E. E. Makhaeva

Swelling behavior of polyelectrolyte gels in the presence of salts

The swelling behavior of weakly crosslinked polyelectrolyte gels based on sodium methacrylate (PMA) and diallyldimethylammonium chloride (DADMAC) in aqueous medium was studied in the presence of different types of salts (NaCI, arginine hydrochloride, cetylpyridinium chloride (CPC), sodium dodecyl sulfate (SDS), and sodium dodecylbenzenesulfonate (SDBS)). It is shown that, starting from some characteristic concentration of a salt, a further increase of the salt concentration results in the shrinking of the gels. This characteristic concentration is defined by the gel parameters (polymer concentration in the gel that is a function of the monomer concentration at the conditions of hydrogel synthesis) and does not depend on the kind of salt used, except for the system polyelectrolyte gel/oppositely charged surfactant (PMA-CPC and DADMAC-SDS or SDBS). It is shown that the initial rate of gel shrinking for all studied systems, including the system gel/oppositely charged surfactant, is determined by the salt concentration and the gel parameters. For the systems PMA-CPC and DADMAC-SDS the gel collapse is a two-step process.

Behaviour of poly(N-vinylcaprolactam) macromolecules in the presence of organic compounds in aqueous solution

Dynamic light scattering measurements have been performed for aqueous solutions of thermosensitive linear poly(N-vinylcaprolactam) (PVCa) macromolecules in the presence of NaCl and different water soluble amphiphilic organic compounds: pyrogallol (neutral amphiphilic compound), cetylpyridinium chloride (cationic surfactant) and sodium dodecylsulfate (anionic surfactant). A decrease in the macromolecular hydrodynamic diameter is observed upon addition of ionic surfactants (SDS, CPC) at low surfactant concentrations. This trend changes to an increase in the macromolecular hydrodynamic diameter at high surfactant concentration at temperatures below the temperature of polymer aggregation. This effect is in contrast with the behaviour of the systems of PVCa–non-ionic organic compounds (pyrogallol) and NaCl where we always observed the weak monotonic decrease of the hydrodynamic diameter with the increase in the concentration of organic compound, NaCl. The behaviour of ternary systems PVCa macromolecules–ionic surfactant–pyrogallol and PVCa macromolecules–ionic surfactant–NaCl was studied. The addition of pyrogallol leads to the suppression of the intermacromolecular aggregation induced by temperature increase that is still observed at low surfactant concentrations and to the decrease of macromolecular hydrodynamic diameter. Also, the addition of NaCl to the PVCa/ionic surfactant systems results in the increase of the macromolecular hydrodynamic diameter. It is speculated that these results are due to the suppression of the cross-linking role of surfactant aggregates upon the addition of NaCl and pyrogallol.

Small-angle X-ray scattering reveals hollow nanostructures in iota- and kappa-carrageenan/surfactant complexes

Complexes of polyelectrolyte gels with oppositely charged surfactants form ordered polymer matrices with unique structure properties, which can be used in a wide range of medical, chemical and physical applications. Ordered matrices made of natural components are of special interest for medical and biological purposes. In the present study, self-organised complexes of native - and -carrageenans formed with oppositely charged cetylpyridinium chloride (CPC) are prepared and structurally characterised using small-angle X-ray scattering (SAXS). Starting from the molar ratio CPC/(charge of carrrageenan) of 0.2, the carrageenan gel shrinks and ordered motifs in its internal structure are formed. The internal order in the sample is reflected by the Bragg peaks in the scattering patterns which permit to compute periodicity and characteristic sizes of the ordered regions. Moreover, strong central scattering appears and the calculated fractal dimensions indicate that these regions are organised in well defined clusters. The periodicity of the ordered motifs computed from the Bragg peaks in the scattering patterns corresponds to the width of the surfactant bilayer (about 4.0 nm) for all the complexes. The crystallite size ranges from 25 nm to 40 nm depending on the type of carrageenan and on the amount of CPC. A model of the ordered fragments is proposed whereby the carrageenan/surfactant bilayers are regularly packed at the walls of hollow cylindric clusters with the outer radius of about 8 nm and height 40 nm. More detailed ab initio models indicate that these particles are formed by bent worm-like substructures with the cross-section coinciding to the thickness of the carrageenan/CPC bilayer. Thanks to a higher charge density per monomer, -carrageenans form more regular structures than -carrageenans.

Polyampholyte gels: swelling, collapse and interaction with ionic surfactants

Abstract Two series of polyampholyte gels formed from sodium methacrylate and diallyldimethylammonium chloride with variable composition were synthesized in water and in aqueous salt solution. It is shown that the swelling properties of polyampholyte gels are directly related to their chemical structure, which is defined by the process of gel synthesis. The swelling ratio of the polyampholyte gels prepared in salt solution is large compared with the gels prepared in pure water i.e. the polyampholyte gels with balanced stoichiometry show minimal swelling. The interaction of the polyampholyte gels with ionic surfactants (cationic, cetylpyridinium chloride and anionic, sodium dodecylbenzenesulphonate) was studied. It was shown that for polyampholyte gels with an excess of the charges of one sign the addition of oppositely charged surfactant leads to the collapse of the gel. It was found that the efficiency of surfactants absorption is determined by the ratio of positive and negative charges in the chains of polyampholyte gels.

Metal colloid formation in the complexes of polyelectrolyte gels with oppositely charged surfactants

Abstract The interaction of Pt, Au and Ni ions with the complexes of cationic gel of polydiallyldimethylammonium chloride (PDADMACl) with two anionic surfactants: sodium dodecyl sulfate (SDS) and sodium dodecylbenzenesulphonate (SDBS) was investigated. After reduction of metal compounds by hydrazine-hydrate or sodium borohydride, colloidal particles of Pt, Au and Ni embedded in the body of the hydrogel were formed. It was found by small-angle X-ray scattering (SAXS) that when the PDADMACl/SDS complexes interact with metal ions, the nanostructures are disturbed and the degree of disordering depends on the type of metal compound. PDADMACl/SDBS complexes seem to be more stable towards metal ion incorporation. By SEM and AFM data it was shown that gold colloid formation is controlled by the ordering in the PDADMACl/SDS complex which prevents the aggregation of metal colloids.

ELECTROOSMOTIC TRANSPORT OF WATER IN POLYELECTROLYTE NETWORKS

SummaryThe phenomenon of contraction of polyelectrolyte gels under the influence of direct current is studied experimentally. It is shown that the number of water molecules per one ion of the electric current is very large N 103. This effect can be explained as electroosmotic transport of water molecules through the gel, which can be represented as an effective fine-porous medium with the diameter of pores equal to the mesh size of a network.

Synthesis, photophysical, and electrochromic properties of new triarylamino-containing polyphenylquinoxalines

New triarylamino-containing bis(α-diketones) are synthesized. On the basis of these compounds, a series of electrochromic organosoluble polyphenylquinoxalines with glass-transition temperatures of 224–315°C are prepared. All polymers intensively fluoresce in solutions and thin films with maxima at 535–600 and 530–560 nm, respectively. Cyclic voltammograms of polyphenylquinoxalines exhibit reversible redox properties in the range E 1/2 = 0.92–1.25 eV. It is shown that, after 15 cycles, all polymers preserve high stability and reversibility of electrochromic characteristics, but their color changes from yellow (neutral form) to wine red (oxidized form).

Complexes of polyelectrolyte hydrogels with organic dyes : Effect of charge density on the complex stability and intragel dye aggregation

The swelling behavior of polyelectrolyte gels based on poly(diallyldimethylammonium chloride) (copolymers of diallyldimethylammonium chloride and acrylamide with the variable composition) and poly(methacrylic acid, sodium salt) in the presence of organic water soluble dyes (alizarin, naphthol blue black, rhodamine) was studied. The collapse of the polyelectrolyte gels in the presence of oppositely charged dyes together with the effective absorption of dyes was observed. The shrinking degree and the dye absorption by the gel depend on the charges of the polymer network and the dye, and also on the dye concentration. Stability of the gel–dye complexes in a salt solution of NaCl and Al2(SO4)3 was studied. It was shown that the complex stability in the salt solution depends on the charge density of the polymer chains forming the gel. The increase of charge density of polymer generally leads to the enhancement of the complex stability. For the systems with the fraction of charged poly(diallyldimethylammonium chloride) monomer units above 0.5 the release of alizarin to the external solution of Al2(SO4)3 reservoir is practically completely suppressed. The obtained results show that oppositely charged dyes are generally from stable complexes with polyelectrolyte gels.

Effect of ionogenic groups on the collapse of thermosensitive gels

The effect of the different kinds of ionogenic groups of copolymers of N-isopropylacrylamide with sodium methacrylate, sodium vinylsulfonate, and diallyldimethylammonium chloride on the temperature-induced conformation transition from a swollen gel to a collapsed gel is studied. The presence of different kinds of ionogenic groups in a thermosensitive copolymer is shown to affect the temperature, collapse amplitude, and reversibility of the transition between the swollen gel and the collapsed gel.

AFM study of the structuration of an ionic surfactant and phenylalanine with κ-carrageenan

Local networks of κ-carrageenan adsorbed in the presence of an ionic surfactant and phenylalanine were examined by atomic force microscopy (AFM). Polymer chains of adsorbed carrageenan are aligned with crystallographic axes. The helical and globular conformations of carrageenan effectively bind the surfactant. Phenylalanine is not involved in the structuration of the carrageenan gel.