Microstructure Considerations of New Five-Component Winsor IV Food-Grade Microemulsions Studied by Pulsed Gradient Spin−Echo NMR, Conductivity, and Viscosity

Abstract

The microstructure of an unusual Winsor IV isotropic region of five-component microemulsions based on nonionic surfactants was studied. The microemulsions are composed of R(+)-limonene, water, propylene glycol (PG), ethanol (EtOH), and polyoxyethylene sorbitan monostearate (Tween 60) with a 1:1:3 R(+)limonene/ethanol/surfactant weight ratio. The phase diagrams of the system are characterized by an extended single continuous isotropic region starting from an oil-rich solution containing no aqueous phase (reverse micelles) to the water/propylene glycol (1/1) corner (swollen direct micelles). The microemulsions seem to be attractive for food applications. The microstructure changes gradually, smoothly, and continuously upon increasing the aqueous phase content. The microemulsion transforms from a water-in-oil (W/O) microemulsion to a bicontinuous phase and to an oil-in-water (O/W) microemulsion. The microstructure of the microemulsion along a selected dilution line, is probed using pulsed gradient spin-echo NMR, conductivity, and viscosity. The results are compared with a corresponding non-food-grade system based on C18:1E10 (Brij 96v). The hydrodynamic radius (RH) of O/W microemulsion samples based on Brij 96v and Tween 60, at 90% aqueous phase, was determined to be 5.4 ( 0.2 and 5.2 ( 0.2 nm, respectively, and the calculated values of the area of the polar headgroup (a) are 87 for Brij 96v and 160 Å 2 for Tween 60-based microemulsions. The ratio of the water self-diffusion coefficient, DW, to the PG self-diffusion coefficient (DPG) (termed the L ratio) was found to be sensitive to the aqueous phase content. In the O/W microemulsions, the water/PG mixture diffuses as hydrogen bonded entity (molecular diffusion controlled), while in the W/O microemulsions, the PG partitions, in part, at the interface and the dominate diffusion process is neither aggregate nor molecular controlled.

Tools and strategies for processing diffusion-ordered 2D NMR spectroscopy (DOSY) of a broad, featureless resonance: an application to methylaluminoxane (MAO)

“…An unresolved problem is the resolution of sums of exponential decays which arises when there is insufficient peak resolution along the chemical shift axis. Several algorithms designed to deconvolute exponential decays have been applied to DOSY data sets: CONTIN [8], CORE [9,10], and DECRA [11,12]. As we prepare to analyze our data with these sophisticated techniques, we have returned to a basic approach of a non-linear least-squares fit using the Levenberg-Marquardt method and f-test.…”

Aggregates in Ionic Liquids and Applications Thereof

“…Its values are sensitive to friction, obstruction and solvatation phenomena, but in particular to confinement in closed domains. They can therefore be used to obtain information on solution microstructure (Fedotov et al, 1996;Yaghmur et al, 2003). Figure 9 shows the values of self-diffusion of bnPyrNTf 2 , TX-100 and toluene as a function of the total volume fraction of TX-100 and IL along dilution line (a) for samples 2, 3 and 4 in Figure 8.…”

Do food microemulsions and dietary mixed micelles interact?

“…The selfdiffusion coefficients (diffusivities) were determined using pulsed field gradient stimulated spin-echo (BPFG-SSE). For more details see Yaghmur et al [30].…”

“…Diffusion coefficients for the ME and DMM components (when observed) were determined from the spectral region between 0.5 and 4.0 ppm (the hydrophobic region of the components). Diffusion coefficients for Tween 60 were determined from signals at 1.2 and 3.8 ppm [30]. Diffusion coefficients for TCDC were determined from the region between 0.0-1.7 and 3.0-4.0 ppm [42].…”

“…The DMM-based structure and ME systems were examined individually and in mixtures of various weight ratios. A variety of physical techniques were utilized to investigate micelle structure: (1) attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy provided information about functional group interactions within the structure, and subsequently on the mobility and packing of the structures, based on the vibrational freedom of the molecular bonds [25][26][27]; (2) electron paramagnetic resonance (EPR) was used to measure the microviscosity, polarity, and order in the two systems separately and together [28,29]; (3) pulse gradient spin-echo nuclear magnetic resonance (PGSE-NMR) elucidated component mobility [5,[30][31][32]; (4) two-dimensional nuclear Overhauser effect (NOE) NMR spectroscopy experiments identified dipolar interactions between spatially proximate hydrogen atoms [33,34]; and (5) fluorescence resonance energy transfer (FRET) experiments provided feedback on the ability of the two systems to communicate [35,36].…”