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X-Ray Studies of Liquid Interfaces in Model Solvent Extraction Systems
Published in Bruce A. Moyer, Ion Exchange and Solvent Extraction: Volume 23, 2019
Vaknin’s group has used several X-ray scattering techniques to study the interaction of DHDP with monovalent Cs+ at the water surface. As one example, they measured anomalous X-ray reflectivity to characterize the Cs+ distribution under these conditions.63 By measuring X-ray reflectivity using X-ray energies near and far from an electronic absorption edge of Cs+ (specifically, the L3 edge), the measured electron-density profile gains a sensitivity to the presence of Cs because its cross-section for X-ray scattering varies significantly at the selected energies (Figure 4.11a). Figure 4.11b shows that the interfacial distribution exhibits a strong dependence on the bulk concentration of Cs+, disagreeing with calculations that assume that all DHDP molecules are fully deprotonated at neutral pH (roughly pH 6). When the effect of competitive hydronium (H3O+) binding to the phosphate head-group was considered in addition to Cs+ binding the data show agreement with Poisson–Boltzmann calculations over five orders of magnitude in bulk ion concentration (Figure 4.11b shows a subset of these data). Note that the spatial resolution of these measurements, 4 Å, is well matched to the size of the head-group and bound ions. The in-plane order of DHDP molecules was also examined in this study by grazing-incidence X-ray diffraction. A close-packed hexagonal structure with a molecular area of 40 Å2 was observed, yielding a maximum surface charge density of 0.4 C m−2 at full deprotonation.
Strain-induced crystallization in natural rubber: The Flory theory revisited
Published in Bertrand Huneau, Jean-Benoit Le Cam, Yann Marco, Erwan Verron, Constitutive Models for Rubber XI, 2019
The physical mechanisms of strain-induced crystallization (SIC) in natural rubber (NR), first noticed by Katz (katz 1925), have been identified by Flory (flory 1947). SIC has been continuously studied since then as many aspects have remained unclear. Also, a key role has been attributed to SIC in the exceptional properties of NR. Also, real-time X-ray diffraction experiments have been made possible by dramatic technical improvements in X ray scattering techniques (Huneau 2011, Toki 2014, Albouy et al. 2012).
Microstructural Characterization of Conjugated Organic Semiconductors by X-Ray Scattering
Published in John R. Reynolds, Barry C. Thompson, Terje A. Skotheim, Conjugated Polymers, 2019
Maged Abdelsamie, Michael F. Toney
In this section, we provide a brief review of the fundamentals of X-ray scattering techniques used in the characterization of organic semiconductors with a focus on thin film characterization. Firstly, we cover the fundamentals of wide-angle X-ray scattering (WAXS) and its application to probe the molecular order and orientation at the small-length-scale. Then, we explain the fundamentals of small-angle x-ray scattering (SAXS) in probing the phase separation at the large-scale.
Physicochemical methods for biofilm removal allow for control of biofilm retention time in a high rate MBBR
Published in Environmental Technology, 2022
Alessandro di Biase, Maciej S. Kowalski, Tanner R. Devlin, Jan A. Oleszkiewicz
Results from biofilm detachment rates tests have shown that the impact of acidic conditions resulted in much higher rates when compared to alkaline conditions (Figure 4). However, an overall greater biofilm detachment was observed at a pH of 12. The difference in biofilm detachment was due to EPSs which develop an electric surface charge through dissociation (i.e. ionization) of superficial functional groups resulting in the repulsion and expansion of pH-dependent biopolymers [25]. Literature reports that at high pH levels the structural integrity of EPSs is compromised, resulting in a stretched conformation and ultimately in its solubilization [25]. This explains the longer time required to achieve maximum detachment rate in an alkaline environment compared to acidic. However, at low pH levels, the structure of biofilm results in morphologically compaction forming aggregates due to the protonation of a higher number of carboxylic groups which, in most cases, are the most abundant groups in EPS matrices [25]. Dogsa et al. [21] have shown through small-angle x-ray scattering techniques that, at low pH levels, the EPS structure appears in denser, heterogenous aggregates. The authors reported that at room temperature EPSs are soluble in alkaline solutions and their solubility decreases with pH until becoming insoluble at low pH values (i.e. approximately 1). For these reasons, subjecting biocarriers to pH levels of 2 at 120 rpm mixing intensity resulted in an immediate detachment of agglomerated colloidal EPSs (Figure 4(B)).
Magnetic field dependence of the hexagonal to isotropic transition temperature of a single-walled carbon nanotubes dispersed lyotropic liquid crystal
Published in Phase Transitions, 2019
D. Vijayaraghavan, Jai Mishra, R. Thejas
Carbon nanotubes (CNTs) possess high aspect ratio and exhibit high tensile strength, anisotropic electrical and thermal conductivities. Due to their unique features, they are expected to find applications in solar cells, sensors and mechanical and electrical nano devices [1–4]. However, to realize most of these applications, uniform alignment of carbon nanotubes is necessary. Thermotropic and lyotropic liquid crystals are often used to disperse and align the CNTs as the liquid crystals impose their orientational order on CNT guests [5–11]. Dispersion of individual nanotubes in thermotropic liquid crystals is not straightforward due to the bundling and aggregation of CNTs even for mild concentration of CNTs. On the other hand, in the case of water-based lyotropic liquid crystals (LLC), a considerable amount of single-walled carbon naotubes (up to 0.2 wt.%) can be dispersed and aligned. Weiss et al. reported the integration of single-walled carbon nanotubes (SWCNTs) in a hexagonal LLC consisting of 50 wt.% TX-100 in water for various concentrations of SWCNTs and studied the alignment of SWCNTs in the LLC using light microscopy imaging and small-angle X-ray scattering techniques [12]. They find both the supramolecular (d-spacing) and macroscopic (viscosity) properties show similar trends with varying SWCNTs concentration in the composite. Recently, we have reported the optical birefringence, electrical conductivity and SAXS studies on 0.01 wt.% SWCNTs containing lyotropic liquid crystal consisting of 25 wt.% CTAB in water. This LLC system exhibits crystalline surfactant + water (Cr), nematic (N), hexagonal (H) and isotropic phases on heating. Our SAXS studies revealed various self-assembled ordering of CNTs in the different phases and in the vicinity of the phase transitions in the system [13]. The temperature dependence of optical birefringence and electrical conductivity and d-spacing of the CNTs of the system showed peaks at the phase transition temperatures indicating a structure–property correlation in the system. In our present study, we report the effect of applied magnetic field on the HI transition temperature of a SWCNTs dispersed hexagonal LLC consisting of 50 wt.% TX-100 in water. We have carried out electrical conductivity of the system as a function of temperature and magnetic field. The temperature dependence of electrical conductivity showed discontinuous changes at the HI transition temperatures for various applied magnetic fields. We find that the magnetic field dependence of the HI transition temperature of our system showed an anomalous behaviour.