Physicochemical effect on shear strength characteristics of clayey soils based on ring-shear experiment

Pore fluid chemistry can significantly influence the shear strength characteristics of a clayey soil. To explore the underlying mechanisms, a series of ring shear experiments are performed on two natural clays, which represent two typical types of clayey minerals, i.e., expansive montmorillonitic clay and low-plasticity kaolinitic clay. The effects of pore solution concentrations on the shear strength of the two clays are experimentally characterized. It is shown that the shear strength of the expansive clay can be significantly influenced by the pore solution chemistry, whereas that of the low-plasticity clay proves to be relatively insensitive to it. To capture the main features of the shear strength behavior of clayey soils, the concept of intergranular stress, which is an extension of the Terzaghi’s effective stress to incorporate physicochemical effect, is introduced to interpret the experimental data. It is found that the evolution of residual shear strength can be very well characterized by using the intergranular stress, showing that the proposed intergranular stress formulation can be used alternatively to describe the stress state of clayey soils saturated with various pore solutions.The accepted manuscript in pdf format is listed with the files at the bottom of this page. The presentation of the authors' names and (or) special characters in the title of the manuscript may differ slightly between what is listed on this page and what is listed in the pdf file of the accepted manuscript; that in the pdf file of the accepted manuscript is what was submitted by the author

Crystal structures of the 2:2 complex of 1,1′-(1,2-phenylene)bis(3-m-tolylurea) and tetrabutylammonium chloride or bromide

The title compounds, tetrabutylammonium chloride–1,1′-(1,2-phenylene)bis(3-m-tolylurea) (1/1), C16H36N+·Cl−·C22H22N4O2 or [(n-Bu4N+·Cl−)(C22H22N4O2)] (I) and tetrabutylammonium bromide–1,1′-(1,2-phenylene)bis(3-m-tolylurea) (1/1), C16H36N+·Br−·C22H22N4O2 or [(n-Bu4N+·Br−)(C22H22N4O2)] (II), both comprise a tetrabutylammonium cation, a halide anion and an ortho-phenylene bis-urea molecule. Each halide ion shows four N—H...X (X = Cl or Br) interactions with two urea receptor sites of different bis-urea moieties. A crystallographic inversion centre leads to the formation of a 2:2 arrangement of two halide anions and two bis-urea molecules. In the crystals, the dihedral angle between the two urea groups of the bis-urea molecule in (I) [defined by the four N atoms, 165.4 (2)°] is slightly smaller than that in (II) [167.4 (2)°], which is probably due to the smaller ionic radius of chloride compared to bromide

Crystal structure of a host–guest complex of the tris-urea receptor, 3-(4-nitrophenyl)-1,1-bis{2-[3-(4-nitrophenyl)ureido]ethyl}urea, that encapsulates hydrogen-bonded chains of dihydrogen phosphate anions with separate tetra-n-butylammonium counter-ions

The title compound, C25H25N9O9·C16H36N+·H2PO4− (I) or (C25H25N9O9)·(n-Bu4N+)·(H2PO4−) (systematic name: 3-(4-nitrophenyl)-1,1-bis{2-[3-(4-nitrophenyl)ureido]ethyl}urea tetrabutylammonium dihydrogen phosphate), comprises a tris-urea receptor (R), a dihydrogen phosphate anion and a tetra-n-butylammonium cation. It crystallizes with two independent formula units in the asymmetric unit. The conformations of the two tris-urea receptors are stabilized by N—H...O and C—H...O intramolecular hydrogen bonds. Each dihydrogen phosphate anion has two O—H...O intermolecular hydrogen-bonding interactions with the other dihydrogen phosphate anion. Inversion-related di-anion units are linked by further O—H...O hydrogen bonds, forming a chain propagating along the a-axis direction. Each dihydrogen phosphate anion makes a total of four N—H...O(H2PO4−) hydrogen bonds with two ureido subunits from two different tris-urea receptors, hence each tris-urea receptor provides the two ureido subunits for the encapsulation of the H2PO4− hydrogen-bonded chain. There are numerous intermolecular C—H...O hydrogen bonds present involving both receptor molecules and the tetra-n-butylammonium cations, so forming a supramolecular three-dimensional structure. One of the butyl groups and one of the nitro groups are disordered over two positions of equal occupancy

Mechanistic Insight into Hydrogen-Bond-Controlled Crystallinity and Adsorption Property of Covalent Organic Frameworks from Flexible Building Blocks

The effective control of crystallinity of covalent organic frameworks (COFs) and the optimization of their performances related to the crystallinity have been considered as big challenges. COFs bearing flexible building blocks (FBBs) generally own larger lattice sizes and broader monomer sources, which may endow them with unprecedented application values. Herein, we report the oriented synthesis of a series of two-dimensional (2D) COFs from FBBs with different content of intralayer hydrogen bonds. Studies of H-bonding effects on the crystallinity and adsorption properties indicate that partial structure of the COFs is “locked” by the H-bonding interaction, which consequently improves their microscopic order degree and crystallinity. Thus, the regulation of crystallinity can be effectively realized by controlling the content of hydrogen bonds in COFs. Impressively, the as-prepared COFs show excellent and reversible adsorption performance for volatile iodine with capacities up to 543 wt %, much higher than all previously reported adsorbents, although the variation tendency of adsorption capacities is opposite to their crystallinity. This study provides a general guidance for the design and construction of highly/appropriately crystalline COFs and ultrahigh-capacity iodine adsorbents