The many facets of polyelectrolytes and oppositely charged macroions complex formation (original) (raw)
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Oppositely Charged Polyelectrolytes. Complex Formation and Effects of Chain Asymmetry
The Journal of Physical Chemistry B, 2004
The formation of complexes in solutions of oppositely charged polyions has been studied by Monte Carlo simulations. The amount as well as the length, and thus, the absolute charge of one of the polyions have been varied. There is an increasing tendency to form large clusters as the excess of one kind of polyion decreases. When all polyions have the same length, this tendency reaches a maximum near, but off, equivalent amounts of the two types of polyions. When one kind of polyion is made shorter, the propensity to form large clusters decreases and the fluctuations in cluster charge increases. Simple free-energy expressions have been formulated on the basis of a set of simple rules that help rationalize the observations. By calculating cluster distributions in both grand canonical and canonical ensembles, it has been possible to show the extent of finite-size effects in the simulations.
Journal of Polymer Science Part A: Polymer Chemistry, 1989
Polyelectrolyte complex formation has been studied between oppositely charged polyelectrolytes, e.g., polyethylene-imine, polymethacrylic acid, and methacrylic acid-methacrylamide copolymer. Formation of complexes could be shown through several experimental techniques, e.g., viscometry, conductometry, potentiometry, and IR spectra. It is suggested that these complexes are perhaps formed as a result of electrostatic cooperative interaction and a "ladder-like" interaction is likely to be more favorable.
Polyelectrolyte complexation of two oppositely charged symmetric polymers: A minimal theory
The Journal of Chemical Physics
Interplay of Coulomb interaction energy, free ion entropy, and conformational elasticity is a fascinating aspect in polyelectrolytes (PEs). We develop a theory for complexation of two oppositely charged PEs, a process known to be the precursor to the formation of complex coacervates in PE solutions, to explore the underlying thermodynamics of complex formation, at low salts. The theory considers general degrees of solvent polarity and dielectricity within an implicit solvent model, incorporating a varying Coulomb strength. Explicit calculation of the free energy of complexation and its components indicates that the entropy of free counterions and salt ions and the Coulomb enthalpy of bound ion-pairs dictate the equilibrium of PE complexation. This helps decouple the self-consistent dependency of charge and size of the uncomplexed parts of the polyions, derive an analytical expression for charge, and evaluate the free energy components as functions of chain overlap. Complexation is o...
Polyelectrolyte complexes: mechanisms, critical experimental aspects, and applications
The polyelectrolyte complexes (PECs) are versatile formulations formed by electrostatic interactions between oppositely charged biopolymers. PECs have been investigated widely by the researchers to explore the virtues of this formulation viz. high biocompatibility, excellent biodegradability, low toxicity, cost-effective, environment-friendly, and energy-efficient production. The prime object of the present review is to present the prominent features of PECs including mechanism of PEC formation, structural models of PECs, interactions involved in PEC formation, steps involved in PEC fabrication, factors affecting the formation of PECs and applications of PECs. The patents pertaining to PECs have briefly been tabulated as well.
The Journal of Chemical Physics, 2001
Complexation of a long flexible polyelectrolyte (PE) molecule with oppositely charged spherical particles such as colloids, micelles, or globular proteins in a salty water solution is studied. PE binds spheres winding around them, while spheres repel each other and form almost periodic necklace. If the total charge of PE in the solution is larger than the total charge of spheres, repulsive correlations of PE turns on a sphere lead to inversion of the net charge of each sphere. In the opposite case when the total charge of spheres is larger, we predict another correlation effect: spheres bind to the PE in such a great number that they invert the charge of the PE. The inverted charge by absolute value can be larger than the bare charge of PE even when screening by monovalent salt is weak. At larger concentrations of monovalent salt, the inverted charge can reach giant proportions. Near the isoelectric point where total charges of spheres and PE are equal, necklaces condense into macroscopic bundles. Our theory is in qualitative agreement with recent experiments on micelles-PE systems.
Advances in Polymer Science, 2004
This chapter presents selected ideas concerning complexes that are formed either by oppositely charged polyelectrolytes or by polyelectrolytes and surfactants of opposite charge. The polyelectrolyte complexes (PECs), which are surfactant-free, form typical structures of a low degree of order such as the ladder-and scrambled-egg structures. In contrast, polyelectrolyte-surfactant complexes (PE-surfs) show a large variety of highly ordered mesomorphous structures in the solid state. The latter have many similarities to liquid-crystals. However, as a result of their ionic character, mesophases of PE-surfs are thermally more stable. Both, PECs and PE-surfs can be prepared as water-soluble and water-insoluble systems, as dispersions and nanoparticles. A stoichiometry of 1:1 with respect to their charges are found frequently for both. Structures and properties of PECs and PE-surfs can be tuned to a large extent by varying composition, temperature, salt-concentration etc. Drug-carrier systems based on PECs and PE-surfs are discussed. Examples are complexes of retinoic acid (PE-surfs) and DNA (PECs). A brief overview is given concerning some theoretical approaches to PECs and PE-surfs such as the formation of polyelectrolyte multilayers.
The mechanism of complex formation of two oppositely charged linear polyelectrolytes dispersed in a solvent is investigated by using dissipative particle dynamics (DPD) simulation. In the polyelectrolyte solution, the size of the cationic polyelectrolyte remains constant while the size of the anionic chain increases. We analyze the influence of the anionic polyelectrolyte size and salt effect (ionic strength) on the conformational changes of the chains during complex formation. The behavior of the radial distribution function, the end-to-end distance and the radius of gyration of each polyelectrolyte is examined. These results showed that the effectiveness of complex formation is strongly influenced by the process of counterion release from the polyelectrolyte chains. The radius of gyration of the complex is estimated using the Fox-Flory equation for a wormlike polymer in a theta solvent. The addition of salts in the medium accelerates the complex formation process, affecting its radius of gyration. Depending on the ratio of chain lengths a compact complex or a loosely bound elongated structure can be formed.
Soft Matter
The mechanism of complex formation of two oppositely charged linear polyelectrolytes dispersed in a solvent is investigated by using dissipative particle dynamics (DPD) simulation. In the polyelectrolyte solution, the size of the cationic polyelectrolyte remains constant while the size of the anionic chain increases. We analyze the influence of the anionic polyelectrolyte size and salt effect (ionic strength) on the conformational changes of the chains during complex formation. The behavior of the radial distribution function, the end-to-end distance and the radius of gyration of each polyelectrolyte is examined. These results showed that the effectiveness of complex formation is strongly influenced by the process of counterion release from the polyelectrolyte chains. The radius of gyration of the complex is estimated using the Fox-Flory equation for a wormlike polymer in a theta solvent. The addition of salts in the medium accelerates the complex formation process, affecting its radius of gyration. Depending on the ratio of chain lengths a compact complex or a loosely bound elongated structure can be formed.
Conformation of a polyelectrolyte complexed to a like-charged colloid
PHYSICAL REVIEW E, 2002
We report results from a molecular dynamics (MD) simulation on the conformations of a long flexible polyelectrolyte complexed to a charged sphere, both negatively charged, in the presence of neutralizing counterions in the strong Coulomb coupling regime. The structure of this complex is very sensitive to the charge density of the polyelectrolyte. For a fully charged polyelectrolyte the polymer forms a dense two-dimensional "disk", whereas for a partially charged polyelectrolyte the monomers are spread over the colloidal surface. A mechanism involving the overcharging of the polyelectrolyte by counterions is proposed to explain the observed conformations.