Show Abstract ▼

Abstract: Ionic liquid (IL) mixtures enable the design of fluids with finely tuned structural and physicochemical properties for myriad applications. In order to rationally develop and design IL mixtures with the desired properties, a thorough understanding of the structural origins of their physicochemical properties and the thermodynamics of mixing needs to be developed. To elucidate the structural origins of the excess molar volume within IL mixtures containing ions with different alkyl chain lengths, 3 IL mixtures containing 1-alkyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide ILs have been explored in a joint small angle X-ray scattering (SAXS) and 129Xe NMR study. The apolar domains of the IL mixtures were shown to possess similar dimensions to the largest alkyl chain of the mixture with the size evolution determined by whether the shorter alkyl chain was able to interact with the apolar domain. 129Xe NMR results illustrated that the origin of excess molar volume in these mixtures was due to fluctuations within these apolar domains arising from alkyl chain mismatch, with the formation of a greater number of smaller voids within the IL structure. These results indicate that free volume effects for these types of mixtures can be predicted from simple considerations of IL structure and that the structural basis for the formation of excess molar volume in these mixtures is substantially different to IL mixtures formed of different types of ions.

Show Abstract ▼

Abstract: A near-monodisperse monohydroxy-terminated polydimethylsiloxane (PDMS; mean degree of polymerization = 66) was esterified using a carboxylic acid-functionalized trithiocarbonate to yield a PDMS66 precursor with a mean degree of functionality of 92 ± 5% as determined by 1H NMR spectroscopy. This PDMS66 precursor was then chain-extended in turn using eight different methacrylic monomers in a low-viscosity silicone oil (decamethylcyclopentasiloxane, D5). Depending on the monomer type, such syntheses proceeded via either RAFT dispersion polymerization or RAFT emulsion polymerization. In each case the target DP of the core-forming block was fixed at 200, and the copolymer concentration was 25% w/w. Transmission electron microscopy studies indicated that kinetically trapped spheres were obtained in almost all cases. The only exception was 2-(dimethylamino)ethyl methacrylate (DMA), which enabled access to spheres, worms, or vesicles. This striking difference is attributed to the relatively low glass transition temperature for this latter block. A phase diagram was constructed for a series of PDMS66–PDMAx nano-objects by systematically increasing the PDMA target DP from 20 to 220 and varying the copolymer concentration between 10 and 30% w/w. Higher copolymer concentrations were required to access a pure worm phase, while only spheres, vesicles, or mixed phases were accessible at lower copolymer concentrations. Gel permeation chromatography studies indicated a linear evolution of number-average molecular weight (Mn) with PDMA DP while dispersities remained below 1.40, suggesting relatively well-controlled RAFT polymerizations. Small-angle X-ray scattering (SAXS) was used to characterize selected examples of spheres, worms, and vesicles. PDMS66–PDMA100–112 worms synthesized at 25–30% w/w formed free-standing gels at 20 °C. Oscillatory rheology studies performed on a 30% w/w PDMS66–PDMA105 worm dispersion indicated a storage modulus (gel strength) of 1057 Pa and a critical gelation concentration (CGC) of approximately 12% w/w. Finally, PDMS66–PDMAx worms could also be prepared in n-dodecane, hexamethyldisiloxane, or octamethylcyclotetrasiloxane. Rotational rheometry studies indicate that such worms are efficient viscosity modifiers for these nonpolar oils.

Show Abstract ▼

Abstract: We determined the intermolecular interaction potential, V(r), of dense lysozyme solutions, which governs the spatial distribution of the protein molecules and the location of its liquid–liquid phase separation (LLPS) region, in various crowding environments applying small-angle X-ray scattering in combination with liquid-state theory. We explored the effect of polyethylene glycol (PEG) on V(r) and the protein’s phase behavior over a wide range of temperatures and pressures, crossing from the dilute to the semidilute polymer regime, thereby mimicking all crowding scenarios encountered in the heterogeneous biological cell. V(r) and hence the protein–protein distances and the phase boundary of the LLPS region strongly depend on the polymer-to-protein size ratio and the polymer concentration. The strongest effect is observed for small-sized PEG molecules, leading to a marked decrease of the mean intermolecular spacing of the protein molecules with increasing crowder concentration. The effect levels off at intermolecular distances where the proteins’ second hydration shells start to penetrate each other. Strong repulsive forces like hydration-shell repulsion and/or soft enthalpic protein-PEG interactions must be operative at short distances which stabilize the protein against depletion-induced aggregation, also at pressures as high as encountered in the deep sea, where pressures up to the kbar-level are encountered.

Show Abstract ▼

Abstract: DNA nanostructures with programmable shape and interactions can be used as building blocks for the self-assembly of crystalline materials with prescribed nanoscale features, holding a vast technological potential. Structural rigidity and bond directionality have been recognised as key design features for DNA motifs to sustain long-range order in 3D, but the practical challenges associated with prescribing building-block geometry with sufficient accuracy have limited the variety of available designs. We have recently introduced a novel platform for the one-pot preparation of crystalline DNA frameworks supported by a combination of Watson–Crick base pairing and hydrophobic forces (Brady et al 2017 Nano Lett. 17 3276–81). Here we use small angle x-ray scattering and coarse-grained molecular simulations to demonstrate that, as opposed to available all-DNA approaches, amphiphilic motifs do not rely on structural rigidity to support long-range order. Instead, the flexibility of amphiphilic DNA building-blocks is a crucial feature for successful crystallisation.

Show Abstract ▼

Abstract: Lactose is the major carbohydrate in milk and, similarly to other sugars, it can exist as two anomers in solution, the α and β forms, with a ratio depending on factors including temperature and pH (mutarotation equilibrium). Lactose is extracted from whey mostly to prevent environmental pollution. In fact, the presence of this sugar can contribute to a dramatic increase in the biological oxygen demand (BOD) of whey, making its direct disposal potentially dangerous for the environment. However, preserving our ecosystem is not the only reason why lactose is recovered. Purified lactose is, in fact, a high value product, commonly used as an excipient in pharmaceutical formulations and as a carrier in dry powder inhalers. Despite the increasing interest that lactose crystallization has recently received, a full understanding of this process is still missing, particularly the link between the process parameters of the crystallization step and the properties of the final product in terms of crystalline structure, purity and particle size and shape distribution. This work is the first comprehensive study of lactose crystallization, exploring cooling and anti-solvent operations, for the determination of the effect of several operative conditions on: (i) the kinetics of nucleation, growth and agglomeration; (ii) the yield of lactose recovery from solution; (iii) the final crystal size and shape distributions; and (iv) the purity of the obtained crystals.