Probe diffusion from dilute to concentrated in polyelectrolyte solution: salt effect

The adsorption behaviors between a positively charged poly(allyamine) hydrochloride (PAH) matrix and negatively charged sulfate polystyrene (PS) particle probe were investigated using dynamic light scattering (DLS) and fluorescence photobleaching recovery (FPR) with reference to the matrix and salt concentration. The system experienced a steep decrease of diffusion (flocculation) under dilute conditions and a gradual decrease above semidilute concentrations. The fluorescence photobleaching recovery and viscometry experiments revealed that the probe behaviors in the polyelectrolyte solution were strongly affected by the coil overlap concentration (0.5 g/L poly(allyamine) hydrochloride). Near the coil overlap concentration, the hydrodynamic radius representing the entanglement dimension of the matrix was approximately 30 nm; however, at higher concentrations the radius gradually decreased, suggesting a transition toward a network structure. In this system, the salt performed two roles: (1) reinforcing the electrostatic interaction, and (2) preventing electrostatic interaction between the probe and the matrix.     

Molecular recognition phenomena in polyelectrolyte systems

The term “molecular recognition” is commonly used to describe various specific interactions, sometimes being not well defined. Let's assume that some species A can separately interact with either species B₁, or B₂, (or B₃, B₄ etc.) forming A·B₁, or A·B₂, (or A·B₃, or A·B₄ etc.) complexes. Here we say “recognition” assuming selective complexation of A with B₁ in the mixture containing also B₂ (B₃, B₄… etc.). At the same time it means discrimination of all other B species except B₁.     

Revisiting some phenomena in polyelectrolyte solutions

This review deals with the counterion distribution around rod‐shaped polyions, the reaction kinetics in polyelectrolyte solutions, the anomalous behavior of poly(methacrylic acid), and the formation of pearl‐necklace‐like structures of polyelectrolytes in poor solvent media. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 1080–1086, 2002     

Electrokinetic phenomena at grafted polyelectrolyte layers

During the last decades the electrokinetic theory of Smoluchowski (Z. Phys. Chem. 92 (1918) 129) was extended to be applicable for soft surfaces (grafted polyelectrolyte layers (PL), biological and artificial membranes, etc.) by either using the Debye approximation or numerical solutions. In the theory of Ohshima (Colloids Surf. A 103 (1995) 249) the nonlinearized Poisson-Boltzmann (PB) equation for thick and uniform PL is solved analytically and a general hydrodynamic equation is derived in an integral form. These advantages in the theory of Ohshima provided a base for the further development of a generalized electrokinetic theory for soft surfaces. In his theory the final equation for the electroosmotic (electrophoretic) velocity is specified for the case of the complete dissociation of ionic sites within PL. Accordingly, the equation may be used only if the difference between pK and pH is very large. However, it turned out that an analytical solution of the nonlinearized PB equation for thick PL is possible for any degree of dissociation. This was achieved using the approximation of excluded coions if the absolute value of the reduced Donnan potential is larger than 2 and due to the simplification in the case of weak dissociation, when the absolute value of the reduced Donnan potential is less than 2. Combining this generalized double layer (DL) theory for PL and the theory of Ohshima enables to obtain an analytical equation for electroosmosis for the general case of any degree of dissociation. This equation creates for the first time a theoretical base for the interpretation of electrokinetic fingerprinting (EF) for the characterization of soft surfaces.     

Relaxation phenomena in critical microemulsion systems

We discuss extensive sets of experimental data including static and dynamic light scattering, ultrasonic velocity measurements and high and low frequency dielectric relaxation, taken in the vicinity the critical point of a ternary microemulsion system. Upon approaching the critical point we observed a slowing down of the dielectric relaxation time and of the first cumulant of the time-dependent droplet density correlation function C²(t) which shows a non-exponential behavior at long time. These features can be well acccounted for by assuming that the microemulsion system is made of polydispersed transient fractal aggregates having a fractal dimension d_f=2.5 and a polydispersity index τ=2.2.     

Relaxation spectra of concentrated polystyrene solutions

The relaxation modulus G(t) and the stress decay after cessation of steady shear flow were measured on concentrated solutions of polystyrenes in diethyl phthalate. Ranges of concentration c and molecular weight M of the polymer were from 0.112 to 0.329 g/ml and from 1.23 × 10⁶ to 7.62 × 10⁶, respectively. The relaxation spectrum H(τ) as calculated from G(t) for the solution of very high M was found to be composed of two parts. One, at relatively short times, was a broad distribution (plateau zone) with height proportional to c². The second, at the long-time end, was very sensitive to concentration and gave rise to a maximum in H(τ) for very high concentrations. The behavior of H(τ) at long times was examined quantitatively by evaluating the longest relaxation time τ₁⁰ and the corresponding relaxation strength G₁⁰ from G(t) and from the stress decay function, on the assumption of a discrete distribution of relaxation times at long times. The longest relaxation time was approximately proportional to M^3.5, even at relatively low concentrations where the zero-shear viscosity was not proportional to M^3.5. The strengths of relaxation modes with the longest few relaxation times are proportional to the third power of concentration.     

Forces between interfaces in concentrated nanoparticle suspensions and polyelectrolyte solutions

This article provides an overview of interactions between charged interfaces across concentrated suspensions of charged nanoparticles or solutions of polyelectrolytes. These systems bear many similarities. We distinguish the like-charged and oppositely charged situations. In the like-charged situation, a layered structure in the proximity of the interface is formed. This structure induces a strongly repulsive energy profile at shorter distances, which originates from a gap that is free of nanoparticles or polyelectrolytes. At larger distances, the profile becomes oscillatory. This energy profile can be quantified with a simple model, which distinguishes the near-field region and the far-field region. The parameters entering the model show characteristic scaling relations. In the oppositely charged situation, a saturated, tightly bound layer at the interface forms. This layer leads to a charge reversal of the interface and induces a similar layered structure as in the like-charged case.     

Laser-Induced formation of transient polyelectrolyte in solution

Ionic photodissociation of N-ethylcarbazole and poly(N-vinylcarbazole) quenched with dimethylterephthalate was investigated by nanosecond laser photolysis. In the case of the polymer system about a tenth of the carhazole chromophores is ionized by intense laser excitation, which indicates photo-induced formation of a transient polyelectrolyte.     

Relaxation phenomena of hydrolyzed polyvinylamine molecules adsorbed at the silica/water interface II. Saturated heterogeneous polymer layers

Surface area exclusion chromatography (SAEC) was employed to determine the individual relaxation of polymer molecules within a saturated heterogeneous layer composed of two polymers of different molecular characteristics. The investigations focused on three systems differing in molecular weight and/or hydrolysis grade. The molecular relaxation process was determined to be different within the heterogeneous layer when compared with the behavior of the same polymer in the homogeneous layer. The modifications in the relaxation process of a given polymer were imposed by the interfacial characteristics of the second polymer. Finally, in heterogeneous layers, the relative variation of the interfacial area of the two polymers is expressed in a single relationship.     

Relaxation phenomena in latex polymers modified with water-soluble phthalocyanine

The relaxation properties of polymer composites based on latex styrene-alkyl methacrylate polymers and water-soluble 2,3,9,10,16,17,23,24-octa[(3,5-biscarboxy)-phenoxy]phthalocyanine are studied in the temperature range from ?150 to +250°C. Characteristic mechanical loss maxima are observed on the inner friction spectra of unmodified and modified polymers corresponding to various patterns of intermolecular mobility and local and segmental types of intermolecular interactions. The modification of the polymers is accompanied by decreases in their glass-transition temperatures. This effect may be explained by a decrease in the intermolecular interactions of copolymer units in the presence of phthalocyanine.     

Boundary phase stability and critical phenomena in higher order solid solution systems II

The thermodynamic treatment of double-pseudobinary solutions of the type (A _xB_y) _{r o}(M _uN_v) _{s o} presented in a preceding publication was extended to include the conditions defining the critical points for the asymmetric case (r _os _o) and approximations for the spinodal and binodal surface near the critical solution point.Closed solutions for the coordinates of the critical points were obtained only for systems with ideal mixing behavior, and the isothermal binodal and spinodal near the critical solution point in such systems are adequately approximated by circles and ellipses, respectively. An axes ratio of is nearly independent of the relative sublattice abundance and the major effect of changes in the ratios _o/r _o is a rotation of the binodal by an angle tg .The principal features of nonideal regular systems for temperatures close to the critical solution point are described by expressions derived from small term expansions of the conditional equations, but generalizations are not possible to the same extent as for the case with ideal boundary systems. The results are discussed and the application of the equations demonstrated on model examples.Mit 6 Abbildungen     

Relaxation phenomena in dense,glassy membranes prepared from a polymer solution,monitored by changes in dielectric properties

The drying of a solvent-cast polymer film is monitored in a non-invasive way, by measuring the changes in time of dielectric properties, using interdigitated or comb electrodes. Experimentally, the vitrification of the polymer solution is observed at a distinct time, followed by the slow evaporation of solvent from the glassy state. As the solvent diffusion coefficient is a strong function of the concentration in the polymer film, removal of residual solvent proceeds at a self-decreasing rate. With a simple model, solvent mass transfer coefficients in the glassy state are determined from the experiments. It is shown that volume relaxation may be slow compared to the drying process, when preparing thin solvent-cast membranes and using solvents that diffuse relatively fast through the glassy polymer film.     

Time-dependent conformational changes of polyelectrolyte complexes in solution

Changes in the conformation of the polyelectrolytes when contacted with oppositely charged polyelectrolytes or when subjected to shifts in solution conditions (pH), have been studied in this work along with reversibility of the changes using fluorescence spectroscopy. While changes due to both of the above are marked, they are measurably different from each other. Thus, the extent of coiling of the complexes formed between the anionic polyelectrolyte, maleicacid anhydride–propene and the cationic polyelectrolytes was much higher than that achieved by the change in pH alone. Also, while the changes due to pH shifts were fast and reversible, that due to complexation between oppositely charged ones involved first a rapid uncoiling followed by slow recoiling to a new structure. Interestingly, shifting the coiled conformation to an even more coiled one resulted in a new reversible state, but shifting to a stretched state by complexation led to a somewhat irreversible structure. Also maximum interaction obtained between the anionic and one cationic polyelectrolyte was markedly higher than that between the former and another cationic polymer. These observations using fluorescence spectroscopy was consistent with that obtained by the potentiometric titration. The study clearly shows the importance of the manner in which the polyelectrolytes are equilibrated to desired solution conditions. These results are interpreted here in terms of deprotonation/protonation of the polyelectroytes upon pH change and complexation with oppositely charged ones resulting in screening of charges as well as stiffening.     

Relaxation phenomena in PPG model networks near the glass-rubber transition

The viscoelastic and dielectric properties of polypropyleneglycol (PPG)-tris-(4-isocyanatophenyl)thiophosphate (Desmodur^®) model networks have been studied. Attention was focused on the relaxation behaviour near the glass transition. Two relaxation mechanisms were observed in the glass transition range, one due to the PPG chain segments and one due to the less mobile cross-link moieties, i.e. the networks show motional heterogeneity. Mechanically only the first mechanism was observed while dielectrically both mechanisms were found. This motional heterogeneity has a profound effect on the dependence of the glass transition temperature on the composition of these networks. The effect of the stage of cure on the temperature of maximum loss and the magnitude of these two relaxation mechanisms was studied dielectrically. Finally, the effect of exchanging the cross-linker molecules with chain extender molecules with similar structure, thus lowering the cross-link density, was studied.     

Zur Theorie der Relaxation und Platzwechselerscheinungen. II

Zusammenfassung Es wird gezeigt, wie die Wahrscheinlichkeitsverteilung für die Potentialwerte innerhalb eines Festk?rpers oder einer Flüssigkeit berechnet werden k?nnen. Damit wird die in Teil I dieser Arbeit aufgestellte Theorie zu einem formalen Abschlu? gebracht. Zwischen Diffusionskonstante und Relaxationszeit ergibt sich ein einfacher Zusammenhang, der als Kriterium zur Identifizierung platzwechselnder Teilchen dienen kann.     

Relaxation phenomena and electrical conductivity of some polymeric films

Electrical conduction in sandwich samples of polyacrylonitrile (PAN) or copolymer of acrylonitrile with butadiene between silver has been studied, measuring the dependence of current on the applied field, temperature and time. The conduction mechanism depends on the polymer type. A polarization contribution is suggested in the conduction mechanism at high temperatures, besides Schottky emission in the case of PAN and the simple carrier jump model in the case of NBR at room temperature. The temporal current variation is explained in terms of dipole orientation. The mobility and charge carrier density are influenced by the applied field, temperature and film thickness.     

Relaxation phenomena associated with microwave pumping of rotational transitions

It is shown that the Bloch equations describing a two-level system in a radiation field can be extended to take proper account of the degenerate magnetic sublevels. By solving the equation for a J = 0 to J = 1 transition in a linear rotor we show that the saturated linewidth depends on the realignment time T₄ as well as on the usual T₁ and T₂. Further we show that the ratio T₁^*/T₂ which enters the saturated linewidth is not exactly unity, and that its deviation from unity is related to the rate of collisional transitions between the two pumped levels. Thus it may be possible to measure collision rates of astrophysical interest which could not be obtained in any other way. Some approximate formulae are derived assuming that only long-range interactions are present.     

Interactions between charged surfaces immersed in a polyelectrolyte solution

With grand canonical simulations invoking a configurationally weighted scheme, we have calculated interactions between charged surfaces immersed in a polyelectrolyte solution. In contrast to previous simulations of such systems, we have imposed full equilibrium conditions (i.e., we have included diffusive equilibrium with a bulk solution). This has a profound impact on the resulting interactions: even at modest surface charge densities, oppositely charged chains will, at sufficiently large separations, adsorb strongly enough to overcompensate for the nominal surface charge. This phenomenon, known as charge inversion, generates a double-layer repulsion and a free-energy barrier. Simpler canonical approaches, where the chains are assumed to neutralize the surfaces perfectly, will not capture this stabilizing barrier. The barrier height increases with the length of the polyions. Interestingly enough, the separation at which the repulsion becomes attractive is independent of chain length. The short chains here are unable to reach across from one surface to the other. We therefore conclude that the transition to an attractive regime is not provided by the formation of such "intersurface" bridges. With long chains and at large separations, charge inversion displays decaying oscillatory behavior (i.e., the apparent surface charge switches sign once again). This is due to polyion packing effects. We have also investigated responses to salt addition and changes in polyelectrolyte concentration. Our results are in qualitative and semiquantitative agreement with experimental findings, although it should be noted that our chains are comparatively short, and the experimental surface charge density is poorly established.