Superflexible Multifunctional Polyvinylpolydimethylsiloxane‐Based Aerogels as Efficient Absorbents,Thermal Superinsulators,and Strain Sensors

Aerogels are porous materials but show poor mechanical properties and limited functionality, which significantly restrict their practical applications. Preparation of highly bendable and processable aerogels with multifunctionality remains a challenge. Herein we report unprecedented superflexible aerogels based on polyvinylpolydimethylsiloxane (PVPDMS) networks, PVPDMS/polyvinylpolymethylsiloxane (PVPMS) copolymer networks, and PVPDMS/PVPMS/graphene nanocomposites by a facile radical polymerization/hydrolytic polycondensation strategy and ambient pressure drying or freeze drying. The aerogels have a doubly cross‐linked organic–inorganic network structure consisting of flexible polydimethylsiloxanes and hydrocarbon chains with tunable cross‐linking density, tunable pore size and bulk density. They have a high hydrophobicity and superflexibility and combine selective absorption, efficient separation of oil and water, thermal superinsulation, and strain sensing.     

Conductance in isodielectric mixed solvents containing triple ions

Formation of higher ion aggregates mainly by hydrogen bonding in solutions of diethylcyclohexylammonium chloride (c-Hex(Et)₂NHCl) has been examined by conductometry in nearly isodielectric mixed solvents: nitrobenzene-acetonitrile (35) and benzonitrile-ethanol (25) at 25°C. At lower acetonitrile content (less than ca. 10% by volume) in mixtures with nitrobenzene the salt gave minimum in the molar conductivities over the concentration range 4x10^–3 to 0.12 mol-dm^–3 which were explained by ion pair (MX), triple ion (M₂X, MX₂), and quadrupole (M₂X₂) formation in the solvent mixtures. The formation constants of the ion aggregates decreased with increasing content of acetonitrile. In benzonitrile-ethanol mixtures, the degrees of ion aggregate formation also decreased with increasing content of ethanol; triple ion formation could not be observed at more than 20% ethanol.     

A new synthesis of β,γ-unsaturated esters from three components, aldehydes, chloromethyl p-tolyl sulfoxide, and tert-butyl acetate, via magnesium carbenoid 1,2-CH and 1,2-CC insertion as the key reaction

Addition reaction of 1-chlorovinyl p-tolyl sulfoxides, which were derived from various aldehydes, with lithium enolate of tert-butyl acetate at −78 °C in THF gave adducts in high yields. Magnesium carbenoids were generated by treatment of these adducts with Grignard reagents via the sulfoxide-magnesium exchange reaction. When the adducts were derived from alkyl aldehydes or electron-deficient aromatic aldehydes, carbenoid 1,2-CH insertion reaction took place from the magnesium carbenoids to afford β,γ-unsaturated butyric esters having a substituent at the β-position. On the contrary, when the adducts were derived from electron-rich aromatic aldehydes, carbenoid 1,2-CC insertion reaction took place from the magnesium carbenoids to give β,γ-unsaturated butyric esters having the aromatic group at the γ-position. Highly stereospecific 1,2-CC insertion reactions were observed in the latter reactions. This procedure provides a good way for a synthesis of β,γ-unsaturated esters from aldehydes with two carbon-carbon bond-formations.     

Novel syntheses of thiazolo[3,2-b]-s-triazoles

The reaction of 2-amino-and 2-acylaminothiazoles with O-mesitylenesulfonylhydroxylamine resulted in the ready formation in the corresponding 3-aminium salts, which were converted into thiazolo[3,2-b]-s-triazoles in high yields.     

Selective separation of flavonoids with a polyvinyl alcohol membrane

In order to develop a selective membrane separation process for flavonoids, i.e. baicalin, baicalein and flavone extracted from a crude drug, “Wogon”, we have measured the permeabilities of these flavonoids through a polyvinyl alcohol membrane, together with their aqueous solubilities. The aqueous solubilities of baicalin and baicalein increase with increasing aqueous solution pH due to the acid dissociation of the saccharic carboxyl group of baicalin or the phenolic hydroxyl group of baicalein. The mass transfer coefficients of flavonoids experimentally obtained in both systems of single and mixed constituents agreed well with the calculated values based on a solution-diffusion model together with the acid dissociation of the carboxyl or hydroxyl groups of baicalin and baicalein, respectively. The selective mutual separation of flavonoids can be achieved from mixed solution of constituents in the neutral pH region. Furthermore, a quantitative discussion of the permeation behavior of flavonoids through the PVA membrane is provided from a molecular modelling computational viewpoint.     

Recognition of phosphate monoester dianion by an alkoxide-bridged dinuclear zinc(II) complex

Recognition of phosphate monoester dianion by an alkoxide-bridged dinuclear zinc(II) complex (Zn2L3+) has been studied (L = alkoxide species of 1,3-bis[bis(pyridin-2-ylmethyl)amino]propan-2-ol). Potentiometric pH titration study disclosed a 1 : 1 phenyl phosphate complexation with Zn2L3+ in aqueous solution. The dissociation constant (= [Zn2L3+][PhOPO3(2-)]/[Zn2L3+-PhOPO3(2-)]) is an extremely small value of 2.5 x 10(-8) mol dm(-3) at 25 degrees C with I = 0.10 (NaNO3). The X-ray crystal analysis of the dizinc(II) complex with p-nitrophenyl phosphate showed that the phosphate dianion binds as a bridging ligand to the two zinc(II) ions.     

Relationship between cation arrangement and photocatalytic activity for Sr-Al-Nb-O double perovskite

The relationship between the photocatalytic activity and the arrangement of metal cations was investigated with Sr-Al-Nb-O double perovskite (SAN) synthesized at 1400 °C for various calcination times using a solid state reaction. Transmission electron microscopic observation revealed that SAN particles had a domain structure of completely B-site ordered (Sr(2)AlNbO(6)) and disordered (SrAl(0.5)Nb(0.5)O(3)) phases. The ordered phase fraction was determined using a newly proposed mixed-phase model for the Rietveld refinement and a method using the relative intensity of the superlattice line of powder X-ray diffraction. It turned out that the mass fraction of the ordered phase in SAN calcined at 1400 °C could be controlled by the calcination time as 33% (10 h), 37% (20 h), 44% (30 h), and 48% (50 h). Photocatalytic activities of SAN for the evolution of H(2) and O(2) respectively from aqueous solutions of methanol and AgF decreased with increasing the calcination time, that is, with increasing the fraction of the ordered phase. These results suggested that the photocatalytic activity of ordered Sr(2)AlNbO(6) should be lower than that of disordered SrAl(0.5)Nb(0.5)O(3). This is practically the first report to reveal the photocatalytic activity of SAN as well as the effect of cation ordering in oxides on the photocatalytic activity.     

Proton diffusion in the room-temperature phase of [(NH4)1−xRbx]3H(SO4)2 as studied by 1H spin-lattice relaxation in the rotating frame

Proton diffusion in the room-temperature phase (phase II) of [(NH₄)_1?xRb_x]₃H(SO₄)₂ (0≤x≤1) has been studied by means of ¹H spin-lattice relaxation times in the rotating frame, T_1ρ. The ¹H T_1ρ values were measured at 200.13 MHz in the range of 380–490 K. The ammonium protons and the acidic protons have independent T_1ρ values in the higher temperature range of phase II, suggesting that the spin diffusion between the two species is ineffective. The translational diffusion of the acidic protons is the most dominant mechanism to relax both the ammonium protons and the acidic protons in phase II. The ¹H T_1ρ values in phase II are analyzed theoretically and the motional parameters are obtained. The results of NMR well explain the macroscopic proton conductivity.