Z. Sh. Idiyatullin

A Fourier transform pulsed-gradient spin echo nuclear magnetic resonance self-diffusion study of microemulsions and the droplet size determination

Abstract Self-diffusion of all components in two different microemulsions has been studied by the Fourier-transform pulsed-gradient spin echo 1 H nuclear magnetic resonance technique. The analysis of hydrodynamic and direct droplet-droplet interactions in microemulsions allows the simultaneous application of the Stokes-Einstein equation for surfactant and oil. The result of this analysis is a simple relation connecting self-diffusion coefficients of components and the size of droplets. It is shown that because of partial solubilization of water in oil the droplet radius can be significantly different from the expected radius.

Self-diffusion in microemulsions and micellar size

Self-diffusion of all components of two different microemulsions have been measured. Application of Stokes-Einstein equations for surfactant and oil gives a simple relation connecting their size and self-diffusion coefficients. Using the measured self-diffusion coefficients and dimensions of oil molecules known from elsewhere, the size of the surfactant droplets was estimated. This approach turns out to be advantageous in practical determination of droplet size in microemulsions.

Aggregation behavior and catalytic activity of systems based on calix[4]resorcinarene derivatives and surfactants. 1. Mixed micellization of aminomethylated calix[4]resorcinarenes with cetyltrimethylammonium bromide in aqueous dimethylformamide

Mixed micellization of amphiphilic aminomethylated calix[4]resorcinarenes and phenols, which are their structural units, with the cationic surfactant cetyltrimethylammonium bromide (CTAB) in aqueous 10—70 vol % DMF decreases the critical micelle concentration; the resulting aggregates are larger than those in the CTAB—DMF—water systems. The micellization of CTAB with aminomethylated calix[4]resorcinarenes proceeds in two steps, while its micellization with phenols is a single-step process. The micellization characteristics depend on the structure and hydrophobicity of the amphiphilic compound and the concentration of DMF.

The influence of hydrophobic amines on hydrolysis of bis(p-nitrophenyl) methylphosphonate in micellar solutions of cetylpyridinium bromide

The kinetics of hydrolysis of bis(p-nitrophenyl) methylphosphonate in the presence of primary aliphatic amines in aqueous micellar solutions of cetylpyridinium bromide was studied. The reaction proceedsvia two routes, alkaline hydrolysis and amine-catalyzed hydrolysis according to the general basic catalysis mechanism. The contributions of these routes and the catalytic effect of micelles depend on the hydrophobicity of the amines. The formation of different types of micelles was found, and their characteristic parameters were determined by tensiometry and high-resolution1H NMR spectroscopy with a magnetic field pulse gradient.

PARTICLE SIZE EFFECT ON TRANSVERSE NMR RELAXATION IN AQUEOUS CHAR SUSPENSIONS

Abstract A strong particle size influence on NMR transverse proton relaxation in aqueous suspensions of several newly synthesized carbon based chars is reported. The results are quantitatively interpreted in terms of a two-stage molecular exchange model. A porous cage effect leads to slow exchange between molecules inside and outside pores, in contrast to fast molecular exchange at the solid–liquid interface, where a familiar two-site formalism can be applied. The dependence of surface properties on the relaxation data was detected. The transverse NMR relaxation time of water protons on the paramagnetic surface of chars is estimated to be T2s≈ 0.5×10−5 s, which is comparable with the EPR relaxation time of the free radical centers. Dynamic nuclear polarization (DNP) is used to estimate the paramagnetic shift Δv of water protons at the surface. The value Δv so obtained is much less than the transverse NMR relaxation rate of water protons on the paramagnetic surface Δ v ⪡ T 2 s −1 . This inequality can account for the independence of the NMR transverse relaxation times on the interval τ observed in CPMG measurements.

Binding of solvent molecules by micelles of ionic surfactants

The distribution of molecules between the free (intermicellar) and the micelle-bound states is found from the results of selective measurements of their self-diffusion coefficients in micellar solutions of ionic surfactants, i.e., sodium dodecylsulfate and cetyltrimethylammonium bromide.

Mobility of molecules of liquid diols in the temperature range of 303–318 K

The self-diffusion coefficients of diols (ethylene glycol (EG), 1,2- and 1,3-propanediols (PD), and 1,4-butanediol (BD)) are measured using the spin echo approach on protons in the temperature range of 303–318 K. The activation energies of self-diffusion are calculated and compared to the activation energies for viscous flow and dipole relaxation in these systems. A conclusion is reached as to the correlation of rotational and translational movements in liquid diols, due to the presence of a spatial network of hydrogen bonds in these solvents.

Effect of Electrolytes on the Catalytic Properties and Sructural Characteristics of Dodecylpyridinium Bromide Micelles

Electrolyte-induced structural rearrangements of dodecylpyridinium bromide micelles affect their catalytic properties in alkaline hydrolysis of phosphonic esters.

Poly(ethylene glycol) and Phospholipid Packing in the Structure of Reverse Micelles

The influence of water substitution by a substance with a different polarity on the structure of phospholipid monolayer interface in water-in-oil microemulsion has been studied by the Fourier-transform pulsed-gradient spin-echo (FT PGSE)1H nuclear magnetic resonance (NMR) and electron spin resonance (ESR) spin-label methods. For this purpose the soybean phosphatidylcholine-based microemulsion and water soluble poly(ethylene glycol) with molecular weight 400 (PEG400) were used. Self-diffusion coefficients of all microemulsion components obtained by the FT PGSE NMR technique provided information about both the size of reverse micelles and distribution of components between different microemulsion compartments. The maximum hyperfine splitting, 2Amax, in the ESR spectra was used to characterize the degree of the phospholipid hydrocarbon chain mobility. It was shown that PEG400 alters significantly the size of the reverse micelles and the motion of the labeled segments of the lipid tails. A mechanism of PEG400 acting in solution of the phospholipid-based reverse micelles on the basis of the rough decrease of the micelle core polarity was suggested.

Efficiency and Kinetics of Extracting Phenol from Aqueous Solutions Using Nonionic Surfactants

The efficiency and kinetics of extracting phenol from aqueous solutions using nonionic surfactants at the cloud point temperature are studied via NMR. The nonionic surfactants are neonoles AF9-8, AF9-9, AF9-10, and AF9-12; ethoxylated fatty alcohols C12E4 and C12E5; pluronics PE6200 and RE6400; and syntanol Brij 35. The efficiency of extraction using neonols and ethoxylated fatty alcohols lies in the range of 40–60%, and reaches 80% when using pluronics PL6200 and PE6400. The obtained data could be of interest to researchers in the field of phase equilibria.