Nuclear Magnetic Resonance Self-diffusion Research Articles

Self-Diffusion Studies in CuBTC by PFG NMR and MD Simulations

Self-diffusion and relaxation time studies of C3 to C6 hydrocarbons adsorbed in the microporous metal−organic framework CuBTC were performed by nuclear magnetic resonance (NMR) in the temperature range of 193−373 K. The presence of paramagnetic copper species in the solid CuBTC framework leads to short longitudinal (T1) and transverse (T2) relaxation times of the hydrocarbons with typical values of T1 ≲ 10 ms and T2 ≲ 3 ms. Under these conditions, pulsed field gradient (PFG) NMR self-diffusion studies could only be performed at short observation times using the primary spin echo sequence with high-intensity pulsed magnetic field gradients. The obtained temperature dependent self-diffusion coefficients were analyzed using an Arrhenius approach. The activation energies of the alkanes are in the range of 6.5−8.5 kJ/mol, increasing slightly with increasing number of carbon atoms. Significantly higher values were found for propene (13.2 kJ/mol) and 1-butene (15.0 kJ/mol). These tendencies are consistent with corresponding measurements of heats of adsorption and with data obtained in molecular dynamics (MD) simulations. The MD simulations show a strong dependence of the heat of adsorption and diffusion on loading and temperature. This is caused by the preferential adsorption of small alkanes such as propane and butane in the side pockets of the CuBTC structure at low loading and temperature.

NMR Study of Surfactant Micelle Shape Transformation with Concentration

The micelle shape transformation of tert-octylpheny phenol polyethylene glycol ether (TX-100), sodium dodecyl benzene sulfonate (SDBS) and tetradecyl trimethyl ammonium bromide (TTAB) in heavy water solutions was studied by H-1 nuclear magnetic resonance (NMR) spectroscopy, including an NMR self-diffusion experiment. These experiments showed that the surfactants formed several shapes of micelles (spherical, ellipsoidal, and rodlike) at the respective concentrations which were far above their critical micelle concentration (cmc). At ambient temperature, normal pressure and when the concentration of the surfactant was above the cmc without other additives, spherical micelles were formed. At higher surfactant concentrations, H-1 NMR spectra and self-diffusion experiments showed that abrupt changes occurred in their chemical shifts (delta) and in their self-diffusion coefficients (D). This indicated that spherical micelles transformed into larger micelles. By careful examination of every proton resonance peak in the H-1 NMR spectra, we found that the protons near the head group experienced larger chemical shift changes than protons near the hydrophobic group. This suggests that the shape of surfactant micelles most likely transforms from spherical to ellipsoidal or rodlike.

Role of the solvent in the dynamical transitions of proteins: The case of the lysozyme-water system

We study the dynamics of hydration water in the protein lysozyme in the temperature range 180 K<T<360 K using Fourier-transform-infrared and nuclear magnetic resonance (NMR) spectroscopies. By analyzing the thermal evolution of spectra of the OH-stretching vibration modes and the NMR self-diffusion (DS) and spin-lattice relaxation time (T1), we demonstrate the existence of two dynamical transitions in the protein hydration water. Below the first transition, at about 220 K, the hydration water displays an unambiguous fragile-to-strong dynamic crossover, resulting in the loss of the protein conformational flexibility. Above the second transition, at about 346 K, where the protein unfolds, the dynamics of the hydration water appears to be dominated by the non-hydrogen-bonded fraction of water molecules.

PFG NMR self-diffusion of small hydrocarbons in high silica DDR, CHA and LTA structures

Pulsed field gradient (PFG) nuclear magnetic resonance (NMR) spectroscopy was used to measure and rationalize the intracrystalline self-diffusion coefficients of small hydrocarbons in high silica DDR (ZSM-58, Si/Al = 190), pure silica chabazite (Si-CHA) and ITQ-29 (Si-LTA) structures. The self-diffusivities of methane, ethane, ethylene and propylene were measured on these materials at 301 K and 101.3 kPa. A clear correlation is shown between the size of the 8-ring windows and the size of the molecules on the measured self-diffusivities. Window sizes were obtained from X-ray diffraction measurements: [3.65 × 4.38 Å] for ZSM-58, [3.70 × 4.17 Å] for Si-CHA and [4.00 × 4.22 Å] for Si-LTA. An increase in self-diffusivity with window size and a decrease with molecular size were clearly observed. The magnitudes of these effects are shown to be very large. For example, at 301 K and 101.3 kPa, the self-diffusivities of methane were 1.6 × 10 −8 cm 2/s, 10.7 × 10 −8 cm 2/s and 142.0 × 10 −8 cm 2/s in ZSM-58, Si-CHA and Si-LTA, respectively; an increase in self-diffusivity of nearly 2 orders of magnitude that is primarily due to window size effects. Similarly, at 301 K and 101.3 kPa, the self-diffusivities of methane, ethylene, ethane and propylene in Si-LTA were 142.0 × 10 −8 cm 2/s, 21.4 × 10 −8 cm 2/s, 20.9 × 10 −8 cm 2/s and 0.0047 × 10 −8 cm 2/s, respectively; a decrease in self-diffusivity with molecular size of more than 4 orders of magnitude. These findings contribute to a fundamental understanding of self-diffusion in microporous materials and have important implications for kinetic based separation schemes in which diffusion plays a key role.

PFG NMR self-diffusion of propylene in ITQ-29, CaA and NaCaA: Window size and cation effects

Pulsed field gradient (PFG) nuclear magnetic resonance (NMR) spectroscopy was used to measure and rationalize the self-diffusion coefficients of propylene in various LTA materials having different framework composition and varying proportions of charge balancing cations: ITQ-29 (Si/Al = ∞), CaA (Si/Al = 1), and six NaCaA (Si/Al = 1) samples at greater than 50% Na + exchange. The critical role of the framework Si/Al ratio on the self-diffusivity of propylene is demonstrated. Changes in self-diffusion driven by changes in framework composition are well documented in the literature. Diffusion frequency response experiments in the pure silica and alumino-phosphate forms of the CHA structure are included in this work to illustrate such situation. For the LTA structures, propylene was chosen as a very sensitive probe molecule because its size is comparable to the size of the 8-ring window apertures in the materials. A clear increase in self-diffusivity with the size of the window apertures, which increases with Al content in the framework, is shown. Thus, ITQ-29 and CaA exhibit the lowest and highest self-diffusivities, respectively. The self-diffusivities in the NaCaA samples lie in between those of ITQ-29 and CaA and increase with the Ca 2+ content. Thus, the presence of extra-framework balancing cations in either CaA or NaCaA does not lead to lower self-diffusivities than in the cation-free ITQ-29. The lower self-diffusivities in ITQ-29, instead, can be largely attributed to its smaller window size, which is a more dominant effect than any reduction in self-diffusivity caused by the cations, at the levels of Na + exchange studied.

Surfactant/Nonionic Copolymer Interaction: A SLS, DLS, ITC, and NMR Investigation

The interactions between an oxyphenylethylene-oxyethylene nonionic diblock copolymer with the anionic surfactant sodium dodecyl sulfate (SDS) have been studied in dilute aqueous solutions by static and dynamic light scattering (SLS and DLS, respectively), isothermal titration calorimetry (ITC), and 13C and self-diffusion nuclear magnetic resonance techniques. The studied copolymer, S20E67, where S denotes the hydrophobic styrene oxide unit and E the hydrophilic oxyethylene unit, forms micelles of 15.6 nm at 25 degrees C, whose core is formed by the styrene oxide chains surrounded by a water swollen polyoxyethylene corona. The S20E67/SDS system has been investigated at a copolymer concentration of 2.5 g dm(-3), for which the copolymer is fully micellized, and with varying surfactant concentration up to approximately 0.15 M. When SDS is added to the solution, two different types of complexes are observed at various surfactant concentrations. From SLS and DLS it can be seen that, at low SDS concentrations, a copolymer-rich surfactant mixed micelle or complex is formed after association of SDS molecules to block copolymer micelles. These interactions give rise to a strong decrease in both light scattering intensity and hydrodynamic radius of the mixed micelles, which has been ascribed to an effective reduction of the complex size, and also an effect arising from the increasing electrostatic repulsion of charged surfactant-copolymer micelles. At higher surfactant concentrations, the copolymer-rich surfactant micelles progressively are destroyed to give surfactant-rich-copolymer micelles, which would be formed by a surfactant micelle bound to one or very few copolymer unimers. ITC data seem to confirm the results of light scattering, showing the dehydration and rehydration processes accompanying the formation and subsequent destruction of the copolymer-rich surfactant mixed micelles. The extent of interaction between the copolymer and the surfactant is seen to involve as much as carbon 3 (C3) of the SDS molecule. Self-diffusion coefficients corroborated light scattering data.

Self-Diffusion NMR Studies of the Host−Guest Interaction between β-Cyclodextrin and Alkyltrimethylammonium Bromide Surfactants

Diffusion measurements by nuclear magnetic resonance (NMR) spectroscopy were used to investigate the host-guest association between beta-cyclodextrin (CD) and alkyltrimethylammonium bromide surfactants with different chain lengths, ranging from 6 up to 16 carbons. The scope and limitations of the method in the study of formation of inclusion complexes are discussed. The influences of the presence of CD in the micellization process have been studied, and the apparent critical micellar concentration and the self-diffusion coefficients of the species present in the systems have been calculated. The stoichiometries of the different complexes have been determined. Evidence for the formation of a 2:1 complex in the case of C(16)TAB has been found.

Influence of fat globule membrane composition on water holding capacity and water mobility in casein rennet gel: A nuclear magnetic resonance self-diffusion and relaxation study

The effects of the composition of the fat globule surface on water holding capacity and water diffusion were studied in different rennet-derived retentates. Water holding capacity was determined from nuclear magnetic resonance (NMR) relaxation measurements; the water diffusion coefficient was estimated using Pulse Field Gradient NMR. Reconstituted fatty retentates were prepared from fat-free retentate mixed with different fat-in-water emulsions stabilized with native phosphocaseinates (NPCs) or sodium caseinates. Coagulation of retentate reconstituted with native fat globules (fresh cream) and of industrial fatty retentate was also investigated. The study showed that the fat droplet/water interface influenced the water diffusion coefficient in the cream-reconstituted retentate gel only. No effect was observed in the NPC- and Na-caseinate-reconstituted retentate and in the fatty industrial retentate after coagulation. The results of the relaxation measurements in the gelled fatty reconstituted retentates showed that the nature and the composition of the fat interface influence the syneresis behaviour.

Characterisation of the Structure and Flow Behaviour of Model Chocolate Systems by Means of NMR and Rheology

Abstract In order to characterise the structure and flow behaviour of model chocolate systems Nuclear Magnetic Resonance (NMR) and rheometry were used to determine the T1 - and T2 - NMR relaxation times and their corresponding flow functions. T1 and T2 characterise the molecular mobility of fluids and correlate with both the zero-shear-rate and infinity viscosity of various chocolate model systems (determined with rotational rheometry and capillary rheometry). Based on this correlation, NMR provides the possibility to determine characteristic viscosities of chocolate masses by means of NMR-relaxation experiments. The viscosities of chocolate masses are important process parameters, as they are used for quality control of the production process. An online process viscosimetry via T2 relaxation would allow the installation of an efficient process control and, thus, a process automation. This NMR application with comparatively short measuring times is especially interesting for disperse systems where the use of conventional rheometric techniques may cause large errors. The only prerequisite for the measurement of the viscosities using NMR is a previous calibration. This was performed with the help of rotational and capillary rheometry. The NMR self-diffusion experiments are especially appropriate to characterise the influence of emulsifiers on the structure and the flow behaviour of chocolate masses.

An NMR study of the freezing of emulsion-containing drops

Various nuclear magnetic resonance (NMR) techniques were used to monitor the freezing behaviour of suspended 2-mm-diameter drops. The drops were composed of hydrocarbon oils emulsified in either water or water/sucrose mixtures. As such they were good model systems for the study of spray freezing, sharing structural similarities with potential products such as ice cream. In particular, simple 1 H NMR spectroscopy was used to monitor and individually quantify the freezing or solidification behaviour of the various constituent species of the drops. In addition, the effect of freezing on the emulsion droplet size distribution (and hence emulsion stability) was also measured based on NMR self-diffusion measurements. The effect of freeze/thaw cycling was also similarly studied. The nucleation temperature of the emulsion droplets was found to depend on the emulsion droplet size distribution: the smaller the droplets, the lower the nucleation temperature. Emulsion droplet sizing indicated that oil-in-sucrose-solution emulsions were more stable, showing minimal coalescence, whereas oil-in-water emulsions showed significant coalescence during freezing and freeze/thaw cycling.

An NMR study of the freezing of emulsion-containing drops

Various nuclear magnetic resonance (NMR) techniques were used to monitor the freezing behaviour of suspended 2-mm-diameter drops. The drops were composed of hydrocarbon oils emulsified in either water or water/sucrose mixtures. As such they were good model systems for the study of spray freezing, sharing structural similarities with potential products such as ice cream. In particular, simple 1H NMR spectroscopy was used to monitor and individually quantify the freezing or solidification behaviour of the various constituent species of the drops. In addition, the effect of freezing on the emulsion droplet size distribution (and hence emulsion stability) was also measured based on NMR self-diffusion measurements. The effect of freeze/thaw cycling was also similarly studied. The nucleation temperature of the emulsion droplets was found to depend on the emulsion droplet size distribution: the smaller the droplets, the lower the nucleation temperature. Emulsion droplet sizing indicated that oil-in-sucrose-solution emulsions were more stable, showing minimal coalescence, whereas oil-in-water emulsions showed significant coalescence during freezing and freeze/thaw cycling.

Water-Based Latex Dispersions. 3. Exchange Dynamics of Nonionic Surfactants and Poly(ethylene glycol) on Colloidal Particles with Different Interfacial Properties

The residence times at equilibrium of nonylphenol ethoxylate or of poly(ethylene glycol) (PEG) in silica and in latex dispersions (polystyrene and poly(methyl methacrylate-co-ethyl acrylate)) have been determined. By means of self-diffusion nuclear magnetic resonance (NMR) it was found that the surfactant with 84 oxyethylene units (NP100) in mean was “irreversibly adsorbed” on all surfaces, with residence times on the order of seconds. For the surfactant with 10 oxyethylene units (NP10) in mean the residence times were shorter, on the order of milliseconds, on both silica and polystyrene. By using PEGs of different molecular weights instead of the surfactants, it was found that the molecular weight of the PEG chain and the nonylphenol group mutually influenced the residence times of the surfactants. For the short PEG chain (196 g/mol), the residence times were shorter than 10 ms on both silica and on polystyrene. Surprisingly, the residence times were shorter than 10 ms also for the longer PEG chain (4120 g/mol). The main contribution to the slow exchange dynamics was therefore, regardless of the surface polarity, due to the hydrophobic nonylphenol group. However, the PEG chain in NP100 adsorbed with train segments on the surfaces, which, like the nonylphenol group, also prolonged the residence times.

Self-diffusion nuclear magnetic resonance, microstructure transitions, and solubilization capacity of phytosterols and cholesterol in Winsor IV food-grade microemulsions.

Microemulsions are of growing interest to the food industry as vehicles for delivering and enhancing solubilization of natural food supplements with nutritional and health benefits. The incorporation of molecular phytosterols, cholesterol-lowering agents, in food products is of great interest to the food industry. In this work is demonstrated the use of water dilutable food-grade microemulsions consisting of ethoxylated sorbitan ester (Tween 60), water, R-(+)-limonene, ethanol, and propylene glycol as vehicles for enhancing the phytosterols solubilization. Phytosterols were solubilized up to 12 times more than the dissolution capacity of the oil [R-(+)-limonene] for the same compounds. The solubilization capacity of phytosterols and cholesterol along a dilution line in a pseudo-ternary phase diagram [on this dilution line the weight ratio of R-(+)-limonene/ethanol/Tween 60 is constant at 1:1:3] was correlated to the microstructure transitions along the dilution line. Structural aspects were studied by self-diffusion NMR spectroscopy. The ability of phytosterols to compete with cholesterol for penetration into bile salt micelles in the gut may be limited to rich aqueous systems (O/W microemulsion).

On the Self-Assembly of Monoolein in Mixtures of Water and a Polar Aprotic Solvent

A new kind of lipid/polymer composite particle, consisting of a biodegradable polymer matrix with well-defined lipid domains, has been created. The lipid used is the water-swelling lipid monoolein (MO), which forms a reversed bicontinuous cubic diamond structure in aqueous solutions. The polymer is poly(d,l-lactide-co-glycolide) (PLG), which degrades into water-soluble monomers through hydrolysis. This new particle might be a good alternative for encapsulation of active substances intended to be released over a longer period of time, i.e. sustained/retained/controlled release.To prepare such particles can be difficult. Suitable phase behaviour and a solvent with the right properties are needed. For this reason, the phase behaviours of several different lipid/polymer/solvent/water systems have been explored. From the phase behaviour of a suitable system (i.e. MO/PLG/ethyl acetate/water), a route for formation of lipid/polymer composite particles has been deduced. Particles have been formed and distinct, water-swelling, lipid domains have been confirmed by characterization by means of confocal laser scanning probe microscopy (CLSM). The sample preparation process has been automated and a method based on using a robotic liquid handler has been developed. Phase diagrams have been determined by examination of macroscopic behaviours and the microstructures of the phases have been studied by small- and wide-angle X-ray scattering (L3, V2, Lα, L), nuclear magnetic resonance self-diffusion (L, L3), viscosimetry (L) and rheology (L). Several different theoretical models have been applied for interpretation of the results. For example, the swelling of the reversed bicontinuous cubic phases and the sponge phase have been modelled by applying the theory of infinite periodical minimal surfaces, the sponge phase has been shown to be bicontinuous according to the theory of interconnected rods and the phase behaviour of the polymer has been described by the Flory-Huggins theory. The main focus of this work (4/5) concerns phase studies in multicomponent systems from a physical-chemical point of view.

Solution and Liquid Crystalline Microstructures in Sodium Taurodeoxycholate/D2O Mixtures

Nuclear magnetic resonance (NMR) and rheology were used as two useful and complementary techniques to characterize the solution and liquid crystalline microstructures of the sodium taurodeoxycholate (NaTDC)/D2O system. NaTDC is very soluble in water. At room temperature NaTDC/D2O mixtures form a low-viscosity isotropic micellar solution up to a concentration of ca. 12 wt % NaTDC. It follows a micellar solution region, 12−25 wt % NaTDC, that behaves as a Newtonian viscous fluid with a well-defined viscosity value. At higher concentration (>25 wt % NaTDC), a region with very high viscosity and viscoelastic behavior exists. At room temperature and at ca. 37 wt % NaTDC, the NaTDC/D2O system exhibits a phase transition into a birefringent phase. In this region, extending to ca. 65 wt %, the samples exhibit a gel-like behavior and behave as a shear thinning fluid. NMR and rheological data indicated that micellar solution is composed of a region with spherical micelles and of another with cylindrical aggregates, starting with 12 wt % NaTDC. The liquid crystalline phase, which disappears to ca. 36 °C, is a direct hexagonal phase as revealed by water self-diffusion NMR and the calculated diffusional obstruction factors. Dynamic viscoelastic measurements showed that micellar solutions (>25 wt % NaTDC) and the liquid crystalline phase behave as a “weak gel”. A possible relationship between the rheological responses and the phase microstructures using a cooperative-flow model was discussed.

Polyamine-nucleic acid interactions and the effects on structure in oriented DNA fibers.

Fibrous oriented calf thymus DNA containing the natural polyamines spermidine (Spd) and putrescine (Put), and the degradation polyamines cadaverine (Cad) and 1,3-diaminopropane (DAP), have been investigated at different water contents using nuclear magnetic resonance (NMR) methods, fiber X-ray diffraction and gravimetric measurements. When judged by X-ray only the DAP and Spd samples seem to undergo a B-A-form transition at reduced water activity. Solid-state two-dimensional rotor-synchronized magic angle spinning (2D-syncMAS) 31P-NMR, however, shows the A-form to be present also in the Put sample, and it appears that the separation between the amine units of diamines is correlated with the amount of A-form present. In addition, the solid-state NMR data show the polyamine-bound DNA samples to have a significant deviation from the ordinary B-form DNA structure, displaying similar amounts of BI and BII nucleotide conformations. The low water content of the samples suggest that the polyamines themselves act as hydrators of DNA. Water 2H-NMR results are in agreement with this observation. The quadrupolar splittings of the polyamine 2H signals for samples at low water content indicate some preferential spatial orientations of the polyamines in the ordered DNA environment. The polyamines show relatively fast macroscopic diffusion as detected by NMR self-diffusion measurements.

Physicochemical characterisation of a drug-containing phospholipid-stabilised o/w emulsion for intravenous administration

Clomethiazole (CMZ) was used as a model drug to be incorporated into an emulsion vehicle. The effects of drug concentration and number of homogenisation steps were evaluated using multiple linear regression. The droplet size, measured as a z-average diameter by photon correlation spectroscopy (PCS), was found to be between 60 and 260 nm in the investigated range of CMZ concentrations, highly dependent on the concentration, but more weakly so on the number of homogenisation steps. Slow-scanning high-sensitivity differential scanning calorimetry (DSC) measurements showed that CMZ depresses the phospholipid chain melting temperature in the emulsion system, whereas 13C nuclear magnetic resonance (NMR) experiments suggested that the CMZ molecules are to a large extent located in the surface region of the emulsion droplets. This interpretation is compatible with results from NMR self-diffusion measurements, which showed that most of the CMZ molecules are rapidly exchanged between emulsion droplets and the aqueous surrounding. It can be concluded that the surface-active drug CMZ has a significant influence on the characteristics of phospholipid-stabilised emulsions through its ability to interact with the phospholipid interface. Thus, the results underline the importance of characterising drug–lipid interactions for the development of lipid-based formulations.

Ionic conduction and self-diffusion near infinitesimal concentration in lithium salt-organic solvent electrolytes

The Debye–Hückel–Onsager and Nernst–Einstein equations, which are based on two different conceptual approaches, constitute the most widely used equations for relating ionic conduction to ionic mobility. However, both of these classical (simple) equations are predictive of ionic conductivity only at very low salt concentrations. In the present work the ionic conductivity of four organic solvent-lithium salt-based electrolytes were measured. These experimental conductivity values were then contrasted with theoretical values calculated using the translational diffusion (also known as self-diffusion or intradiffusion) coefficients of all of the species present obtained using pulsed-gradient spin–echo (1H, F19 and Li7) nuclear magnetic resonance self-diffusion measurements. The experimental results verified the applicability of both theoretical approaches at very low salt concentrations for these particular systems as well as helping to clarify the reasons for the divergence between theory and experiment. In particular, it was found that the correspondence between the Debye–Hückel–Onsager equation and experimental values could be improved by using the measured solvent self-diffusion values to correct for salt-induced changes in the solution viscosity. The concentration dependence of the self-diffusion coefficients is discussed in terms of the Jones–Dole equation.

Liquid polyethylene glycol dispersed in a poly(styrene)-b-poly(ethylene/butylene)-b-poly(styrene) elastomer: determination of morphology and molecular mobility by light and electron microscopy as well as nuclear magnetic resonance self-diffusion andT2 measurements

An emulsion of liquid polyethylene glycol (PEG) in a rubbery poly(styrene)-b-poly(ethylene/butylene-b-poly-(styrene) (SEBS) matrix was prepared using a poly-(butadiene-b-poly(ethylene oxide) (PB-b-PEO) diblock copolymer as emulsifier. In addition to its emulsifying effect, it was shown that a block copolymer containing a crystalline PEO sequence has a tendency to form micelles as well as supramolecular structures in form of square platelets when they are solubilized in nonpolar solvent such as methylcyclohexane. The filmification of the emulsion by solvent evaporation and the film morphology were examined by light and electron microscopy and by nuclear magnetic resonance (NMR) T2 and self-diffusion measurements. Microscopic evaluations have shown cavities having an average size, depending on the copolymer content, of a few micrometers and filled with liquid PEG. Additionally, smaller structures typically in the range of 30–50 nm have been observed by transmission electron microscopy and are attributed to crystalline lamellae formed by the copolymer in the matrix. The T2 measurements reveal three contributions to the transverse magnetization decay: one of the SEBS matrix, one of the liquid within the cavities and one of the liquid dissolved in the smaller structures formed by the copolymer in the matrix. In the pulsed field gradient NMR self-diffusion experiments two self-diffusion coefficients were found, one of the liquid in the cavities and one of the liquid dissolved in the matrix within the smaller structures. Generally, a restricted diffusion is observed in that latter case owing to confining structures for the diffusing liquid molecules. © 1998 John Wiley & Sons, Ltd.

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

Self-diffusion of all components in two different microemulsions has been studied by the Fourier-transform pulsed-gradient spin echo 1H 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.