Synthesis and characteristics of multi-aryl substituted molecular glasses bearing biphenyl core

Two novel compounds based on biphenyl structure, 2,2′-di(3,5-di(tert-butylcarbonate)phenyl)-4,4′-di(tert-butylcarbonate)biphenyl (A) and 2,2′,4,4′-tetra(3,5-di(tert-butylcarbonate)phenyl)biphenyl (B) were synthesized by commercially available materials. The products were fully characterized by FTIR, NMR and elemental analysis. The thermal stability and the phase transition of these compounds had been studied by TGA and DSC techniques. For compound A, thermal decomposition temperature was of 176 °C and glass transition temperature (T_g) was of 105 °C. While for compound B, the thermal decomposition occurred at 186 °C and T_g was of 122 °C. The synthesized compounds were found to be amorphous materials by XRD analysis and good film-forming ability by AFM analysis. These results indicated that the synthetic molecular glasses would be suitable for low molecular weight photo resists in EUV lithography.     

Influence of polyelectrolytes on crystallization of zeolite Y

In this study, the influence of polyelectrolytes on the crystallization of zeolite Y is investigated. The prepared synthesis mixtures are aged at room temperature for 24 h and then left to crystallize. The compositional and structural information are provided by elemental analysis obtained by ICP, X-ray diffraction spectroscopy (XRD), scanning electron microscopy (SEM), particle size analyzer and adsorption and desorption isotherms of nitrogen by a volumetric adsorption instrument. The first group of synthesis studies is conducted by using solutions containing no additive (WA), nonionic (NI), 100% anionic (100A), and 100% cationic (100C) polyelectrolytes. The crystallization temperature and crystallization time are kept at 100 ºC and 48 h, respectively. The experimental results show that nonionic polyelectrolyte has the most influence on the crystallization of zeolite NaY. In the second group of synthesis studies, the effects of polyelectrolytes with various degrees of anionic properties (10%, 50% and 70%) of the same chemical structure are investigated by conducting crystallization experiments at 100 °C for a duration of 48 h. The results suggest that; particle size, crystallinity and BET surface area (S_BET) can be controlled by adding anionic polyelectrolytes to the solution.     

Synthesis and characterization of CoFe2O4–PVP nanocomposites

Cobalt ferrite–poly(N-vinyl-2-pyrrolidone) nanocomposites were prepared by drying a dispersion of cobalt ferrite (CoFe₂O₄) nanoparticles and poly(N-vinyl-2-pyrrolidone). Magnetic measurements indicate a superparamagnetic behavior. Zero-field-cooling magnetization experiments at 100 Oe show different trends depending on the CoFe₂O₄ nanoparticles size. For the smaller ones (3.9 nm), the blocking temperatures shift to lower temperatures with increasing concentration; however, this shift is not observed for the larger ones (6.6 nm). These differences can be related to the anisotropy constant of the CoFe₂O₄ nanoparticles and the interparticle dipolar interactions.     

Nucleating characteristics of Pseudomonas aeruginosa above 0 °C and the role of l-leucine

It has been reported earlier that the bacteria Pseudomonas aeruginosa have the ability to nucleate ice over a long temperature range below 0 °C. In the present work, the same bacteria are shown to have nucleating ability even above 0 °C. It is found to reach a peak at 4 °C and then gradually falls off as the temperature is raised, vanishing altogether at 12 °C. When the bacteria are irradiated by UV-rays, the nucleating ability above 0 °C has the same variational pattern with change of temperature, though the ability is significantly less. When the bacterial medium is boiled for 20 min, the bacteria loose their nucleating ability completely.Since ice cannot exist above 0 °C, some supporting experiments are performed to establish the identity of the nucleated crystals:

• (a)Crystals grown around a small sample of cultured P. aeruginosa in an incubator were shown to be identical with the nucleated crystals in the Cold Room experiments.
• (b)X-ray diffraction (XRD) spectrum of the grown crystals is found to be consistent with the presence of amino acids like l-leucine, isoleucine and l-isoleucine, amongst which l-leucine is the most abundant.

When droplets of an aqueous solution of l-leucine are seeded, their nucleation characteristics are similar to those with P. aeruginosa. From XRD, nuclear magnetic resonance (NMR) and thermal analysis, one can conclude that the crystals formed by P. aeruginosa above 0 °C are hydrate crystals with water phase caging around the seeded agent; the amino acid l-leucine present in the protein of the bacteria plays the dominant role in the nucleation.     

The shoving model for the glass-former LiCl·6H2O: A molecular dynamics simulation study

Molecular dynamics (MD) simulations of LiCl·6H₂O showed that the diffusion coefficient D, and also the structural relaxation time <τ>, follow a power law at high temperatures, D^?1 ∝ (T ? T_o)^?μ, with the same experimental parameters for viscosity (T_o = 207 K, μ = 2.08). Decoupling between D and <τ> occurs at T_x ～ 1.1T_o. High frequency acoustic excitations for the LiCl·6H₂O model were obtained by the calculation of time correlation functions of mass current fluctuations. The temperature dependence of the instantaneous shear modulus, G_∞(T), was considered in the shoving model for supercooled liquids [J.C. Dyre, T. Christensen, N.B. Olsen, J. Non-Cryst. Solids 352 (2006) 4635] resulting in a linear relationship log (D^?1) vs. G_∞/T.     

Thermal,vibrational and Ac impedance studies on proton conducting polymer electrolytes based on poly(vinyl acetate)

Proton conducting polymer electrolytes based on poly(vinyl acetate) (PVAc) and perchloric acid (HClO₄) have been prepared by solution casting technique with various compositions. The X-ray diffraction analysis confirms the polymer–HClO₄ complex formation. FTIR spectra analysis reveals the interaction between proton and ester oxygen of poly(vinyl acetate) (PVAc). The shift in T_g towards the lower temperature indicates that the polymer salt interaction takes places in the amorphous phase of the polymer matrix. Ac impedance spectroscopy reveals that 75 mol% PVAc:25 mol% HClO₄ exhibits maximum conductivity, 3.75 × 10^? 3 S cm^? 1 at room temperature (303 K). The increase in conductivity with increase in dopant concentration and temperature may be attributed to the enhanced mobility of the polymer chains, number of charge carriers and rotations of side chains. The temperature dependence of conductivity shows non-Arrhenius behavior at higher temperatures.     

Bioactive borate glass scaffold for bone tissue engineering

Borate glass particles and microspheres with size distributions in the range of approximately 100–400 μm, were loosely compacted and sintered for 10 min at 600 °C to form a porous, three-dimensional construct (porosity 25–40%). Conversion of the borate glass to hydroxyapatite was investigated by soaking the constructs in a solution of K₂HPO₄ (0.25 M) at 37 °C and with a pH value of 9.0, and measuring the weight loss of the constructs as a function of time. Almost full conversion of the borate glass to hydroxyapatite was achieved in less than 6 days. X-ray diffraction revealed an initially amorphous product that subsequently crystallized to hydroxyapatite. The biocompatibility of the porous constructs was investigated by in vitro cell culture with human mesenchymal stem cells derived from bone marrow (bMSC) and human mesenchymal stem cell derived osteoblasts (MSC-Ob). The cells adhered to the scaffolds and the MSC-Obs produced alkaline phosphatase which is an indication of osteogenic differentiation. The data suggest strong bioactive characteristics for the borate glass constructs and the potential use of the constructs as scaffolds for tissue engineering of bone.     

Preparation of polymer/silica hybrid hard coatings with enhanced hydrophobicity on plastic substrates

In this study, an easy method to increase hydrophobicity of the polymer/silica hybrid coating was demonstrated. UV-curable nano-sized colloidal silica was synthesized and surface-modified both by a coupling agent, 3-(trimethoxysilyl)propyl methacrylate (MSMA), and a capping agent, trimethyethoxysiliane (TMES). The formed particles were introduced into the poly(2-hydroxyethyl methacrylate) (PHEMA) matrix to yield PHEMA/silica hybrid hard coatings on plastic substrates via a UV-curing process. Differential scanning calorimetric (DSC) analyses of the hybrids indicated increases of the glass transition temperature (T_g) with increasing silica content in the hybrids; in general, an increase of 23 °C could be achieved for hybrids doped with 15 wt.% silica. Thermal decomposition temperature (T_d), as measured by the thermal gravimetric analyzer (TGA), was found to depend on the silica content in a trend similar to that on T_g. Specifically, a large increase of 25 °C was observed when the sample contained 15 wt.% silica. The pencil hardness of the PHEMA/silica hybrids coated on poly(methyl methacrylate) (PMMA) substrates can reach 5H, in comparison with 2H for pure PHEMA coating. Abrasion resistance was enhanced when silica nanoparticles were incorporated. Furthermore, due to the incorporation of TMES, hydrophobicity of the hybrid coating increased considerably as the TMES content was increased. In the extreme case, a hard surface with a water contact angle (92°) has been obtained.     

Influence of maghemite concentration on magnetic interactions in maghemite/PTT-block-PTMO nanocomposite

Temperature dependence of dc magnetization and ferromagnetic resonance (FMR) of two samples containing γ-Fe₂O₃ (maghemite) magnetic nanoparticles dispersed at low concentration (0.1 and 0.3 wt%) in a nanocomposite based on a poly(ether–ester) multiblock copolymer (PTT-block-PTMO) matrix was investigated. The polymer filler was in a powder form consisting of small-sized magnetic nanoparticles arranged in agglomerates 2–3 μm long and 100 nm thick. The studied samples were characterized by SEM spectroscopy. The SEM showed that the concentration of magnetic nanoparticles was homogenous in both samples The temperature dependence of the dc magnetization revealed that the blocking was about 100 K and the ZFC (zero-field cooling) mode at low magnetic fields uncovered the presence of magnetic interactions between magnetic nanoparticles depending on the properties of the matrix. FMR measurements were carried out in the temperature range 4.2–300 K. An intense resonance absorption line attributed to γ-Fe₂O₃ nanoparticles was recorded with a slightly asymmetric lineshape. At room temperature the resonance line was centered at H_r = 3241(2) and 3253(2) G, with linewidths of ΔH = 1069(1) and 1070(1) G for samples with concentrations of 0.1 and 0.3 wt%, respectively. All FMR parameters showed an anomalous behavior at matrix critical temperatures. It was shown that the difference in concentration of magnetic nanoparticles could be responsible for the observed differences in the thermal behavior of the FMR spectra.     

Formation of bulk Pt–Pd–Ni–P glassy alloys

The thermal behavior of (Pt_0.4Pd_0.3Ni_0.3)_100−xP_x (x = 16–25 at.%) glassy alloys has been investigated. It is found that the crystallization behavior of the (Pt_0.4Pd_0.3Ni_0.3)_100−xP_x glassy alloys changes from a single-stage exothermic reaction to a two-stage exothermic reaction depending on phosphorous content. When the phosphorous content is 23 at.%, the glassy alloy exhibits the largest supercooled liquid region (ΔT_x) and a sharp single exothermic peak. Fixing the phosphorous content at 23 at.%, the Pt_77−x−yPd_xNi_yP₂₃ (x = 7.7–61.6 at.%, y = 7.7–61.6 at.%) glassy alloys have a wide composition range in which the glassy alloys exhibit a large supercooled liquid region (ΔT_x beyond 60 K). In this range, the Pt_30.8Pd_23.1Ni_23.1P₂₃ glass has the largest ΔT_x (77 K) and a high reduced glass transition temperature (T_rg) of 0.60. This alloy can be cast into fully glassy rods with a diameter of 3 mm. Under uni-axial compression, bulk Pt_30.8Pd_23.1Ni_23.1P₂₃ glassy alloy has an elastic strain of ∼2%, an ultimate strain (to fracture) of ∼6.4%, a Young’s modulus of ∼106 GPa and a failure strength of ∼1390 MPa.     

Influence of europium ions on structure and crystallization properties of bismuth borate glasses and glass ceramics

Glasses of the xEu₂O₃ · (100?x)[2Bi₂O₃ · B₂O₃] system with 0 ? x ? 25 mol% have been characterized by X-ray diffraction and FTIR spectroscopy measurements. Melting at 1100 °C and the rapid cooling at room temperature permitted us to obtain glass samples. In order to improve the local order and to develop crystalline phases, the glass samples were kept at 625 °C for 24 h. After heat treatment two crystalline phases were put into evidence. One of the crystalline phases was observed for the host glass matrix, the x = 0 mol% sample, and belongs to the cubic system. The second one was observed for the x = 25 mol% sample and was find to be orthorhombic with two unit cell parameters very close to each other. For the samples with 0 < x < 25 mol% there is a mixture of the two mentioned phases. FTIR spectroscopy data suggest that both Bi₂O₃ and B₂O₃ play the glass network former role while the europium ions play the network modifier role in the studied glasses.     

Dielectric properties of fine-grained triglycine sulphate (TGS)

The dielectric permittivity ε′ values of triglycine sulphate (TGS) compressed powders with different grain sizes: (1–300) μm have been measured from 300 to 350 K. It has been shown that ε′_max and transition temperature T_c for the average grain size of about 30 μm behave as predicted by the theory of Wang et al. [J. Phys: Condens. Matter 7 (1995) 7163] for cylindric particle geometry.     

The effect of polyacrylamide on the crystallization of calcium carbonate: Synthesis of aragonite single-crystal nanorods and hollow vatarite hexagons

CaCO₃ nanorods were synthesized via a facile solution route by polymer-controlled crystallization in the presence of polyacrylamide (PAM). The morphology, size and crystal structure were characterized by means of scanning electron microscope (SEM), transmission electron microscope (TEM), and X-ray diffraction (XRD). The results suggest that the as-synthesized product was CaCO₃ (aragonite) nanorods with diameter ca. 50 nm and length ca. 1 μm. Selected area electron diffraction (SAED) pattern shows the single-crystal nature of CaCO₃ nanorods. The reaction time, temperature, pH and reactant concentration were systemically investigated. With the increase in the reaction time, hollow vaterite hexagonal disks can be obtained.     

Free induction decays in entangled polymer melts

The relaxation of the transverse magnetization components caused by both dipolar interactions between the spins of different polymer chains and the dipolar coupling between CH-protons on an isolated Kuhn segment along a single polymer chain have been calculated. Explicit expressions for the transverse relaxation function are given in terms of the absolute mean squared displacement of the Kuhn segment during melt g_r(t), the tangent vector dynamical correlation function 〈b_n(t)b(0)〉, the segmental relaxation time τ_s, the Kuhn segment length b, the bond length a₀, the internuclear distance d, and the spin number density ρ_s. It is shown that the functional dependence of the intramolecular relaxation function on 〈b_n(t)b(0)〉 is fairly weak. The time-dependence of the intramolecular contribution to the transverse relaxation function is dominated by the probability density distribution function of the end-to-end vector of the Kuhn segment. The long-time decay of the intramolecular contribution to the transverse relaxation function is found to scale as t^? 3/2 for τ_s < < t < < τ_max, where τ_maxis the maximum relaxation time of polymer chains in melts. For times much less than the spin–spin relaxation time, T₂ ≈ 10^? 3 ? 10^? 2s, we show that the intermolecular contribution to the relaxation function is given by the following expression: exp(? λ₁(b, τ_s, ρ_s)t²/g_r^3/2(t)). Both the numerical coefficient and the functional dependence of λ₁on b, τ_s and ρ_s reproduce the expression obtained from the frequently used second cumulant approximation. For longer times (T₂ ≤ t < < τ_max), the intermolecular contribution is determined by the following relation: exp(? λ₂(b, τ_s, ρ_s, t)g_r(t)). We show that λ₂ increases logarithmically with t. The molecular mass independence of λ₁and λ₂ shows that, in polymer melts with molecular masses M_w far above the critical value M_c, the relevant experimental window for the decay of the intermolecular relaxation function is connected with the anomalous diffusion regime. Comparison with the experimental data suggests that the intermolecular contribution plays a significant role in the NMR relaxation process in polymer systems close to the melting point.     

Simulation study of pores and pore clusters in amorphous alloys Co100−xBx and Fe100−yPy

The simulation of microstructure has been done for amorphous Co_100−xB_x and Fe_100−yP_y systems, containing 1 00 000 atoms, where x = 10, 18.5, 30 and y = 10, 20, 25. The present work is focused on the point defects like large pores and its grouping in more complicated forms. The simulation predicted existence in significant concentration of these defects, which strongly depends on metalloid concentration and relaxation. Other local characteristics such as volume of pore cluster, angle distribution, etc., were also calculated and yielded a new insight in the short range order of amorphous metal–metalloid alloys.     

Temperature dependent blue second harmonic generation in Ba5Li2Ti2Nb8O30 microcrystals embedded in TeO2 glass–matrix

The as-quenched samples in the system (100 ? x) TeO₂-(x) Ba₅Li₂Ti₂Nb₈O₃₀ (2 ? x ? 8) were found to be embedded with 10–20 μm sized crystallites of the polar phase Ba₅Li₂Ti₂Nb₈O₃₀ (BLTN). Blue (400 nm) second harmonic generation (SHG) was observed in transmission mode when 800 nm laser light was allowed to pass through the individual crystallites. The blue SHG signal was temperature dependent and its intensity was maximum at ～175 °C which was tentatively attributed to the concomitant changes associated with the refractive indices of the BLTN crystallites. The SHG intensity attained a minimum value around the Curie temperature of BLTN crystals.     

Dielectric low-k composite films based on PMMA,PVC and methylsiloxane-silica: Synthesis,characterization and electrical properties

This report describes the preparation of low-k inorganic–organic hybrid dielectric films, based on a polymethylmethacrylate–polyvinylchloride (PMMA–PVC) blend and a silica powder functionalized on the surface with methylsiloxane groups (m-SiO₂). By dispersing m-SiO₂ into a [(PMMA)_x(PVC)_y] 50/50 (x/y) wt% polymer blend, six [(PMMA)_x(PVC)_y]/(m-SiO₂)_z hybrid inorganic–organic materials were obtained, with z ranging from 0 to 38.3 wt% and x = y = (100 − z)/2. The transparent, homogeneous, crack-free films were obtained by a solvent casting process from a THF solution. The morphology, thermal stability and transitions of hybrid materials were studied by environmental scanning electron microscopy (ESEM), thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). ESEM revealed that hybrid dielectric films are very homogeneous materials. The electrical response of the dielectric films was studied by detailed broadband dielectric spectroscopy (BDS). BDS measurements were performed at frequencies of 40 Hz to 10 MHz and a temperature range of 0–130°C. In these temperature and frequency ranges the proposed materials have a dielectric constant of <3.5 and a tan δ of <0.05. BDS also revealed molecular relaxation events in [(PMMA)_x(PVC)_y]/(m-SiO₂)_z materials as a function of temperature and sample composition. Results showed that these films with z in the range 25–35 wt% are very promising low-k dielectrics for applications in organic thin film transistor (OTFT) devices.     

Conductivity percolation transition of Agx(Ge0.25Se0.75)100−x glasses

The ionic conductivity of several chalcogenide glasses increases abruptly with mobile ion addition from values typical of insulating materials (10⁻¹⁶–10⁻¹⁴ Ω⁻¹ cm⁻¹) to values of fast ionic conductors (10⁻⁷–10⁻¹ Ω⁻¹ cm⁻¹). This change is produced in a limited concentration range pointing to a percolation process. In a previous work [M. Kawasaki, J. Kawamura, Y. Nakamura, M. Aniya, Solid State Ionics 123 (1999) 259] the transition from semiconductor to fast ionic conductor of Ag_x(Ge_0.25Se_0.75)_100−x glasses was detected at x¹ ≅ 10 at.% in the form of a steep change in the conductivity. Ag_x(Ge_0.25Se_0.75)_100−x glasses with x ⩽ 25 at.%, prepared by a melt quenching method, are investigated by impedance spectroscopy in the frequency range 5 Hz–2 MHz at different temperatures, T, from room temperature to 363 K and by DC measurements at room temperature. The conductivity of the glasses, σ, was obtained as a function of silver concentration and temperature. For x ⩾ 10 at.% our results are in agreement with those reported by Kawasaki et al. [M. Kawasaki, J. Kawamura, Y. Nakamura, M. Aniya, Solid State Ionics 123 (1999) 259]. The percolation transition was observed in the range 7 ⩽ x ⩽ 8. The temperature dependence of the ionic conductivity follows an Arrhenius type equation σ = (σ_o/T) · exp(−E_σ/kT). The activation energy of the ionic conductivity, E_σ, and the pre-exponential term, σ_o, are calculated. The results are discussed in connection with other chalcogenide and chalcohalide systems and linked with the glass structures.     

Structural study of AsS2–Ag glasses over a wide concentration range

(As_0.33S_0.67)_100-xAg_x (0 ≤ x ≤ 28) bulk glasses showing micro-phase separation in a wide concentration range have been studied by X-ray diffraction, neutron diffraction and extended X-ray absorption fine structure measurements. The AsAgS₂ composition, which forms a homogeneous glass, is modeled with the reverse Monte-Carlo simulation technique. It is established that Ag prefers the environment of S; Ag―As bonding cannot be observed. Similarly to the AsAgS₂ crystalline modifications smithite and trechmannite, the main structural units of the glass are AsS₃ pyramids. The covalent network of As and S atoms becomes fragmented in the glassy AsAgS₂ unlike in the glassy AsS₂. The environment of Ag atoms in the AsAgS₂ glass differs from that in the crystalline state. In average, each Ag atom has four nearest neighbors, three of them being S and one being Ag.