poly(ethylene glycol) chain fully expanded or with it partially or fully submerged in solution. The first state is most probable at surface pressures less than 5 mN m⁻¹, and the second is probable at a pressure of about 8–10 mN m⁻¹. At pressures larger than 15–20 mN m⁻¹, the poly(ethylene glycol) chain is fully submerged in the solution. The Triton X-100 molecule can also expand its poly(ethylene glycol) chain at low pressures and fully submerges it in the solution at higher values of the surface pressure.