In-situ Investigations of Molecular Self-Assembly Using Microfluidics

© 2018 Dr Susanne SeibtThe general aim of this work was to study the growth kinetics of nanoparticles, self-assembly processes of hydrogelators and polymers as well as the flow-orientated alignment of anisotropic particles. This was enabled by the combination of highly optimised microfluidic devices with material-dependent analytical methods, including optical spectroscopy, fluorescence microscopy and X-ray scattering. In particular, this thesis focuses on the in-situ kinetic investigations of processes occurring during the reactions. Providing temporal resolutions down to milliseconds, direct insights in reactions were possible

Microfluidics for Time-Resolved Small-Angle X-Ray Scattering

With the advent of new in situ structural characterisation techniques including X-ray scattering, there has been an increased interest in investigations of the reaction kinetics of nucleation and growth of nanoparticles as well as self-assembly processes. In this chapter, we discuss the applications of microfluidic devices specifically developed for the investigation of time resolved analysis of growth kinetics and structural evolution of nanoparticles and nanofibers. We focus on the design considerations required for spectrometry and SAXS analysis, the advantages of using a combination of SAXS and microfluidics for these measurements, and discuss in an applied fashion the use of these devices for time-resolved research

In-situ investigations of molecular self-assembly using microfluidics

© 2018 Dr Susanne SeibtThe general aim of this work was to study the growth kinetics of nanoparticles, self-assembly processes of hydrogelators and polymers as well as the flow-orientated alignment of anisotropic particles. This was enabled by the combination of highly optimised microfluidic devices with material-dependent analytical methods, including optical spectroscopy, fluorescence microscopy and X-ray scattering. In particular, this thesis focuses on the in-situ kinetic investigations of processes occurring during the reactions. Providing temporal resolutions down to milliseconds, direct insights in reactions were possible

Hydrogelation Kinetics Measured in a Microfluidic Device with in Situ X-ray and Fluorescence Detection

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

Hydrogelation Kinetics Measured in a Microfluidic Device with in Situ X‑ray and Fluorescence Detection

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

Stress sensitivity of gypsum dehydration kinetics at constant uniaxial stress under dry conditions

We recently showed that the dehydration of alabaster, natural gypsum rock with randomly oriented grains, can be accelerated by a factor of two through the application of an elastic differential pre-stress of ~ 5 MPa applied via a uniaxial constant-displacement boundary condition (https://doi.org/10.1038/s43246-021-00156-9). Here, we present a novel series of gypsum dehydration experiments using a new in-situ experimental cell monitored with fast synchrotron transmission small- and wide-angle X-ray scattering (SAXS/WAXS) to investigate if an acceleration of the kinetics also occurs at constant uniaxial stress. Prior to stressing and heating, the loaded sample chamber was flushed with nitrogen to remove atmospheric moisture and finally locked filled with the nitrogen atmosphere pressurised to 1 bar. Six increasing uniaxial stresses in the interval [0;10] MPa were studied at a dehydration temperature of 142˚C. A strongly nonlinear acceleration of dehydration rate is observed over the studied stress interval. At 10 MPa, the reductions of induction and characteristic time amount to ~60% and ~50%, respectively. 2D SAXS patterns generally evolve from isotropic to highly anisotropic shapes, indicating preferential growth of nano-scatterers. Post-mortem scanning-electron imaging reveals that the phase transformation occurs via pseudomorph replacement. These results are largely consistent with our previous experiments and support the notion that tectonic stresses affect mineral transformation kinetics

Correlating structure and activity of pepsin enzyme in H2O and D2O for the study of gastric digestion

D2O, an isotope of H2O, is commonly used as a solvent in neutron scattering; the large difference in scattering length density between H and D can provide better contrast between the sample and the solvent. However, this is of concern for studies using enzymes as the use of D2O can influence protein interactions (due to differences in hydrogen bonding) and is therefore expected to affect the function, activity and solubility of enzymes. Neutron-based in vitro digestion assays on proteins, including those found in food or as oral protein and peptide drugs, often involve different solvents or pH conditions where the activity of the digestive enzyme may not be optimal. Herein, we investigate the structure and activity of the main gastric protease, porcine pepsin, in both H2O and D2O at pH values in the range 1 – 8. We showed that the activity of pepsin was lower in D2O, although the relative change in activity with pH was similar for both solvents. We demonstrated using a combination of SAXS and CD that this relative change in activity was not related to any structural change within the protein but was, rather, linked to relative changes in solubility of the protein

Bicontinuous microemulsions with extremely high temperature stability based on skin friendly oil and sugar surfactant

Schulreich C, Angermann C, Hoehn S, et al. Bicontinuous microemulsions with extremely high temperature stability based on skin friendly oil and sugar surfactant. Colloids And Surfaces A Physicochemical And Engineering Aspects. 2013;418:39-46.In the present article the phase behavior of microemulsions based on isononyl isononanoate (Lanol 99), sugar surfactant Simulsol SL55 (C-12/14 G(1.3)), D2O/water, and the cosurfactant benzyl alcohol is studied and the bicontinuous phase is identified. Using small angle neutron scattering (SANS) the internal structure of the bicontinuous phase is characterized. In the experiments a temperature range from 261 K to 343 K was covered. The prepared microemulsions were found to exhibit nearly no temperature dependence with respect to their structure and phase behavior. At low temperatures inside the microemulsions water exists in a supercooled liquid state. (C) 2012 Published by Elsevier B.V