Evidence for Polyelectrolyte/Ionomer Behavior in the Collapse of Polycationic Gels

Starodoubtsev, S. G.; Khokhlov, Alexei R.; Sokolov, Eugene L.; Chu, Benjamin

doi:10.1021/ma00115a027

Cited by 104 publications

(104 citation statements)

References 8 publications

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“…39 It is a general observation, as also suggested by theoretical considerations, that the interaction between a polyelectrolyte and an oppositely charged surfactant becomes stronger as the polyion linear charge density increases; this is inter alia borne out in cac values and in phase diagrams. [41][42][43][44] Our observations are thus contrary to expectations. There are two possible explanations for why simple electrostatic considerations fail.…”

Section: Resultscontrasting

confidence: 99%

Interaction between DNA and Cationic Surfactants: Effect of DNA Conformation and Surfactant Headgroup

et al. 2008

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The interactions between DNA and a number of different cationic surfactants, differing in headgroup polarity, were investigated by electric conductivity measurements and fluorescence microscopy. It was observed that, the critical association concentration (cac), characterizing the onset of surfactant binding to DNA, does not vary significantly with the architecture of the headgroup. However, comparing with the critical micelle concentration (cmc) in the absence of DNA, it can be inferred that the micelles of a surfactant with a simple quaternary ammonium headgroup are much more stabilized by the presence of DNA than those of surfactants with hydroxylated headgroups. In line with previous studies of polymer-surfactant association, the cac does not vary significantly with either the DNA concentration or its chain length. On the other hand, a novel observation is that the cac is much lower when DNA is denaturated and in the single-stranded conformation, than for the double-helix DNA. This is contrary to expectation for a simple electrostatically driven association. Thus previous studies of polyelectrolytesurfactant systems have shown that the cac decreases strongly with increasing linear charge density of the polyion. Since double-stranded DNA (dsDNA) has twice as large linear charge density as single-stranded DNA (ssDNA), the stronger binding in the latter case indicates an important role of nonelectrostatic effects. Both a higher flexibility of ssDNA and a higher hydrophobicity due to the exposed bases are found to play a role, with the hydrophobic interaction argued to be more important. The significance of hydrophobic DNA-surfactant interaction is in line with other observations. The significance of nonelectrostatic effects is also indicated in significant differences in cac between different surfactants for ssDNA but not for dsDNA. For lower concentrations of DNA, the conductivity measurements presented an "anomalous" feature, i.e., a second inflection point for surfactant concentrations below the cac; this feature was not displayed at higher concentrations of DNA. The effect is attributed to the presence of a mixture of ss-and dsDNA molecules. Thus the stability of dsDNA is dependent on a certain ion atmosphere; at lower ion concentrations the electrostatic repulsions between the DNA strands become too strong compared to the attractive interactions, and there is a dissociation into the individual strands. Fluorescence microscopy studies, performed at much lower DNA concentrations, demonstrated a transformation of dsDNA from an extended "coil" state to a compact "globule" condition, with a broad concentration region of coexistence of coils and globules. The onset of DNA compaction coincides roughly with the cac values obtained from conductivity measurements. This is in line with the observed independence of cac on the DNA concentration, together with the assumption that the onset of binding corresponds to an initiation of DNA compaction. No major changes in either the onset of compaction or complete compaction...

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Section: Resultscontrasting

confidence: 99%

Interaction between DNA and Cationic Surfactants: Effect of DNA Conformation and Surfactant Headgroup

et al. 2008

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“…It can be expected that the aforementioned transition from the polyelectrolyte to the ionomer state will greatly depend on the counterion size, which can markedly affect the formation of ion pairs [14]. So far, the dual polyelectrolyte-ionomer behavior was experimentally studied in the presence of lithium and sodium ions ensuring a substantial energy gain upon the formation of ion pairs.…”

Section: Introductionmentioning

confidence: 99%

Dual polyelectrolyte-ionomer behavior of poly(acrylic acid) in methanol: 1. Salt-free solutions

2004

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The behavior of poly(acrylic acid) (PAA) partly neutralized with tetramethylammonium hydroxide in methanol was studied by the viscometry, 1 H NMR spectroscopy, light scattering, and conductivity methods. It was shown that, when the degree of PAA neutralization increases from 0.1 to 0.2, a transition from a polyelectrolyte to ionomer state occurs. This transition is caused by the formation of ion pairs due to the binding of counterions with the charged groups of the polymer chain and is accompanied by a macromolecule collapse. Collapsed macromolecules aggregate. At degrees of neutralization above 0.4, the restored polyelectrolyte state is accompanied by polymer swelling. The data obtained are qualitatively explained.

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“…The ratio between these two forms of counterions is governed by the balance between the counterion translational entropy, which facilitates the dissociation of ion pairs, and the formation energy of ion pairs between the charged groups of a macromolecular chain and the counterions [3][4][5][6][7][8][9][10]. The addition of a low-molecular-weight salt decreases the gain in the translational entropy of polymer counterions; hence, it can be expected that the addition of low-molecular-weight salt will promote the transition from the polyelectrolyte to the ionomer state.…”

Section: Introductionmentioning

confidence: 99%

Dual polyelectrolyte-ionomer behavior of poly(acrylic acid) in methanol: 2. Salt solutions

Volkov¹,

Филиппова²,

Khokhlov³

2004

Colloid J

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The influence of tetramethylammonium chloride on a polyelectrolyte-ionomer behavior of poly(acrylic acid) (PAA) partly neutralized with tetramethylammonium hydroxide in methanol was studied by the viscometry and conductivity methods. It was shown that the addition of a small amount of this low-molecular-weight salt decreases the size of macromolecules in the polyelectrolyte state. When the salt concentration rises, the tendency toward formation of ion pairs is enhanced and the ionomer state becomes thermodynamically more advantageous than the polyelectrolyte state. As a result, macromolecules are transformed into the ionomer state at degrees of polymer neutralization corresponding to the polyelectrolyte behavior of salt-free solutions.

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Evidence for Polyelectrolyte/Ionomer Behavior in the Collapse of Polycationic Gels

Cited by 104 publications

References 8 publications

Interaction between DNA and Cationic Surfactants: Effect of DNA Conformation and Surfactant Headgroup

Interaction between DNA and Cationic Surfactants: Effect of DNA Conformation and Surfactant Headgroup

Dual polyelectrolyte-ionomer behavior of poly(acrylic acid) in methanol: 1. Salt-free solutions

Dual polyelectrolyte-ionomer behavior of poly(acrylic acid) in methanol: 2. Salt solutions

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