The orientation ordering and assembly behavior of silica–nickel Janus particles in a static external magnetic field were probed by ultra small-angle X-ray scattering (USAXS). Even in a weak applied field, the net magnetic moments of the individual particles aligned in the direction of the field, as indicated by the anisotropy in the recorded USAXS patterns. X-ray photon correlation spectroscopy (XPCS) measurements on these suspensions revealed that the corresponding particle dynamics are primarily Brownian diffusion [Zinn, Sharpnack & Narayanan (2023). Soft Matter, 19, 2311–2318]. At higher fields, the magnetic forces led to chain-like configurations of particles, as indicated by an additional feature in the USAXS pattern. A theoretical framework is provided for the quantitative interpretation of the observed anisotropic scattering diagrams and the corresponding degree of orientation. No anisotropy was detected when the magnetic field was applied along the beam direction, which is also replicated by the model. The method presented here could be useful for the interpretation of oriented scattering patterns from a wide variety of particulate systems. The combination of USAXS and XPCS is a powerful approach for investigating asymmetric colloidal particles in external fields.

The orientation behavior and the translational dynamics of spherical magnetic silica-nickel Janus colloids in an external magnetic field have been studied by small-angle X-ray scattering and X-ray photon correlation spectroscopy at ultra small-angles. For weak applied fields and at low volume fractions, the particle dynamics is dominated by Brownian motion even though the net magnetic moments of the individual particles are aligned in the direction of the field as indicated by the anisotropy in the small-angle scattering patterns. For higher fields the magnetic forces result in more complex structural changes with nickel caps of Janus particles pointing predominantly along the applied magnetic field. The alignment ultimately leads to chain-like configurations and the intensity-intensity autocorrelation functions, g2(q,t), show a second slower decay which becomes more pronounced at higher volume fractions. A direction dependent analysis of g2(q,t) revealed a faster than exponential decay perpendicular to the field which is related to the sedimentation of magnetically ordered domains. The corresponding velocity fluctuations could be decoupled from the diffusion of particles by decomposing g2(q,t) into advective and diffusive contributions. Finally, the particle dynamics becomes anisotropic at higher volume fractions and strong magnetic fields. The derived translational diffusion coefficients indicate slower particle dynamics perpendicular to the field as compared to the parallel direction.

Organic sulfur plays a crucial role in the biogeochemistry of aquatic sediments, especially in low sulfate (< 500 mu M) environments like freshwater lakes and the Earth's early oceans. To better understand organic sulfur cycling in these systems, we followed organic sulfur in the sulfate-poor (< 40 mu M) iron-rich (30-80 mu M) sediments of Lake Superior from source to sink. We identified microbial populations with shotgun metagenomic sequencing and characterized geochemical species in porewater and solid phases. In anoxic sediments, we found an active sulfur cycle fueled primarily by oxidized organic sulfur. Sediment incubations indicated a microbial capacity to hydrolyze sulfonates, sulfate esters, and sulfonic acids to sulfate. Gene abundances for dissimilatory sulfate reduction (dsrAB) increased with depth and coincided with sulfide maxima. Despite these indicators of sulfide formation, sulfide concentrations remain low (< 40 nM) due to both pyritization and organic matter sulfurization. Immediately below the oxycline, pyrite accounted for 13% of total sedimentary sulfur. Both free and intact lipids in this same interval accumulated disulfides, indicating rapid sulfurization even at low concentrations of sulfide. Our investigation revealed a new model of sulfur cycling in a low-sulfate environment that likely extends to other modern lakes and possibly the ancient ocean, with organic sulfur both fueling sulfate reduction and consuming the resultant sulfide.

In situ X-ray scattering kinetics and population balance modeling of crystal nucleation and growth.

Membrane-delimited compartments, as lipid vesicles, are ubiquitous in natural and synthetic systems. The mechanical properties of such vesicles are crucial for several physical, chemical, and biological processes. However, their accurate determination is still challenging and requires sophisticated instruments and data analysis. Here we report the first evidence that the surface plasmon resonance (SPR) of citrated gold nanoparticles (AuNPs) adsorbed on synthetic vesicles is finely sensitive to the vesicles’ mechanical properties. We leverage this finding to demonstrate that the spectrophotometric tracking of the SPR provides quantitative access to the stiffness of vesicles of synthetic and natural origin, such as extracellular vesicles (EVs). This plasmon-based “stiffness nanoruler” paves the way for developing a facile, cost-effective, and high-throughput method to assay the mechanical properties of vesicles of nanometric size and unknown composition.

The structural organization of the concentration polarization layer (CPL) during the cross-flow membrane separation process of anisometric aqueous suspensions of colloidal cellulose nanocrystals and beidellite clay particles has been characterized by in situ time-resolved small-angle X-ray scattering (SAXS). Dedicated cross-flow filtration cells were implemented on the ID02 TRUSAXS beamline at the European Synchrotron Radiation Facility (Grenoble, France). From the analysis of the scattered intensities and structure factors of particles in the CPL, both the concentration profiles ɸ(Δz,Δt) and anisotropic structural organization have been characterized as a function of filtration time (Δt) and distance from the membrane surface (Δz). Remarkably, a coupling between concentration and anisotropy was revealed and modeled using either a simple or stretched exponential trend for rod- or disk-like systems, respectively. Using a simple filtration model, the time evolution of the deposit thickness, membrane resistance and specific resistance of the deposit, deduced from an analysis of the normalized concentration profiles, allowed directly predicting the rapid decay of permeate flux associated to the exponential growth of concentration and anisotropic organization inside the CPL. Ex situ scanning electron microscopy (SEM) observations and wide-angle X-ray diffraction (WAXD) analyses performed on dried deposits parallel and perpendicular to the membrane surface revealed well-defined layered structures from nanometer to micrometer length scales.

We have used time-resolved small-angle X-ray scattering (SAXS) to study the adhesion of lipid vesicles in the electrostatic strong-coupling regime induced by divalent ions. The bilayer structure and the interbilayer distance d(w) between adhered vesicles was studied for different DOPC:DOPS mixtures varying the surface charge density of the membrane, as well as for different divalent ions, such as Ca2+, Sr2+, and Zn2+. The results are in good agreement with the strong coupling theory predicting the adhesion state and the corresponding like-charge attraction based on ion-correlations. Using SAXS combined with the stopped-flow rapid mixing technique, we find that in highly charged bilayers the adhesion state is only of transient nature, and that the adhering vesicles subsequently transform to a phase of multilamellar vesicles, again with an inter-bilayer distance according to the theory of strong binding. Aside from the stopped-flow SAXS instrumentations used primarily for these results, we also evaluate microfluidic sample environments for vesicle SAXS in view of future extension of this work.

We have discovered the existence of polydisperse high internal-phase-ratio emulsions (HIPE) in which the internal-phase droplets, present at 95% volume fraction, remain spherical and organise themselves according to Apollonian packing rules. These polydisperse HIPEs are formed by emulsifying oil dropwise in a surfactant-poor aqueous continuous phase. After stirring has ceased, their droplet size distributions begin to evolve spontaneously and continuously through coalescence towards well-defined power laws with the Apollonian exponent. Small-angle X-ray Scattering performed on aged HIPEs demonstrate that the droplet packing structure agrees with that of a numerically simulated random Apollonian packing. We argue that when such concentrated emulsions are allowed to evolve, the coalescing droplets must obey volume and sphericity conservation. This leads to a mechanism that differs from typical coalescence in dilute emulsions.

Different phoretic effects have been widely exploited for designing self-propelled colloidal systems, but the underlying wave vector dependent dynamics has been little investigated. In this work, the out-of-equilibrium dynamics of colloids in near-critical liquid mixtures undergoing spinodal phase separation was probed by x-ray photon correlation spectroscopy (XPCS). The emergent dynamics of charge stabilized silica and silica-nickel Janus particles upon a temperature jump into the two-phase region of the solvent mixture displayed similar features at the initial stage. In both systems, the phoretic dynamics is dominated by velocity fluctuations induced by the solvent concentration fluctuations and the hydrodynamic flow during the coarsening process. Furthermore, relaxation rates of the diffusive part of the dynamics manifested an anomalous wave vector dependence akin to the superdiffusive behavior with an effective diffusion coefficient significantly larger than the Brownian limit. For smaller temperature jumps, velocity fluctuations exhibited a broader distribution with silica and Janus colloids showing qualitatively different behavior. The velocity fluctuations decayed with time and the dynamics reverted to diffusive behavior upon completion of the phase separation. Presented results illustrate the ability to probe faster collective dynamics pertinent to active colloids using multispeckle XPCS.

A series of bis(4-alkoxyphenyl) viologen bis(triflimide) salts with alkoxy chains of different lengths were synthesized by the metathesis reaction of respective bis(4-alkoxyphenyl) viologen dichloride salts, which were in turn prepared from the reaction of Zincke salt with the corresponding 4-n-alkoxyanilines, with lithium triflimide in methanol. Their chemical structures were characterized by 1H and 13C nuclear magnetic resonance spectra and elemental analysis. Their thermotropic liquid-crystalline (LC) properties were examined by differential scanning calorimetry, polarizing optical microscopy, and variable temperature X-ray diffraction. Salts with short length alkoxy chains had crystal-to-liquid transitions. Salts of intermediate length alkoxy chains showed both crystal-to-smectic A (SmA) transitions, Tms, and SmA-to-isotropic transitions, Tis. Those with longer length of alkoxy chains had relatively low Tms at which they formed the SmA phases that persisted up to the decomposition at high temperatures. As expected, all of them had excellent thermal stabilities in the temperature range of 330–370 °C. Their light-emitting properties in methanol were also included.

Advances in modern interface- and material sciences often rely on the understanding of a system's structure-function relationship. Designing reproducible experiments that yield in situ time-resolved structural information at fast time scales is therefore of great interest, e.g., for better understanding the early stages of self-assembly or other phase transitions. However, it can be challenging to accurately control experimental conditions, especially when samples are only available in small amounts, prone to agglomeration, or if X-ray compatibility is required. We address these challenges by presenting a microfluidic chip for triggering dynamics via rapid diffusive mixing for in situ time-resolved X-ray investigations. This polyimide/Kapton-only-based device can be used to study the structural dynamics and phase transitions of a wide range of colloidal and soft matter samples down to millisecond time scales. The novel multiangle laser ablation three-dimensional (3D) microstructuring approach combines, for the first time, the highly desirable characteristics of Kapton (high X-ray stability with low background, organic solvent compatibility) with a 3D flow-focusing geometry that minimizes mixing dispersion and wall agglomeration. As a model system, to demonstrate the performance of these 3D Kapton microfluidic devices, we selected the non-solvent-induced self-assembly of biocompatible and amphiphilic diblock copolymers. We then followed their structural evolution in situ at millisecond time scales using on-the-chip time-resolved small-angle X-ray scattering under continuous-flow conditions. Combined with complementary results from 3D finite-element method computational fluid dynamics simulations, we find that the nonsolvent mixing is mostly complete within a few tens of milliseconds, which triggers initial spherical micelle formation, while structural transitions into micelle lattices and their deswelling only occur on the hundreds of milliseconds to second time scale. These results could have an important implication for the design and formulation of amphiphilic polymer nanoparticles for industrial applications and their use as drug-delivery systems in medicine.

The hydrophobic collapse is a structural transition of grafted polymer chains in a poor solvent. Although such a transition seems an intrinsic event during clustering of polymer-stabilized nanoparticles in the liquid phase, it has not been resolved in real time. In this work, we implemented a microfluidic 3D-flow-focusing mixing reactor equipped with real-time analytics, small-angle X-ray scattering (SAXS), and UV-vis-NIR spectroscopy to study the early stage of cluster formation for polystyrene-stabilized gold nanoparticles. The polymer shell dynamics obtained by in situ SAXS analysis and numerical simulation of the solvent composition allowed us to map the interaction energy between the particles at early state of solvent mixing, 30 ms behind the crossing point. We found that the rate of hydrophobic collapse depends on water concentration, ranging between 100 and 500 nm/s. Importantly, we confirmed that the polymer shell collapses prior to the commencement of clustering.

Successful implementation of the single-photon-counting Eiger 500k pixel array detector for sub-millisecond X-ray photon correlation spectroscopy (XPCS) measurements in the ultra-small-angle scattering region is reported. The performance is demonstrated by measuring the dynamics of dilute silica colloids in aqueous solvents when the detector is operated at different counter depths, 4, 8 and 12bit. In the fastest mode involving 4bit parallel readout, a stable frame rate of 22kHz is obtained that enabled measurement of intensity-intensity autocorrelation functions with good statistics down to the 50 mu s range for a sample with sufficient scattering power. The high frame rate and spatial resolution together with large number of pixels of the detector facilitate the investigation of sub-millisecond dynamics over a broad length scale by multispeckle XPCS. This is illustrated by an example involving phoretic motion of colloids during the phase separation of the solvent.

A series of extended, symmetric viologen triflimides were synthesised by the metathesis reaction of lithium triflimide with the respective viologen tosyalates in methanol. Their chemical structures were characterised by Fourier Transform Infrared, H-1 and C-13 Nuclear Magnetic Resonance spectroscopy and elemental analysis. Their thermotropic liquid-crystalline (LC) properties were examined by a number of experimental techniques including differential scanning calorimetry, thermogravimetric analysis, polarising optical microscopy and variable temperature X-ray diffraction. The viologen salts containing alkyl chain of two carbon and three carbon atoms were relatively low melting salts. Those of alkyl chains of four carbon and five carbon atoms formed ionic liquids at 88 and 42 degrees C, respectively. Those of alkyl chain of 9, 10 and 11 carbon atoms were high melting salts, as high as 166 degrees C. Those of higher alkyl chains of 16, 18 and 20 carbon atoms showed thermotropic LC phases forming SmC, SmA and an unidentified smectic (SmX) phases, and showed SmA to isotropic transitions at high temperatures. As expected, all the viologen triflimides had excellent stabilities in the temperature range of 338-365 degrees C. [GRAPHICS] .

Recent inelastic X-ray scattering (IXS) experiments on mesogens have revealed entirely new capabilities with regards to their nanoscale phonon-assisted heat management. Mesogens such as nematic liquid crystals (LCs) are appealing systems for study because their structure and morphology can easily be tuned. We report on Q-resolved ultra-high-resolution IXS, X-ray diffraction, and THz time-domain spectroscopy experiments combined with large-scale all-atom molecular dynamics simulations on the dynamic properties of 5CB LCs. For the first time, we observe a strong mixing of phonon excitations originating from independent in-phase and out-of-phase van-der-Waals-mediated displacement patterns. The coexistence of transverse acoustic and optical modes of 5CB LCs at near room temperature is revealed through the emergent transverse phonon gap and THz light-phonon coupling taking place within the same energy range. Furthermore, our experimental observations are supported by analysis showing correlations of spontaneous fluctuations of LCs on picosecond time scales. These findings are significant for the design of a new generation of soft molecular vibration-sensitive nanoacoustic and optomechanical applications.

Recent studies of photoalignment of liquid crystals (LCs) on chalcogenide surfaces have a rich variety of mechanisms responsible for the photoalignment on these materials. Both chalcogenide surface-mediated and LC bulk-mediated photoalignment were observed. We report on investigation toward understanding the origin of the chalcogenide surface-mediated photoalignment. The contributions of light-induced optical and surface morphological anisotropy of the chalcogenide surface were studied. Light-induced optical anisotropy in the film was observed by polarization interferometry and the surface anisotropy was measured by high-resolution x-ray reflectivity. The data reveals the lack of a strong anisotropy in the surfaces' morphology after irradiation with polarized blue light. At the same time, an evident correlation between the anchoring energy and the quality of the photoalignment was observed. This allows us to conclude that the photoalignment of LCs on chalcogenide surfaces is mainly determined by a light-induced anisotropic distribution of the glass structural elements in the bulk and on the chalcogenide surface.

The results of high-resolution x-ray reflectivity study of nano-dimensionally thin arsenic trisulfide (As2S3) glass films reveal surface roughness anisotropy upon prolonged irradiation with polarized 436 nm blue light. The anisotropy correlates with the photoinduced anisotropy and LC photoalignment observed on these thin films. However, the As2S3 film's thickness reduces drastically during the reflectivity experiments, and ambient oxygen and moisture penetrate the film and create a second altered thin layer on top of a thicker film of As2S3. The results confirm the viability of As2S3 films for non-contact LC photoalignment material but suggests the need for further process optimization to reduce the films' degeneration to increase their effectiveness.

The investigation of phononic collective excitations in soft matter systems at the molecular scale has always been challenging due to limitations of experimental techniques in resolving low-energy modes. Recent advances in inelastic X-ray scattering (IXS) enabled the study of such systems with unprecedented spectral contrast at meV excitation energies. In particular, it has become possible to shed light on the low-energy collective motions in materials whose morphology and phase behavior can easily be manipulated, such as mesogenic systems. The understanding of collective mode behavior with a Q-dependence is the key to implement heat management based on the control of a sample structure. The latter has great potential for a large number of energy-inspired innovations. As a first step toward this goal, we carried out high contrast IXS measurements on a liquid crystal sample, D7AOB, which exhibits solid-like dynamic features, such as the coexistence of longitudinal and transverse phononic modes. For the first time, we found that these terahertz phononic excitations persist in the crystal, smectic A, and isotropic phases. Furthermore, the intermediate smectic A phase is shown to support a van der Waals-mediated nonhydrodynamic mode with an optical-like phononic behavior. The tunability of the collective excitations at nanometer-terahertz scales via selection of the sample mesogenic phase represents a new opportunity to manipulate optomechanical properties of soft metamaterials.

A series of 4,4'-dialkoxy-3,3'-diaminobiphenyl compounds were synthesised by three-step procedure that involves alkylation, nitration and reduction reactions. Their chemical structures were characterised by FTIR, H-1 and C-13 spectroscopy and elemental analysis. Their thermotropic liquid-crystalline (LC) properties were examined by a number of experimental techniques including differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), polarising optical microscopy (POM) and variable temperature X-ray diffraction (VT-XRD). The 4,4'-dialkoxy-3,3'-dinitrobipheyl compounds, precursors to the diamine compounds, were also examined for their thermotropic LC properties. POM studies of focal conic textures and VT-XRD of the 3,3'-diaminobiphenyl derivatives having flexible alkyl chains (C-6-C-12) exhibited the smectic A (SmA) phase independent of the length of alkyl chains. Similarly, the 3,3'-dinitrobiphenyl derivatives containing alkyl chains C-7, and C-9-C-11 exhibit the SmA phase, those containing C-8 formed the smectic C (SmC) phase and C-12 formed both the SmA and smectic B (SmB) phases, respectively. The 3,3'-diaminobiphenyl derivatives had excellent thermal stability in the temperature range of 237-329 degrees C, while those of 3,3'-dinitrobiphenyl derivatives were in the temperature range of 270-321 degrees C. The 3,3'-diaminobiphenyl derivatives emitted UV light both in chloroform and acetonitrile.[GRAPHICS].

Thermotropic properties of catanionic surfactants are influenced by the headgroups as well as hydrocarbon chains. A series of eight catanionic surfactants were synthesized from quaternary ammonium surfactants as the cationic counterpart and dodecylbenzenesulfonate (DBS) as the anionic counterpart and their structures and purities established. Thermal Gravimetric Analysis (TGA), Differential Scanning Calorimetry (DSC), Hot-Stage Polarized Light Microscopy (HSPLM), and X-ray Diffraction (XRD) were used to characterize the thermal and liquid crystalline properties of the derived catanionic surfactants. These surfactants form hexagonal columnar (Col(h)) phase before isotropization. Their phase behavior is rather complex depending on the chain length, symmetry, and number of chains. In all these surfactants, the thermal stability is influenced by the nature of the headgroup. Mesomorphism on the other hand is a result of the interplay between headgroup interactions and chain interactions. In general, formation of mesophases at lower temperature is favored as the number of CH2 groups per molecule is increased. (C) 2014 Elsevier B.V. All rights reserved.