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Efficient hydrogelators will gel water fast and at low concentrations. Small molecule gelling agents that assemble into fibers and fiber networks are particularly effective hydrogelators. Whereas it is straightforward to determine their critical concentration for hydrogelation, the kinetics of hydrogelation is more difficult to study because it is often very fast, occurring on the subsecond time scale. We used a 3D focusing microfluidic device combined with fluorescence microscopy and in situ small-angle X-ray scattering (SAXS) to study the fast pH-induced gelation of a model small molecule gelling agent at the millisecond time scale. The gelator is a 1,3,5-benzene tricarboxamide which upon acidification assembles into nanofibrils and fibril networks that show a characteristic photoluminescence. By adjusting the flow rates, the regime of early nanofibril formation and gelation could be followed along the microfluidic reaction channel. The measured fluorescence intensity profiles were analyzed in terms of a diffusion-advection-reaction model to determine the association rate constant, which is in a typical range for the small molecule self-assembly. Using in situ SAXS, we could determine the dimensions of the fibers that were formed during the early self-assembly process. The detailed structure of the fibers was subsequently determined by cryotransmission electron microscopy. The study demonstrates that 3D focusing microfluidic devices are a powerful means to study the self-assembly on the millisecond time scale, which is applied to reveal early state of hydrogelation kinetics. In combination with in situ fluorescence and X-ray scattering, these experiments provide detailed insights into the first self-assembly steps and their reaction rates.

Liquid microjets play a key role in fiber spinning, inkjet printing, and coating processes. In all of these applications, the liquid jets carry dispersed particles whose spatial and orientational distributions within the jet critically influence the properties of the fabricated structures. Despite its importance, there is currently no knowledge about the orientational distribution of particles within microjets and droplets. Here, we demonstrate a microfluidic device that allows to determine the local particle distribution and orientation by X-ray scattering. Using this methodology, we discovered unexpected changes in the particle orientation upon exiting the nozzle to form a free jet, and upon jet break-up into droplets, causing an unusual biaxial particle orientation. We show how flow and aspect ratio determine the flow orientation of anisotropic particles. Furthermore, we demonstrate that the observed phenomena are a general characteristic of anisotropic particles. Our findings greatly enhance our understanding of particle orientation in free jets and droplets and provide a rationale for controlling particle alignment in liquid jet-based fabrication methodologies.

A F-rich potassium hectorite, [K(0.48(2))](inter)[Mg(2.54(8))Li(0.43)](oct)[Si(4)](tet)O(10)F(2), with a layer charge of x = 0.48 per formula unit (pfu) was synthesized by high temperature melt synthesis. After Mg-exchange, the layer charge could be reduced significantly post synthesis by annealing (250 °C) as confirmed by alkylammonium exchange and cation exchange capacity. By pillaring this new low charge material with Me(2)DABCO(2+) (N,N-dimethyl-1,1-diazabicyclo [2.2.2]octane dication) and Rh(bpy)(3)(3+) (rhodium-tris-2,2'-bipyridin trication), we observed a remarkable increase in micropore volume and pore diameter by Ar/Ar(l) physisorption measurements. This method allows the tailoring of pore sizes of pillared clays by reducing the layer charge and consequently the pillar density.