Insights into the Reactivity of La1?xSrxMnO3 (x?=?0?÷?0.7) in High Temperature N2O Decomposition

Abstract  

In this paper a wide range of La_1−x Sr _x MnO₃ (x = 0–0.7) perovskites was synthesized by Pechini route, characterized by XRD (including high temperature measurements), XPS, differential dissolution phase analysis, TPR H₂, oxygen exchange and tested in N₂O decomposition at 900 °C. At low degree of Sr substitution for La (x ≤ 0.3), high catalytic activity was found for perovskites with hexagonal structure (x = 0.1–0.2) and can be related to fast oxygen mobility caused by the lattice disordering during polymorphic phase transition from the hexagonal to cubic structure. For multiphase samples (x > 0.3) increase of activity and oxygen mobility can be attributed to the formation of the layer-structured perovskite–LaSrMnO₄ on the surface.     

Side chain effect on the self-assembly of coil-comb copolymer by self-consistent field theory in two dimensions

The phase behavior of coil-comb copolymers A–(B_m+1C_m) (side chain number m = 1–5) is investigated by real-space self-consistent field theory (SCFT). Depending on the copolymer composition and architecture, eight two-dimensional ordered phases are observed, including two-color lamellae (LAM₂), three-color lamellae (LAM₃), hexagonal cylinders (HEX), core–shell hexagonal phase (CSH), hexagon outside hexagonal phase (HEX₂), two interpenetrating tetragonal phase (TET₂), lamellae with beads inside (LAM + BD), and lamellae with core–shell beads (LAM₃ + CSB). When the volume fractions are comparable, i.e., f_A ≈ f_B ≈ f_C, LAM_3 phase is found to be stable for m = 1 while the hexagonal phases (core–shell hexagonal phase CSH or hexagon outside hexagonal phase HEX₂) are stable if m > 1. The phase region of the hexagonal phases HEX, CSH or HEX₂ enlarges with increasing m. For short coil length, such as f_A = 0.1, the phase diagram is complex, especially when m = 1. For longer coil length, the lamellae become the dominant phase. The phase transition from lamellar phase to hexagonal phase is observed with the increase of the side chain length when the side chain number m is large, which is in agreement with the experimental results. Our results give a good way to tailor the phase behavior of block copolymer and are very useful to further study the hierarchical structure of the coil-comb block copolymer.     

Phase structure and electrochemical properties of Ml1?xMgxNi2.78Co0.50Mn0.11Al0.11 hydrogen storage alloys

The effect of magnesium content on the phase structure and electrochemical properties of Ml_1−x Mg _x Ni_2.78Co_0.50Mn_0.11Al_0.11 (x = 0.05, 0.10, 0.20, 0.30) hydrogen storage alloys was investigated. The results of X-ray diffraction reveal that all the alloys consist of the major phase (La, Mg)Ni₃ and the secondary phase LaNi₅. With increase in x, the relative content of the (La, Mg)Ni₃ phase increases gradually, and the maximum capacity and low temperature dischargeability of the alloy electrodes first increase and then decrease. When x is 0.20, the discharge capacity of the alloy electrode reaches 363 mAh g⁻¹ at 293 K and 216 mAh g⁻¹ at 233 K, respectively. The high rate dischargeability of the alloy electrodes increases with increase in x. When the discharge current density is 1200 mA g⁻¹, the high rate dischargeability of the alloy electrodes increases from 22.0% to 50.4% with x increasing from 0.05 to 0.30. The cycling stability of the electrodes decreases gradually with increase in magnesium content.     

Solid-state synthesis and characterisation of mesoporous zirconia with lamellar and wormhole-like mesostructures

Mesostructured zirconia with lamellar and wormhole-like mesostructure was synthesized using a solid-state reaction route. Ordered lamellar mesostructure is achieved at low OH⁻/Zr ratio; while high OH⁻/Zr ratio leads to less ordered wormhole-like mesostructure. The varying synthesis conditions result in different inorganic frameworks with amorphous (in lamellar mesostructure) or tetragonal phase pore walls with different thermal stability. The surface area and pore structure of zirconia prepared by this method can be tailored using simple synthesis parameters such as OH⁻/Zr ratio and crystallization temperature. High surface area up to 716 m²/g can be achieved in the lamellar structured zirconia. However, the wormhole-like structured zirconia possesses high thermal stability. The results strongly suggest that in solid-state synthesis system mesostructure formation still follows the supramolecular self-assembly mechanism. In such synthesis system, the lamellar and reverse hexagonal structure can be transformed at different OH⁻/Zr ratios in order to minimize the surface energy of the mesophases formed.     

Exploring the effect of alkyl end group on poly(L-lactide) oligo-esters. Synthesis and characterization

Poly(L-lactide) (PLLA) oligo-esters with α-hydroxyl-ω-alkyl (alkyl = −CH₂−[CH₂−CH₂]_m−CH₃, where m = 1, 2, 4, 5, 6, 7, 8, 9, and 10) end groups were synthesized by ring-opening polymerization of L-lactide (L-LA) catalyzed by tin(II) 2-ethylhexanoate Sn(Oct)₂ in the presence of aliphatic alcohols as initiators (HO−CH₂−[CH₂−CH₂]_m−CH₃, where m = 1, 2, 4, 5, 6, 7, 8, 9, and 10). High yields (~ 62 to 71%) and M _n(NMR) in the range of 2120–2450 Da (PLLA) were obtained. Effects of alkyl end groups on thermal properties of the oligo-esters were analyzed by DSC, TGA and SAXS. Glass transition temperature (T _g) gradually decreases with increase in the percent of−CH₂−[CH₂−CH₂]_m−CH₃ end group, as results alkyl end group provides most flexibility to PLLA. An important effect of alkyl end group on a double cold crystallization (T _c1 and T _c2) was observed, and is directly related with the segregation phase between alkyl end group and PLLA. TGA analysis revealed that PLLA oligo-esters are more thermally stable with docosyl (−C₂₂H₄₅) respect to the butyl (−C₄H₉) end group, probably is due to steric hindrance of the end group (docosyl respect to butyl) toward intermolecular and intramolecular transesterification. SAXS analysis showed that alkyl end group as docosyl restricted the growth of lamellae thickness (D) due to steric hindrance. Characterization of hydroxyl and alkyl end groups in the PLLA oligo-esters was determined by MALDI-TOF, GPC, FT-IR and ¹ H and ¹³ C NMR.     

Sb doping effects on the piezoelectric and ferroelectric characteristics of lead-free Na0.5K0.5Nb1−x SbxO3 piezoelectric ceramics

The piezoelectric, phase structure and ferroelectric properties of lead-free Na_0.5K_0.5Nb_1−xSb_xO₃ piezoelectric ceramics were systematically investigated. (Na_0.5K_0.5)Nb_1−xSb_xO₃ ceramics were synthesized using the conventional solid-state reaction method. The effect of B-site Sb⁵⁺ substitution for Nb⁵⁺ on the structural characteristics and piezoelectric properties of samples was determined. According to XRD patterns, the phase gradually changes from tetragonal to orthorhombic with increasing Sb content. At x = 0.03, the tetragonal and orthorhombic phases coexist and relatively high piezoelectric properties were obtained. The relatively high Q_m value obtained after substitution with Sb⁵⁺ ions might be due to the increased electronegativity and decreased ionic radius at the morphotropic phase boundary (MPB) at x = 0.03. However, the Q_m value decreases with further Sb addition. Relatively high piezoelectric properties at x = 0.03 of k_p = 0.42, k_t = 0.48, ?_r = 446, Q_m = 143, tan δ = 2.3%, and density = 4.31 g/cm³, d₃₃ = 123 pC/N, were obtained.     

Effects of iron and cerium in La1−yCeyCo1−xFexO3 perovskites as catalysts for VOC oxidation

Perovskite-type mixed oxides La_1−yCe_yCo_1−xFe_xO₃ with high specific surface area were prepared by reactive grinding. These catalysts were characterized by N₂ adsorption, X-ray diffraction, oxygen storage capacity (OSC), H₂-temperature-programmed reduction (TPR-H₂), O₂-, and CH₃OH-temperature-programmed desorption (TPD). The catalytic performance of the samples for volatile organic compounds (VOC), CH₃OH, CO and CH₄ oxidation was evaluated. Cerium allows an enhancement of the reducibility of the B-site cations in perovskite structure during OSC and TPR-H₂ and an increase in the amount of β-O₂ desorbed during TPD-O₂. As opposed to cerium, the addition of iron in the perovskite structure causes a drop in B-site cations reducibility and a decrease of the oxygen mobility in the bulk. As a consequence, the catalytic activity in VOC oxidation is enhanced by introduction of cerium and weakened by iron in the lattice.     

Structure and physicochemical properties of glasses in the (As2Se3)1 ? z-(SnSe2)z ? x-(Tl2Se)x and (As2Se3)1 ? z-(SnSe)z ? x-(Tl2Se)x systems

A comparative investigation of glasses in the As₂Se₃)_{1 − z} -(SnSe₂) _{z − x} -(Tl₂Se) _x and (As₂Se₃)_{1 − z} -(SnSe) _{z − x} -(Tl₂Se) _x systems has been performed. In both systems, the glass formation regions are shifted toward the As₂Se₃ compound. Only tin(IV) in the structure of glasses in the (As₂Se₃)_{1 − z} -(SnSe) _{z − x} -(Tl₂Se) _x system is identified by M?ssbauer spectroscopy, whereas glasses in the (As₂Se₃)_{1 − z} -(SnSe) _{z − x} -(Tl₂Se) _x system contain both Sn(II) and Sn(IV). The presence of tin in the oxidation state 2+ in the structural network of the glasses does not lead to impurity conduction. The dependences of the density, the microhardness, and the glass transition temperature on the glass composition are explained in the framework of the model according to which the structure of these glasses is built up of structural units corresponding to the As₂Se₃, AsSe, TlAsSe₂, Tl₂Se, SnSe, and SnSe₂ compounds. It is established that, for crystalline alloys in the (As₂Se₃)_{1 − z} -(SnSe) _{z − x} -(Tl₂Se) _x system, there exist two compounds (Tl₂SnSe₃ and Tl₄SnSe₄), which are formed by the peritectic reactions; however, structural units of these compounds are not formed in the structural network of glasses.     

Aerogel VOx/MgO catalysts for oxidative dehydrogenation of propane

VO_x/MgO aerogel catalysts were synthesized using three different preparation methods: by mixing the aerogel MgO support with dry ammonium vanadate, by vanadium deposition from a precursor solution in toluene, and by hydrolysis of a mixture of vanadium and magnesium alkoxides followed by co-gelation and supercritical drying. The latter aerogel technique allowed us to synthesize mixed vanadium–magnesium hydroxides with the surface areas exceeding 1300 m²/g. The synthesized catalysts were studied by a number of physicochemical methods (XRD, Raman spectroscopy, XANES and TEM). A common feature of all synthesized samples is the lack of V₂O₅ phase. In all cases vanadium was found to be a part of a surface mixed V–Mg oxide (magnesium vanadate), its structure depending on the synthesis method. The VO_x/MgO mixed aerogel sample had the highest surface area 340 m²/g, showed higher catalytic activity and selectivity in oxidative dehydrogenation of propane compared to the catalysts prepared by impregnation and dry mixing. The addition of iodine vapor to the feed in 0.1–0.25 vol.% concentrations was found to increase to propylene yield by 40–70%.     

Synthesis and structure of the n = 4 member of the framework aluminium alkylenediphosphonate series Al2[O3PCnH2nPO3](H2O)2F2

We report here the solvothermal synthesis and crystal structure of the hybrid inorganic-organic framework material Al₂[O₃PC₄H₈PO₃](H₂O)₂F₂⋅2H₂O (monoclinic, 1P2₁/m, a = 4.961(2) ?, b = 11.930(5) ?, c = 10.727(5) ?, β = 93.972(6)^∘, Z = 2, R(F, F² > 2σ) = 0.094, R_w(F², all data) = 0.262), the third member of the Al₂[O₃PC_nH_2nPO₃](H₂O)₂F₂ framework series. The structure is formed from corrugated chains of corner-sharing AlO₄F₂ octahedra in which alternating AlO₄F₂ octahedra contain two fluorine atoms in a trans or a cis configuration. The diphosphonate groups link the chains together through Al-O-P-O-Al bridges and through the butyl groups to form a three-dimensional framework structure containing a one-dimensional channel system consisting of one type of channel only. The channels contain four extra-framework water molecules per unit cell. The formation of this member of the series shows that the form of the alkyl chain can successfully define the number of channel types and the channel length in this hybrid framework system.     

Phase behavior and structural properties for the triton X-100/<Emphasis Type="Italic">n</Emphasis>-C<Subscript>n</Subscript>H<Subscript>2n+1</Subscript>COOH/H<Subscript>2</Subscript>O system

In the Triton X-100/n-C_nH_2n+1COOH/H₂O system, n-C_nH_2n+1COOH can be used as a cosurfactant. As its chain length increases, the regions of the microemulsions showing oil-in-water (O/W), water-in-oil (W/O), and bicontinuous structures decrease and at the same time, the region of the lamellar liquid crystal increases. In the O/W region, the distribution coefficient K of n-C_nH_2n+1COOH between Triton X-100 micellar phase and water phase increases with the chain length of saturated unbranched monocarboxylic acid. The relationship between the standard solubilization Gibbs free energy of saturated unbranched monocarboxylic acid and the number of methylene groups in the saturated unbranched monocarboxylic acid is given by the equation: ΔG _m ⁰=−2.364−2.818 n(CH₂) kJ·mol⁻¹ in the Triton X-100 micellar system. In the lamellar liquid crystal region, small-angle X-ray diffraction shows that the thickness of the bilayer d ₀ is independent of the weight ratio of n-C_nH_2n+1COOH to Triton X-100, but the volume of the solvent penetrating from the solvent layer to the amphiphilic bilayer increases with the weight ratio of n-C_nH_2n+1COOH to Triton X-100. Furthermore, the d ₀ value increases with the chain length of saturated unbranched monocarboxylic acid, which will contribute to the formation and stabilization of the lamellar liquid crystal.     

Synthesis of La1−xSrxMnO3 powders by polymerizable complex method: Evaluation of structural, morphological and electrical properties

Lanthanum strontium manganite (La_1−xSr_xMnO₃, LSM) powders were synthesized by polymerizable complex method, based on complexation of metal ions (MI) with citric acid (CA) and polyesterification between CA and ethylene glycol (EG). Firstly, the effect of the molar ratio of CA:MI (=1–3) was investigated on the synthesis of La_0.7Sr_0.3MnO₃ powders, which were characterized by thermal analysis (TGA/DTA), X-ray diffraction (XRD), and scanning electron microscopy (SEM). The results indicated that the molar ratio CA:MI = 3 is adequate for a good crystallization of pure perovskite phase after calcination, with nanometric crystallite sizes and porous microstructure. For the La_0.7Sr_0.3MnO₃ sample synthesized with CA:MI ratio of 3, it was investigated the effect of calcination temperature, showing that the perovskite structure is better crystallized at 900 °C, without secondary phase formation. Using this same CA:MI ratio and calcination temperature, powders with different Sr content (x = 0.2–0.4) were synthesized, with surface areas of 4–10 m² g⁻¹. These powders were sintered at 1100 °C to produce porous pellets. The porosity of the sintered pellets and the electrical conductivity, measured by two-probe technique, increased with increasing Sr content.     

Crystal Structure and Elastic Properties of Hypothesized MAX Phase‐Like Compound (Cr2Hf)2Al3C3

The term “MAX phase” refers to a very interesting and important class of layered ternary transition‐metal carbides and nitrides with a novel combination of both metal and ceramic‐like properties that have made these materials highly regarded candidates for numerous technological and engineering applications. Using (Cr₂Hf)₂Al₃C₃ as an example, we demonstrate the possibility of incorporating more types of elements into a MAX phase while maintaining the crystallinity, instead of creating solid solution phases. The crystal structure and elastic properties of MAX phase‐like (Cr₂Hf)₂Al₃C₃ are studied using the Vienna ab initio Simulation Package. Unlike MAX phases with a hexagonal symmetry (P6₃/mmc, #194), (Cr₂Hf)₂Al₃C₃ crystallizes in the monoclinic space group of P2₁/m (#11) with lattice parameters of a = 5.1739 Å, b = 5.1974 Å, c = 12.8019 Å; α = β = 90°, γ = 119.8509°. Its structure is found to be energetically much more favorable with an energy (per formula unit) of ?102.11 eV, significantly lower than those of the allotropic segregation (?100.05 eV) and solid solution (?100.13 eV) phases. Calculations using a stress versus strain approach and the VRH approximation for polycrystals also show that (Cr₂Hf)₂Al₃C₃ has outstanding elastic moduli.     

Fluorescence Quenching in Three to Zero Dimensions: Effect of Dimensionality on a Diffusion-Limited Reaction

The diffusion-limited fluorescence quenching of pyrene by a hydrophobic benzophenone derivative, 1-(4-benzoyl)-phenylhexane, was investigated in the different phases of the binary system hexaethyleneglycol-mono-n-dodecylether (C₁₂E₆)-water, from the normal homogeneous solution of the neat surfactant, via a sequence of liquid crystalline phases, to the aqueous micellar solution. These phases provide nonpolar domains of various dimensionality for the reactants: three dimensions in the neat surfactant, two in the lamellar phase, one in the hexagonal phase, and zero in the small micelles. The results were evaluated using models with appropriate dimension for the diffusion-controlled reaction. The resulting diffusion coefficients at 20°C were obtained as 3 × 10⁻¹¹ m² s⁻¹ in the neat surfactant, around 6 × 10⁻¹¹ m² s⁻¹ in the lamellar phase, and 10 × 10⁻¹¹ m² s⁻¹ in the hexagonal phase. The activation energy for the diffusion process increased from 32 kJ mol⁻¹ in the neat surfactant to 42 kJ mol⁻¹ in the hexagonal phase. The differences between the phases may be due to the uncertainty in the values of the size parameters for the structures; in any case, they are not large, indicating that it is mainly the geometry that is important for the deactivation kinetics, whereas the mobilities of the reactants are less affected by changes in packing.     

Highly active TiO2−x−yNxFy visible photocatalyst prepared under supercritical conditions in NH4F/EtOH fluid

A novel N and F co-doped TiO₂ (TiO_2−x−yN_xF_y) photocatalyst is prepared by treating the TiO₂ precursor in NH₄F/ethanol fluid under supercritical conditions. During photocatalytic degradation of methylene blue under visible light irradiation, the as-prepared TiO_2−x−yN_xF_y exhibits higher activity than the undoped TiO₂, N-doped TiO₂ (TiO_2−xN_x), and F-doped TiO₂ (TiO_2−yF_y). Based on the characterizations including XRD, Raman, FTIR, TEM, PLS, UV–vis DRS, N₂ adsorption–desorption isotherms, XPS and NH₃-TPD, the synergetic promotions of N- and F-dopants incorporated into the TiO₂ lattice are discussed based on the enhanced spectral response in visible region, oxygen vacancies, and surface acidic sites. Meanwhile, the supercritical treatment also promotes the activity owing to the increase in both the surface area and the crystallization degree of anatase, and the enhanced incorporation of N- and F-dopants into the TiO₂ lattice.     

Porous properties of mesoporous silicas from two silica sources (acid-leached kaolinite and Si-alkoxide)

Two different mesoporous silicas (MesoPS) were synthesized by hydrothermal treatment in NaOH solution of two silica sources. One of these starting silicas was derived from selectively acid leached metakaolinite, and the other was from tetraethylorthosilicate (TEOS). The syntheses used a surfactant, cethyltrimethylammonium bromide (CTABr) and were carried out at different CTABr/Si, NaOH/Si and H₂O/Si ratios. In the MesoPS from kaolinite, the specific surface areas (S _BET) of the products were >1500 m²/g when prepared with 0.2 ≤ CTABr/Si ≤ 0.4, 0.3 ≤ NaOH/Si ≤ 0.6 and H₂O/Si = 150. These S _BET values are higher than those obtained from TEOS (ca. 1300 m²/g). The XRD patterns of these products contain a hexagonal (10-) peak with a lattice parameter a ₀ = 4.2–5.2 nm in the MesoPS derived from kaolinite and a ₀ = 4.0–4.6 nm in the products from TEOS. The regularity of the hexagonal structure is higher in the MesoPS derived from TEOS than from kaolinite. The pore size distributions of the products show a sharp peak at 2.8 nm in the MesoPS from kaolinite and at 2.4–2.5 nm in those from TEOS. The meso-structure is found to be formed during the stirring step of the synthesis and becomes more regular after hydrothermal treatment. The differences in the porous properties of the two MesoPSs from kaolinite and TEOS are attributed to differences in the dissolution rates and silica concentrations in the synthesis solutions. The ²⁹Si MAS NMR spectra show a higher number of Q ³ (Si(OSi)₃OH) units in the MesoPS from kaolinite and this is suggested to be related to the difference in their porous properties.     

Preparation, structure and electrical conductivity of pyrochlore-type Gd1−xEu2xSm1−xZr2O7 ceramics with a constant lattice parameter

A novel series of Gd_1−xEu_2xSm_1−xZr₂O₇ (x = 0, 1/3, 1/2, 2/3, 1) ceramics with a constant lattice parameter are prepared by solid-state reaction, and are then evaluated as possible solid electrolytes. The microstructure and electrical properties of Gd_1−xEu_2xSm_1−xZr₂O₇ ceramics have been investigated by means of X-ray diffraction (XRD), scanning electron microscopy (SEM) and complex impedance analysis. Gd_1−xEu_2xSm_1−xZr₂O₇ ceramics exhibit a single phase of pyrochlore-type structure. The total conductivity of Gd_1−xEu_2xSm_1−xZr₂O₇ ceramics obeys the Arrhenius relation, and gradually increases with increasing temperature from 723 to 1173 K. At 973–1173 K, the composition has little effect on electrical conductivity of Gd_1−xEu_2xSm_1−xZr₂O₇ ceramics. Gd_1−xEu_2xSm_1−xZr₂O₇ ceramics are oxide-ion conductors in the oxygen partial pressure range of 1.0 × 10⁻⁴ to 1.0 atm at all test temperature levels. The maximum total conductivity of Gd_1−xEu_2xSm_1−xZr₂O₇ ceramics is about 1.01 × 10⁻² S cm⁻¹ at 1173 K in air.     

Perovskite-Based Lean-Burn NOx Trap Catalysts Without Using Platinum Group Metals: K/LaCoO3/Ce1?xZrxO2

Abstract  

A series of Ce_1−x Zr _x O₂ (x = 0, 0.1, 0.2, 0.3) solid solution supported lean-burn NO _x trap (LNT) catalysts K/LaCoO₃/Ce_1−x Zr _x O₂ were prepared by successive impregnation. After sulfation the supported perovsikte LaCoO₃ was well maintained; reducing treatment partly destroyed the perovsikte, but it can be well recovered by re-oxidation treatment. Based on NO _x storage and sulfur-resisting performance of the catalysts, the optimal atomic ratio of Zr in Ce_1−x Zr _x O₂ support is x = 0.2. The catalyst K/LaCoO₃/Ce_0.8Zr_0.2O₂ exhibits much better NO _x storage capacity than the Pt-based catalyst Pt/K/Ce_0.8Zr_0.2O₂, which is highly related to its stronger capability for NO to NO₂ oxidation. During NO _x storage much larger amounts of nitrate and nitrite species were identified by in situ DRIFTS over perovskite-based catalysts than over Pt-based one. The H₂-TPR results reveal that after deep sulfation little sulfur species were deposited on the catalyst K/LaCoO₃/Ce_1−x Zr _x O₂, showing strong sulfur-resisting ability. As a result, it is thought that the full replacement of Pt by perovskite LaCoO₃ in the corresponding LNT catalysts is feasible.     

Gemini surfactant controlled preparation of well-ordered lamellar mesoporous molybdenum oxide

A series of well-ordered lamellar mesoporous molybdenum oxides were prepared using gemini surfactant [C _n H_2n+1N⁺(CH₃)₂–(CH₂)₂–N⁺(CH₃)₂C _n H_2n+1] · 2Br⁻(denoted as C _n-2-n , n = 12, 14 and 16) as the structure-directing agent and ammonium heptamolybdate tetrahydrate (NH₄)₆Mo₇O₂₄ · 4H₂O as the precursor. The obtained samples were characterized by X-ray powder diffraction, thermal analysis, transmission electron microscopy and nitrogen adsorption–desorption. Results showed that contrary to complete structure collapse after removing tetradecyltrimethylammonium bromide (TTAB) from molybdenum oxide/TTAB composite, the lamellar mesostructure was retained after removal of C _n-2-n from corresponding composite. The effects of alkyl chain length and concentration of gemini surfactants on the structure of the mesoporous molybdenum oxide were also investigated. The specific surface area of extracted sample was as high as 116 m² g⁻¹. The maintenance of the lamellar mesostruture was due to the strong self-assembly ability of gemini surfactants and the strong electrical interaction between gemini surfactants and molybdenum oxide.     

Synthesis and characterization of biodegradable amphiphilic triblock copolymers methoxy-poly(ethylene glycol)-b-poly(L-lysine)-b-poly(L-lactic acid)

Starting from MPEG-NH₂, a series of amphiphilic triblock copolymers MPEG-b-PLL-b-PLA were synthesized through PEG-NH₂-initiated ring-open polymerization of N ^ε-benzyloxycarbonyl-L-lysine, followed by acylation coupling between the amino-terminated MPEG-b-PZLL-NH₂ and carboxyl-terminal PLA and the deprotection of amines. The block copolymers were characterized by FT-IR, ¹H NMR, GPC, DSC and TEM. The copolymer functional groups, molecular and block structures were verified by FT-IR, ¹H NMR and DSC, respectively. The GPC results indicate that the chain lengths of each block can be controlled by varying the feed ratios of the monomer and initiator, providing the polymer samples with a narrow molecular weight distribution (M _w /M _n = 1.10 ~ 1.25). The TEM analysis shows that the triblock polymers can self-assemble into polymeric micelles in aqueous solution with spherical morphology. The cell-cytotoxicity assay indicates that the triblock polymers show no obvious cytotoxicity against Bel7402 human hepatoma cells.