M. V. Motyakin

EFFECT OF POLYCARBONIC ACIDS ON THE MOLECULAR MOBILITY OF CATIONIC SURFACTANTS IN MICELLES

Abstract The rotational mobility of a spin probe in the micelles of alkyltrimethylammonium bromides and in their complexes with poly(acrylic acid) and poly(methacrylic acid) has been studied at pH 6. Formation of the polyelectrolyte–surfactant complexes (PSC) causes the decrease in the molecular mobility of surfactant ions in the PSC micelles as compared with the micelles of the free surfactant. It was found that the surfactant ion mobility in PSC micelles is almost independent of the complex composition and even its phase state. The chemical structure of the polyacid has little effect on the molecular mobility of the surfactant ions in the micelles of the complexes. It was shown that the rotational mobility of the surfactant ions in micelles depends on the hydrocarbon chain length of surfactant molecules. Increase in surfactant ion alkyl chain length causes the decrease of their molecular mobility in micelles. Dissociation of the ionic bonds between polyelectrolyte and the surfactant as a result of the increase in the concentration of NaCl in the solution leads to the enhancement of the mobility of the surfactant ions in PSC micelles. It was shown that solubilization of isopropyl alcohol in complex micelles leads to an increase of surfactant ion mobility even at a very low (

Structural-dynamic characteristics of matrices based on ultrathin poly(3-hydroxybutyrate) fibers prepared via electrospinning

Structural-dynamic analysis based on combined thermophysical and molecular mobility measurements via spin-probe ESR spectroscopy has been applied to films and fibrous matrixes based on poly(3-hydroxybutyrate). The dynamic behaviors of partially crystalline samples during deformation under conditions of electrospinning and cold rolling have been compared. The comparative results of the complex investigation of films and ultrathin fibers in the poly(3-hydroxybutyrate) matrix have shown that the electromechanical action leads to additional crystallization of the crystalline regions, spherulites, and lamellas in the polymer. The changes in the crystalline phase of the polymer are accompanied by an increase in the packing density of macromolecules in the intercrystalline space. With the use of the spin-probe ESR method, the effect of water and the oxidant ozone on the morphology of the amorphous phase of poly(3-hydroxybutyrate) ultrathin fibers has been determined. The measurements of the dynamics of spin-probe rotation in samples before and after cold rolling have shown that the additional orientation of poly(3-hydroxybutyrate) spherulites in a mechanical field results in stabilization of amorphous regions more resistant to the aggressive effects of ozone.

Macromolecular and morphological evolution of poly(styrene sulfonate) complexes with tetradecyltrimethylammonium bromide.

Macromolecular characteristics and morphology of water-soluble complexes between sodium poly(styrene sulfonate) (PSS) and tetradecyltrimethylammonium bromide have been followed as a function of surfactant-to-polymer charge ratio (S/P) to elicit possible changes in the complexation mechanism. As revealed by light scattering, shorter PSS (30 and 150 repeat units) yield multichain complexes while longer PSS (450 and 5000 repeat units) form single-chain species throughout 0 < S/P < 0.9. Irrespective of PSS chain length, the complexes exist in solution in a swollen coil conformation and undergo a compaction with S/P but never collapse into a globule. Even when the free PSS chain is too short to coil (30 repeat units), the complexes adopt a coiled conformation due to multichain aggregation. Morphological changes (manifested by a hypochromic shift in UV spectra of the complexes at S/P < 0.5 and an increase in the local surfactant mobility observed at S/P > 0.5 by ESR) strongly suggest a change in the formation mechanism of the complexes with a transition near S/P = 0.5.

Interaction of cationic monomer with sodium dodecyl sulfate in dilute aqueous solutions: ESR study

The effect of a cationic monomer (N,N,N,N-trimethyl[methacryloxyethyl]ammonium methyl sulfate) on the formation, structure, and local dynamics of associates resulted from the interaction of the monomer with sodium dodecyl sulfate in aqueous solutions was studied by ESR spectroscopy. In the presence of the monomer, micelles are formed at concentrations much lower than the CMC of the pure surfactant with the monomer molecules that form a condensed layer of counterions around a micelle of sodium dodecyl sulfate. The binding of surfactant micelles with the cationic monomer causes a significant decrease in the local molecular mobility of dodecyl sulfate ions.

Local mobility and structure of cationic amphiphilic diblock copolymer micelles in aqueous solutions

The local mobility and organization of micelles formed by the cationic diblock copolymer PS-poly(N-ethyl-4-vinylpyridinium bromide) in dilute aqueous solutions is studied by spin-probe ESR spectroscopy. Micelles composed of a hydrophobic PS core and a lyophilizing polyelectrolyte corona are prepared by two methods: dialysis from a nonselective solvent and direct dispersion of the diblock copolymer in water under long-term heating. Velocity-sedimentation studies and static and dynamic light-scattering measurements show that the micelles obtained by dialysis have smaller mean hydrodynamic sizes and weight-average molecular masses and are less polydisperse than micelles prepared by direct dispersion. The ESR spectra of spin probes localized in micelles of both types are found to be identical. This finding suggests that their local structure is independent of the dispersion procedure and molecular-mass characteristics. Probes are localized in the outer layer of the PS core near the core/shell boundary, and their local mobility is a factor of ∼2 higher than the local mobility of probes in the phase of the solid PS. It is inferred that the structure of the outer layer of the PS core in micelles is looser than the structure of PS in the solid phase. The localization sites of spin probes are partially penetrated by water.

Local mobility in network junctions of gels based on hydrophobically modified polyacrylamides

Spin-probe ESR spectroscopy is employed to study the local mobility in junctions of physical networks in gels of hydrophobically modified polyacrylamides. These junctions are formed owing to self-association of alkyl groups containing 12 carbon atoms. It is shown that, irrespective of the mode of covalent binding between the alkyl groups and the polymer backbone (via either ester or amide groups) and the degree of macromolecule blockiness, the local mobility in the gel network junctions is almost an order of magnitude lower than that in the hydrophobic core of a micelle of the low-molecular-mass surfactant sodium dodecyl sulfate.

ESR study of the fullerene C60 under axial and shear deformation

Abstract Electron spin resonance spectra of the fullerene C 60 were measured at pressures up to 4 GPa (40 kbar) and under shear deformation at ambient temperature. The ESR signal grows in intensity with pressure. The shear deformation transforms C 60 molecules to lower-symmetry structures.

Spin probes in micellar and polymer self-associating systems

The results of studies of micellar and self-associating polymer systems by spin probe ESR spectroscopy are summarized. The local dynamics and structures of low-molecular-weight micelles built of cationic surfactants bearing long alkyl chains (from C16 to C22), gels of hydrophobically modified polymers, polymer micelles, micellar complexes of nonionic surfactant (Brij58) with hydrogels based on polyacrylic acid, and associates formed in aqueous solutions of poly(diphenylenesulfophthalide) are discussed. Interest in these systems is caused by prospects of their practical use as carriers in drug delivery, in biotechnology, for the enhancement of oil production, and in other purposes.

Interaction between cationic monomer and sodium dodecyl sulfate in concentrated aqueous solutions: EPR spectroscopy and rotational viscometry

The interaction of a cationic monomer, trimethyl[methacryloxyethyl]ammonium methyl sulfate, with sodium dodecyl sulfate (SDS) has been studied in relatively concentrated solutions containing SDS (70–500 mM) and the monomer (from 7 mM to 2.5 M). The high concentrations of the components do not prevent the monomer from bonding to oppositely charged SDSs, which confirms the possibility in principle to polymerize ionic monomers through a template mechanism using micelles of oppositely charged surfactants as templates. The range of component ratios 0.5 ≤ [monomer]/[SDS] ≤ 2 is most promising for realization of the template mechanism of polymerization. The effect of SDS on the macroscopic and microscopic properties of the system significantly and to a maximum extent decreases upon a further rise in the relative concentration of the monomer.

Local mobility of micelles of new cationic surfactants and their interactions with hydrophobically modified polyacrylamides

The local dynamics and organization of micelles of new long-chain cationic surfactants with saturated hydrocarbon fragments (from C16 to C22) are investigated via the EPR spin-probe technique. The local mobility of spin probes in the hydrocarbon core of a micelle changes insignificantly, while the order parameter noticeably increases with lengthening of the hydrocarbon fragment of the surfactant molecule. The specific features of the interaction of the surfactants with network junctions of the gels formed by two types of hydrophobically modified polyacrylamides—either containing charged groups (sodium acrylate) in the backbone or lacking these groups—are studied. In both cases, the local mobility of network junctions of the gel increases after the introduction of the surfactant (C18). Moreover, for surfactant with a long alkyl group (C2), the microscopic viscosity of the gel based on the uncharged polymer decreases, although the local mobility of the network junctions increases. Possible causes of the observed specific features are discussed.