Comparison of USAXS information with RMSA prediction for the effect of added salt on colloidal crystal structure

Charged colloidal particles form so‐called colloidal crystals in dispersions because of electrostatic interparticle interactions between them. We performed a systematic and quantitative investigation of the effect of salt on the interparticle distance in colloidal crystals with the ultra‐small‐angle X‐ray scattering (USAXS) technique. We accumulated a great deal of significant information about the mechanism of the colloidal crystal formation by USAXS. We found that the interparticle distance in colloidal crystals shows a maximum as a function of the added salt concentration. The maximum position of the interparticle distance was located around κa = 1.3 (κ⁻¹ is the Debye length, and a is the particle radius). The behavior of the decrease of the interparticle distance with the increase of the added salt concentration at κa > 1.3 could be explained not quantitatively but qualitatively with the effective hard‐sphere theory. Thus, it was suggested that the dependence of the interparticle distance on the salt concentration at κa > 1.3 was reasonable according to the classical theories, such as the Derjaguin–Landau–Verwey–Overbeek (DLVO) theory. In this article, we advance this theoretical approach with the classical theory, that is, with the assumption of the only repulsive force for the interparticle interaction, to elucidate the origin of the curious behavior of the interparticle distance. We estimated the structure factor by the rescaled mean spherical approximation (RMSA) with a Yukawa‐type interparticle interaction potential. A comparison between the prediction of the RMSA data and USAXS experimental data was performed. In this analysis, the charge renormalization procedure was applied. Although the origin of the behavior of the interparticle distance at κa < 1.3 is still a mystery, we concluded that the behavior at κa > 1.3 could be interpreted as a result from the DLVO manner. The effective surface charge number was on the order of several percentages of the analytical surface charge number. This experimental fact certainly proves the validly of our USAXS observation quantitatively and also predicts the existence of novel factors for κa ≤ 1.3, the real origin of colloidal crystal formation, which have never been taken into account previously. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 39: 78–90, 2001     

Photo-tunable Stationary Phases for Semi-micro HPLC

To develop photo-tunable chromatography, several azobenzene derivatives were immobilized or modified on silica gels or incorporated into polymers. The supports prepared were used as stationary phases in semi-micro HPLC, and the photo-dependence of their retention evaluated. On these stationary phases, the retention measured with 2-propanol in hexane was increased by UV irradiation; in contrast, the retention was decreased when methanol was used as mobile phase. It was assumed that the polarity of the stationary phase increases when the molecular structure of the azobenzene moieties changes from the trans to the cis form. On irradiation of the column with visible light after UV irradiation and with methanol as mobile phase, the change of retention proved to be reversible. However, this reverse change was less dramatic than the initial change. Such retention behavior is attributable to photo-isomerization of the azobenzene moieties. These findings will be exploited in our development of new photo-tunable stationary phases and new photo-controlled separation systems.     

Optical-limiting property of cyclic phenylacetylene oligomer synthesized under high pressure

The optical-limiting property of a new cyclic phenylacetylene oligomer was investigated. Toluene solutions of the oligomer contained within a quartz cell were irradiated with the pulse from frequency doubled Nd: Yag laser at 532 nm. At low input fluence, the transmittance of the toluene solution was constant and agreed well with that obtained by spectrophotometer. At high input fluence, the transmittance of the solution above a concentration of 5 wt % decreased with input fluence. The oligomer had an optical limiting property. As the concentration of the oligomer increased from 5 to 20 wt %, the threshold for optical limiting decreased. The threshold was independent of the molecular weight. The optical limiting property was analyzed by the following equation obtained according to the reverse saturable absorption mechanism; log(I₀/I) = K(I₀ - I) + A_g, where I₀ is the input fluence, I is the output fluence, K is a parameter depending on the absorption cross section and the relaxation time, and A_g is the absorbance of the ground state. © 1996 John Wiley & Sons, Inc.     

Syntheses and properties of a series of amphiphilic polyacrylamides bearing two long alkyl chains and phosphatidylcholine analogous groups in the side chains

A novel vinyl monomer 2-{(3-acrylamidopropyl)dimethyl ammonio}ethyl 2′-isopropyl phosphate (AAPI) having phosphatidylcholine analogous moiety and a series of new acrylamide monomers containing two long alkyl chains [stearyloleylacrylamide (SOAAm), distearylacrylamide (SSAAm), and n-docosyloleylacrylamide (DOAAm)] were synthesized and characterized. The polyacrylamides ( Va, Vb , and Vc ) were obtained from radical copolymerization of SOAAm, SSAAm, or DOAAm with AAPI in the presence of AIBN as an initiator. The investigations of these copolymers were carried out by x-ray analysis method, DSC, TG-DTA, and viscosity measurement, respectively. The copolymer Vb containing distearyl groups as hydrophobic side chains shows a crystalline state at room temperature, and the ordered structure disappears at high temperature. The phase transition from a crystalline state to a liquid-crystalline state was observed obviously only for copolymer Vb . In addition, the II-A isotherms and A-T isobars of these copolymers were measured and their stable LB films were also prepared. © 1996 John Wiley & Sons, Inc.     

Synthesis and properties of poly(acrylamide)s containing both long chain alkyl groups and phosphatidylcholine analogues in the side chains

A series of new phospholipid analogous acrylamide monomers ( 4a–e ) containing long alkyl chains as hydrophobic groups and containing phosphatidylcholine analogues as hydrophilic group were synthesized in high yields. The homopolymerizations and copolymerization ( 4b with 4e ) were carried out in the presence of a radical initiator. The structures and thermal properties of these polymers were investigated by x-ray diffraction analysis, DSC, and polarizing microscopy measurements. It has been revealed that these homopolymers ( 5b, 5c , and 5d ) which bear saturated long-hydrocarbon chains in the side chains exhibited not only orderly stacked bilayer structures at room temperature but also clear liquid crystalline behavior within a wide temperature range. The viscosity behavior of all polymers was found similar to usual polyelectrolytes in porlar solvent. The polymers obtained were also characterized by ¹H-NMR, IR, and melting point, respectively. © 1996 John Wiley & Sons, Inc.     

Relativistic well-tempered gaussian basis sets

The effectiveness of well-tempered Gaussian basis sets has been tested for the atoms He-Ar, Ag, and Xe. It has been found that orbital exponents optimized through the well-tempered scheme for non-relativistic atoms can be carried over to relativistic calculations to produce wavefunctions close to the relativistic Hartree-Fock limit.     

Application of partial least square on quantitative analysis of L-, D-, and DL-tartaric acid by terahertz absorption spectra

Absorption spectra of polycrystalline L-, D-, and DL-tartaric acid have been measured by terahertz time domain spectroscopy (THz-TDS). Different absorption bands are observed for DL-tartaric acid and its enantiomers (L- and D-tartaric acid). This result shows that the THz-TDS can be used for distinguishing between DL-tartaric acid and enantiomers (L- and D-tartaric acid). Moreover, partial least square (PLS) can be found to improve the quantitation of L-tartaric acid in L- and DL-tartaric acid mixture by THz-TDS.     

Designing 3D‐MoS2 Sponge as Excellent Cocatalysts in Advanced Oxidation Processes for Pollutant Control

3D‐MoS₂ can adsorb organic molecules and provide multidimensional electron transport pathways, implying a potential application for environment remediation. Here, we study the degradation of aromatic organics in advanced oxidation processes (AOPs) by a 3D‐MoS₂ sponge loaded with MoS₂ nanospheres and graphene oxide (GO). Exposed Mo⁴⁺ active sites on 3D‐MoS₂ can significantly improve the concentration and stability of Fe²⁺ in AOPs and keep the Fe³⁺/Fe²⁺ in a stable dynamic cycle, thus effectively promoting the activation of H₂O₂/peroxymonosulfate (PMS). The degradation rate of organic pollutants in the 3D‐MoS₂ system is about 50 times higher than without cocatalyst. After a 140 L pilot‐scale experiment, it still maintains high efficiency and stable AOPs activity. After 16 days of continuous reaction, the 3D‐MoS₂ achieves a degradation rate of 120 mg L^?1 antibiotic wastewater up to 97.87 %. The operating cost of treating a ton of wastewater is only US$ 0.33, suggesting huge industrial applications.     

Stiffness-Tunable Hydrogel-Sandwich Culture Modulates the YAP-Mediated Mechanoresponse in Induced-Pluripotent Stem Cell Embryoid Bodies and Augments Cardiomyocyte Differentiation

Microenvironmental factors, including substrate stiffness, regulate stem cell behavior and differentiation. However, the effects of substrate stiffness on the behavior of induced pluripotent stem cell (iPSC)- derived embryoid bodies (EB) remain unclear. To investigate the effects of mechanical cues on iPSC-EB differentiation, a 3D hydrogel-sandwich culture (HGSC) system is developed that controls the microenvironment surrounding iPSC-EBs using a stiffness-tunable polyacrylamide hydrogel assembly. Mouse iPSC-EBs are seeded between upper and lower polyacrylamide hydrogels of differing stiffness (Young's modulus [E’] = 54.3 ± 7.1 kPa [hard], 28.1 ± 2.3 kPa [moderate], and 5.1 ± 0.1 kPa [soft]) and cultured for 2 days. HGSC induces stiffness-dependent activation of the yes-associated protein (YAP) mechanotransducer and actin cytoskeleton rearrangement in the iPSC-EBs. Moreover, moderate-stiffness HGSC specifically upregulates the mRNA and protein expression of ectoderm and mesoderm lineage differentiation markers in iPSC-EBs via YAP-mediated mechanotransduction. Pretreatment of mouse iPSC-EBs with moderate-stiffness HGSC promotes cardiomyocyte (CM) differentiation and structural maturation of myofibrils. The proposed HGSC system provides a viable platform for investigating the role of mechanical cues on the pluripotency and differentiation of iPSCs that can be beneficial for research into tissue regeneration and engineering.