Pressure Changes Across a Membrane Formed by Coacervation of Oppositely Charged Polymer-Surfactant Systems.

We investigate the mass transfer and membrane growth processes during capsule formation by the interaction of the biopolymer xanthan gum with CnTAB surfactants. When a drop of xanthan gum polymer solution is added to the surfactant solution, a membrane is formed by coacervation. It encapsulates the polymer drop in the surfactant solution. The underlying mechanisms and dynamic processes during capsule formation are not yet understood in detail. Therefore, we characterized the polymer-surfactant complex formation during coacervation by measuring the surface tension and surface elasticity at the solution-air interface for different surfactant chain lengths and concentrations. The adsorption behavior of the mixed polymer-surfactant system at the solution-air interface supports the understanding of observed trends during the capsule formation. We further measured the change in capsule pressure over time and simultaneously imaged the membrane growth via confocal microscopy. The cross-linking and shrinkage during the membrane formation by coacervation leads to an increasing tensile stress in the elastic membrane, resulting in a rapid pressure rise. Afterward, the pressure gradually decreases and the capsule shrinks as water diffuses out. This is not only due to the initial capsule overpressure but also due to osmosis caused by the higher ionic strength of the surfactant solution outside the capsule compared to the polymer solution inside the capsule. The influence of polymer concentration and surfactant type and concentration on the pressure changes and the membrane structure are studied in this work, providing detailed insights into the dynamic membrane formation process by coacervation. This knowledge can be used to produce capsules with tailored membrane properties and to develop a suitable encapsulation protocol in technological applications. The obtained insights into the mass transfer of water across the capsule membrane are important for future usage in separation techniques and the food industry and allow us to better predict the capsule time stability.

Evaluation of Interfacial Structure of Self-Assembled Nanoparticle Layers: Use of Standard Deviation between Calculated and Experimental Drop Profiles as a Novel Method.

The self-assembly of nanoparticles (NPs) at interfaces is currently a topic of increasing interest due to numerous applications in food technology, pharmaceuticals, cosmetology, and oil recovery. It is possible to create tunable interfacial structures with desired characteristics using tailored nanoparticles that can be precisely controlled with respect to shape, size, and surface chemistry. To address these functionalities, it is essential to develop techniques to study the properties of the underlying structure. In this work, we propose an experimental approach utilizing the standard deviation of drop profiles calculated by the Laplace equation from experimental drop profiles (STD), as an alternative to the Langmuir trough or precise microscopic methods, to detect the initiation of closely packed conditions and the collapse of the adsorbed layers of CTAB-nanosilica complexes. The experiments consist of dynamic surface/interfacial tension measurements using drop profile analysis tensiometry (PAT) and large-amplitude drop surface area compression/expansion cycles. The results demonstrate significant changes in STD values at the onset of the closely packed state of nanoparticle-surfactant complexes and the monolayer collapse. The STD trend was explained in detail and shown to be a powerful tool for analyzing the adsorption and interfacial structuring of nanoparticles. Different collapse mechanisms were reported for NP monolayers at the liquid/liquid and air/liquid interfaces. We show that the interfacial tension (IFT) is solely dependent on the extent of interfacial coverage by nanoparticles, while the surfactants regulate only the hydrophobicity of the self-assembled complexes. Also, the irreversible adsorption of nanoparticles and the increasing number of adsorbed complexes after the collapse were observed by performing consecutive drop surface compression/expansion cycles. In addition to a qualitative characterization of adsorption layers, the potential of a quantitative calculation of the parameter STD such as the number of adsorbed nanoparticles at the interface and the distance between them at different states of the interfacial layer was discussed.

Synthesis, Structure, and Heat Capacity of Some Basic Hydroxohalide Glasses of Zirconium and Hafnium.

This work highlights the synthesis and properties of novel basic hydroxohalide glasses of zirconium and hafnium. The hydroxohalide glasses are M(OH)4-αXα·(n)H2O where M represents either zirconium or hafnium, and X represents either chloride or bromide. The chemical structure is investigated using X-ray diffraction, total scattering, and the pair distribution function method to identify the local structure and any short-range connectivity. The thermodynamic properties of the glasses are probed using low-temperature heat capacity, where a gap in the phonon density of states is discussed and related to boson peaks in the heat capacity of the glasses. These results represent the first published synthesis and thermodynamic properties of zirconium and hafnium basic hydroxohalide glasses. Synthesis methods, structural determination, and analysis of the heat capacity data allow for a comprehensive look at the makeup and unique properties of these novel glassy materials. Values of the standard thermodynamic functions Cp,m°, Δ0TSm°, Δ0THm°, and Φm° are also reported.

Ba6Ge2Se12 and Ba7Ge2Se17: Two Centrosymmetric Barium Seleno-Germanates with Polyatomic Anion Disorder.

Herein, the crystal structures and physical properties of two previously unreported barium seleno-germanates, Ba6Ge2Se12 and Ba7Ge2Se17, are presented. Ba6Ge2Se12 adopts the P21/c space group with a = 10.0903(2) Å, b = 9.3640(2) Å, c = 25.7643(5) Å, and ß = 90.303(1)°, whereas Ba7Ge2Se17 crystallizes in the Pnma space group with a = 12.652(1) Å, b = 20.069(2) Å, c = 12.3067(9) Å. Both structures feature polyatomic anion disorder: [Se2]2- in the case of Ba6Ge2Se12 and [GeSe5]4- in the case of Ba7Ge2Se17. The anion disorder is verified by comparing pair distribution functions of ordered and disordered models of the structures. These anions are split unevenly across two possible sets of atomic coordinates. The optical band gaps obtained from the powdered samples are found to be 1.75 and 1.51 eV for Ba6Ge2Se12 and Ba7Ge2Se17, respectively. Differential scanning calorimetry experiments indicate that the compounds are stable under the exclusion of air up to at least 673 K. The thermal diffusivity measurements revealed thermal conductivities reaching values as low as 0.33 W m-1 K-1 in both compounds at 573 K.

Enhanced Piezoelectric Properties From the Electric Field-Induced Ferroelectric Transition at the MPB of BiGaO3-Substitued Na1/2Bi1/2TiO3-BaTiO3(NBT-BT).

A ternary solid solution of lead-free Na1/2Bi1/2TiO3-BaTiO3 and BiGaO3 (NBT-BT-BG) was prepared using conventional, solid-state synthesis. Compositions were prepared near the morphotropic phase boundary (MPB) of ( 1- x )NBT- x BT, located near x = 0.04 -0.09 , and then systematically substituted with 2-5 mol% BG to investigate the effect of the compositional change on the accompanying properties. Dielectric, ferroelectric (FE), and piezoelectric properties were analyzed and compared for all prepared compositions. The FE to ergodic (ER) relaxor transition temperature ( [Formula: see text]) and the reversible electric field-induced relaxor to FE transition were investigated to determine their effects on the strain response. It was found that the MPB composition of 0.93NBT-0.07BT required the least amount of the tertiary phase, 3 mol% BG, to reach a disordered, ER state while also requiring the largest electric fields to induce an FE phase compared with similarly substituted NBT- x BT samples. This led to a maximum unipolar strain of 0.53% (d33* = 866 pm/V) for the 0.93NBT-0.07BT-0.04BG composition. The largest strains for each system occurred in compositions that were in the ER region at room temperature. These results demonstrate that the addition of BG most effectively destabilizes the long-range dipole order near the MPB composition of NBT-BT, which results in an enhanced electric field-induced strain.

Dielectric Properties of x BiInO3-(1-x) Pb(Zr0.52Ti0.48)O3 Solid Solutions.

This study focused on the synthesis and electrical property measurements of the lead zirconate titanate (PZT)-bismuth indate (BI) perovskite solid solution system. As the PZT binary system is a very well-developed and integrated materials system, identifying new ternary systems based on PZT would allow for a new dimension of control into the exploration and improvement of its electrical properties, which could enable enhancements in the performance of current technology and devices. Here, the solid solution of BiInO3-PbZrO3-PbTiO3 ( x BI-(1- x ) PZT 52/48) was explored. Through calcination studies, stable solid solutions were obtained, and compositions up to a maximum of 15-mol% BI were synthesized. With increasing BI content, the symmetry transitioned from a tetragonal P4mm phase toward a rhombohedral R3m phase. The Curie temperature of these samples decreased with increasing mol% BI from ~390 °C in pure PZT 52/48 to 322 °C in 10% BI. Ferroelectric and piezoelectric studies of the 2.5% BI sample showed a coercive field of 14.4 kV/cm, [Formula: see text]/cm2, [Formula: see text]/cm2, and a d33∗ = 280 pC/N under a maximum applied field of 70 kV/cm at 1 Hz.

Neutron Total Scattering Studies of Group II Titanates (ATiO3, A2+ = Mg, Ca, Sr, Ba).

Neutron total scattering measurements were conducted on MgTiO3, CaTiO3, SrTiO3, and BaTiO3 to simultaneously investigate the local and average structure of these materials. The local structures of MgTiO3, CaTiO3, and SrTiO3 were well modelled using the refined average structural models: trigonal R[Formula: see text], orthorhombic Pbnm, and cubic Pm[Formula: see text]m respectively. However the local structure for BaTiO3, at both temperatures where the average structure is orthorhombic Amm2 and tetragonal P4mm, was best described by the rhombohedral R3m model. Only the R3m model was able to account for the observed displacement of titanium in the [111] direction. Furthermore, box-car type refinements were conducted. These refinements show that the coherence length of the rhombohedral distortion is around 10 Å, at larger r-ranges the local distortions become misaligned and average out to Amm2 and P4mm.

Structural convergence properties of amorphous InGaZnO4 from simulated liquid-quench methods.

The study of structural properties of amorphous structures is complicated by the lack of long-range order and necessitates the use of both cutting-edge computer modeling and experimental techniques. With regards to the computer modeling, many questions on convergence arise when trying to assess the accuracy of a simulated system. What cell size maximizes the accuracy while remaining computationally efficient? More importantly, does averaging multiple smaller cells adequately describe features found in bulk amorphous materials? How small is too small? The aims of this work are: (1) to report a newly developed set of pair potentials for InGaZnO4 and (2) to explore the effects of structural parameters such as simulation cell size and numbers on the structural convergence of amorphous InGaZnO4. The total number of formula units considered over all runs is found to be the critical factor in convergence as long as the cell considered contains a minimum of circa fifteen formula units. There is qualitative agreement between these simulations and X-ray total scattering data - peak trends and locations are consistently reproduced while intensities are weaker. These new IGZO pair potentials are a valuable starting point for future structural refinement efforts.

Aqueous tantalum polyoxometalate reactivity with peroxide.

Peroxide ligation of aqueous metal-oxo clusters provides rich speciation and structural diversity, radiation sensitivity for manipulation with light, and both broadens and shifts pH-range stability. Here we demonstrate peroxide ligation of the polyoxometalate (POM) [Ta6O19]8-. We study in detail solution speciation of the peroxide-substituted cluster, and benchmark it to the peroxide-ligated niobate analogue, [Nb6O10(OH)3(O2)6]5-, whose solid-state structure has been reported. Raman and electrospray ionization mass spectroscopy do not detect any significant differences between the two analogues. However, small and wide-angle and total X-ray scattering strongly indicate that peroxide promotes linking of the hexameric tantalate clusters, rather than terminating and capping the clusters, as observed for the niobate analogue. We used computational studies to identify Raman peak positions, determine the energetics of exchange of oxo-ligands for peroxo-ligands, and provide models to help explain the X-ray scattering data. Understanding the solution speciation of peroxide-substituted polyoxotantalates is an important step towards its use in solution processed thin film materials, as well as developing new Ta-POM chemistry.

New Mechanistic Insights on Na-Ion Storage in Nongraphitizable Carbon.

Nongraphitizable carbon, also known as hard carbon, is considered one of the most promising anodes for the emerging Na-ion batteries. The current mechanistic understanding of Na-ion storage in hard carbon is based on the "card-house" model first raised in the early 2000s. This model describes that Na-ion insertion occurs first through intercalation between graphene sheets in turbostratic nanodomains, followed by Na filling of the pores in the carbon structure. We tried to test this model by tuning the sizes of turbostratic nanodomains but revealed a correlation between the structural defects and Na-ion storage. Based on our experimental data, we propose an alternative perspective for sodiation of hard carbon that consists of Na-ion storage at defect sites, by intercalation and last via pore-filling.

Synthesis and solid-state structural characterization of a series of aqueous heterometallic tridecameric group 13 clusters.

The synthesis and solid-state characterization of a complete series of new heterometallic aqueous nanoscale Ga/In tridecameric clusters is presented. These hydroxo-aquo species significantly expand the library of discrete, aqueous group 13 clusters. This report details the synthetic and structural characterization of these compounds, which are of interest as precursors (inks) for thin-film oxides with materials applications. Single-crystal X-ray diffraction (XRD) data show that the hexagonal unit cell lengths of these clusters fall within the range a, b = 20.134-20.694 Å and c = 18.266-18.490 Å. The unit cell volumes become larger (V = 6494-6774 A(3)) with increasing indium occupancy. The compositions of several Ga/In clusters determined by electron probe microanalysis and elemental analysis are in agreement with single-crystal XRD results. The transformation of the Ga/In clusters to metal oxides at high temperature was studied using variable-temperature powder XRD. With heating, the Ga/In clusters with lower indium occupancies convert to the ß-Ga2O3 structure. For clusters with higher indium occupancies, phase separation occurs, and an In2O3 bixbyite-type structure forms. The stoichiometric control at the molecular level demonstrated herein is important in designing functional thin films of metal oxides due to the tunable nature of these heterometallic solution precursors. In addition, information about the solid-state structure of these compounds leads to a fundamental understanding of the materials properties of these clusters for future thin-film and precursor development.

Molecular packing and magnetic properties of lithium naphthalocyanine crystals: hollow channels enabling permeability and paramagnetic sensitivity to molecular oxygen.

The synthesis, structural framework, magnetic and oxygen-sensing properties of a lithium naphthalocyanine (LiNc) radical probe are presented. LiNc was synthesized in the form of a microcrystalline powder using a chemical method and characterized by electron paramagnetic resonance (EPR) spectroscopy, magnetic susceptibility, powder X-ray diffraction analysis, and mass spectrometry. X-Ray powder diffraction studies revealed a structural framework that possesses long, hollow channels running parallel to the packing direction. The channels measured approximately 5.0 × 5.4 Å(2) in the two-dimensional plane perpendicular to the length of the channel, enabling diffusion of oxygen molecules (2.9 × 3.9 Å(2)) through the channel. The powdered LiNc exhibited a single, sharp EPR line under anoxic conditions, with a peak-to-peak linewidth of 630 mG at room temperature. The linewidth was sensitive to surrounding molecular oxygen, showing a linear increase in pO(2) with an oxygen sensitivity of 31.2 mG per mmHg. The LiNc microcrystals can be further prepared as nano-sized crystals without the loss of its high oxygen-sensing properties. The thermal variation of the magnetic properties of LiNc, such as the EPR linewidth, EPR intensity and magnetic susceptibility revealed the existence of two different temperature regimes of magnetic coupling and hence differing columnar packing, both being one-dimensional antiferromagnetic chains but with differing magnitudes of exchange coupling constants. At a temperature of ∼50 K, LiNc crystals undergo a reversible phase transition. The high degree of oxygen-sensitivity of micro- and nano-sized crystals of LiNc, combined with excellent stability, should enable precise and accurate measurements of oxygen concentration in biological systems using EPR spectroscopy.

Quasiclassical trajectory study of the vibrational quenching of hydroxyl radicals through collision with O atoms.

The collisional removal of vibrationally excited OH radicals by O atoms is studied by the quasiclassical trajectory method. To evaluate the effect of different topological features on the scattering processes two different global potential energy surfaces, DMBE IV and TU, are used. Results for reactive, exchange, and inelastic scattering probabilities are reported for central collisions (with zero total angular momentum) with a fixed relative translational energy for vibrational levels of OH ranging from nu=1 to v=8. Vibrational state distributions of product molecules are also compared on the two potential energy surfaces. Both surfaces predict higher probabilities for reaction than for exchange or inelastic scattering. The vibrational state distributions of the product diatomic molecules are different on the two surfaces. In particular, the two surfaces give substantially different probabilities for multiquantum OH vibrational relaxation transitions OH(v)+O-->OH(v')+O.

Magnetic behaviour of layered Ag(II) fluorides.

Fluoride phases that contain the spin-1/2 4d9 Ag(II) ion have recently been predicted to have interesting or unusual magnetochemistry, owing to their structural similarity to the 3d9 Cu(II) cuprates and the covalence associated with this unusual oxidation state of silver. Here we present a comprehensive study of structure and magnetism in the layered Ag(II) fluoride Cs2AgF4, using magnetic susceptometry, inelastic neutron scattering techniques and both X-ray and neutron powder diffraction. We find that this material is well described as a two-dimensional ferromagnet, in sharp contrast to the high-T(C) cuprates and a previous report in the literature. Analyses of the structural data show that Cs2AgF4 is orbitally ordered at all temperatures of measurement. Therefore, we suggest that orbital ordering may be the origin of the ferromagnetism we observe in this material.