Nuclear singlet states may have lifetimes T S that exceed the conventional magnetization relaxation time T 1 by an order of magnitude. [1][2][3][4][5][6][7][8][9][10][11] Applications of these states to the NMR measurements of slow molecular diffusion, chemical exchange, and the transportofhyperpolarizednuclearspinorderhavebeendemonstrated. [8][9][10][11] So far, long-lived nuclear singlet states have only been observed for proton pairs. We now demonstrate an extraordinarily long lifetime (T S ) of ∼26 min for the nuclear spin singlet of 15 N 2 -nitrous oxide (dinitrogen monoxide, N 2 O) in solution. This result has high potential importance since nitrous oxide is soluble in many important fluids such as water, oil, and blood. It is used routinely as a food additive, a gas propellant, and an anesthetic.Doubly labeled 15 N 2 O gas, purchased from CK-gas (UK), was dissolved in a degassed solution of DMSO-d 6 at a pressure of ∼3. Figure 1a.The slow relaxation of singlet states is revealed by suppressing their interconversion with the triplet states, either by using a resonant radiofrequency field [3][4][5][6] or by reducing the static magnetic field to a very low value. 1,2 The radiofrequency method is not feasible for The spin system is allowed to reach thermal equilibrium, and two strong 90°pulses with a relative phase of 90°are applied at the mean chemical shift frequency of the two 15 N sites. The delay between the pulses, τ 1 ) 0.198 ms, was chosen so that the transverse magnetization vectors of the two 15 N sites precess through 180°r elative to each other. The two pulses act as a selective 180°pulse on one of the 15 N sites and lead to a spin density operator 10 of the formwhere the two sites are denoted j and k and the selective inversion is assumed to act on site j. In this and the following equations, the subscript refers to a time point in Figure 2. The sample is transported out of the magnetic field by activating a stepper motor to wind up a string attached to the sample holder. The transport process takes τ tr ) 40 s and transports the sample into a region of low magnetic field, B low ≈ 2 mT, estimated by a Hall effect device. As shown in ref 2, slow adiabatic transport converts the population of each high-field state into that of the corresponding low-field state, leading to a density operator of the formwhere the low-field eigenstates areThe sample is left in the low-field region for a variable time τ LF . During the first few minutes, the three triplet populations equilibrate with each other on a time scale set by the relaxation constant T 1 . The density operator after several minutes in low magnetic field is therefore given approximately byThe sample is transported back into the high-field region by running the stepper motor in the opposite direction. Adiabatic transport from the density operator in eq 3 leads to

A method was developed allowing in situ adjustment of water-in-oil-in-water double emulsion (W/O/W) morphologies by tailoring the osmotic pressure of the water phases. The control of internal droplet size is achieved by altering the chemical potential of the external and internal water phases by dissolving neutral linear polysaccharides of suitable molecular weights. As a consequence of the different chemical potentials in the two aqueous phases, transport of water takes place modifying the initial morphology of the double emulsion. Self-diffusion 1H nuclear magnetic resonance (1H NMR) was used to assess transport mechanisms of water in oil, while a numerical model was developed to predict the swelling/shrinking behavior of W/O/W double emulsions. The model was based on a two-step procedure in which the equilibrium size of a single internal water droplet was first predicted and then the results of the single droplet were extended to the entire double emulsion. The prediction of the equilibrium size of an internal droplet was derived by the equalization of the Laplace pressure with the osmotic pressure difference of the two aqueous phases, as modeled by mean-field theory. The double emulsion equilibrium morphologies were then predicted by upscaling the results of a single drop to the droplet size distribution of the internal W/O emulsion. Good agreement was found between the theoretical predictions and the measurement of double emulsion droplet size distribution. Therefore, the present model constitutes a valuable tool for in situ control of double emulsion morphology and enables new possible applications of these colloidal systems.

This contribution reports on the mass transport kinetics of osmotically imbalanced water-in-oil-in-water (W1/O/W2) emulsions. Although frequently studied, the control of mass transport in W1/O/W2 emulsions is still challenging. We describe a microfluidics-based method to systematically investigate the impact of various parameters, such as osmotic pressure gradient, oil phase viscosity, and temperature, on the mass transport. Combined with optical microscopy analyses, we are able to identify and decouple the various mechanisms, which control the dynamic droplet size of osmotically imbalanced W1/O/W2 emulsions. So, swelling kinetics curves with a very high accuracy are generated, giving a basis for quantifying the kinetic aspects of transport. Two sequential swelling stages, i.e., a lag stage and an osmotically dominated stage, with different mass transport mechanisms are identified. The determination and interpretation of the different stages are the prerequisite to control and trigger the swelling process. We show evidence that both mass transport mechanisms can be decoupled from each other. Rapid osmotically driven mass transport only takes place in a second stage induced by structural changes of the oil phase in a lag stage, which allow an osmotic exchange between both water phases. Such structural changes are strongly facilitated by spontaneous water-in-oil emulsification. The duration of the lag stage is pressure-independent but significantly influenced by the oil phase viscosity and temperature.

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