Characterization of emulsions by NMR methods (original) (raw)
Related papers
NMR Self-Diffusion Studies of the Water and the Oil Components in a W/O/W Emulsion
Journal of Colloid and Interface Science, 1997
With regard to fundamental aspects of multiple emulsions, The application of the pulsed field gradient NMR technique to a relatively little is known. The aim of the work presented double emulsion is presented. This method determines the diffusion here is to apply pulsed field gradient (PFG) NMR techniques behavior of the different components of the emulsion. The details of (14-16) to a W/O/W emulsion. With this approach one the system studied, which is of the W/O/W type, have been taken from measures the mean displacements of the constituents of the the literature. Information obtained pertains to the size distribution of emulsion, the values of which convey information with rethe water droplets in both the starting emulsion and the double emulgard to the structure and dynamics of the emulsions. Thus sion. In addition, the different phenomena that govern the oil diffusion one may use the technique to study structural aspects of in both systems have been identified and discussed. ᭧ 1997 Academic Press emulsions such as the droplet size distribution (17) as well
Advances in Colloid and Interface Science, 2003
The procedure proposed by Packer and Rees (J. Colloid Interface Sci. 40 (1972) 206) to interpret pulsed field gradient spin-echo (PGSE) experiments on emulsions is commonly used to resolve for the distribution of droplet sizes via nuclear magnetic resonance (NMR). Nevertheless, such procedure is based on several assumptions that may restrict its applicability in many practical cases. Among such constrains, (a) the amplitude of the spin-echo (signal) must be influenced solely by the drop phase, and not by the continuous phase; and (b) the shape of the drop size distribution must be assumed a priori. This article discusses new theory to interpret results from PGSE experiments and a novel procedure that couples diffusion measurements (PGSE) with transverse relaxation rate experiments (the so-called CPMG sequence) to overcome the above limitations. Results from experiments on emulsions of water dispersed in several crude oils are reported to demonstrate that the combined CPMG-PGSE method renders drop size distributions with arbitrary shape, the wateryoil ratio of the emulsion and the rate of decay of magnetization at the interfaces, i.e. the surface relaxivity. It is also shown that the procedure allows screening if the dispersion is oil-inwater (oyw) or water-in-oil (wyo) in a straightforward manner and that it is suitable to evaluate stability of emulsions. ᮊ
Colloids and Surfaces A: Physicochemical and Engineering Aspects, 1997
Self-diffusion of all components in two different microemulsions has been studied by the Fourier-transform pulsedgradient 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. © 1997 Elsevier Science B.V.
Langmuir, 1999
Diffraction-like effects have been observed by applying pulsed-field-gradient spin-echo (PFG-SE) NMR to a highly concentrated W/O emulsion, made from the nonionic surfactant C12E4 (CH3(CH2)11(OCH2-CH2)4OH), n-decane, and brine (1 wt % NaCl(aq) solution). The q-space plots of the PFG-SE NMR data show one pronounced maximum and the shoulder of a second maximum in the attenuation curve of the NMR signal of water. Such peaks are often referred to as diffraction-like peaks, because of the close analogy of their origin to the origin of peaks observed in scattering experiments. In this paper it is suggested that the peak positions in the "diffusion diffractograms" can be related to the structure of the emulsion, i.e., to the three-dimensional packing of the (nonspherical) emulsion droplets. Furthermore, the characteristic distances in the emulsion system, in this case related to the average size of an emulsion droplet, can be determined from the positions of the diffraction-like peaks. This can be achieved without the need to invoke models for the diffusion. (26) Kabalnov, A.; Wennerström, H. Langmuir 1996, 12, 276.
Emulsion Stability Studied by Nuclear Magnetic Resonance (NMR)
Energy & Fuels, 2010
A method using low-field nuclear magnetic resonance (NMR) for measurement of water-in-crude oil emulsion stability has been optimized and compared to light transmission measurements. Two NMR sequences have been used; one of them applies a diffusion T 2-weighted profile measurement sequence, which can return a water profile of an emulsion within 30 s. The stability of the emulsions was compared by studying emulsions in parallel in Turbiscan and NMR. Three different crude oils were used in the experiment. The emulsions prepared had water cut at 50%. The correlation between NMR and Turbiscan regarding the free water formation was good for the emulsions. The potential limitations and advantages of the technique are discussed.
Journal of Colloid and Interface Science, 2016
h i g h l i g h t s A multi-nuclear diffusion analysis of W/O/W emulsions was performed using diffusion NMR. The water diffusion signal was recorded by low and high-resolution NMR. The water-soluble marker diffusion signal was recorded by highresolution NMR. Signal comparison enables the evaluation of molecular exchange. The accuracy of the estimated water droplet size of W/O/W emulsions was evaluated upon signal analysis.
Methods for Droplet Size Distribution Determination of Water-in- oil Emulsions using Low-Field NMR
A method using Pulsed Field Gradient Nuclear Magnetic Resonance PFG-NMR for water-incrude oil emulsion droplet size determination has been optimized and compared with optical microscope for validation. The method applies a combination of Pulsed-Field Gradient (PFG) NMR, Stimulated Echo (STE), and Carr-Purcell-Meimboom-Gill (CPMG) sequences for measuring diffusion, resolving oil and water signal and for measuring the attenuation due to a distribution in T 2 values. This returns the droplet size distributions of water-in-oil emulsions within a minute. No prior assumption is made on the shape of the droplet size distribution, which enables the method to resolve for instance bimodal distributions. To validate this method, three different crude oils were used in the experiment. The emulsions prepared had water cuts from 10 to 40 %. The correlation between PFG-NMR and optical microscopy was good for the emulsions. Any potential discrepancies between the two techniques are discussed, so are the limitations and advantages of the methods.
Evidence of coexisting microemulsion droplets in oil-in-water emulsions revealed by 2D DOSY 1H NMR
Journal of Colloid and Interface Science, 2018
Optimizing the macroscopic properties, shelf-life and stability of emulsion products requires a better understanding of the microstructural characteristics such as the type (nano, micro and macro) and the relative distribution of components (i.e., oil and surfactant) within the emulsion droplets. We used Diffusion-Ordered NMR Spectroscopy (DOSY NMR) to evaluate these characteristics in model oil-in-water emulsion containing Tween 80 and medium chain triglycerides (MCT). At low MCT concentrations, the solutions were transparent but from 1 to 5 wt% MCT, they became translucent then opaque. 1 wt% MCT was the upper boundary for the appearance of nanoemulsion phase. From the decays of the chemical shift signals of MCT and Tween 80, the DOSY results clearly demonstrate that the self-diffusion coefficients (D) are dependent on oil concentration. Small microemulsion droplets of almost uniform size (d = 12-22 nm) coexist with two sets of large nanoemulsion (d < 200 nm) and emulsion (d > 200 nm) droplets. The large droplets increase significantly in size with increasing MCT. The most striking result is the clear evidence for the presence of microemulsion droplets of nearly uniform size in the aqueous phase from below to above the nanoemulsion transition concentration at 1 wt% MCT.
Fourier transform NMR self-diffusion measurements on microemulsions
Journal of Magnetic Resonance (1969), 1980
Multicomponent amphiphile systems have wide biological, technical, and theoretical interest. As an example, many four-component systems of ionic surfactant, short-chain alcohol, hydrocarbon, and water form, in wide concentration regions, so-called microemulsions (I, 2)) which are thermodynamically stable isotropic solutions of low viscosity. Microemulsions have found many technical applications and presently many physicochemical techniques are being applied in attempts to establish the structure of microemulsions and their microdynamic behavior. For both these aspects it is of great importance to measure the translational mobilities of all the components making up the system. We have investigated the feasibility of self-diffusion measurements on individual components in various multicomponent systems by a newly developed technique, which is readily implementable on standard pulsed FT NMR spectrometers (3, 4). The technique appears to be particularly favorable for investigations of the microdynamic behavior of microemulsions and we therefore wish to communicate its advantages relative to the alternative radioactive tracer (5,6) or non-FYI nuclear spin-echo methods (6, 7). Basically, the method is based on James and McDonald's Fourier transform modification (8) of the pulsed-gradient spin-echo (PGSE) experiment suggested by Stejskal and Tanner (9). In our implementation (3,4) the normal homospoil coils of the spectrometer are utilized for the softwarecontrolled magnetic field gradient pulses (=l G cm-' for typically lo-100 msec), Tz is measured separately, series of normal absorption spectra for various pulse lengths are generated automatically (as in a normal spin-relaxation time measurement), and the data are subjected to nonlinear least-squares analysis off line. The method is capable of accuracies better than 40.5% in the determination of selfdiffusion coefficients (D) of small molecules with single-line NMR spectra (3) and typically has a lower measurement limit of D in the 10-l' m2 set-l range. Certain applications, which are hampered by J-modulation effects from homonuclear spin couplings or from overlapping signals in proton spectra, can alternatively be made on 13C nuclei instead (4, ZO), although the lower limit ofD will then become higher, and the experiment more time-consuming.
Characterization of O/W Pickering emulsion by NMR
2019
Nuclear magnetic resonance (NMR) is defined as a non-invasive technique for measuring emulsion droplet size. The diffusion of oil molecules in oil-in-water (O/W) emulsions is restricted within oil droplet which directly affected by the oil droplet radius. Thus, restricted diffusion of oil molecules can be used to determine the oil droplet diameter. This research was aimed to investigate the influence of emulsifier type on emulsion droplet diameter by NMR comparing with conventional light scattering technique. The 10% wt oil O/W emulsions were prepared using nanofibrillated cellulose (NFC) or whey protein isolate (WPI) at concentration of 0.3, 0.5 and 0.7% wt as an emulsifier. Diffusion coefficients ( D ) were measured by pulsed-field-gradient stimulated spin-echo (PFG-STE) pulse sequence using High-field NMR. The results showed that the diffusion coefficients of the O/W emulsions were dependence on diffusion time ( Δ ). The increase in diffusion time found the decay of attenuation o...