Enthalpy and volume relaxation of PMMA, PC, and a-Se: evaluation of aging bulk moduli

Enthalpy, h, and volume, v, relaxation of poly(methyl methacrylate), PMMA, and polycarbonate, PC, were measured using differential scanning calorimetry and mercury-in-glass dilatometry. For PMMA both temperature down-jumps and up-jumps were studied. Attention was paid to the influence of cooling/heating rates on aging process with the result that it is related to the corresponding shift of glass transition temperature, T_g. From the time dependence of enthalpy, h, and volume, v, the aging modulus was defined as K_a = (∂h/∂v)_T, and was found to be ca. 2 GPa. This corresponds roughly to the inverse value of the compressibility, κ_l, in the vicinity of T_g. The results of the measurements on amorphous selenium supported the notion that K_a assumes values close to 1/κ_l. The measured K_a values were about 5 GPa, in fair agreement with compressibility data extracted from pvT measurements.     

Apparent activation energy of structural relaxation for Se70Te30 glass

Differential scanning calorimetry and dc conductivity measurements were used to study structural relaxation of Se₇₀Te₃₀ glass. A single set of Tool-Narayanaswamy-Moynihan (TNM) parameters was obtained from the curve-fitting procedure. The value of apparent activation energy Δh∗ was further confirmed by two non-fitting techniques. Results of the Δh∗ evaluation from the T_g dependence on cooling rate are discussed in terms of how the T_f determination might be influenced by the material’s structure type and by the interference of the crystallization process.     

Deduction of activation energy for diffusion by analyzing soft impingement in non-isothermal solid-state precipitation

Physically realistic analytical treatment of soft impingement has been developed for solid-state precipitations in a non-isothermal process following the basic assumptions (i.e., a two-stage transformation including a site saturation of nucleation, an isotropic growth and a linear approximation for a concentration gradient in front of the precipitate/matrix interface). Based on the analytical treatment, Kissinger-like approach has been obtained to deduce the activation energy Q for diffusion during soft impingement in the non-isothermal process.     

Critical considerations on the Augis and Bennett method for evaluating the crystallization activation energy by means of non-isothermal data

The problems resulting from deriving the equation underlying the Augis and Bennett method (J. A. Augis, J. E. Bennett, J. Therm. Anal., 13 (1978) 183) often used in assessing the crystallization process activation energy (E), are critically analyzed. Solving such problems has resulted in a new iterative procedure for the E evaluation by making use of the non-isothermal data recorded at some heating rates. The theoretical results were checked for some experimental data given in late literature.     

Comparison of the energy histograms and conformations between different lattice models of copolymers

Based on large-scale Monte Carlo simulations the energy probability distribution functions are investigated for a large set of primary sequences in distinct lattice models of copolymers at low temperatures below transitions to compacted states. Amphiphilic copolymers with hydrophobic and hydrophilic units are found to produce single or double peak energy distributions corresponding to mono- or multi-meric micellar conformations. However, copolymers with short-ranged random ‘charge’ interactions in some cases are found to produce energy distribution functions with a well pronounced lowest energy state and a gap separating it from the rest of the spectrum. These, however have rather peculiar conformations corresponding to effectively immiscible domains comprised from monomers of likewise species. The relevance of these observations for coarse-grained models for protein folding is discussed.     

Effect of external field on bond energy and activation barrier for surface diffusion

Surface diffusion is one of the most common phenomena during the thin-film growth. The microstructure of the thin film depends on the rate of surface diffusion of the adatoms. In this paper, we theoretically show the effect of external field on surface diffusion barrier using gallium nitride as an example. We show, via density functional calculation, that the desorption energy of surface adsorbed atom and activation barrier for surface diffusion process can be altered by application of external field. Finally, based on the arguments of the electronic effect, we analyze the origin of the effect of the external field and its orientation on desorption energy and activation barrier for surface diffusion.     

Investigation of characteristics of activation energy of α-LiIO3 crystals by dielectric breakdown

α-LiIO₃ crystal is an essential quasi-one-dimensional ionic conductor, and its ionic conductivity is typically anisotropic. The activation energy of α-LiIO₃ has been calculated by the dielectric breakdown method. The calculating result shows that the anisotropism of the activation energy is consistent with that of conductivity.     

Semi-interpenetrating polymer networks based on polyurethane and poly(2-hydroxyethyl methacrylate): Dielectric study of relaxation behavior

The study of molecular dynamics by broadband dielectric spectroscopy (BDS) is presented for polyurethane (PU), poly(2-hydroxyethyl methacrylate) (PHEMA) and for semi-IPNs based on PU and PHEMA synthesized by photopolymerization. The dielectric properties were performed in wide range of frequencies and temperatures with the goal to establish the relation between the relaxations and the structure. Five relaxation phenomena were finally detected for PHEMA : γ-, βsw-, β-relaxations at low temperatures and α-relaxation at 150 °C at high frequencies plus ionic conductivity relaxation which starts at 0 °C. For semi-IPNs the overlapping of γ- and βsw-relaxations of PHEMA (?125/?75 °C), then with increasing the temperature α-relaxation in PU (?75/0 °C), next ionic conductivity relaxation which starts at 0 °C, and finally the α-relaxation of PHEMA (+125/+170 °C) were detected. The α-relaxation of PHEMA in semi-IPNs shifts to lower temperatures and became broader with increasing amount of PU due to incomplete phase separation in the system and formation of interphases. The dielectric relaxation phenomena were fitted with Havriliak–Negami equation. Activation energy, τ_o and α parameters were calculated. For α-relaxations corresponding dielectric characteristics have been determined from Vogel–Fulcher–Tammann equation. The relaxation map for investigated PU, PHEMA and semi-IPNs was built.     

Determination of size distribution and the activation energy of growth of the crystalline particle in TiNi thin films

Ti-49 at.% Ni thin films prepared by magnetron sputtering were annealed at 733-793 K for several time periods. Using small angle X-ray scattering, we have investigated the growth behavior of the crystalline particles in the TiNi films. We have obtained the size distribution of the samples annealed at 753 and 793 K for several time periods. The activation energy of growth of the crystalline particle was obtained.     

Thermo-optical characterization of tellurite glasses by thermal lens,thermal relaxation calorimetry and interferometric methods

In this work the thermal lens, thermal relaxation calorimetry and interferometric methods are applied to investigate the thermo-optical properties of tellurite glasses (in mol%: 80TeO₂–20 Li₂O(TeLi), 80TeO₂–15Li₂O–5TiO₂ (TeLiTi-5) and 80TeO₂–10Li₂O–10TiO₂ (TeLiTi-10)). Thermal diffusivity, thermal conductivity, specific heat and the temperature coefficients of refractive index, optical path length, thermal expansion and electronic polarizability were determined. The use of three independent methods was useful for a complete characterization of the studied tellurite glasses. In addition, our results showed that the thermal expansion coefficient and the temperature coefficient of the optical path length (dS/dT) were significantly modified with the introduction of titanium, which may be relevant for the application of these glasses in the photonic area.     

Switchable control of hydrophilicity and hydrophobicity in conjugated polymer nanoparticles by carbon dioxide

Abstract

We synthesized yellow-emissive, fluorine-based conjugated polymer to fabricate CO₂-responsive conjugated polymer nanoparticles (CPNPs). The CPNPs were functionalized with tertiary amine to have responsiveness to CO₂. The amine-functionalized CPNPs became hydrophilic by CO₂, bubbling because the bubbling led to formation of cationic ammonium ions at the side chains of the hydrophobic CPNPs. This resulted in high dispersion stability in aqueous phase even after vigorous mixing in the presence of organic phase (1-octanol). Subsequent N₂ bubbling was done to remove CO₂ present in water, leading to deprotonation of the side chains of CPNPs. The CPNPs became hydrophobic and moved to the organic phase. The CO₂-responsive property was based on the amine groups in the side chain of polymer that reversibly interacted with bicarbonate ion (HCO₃^-), formed by dissolving CO₂ in water, generating switchable hydrophilicity and hydrophobicity.     

The thermal stability and activation energy of crystallization of (Cu61.8Zr38.2)1−xAlx bulk metallic glasses

The present paper reports on the thermal stability and activation energy of crystallization of bulk metallic glasses (BMGs) (Cu_61.8Zr_38.2)_1−xAl_x. The (Cu_61.8Zr_38.2)_1−xAl_x composition series, prepared by copper mould suction casting into bars with a diameter of 3 mm, form BMGs with an e/a range of 1.24–1.3. These BMGs manifest increased thermal stability with increased e/a ratios. The activation energies (ΔE) of crystallization as derived from thermal analysis at different heating rates follow a similar tendency to that of the thermal stability, indicating stronger short-range ordering with increasing e/a ratios. The optimum BMG Cu_58.1Zr_35.9Al₆ exhibits the highest thermal stability and the largest ΔE.     

Preparation of Al-Cu-Fe quasicrystalline powdered alloys and related materials by mechanical activation

A mechanochemical method is developed for preparing quasicrystalline powdered alloys in the Al-Cu-Fe system and related materials. Quasicrystals are designed and proposed for use in practice as filling materials for metal and polymer matrices. The structure and mechanical properties of the designed materials are described. The possible fields of application of the materials under consideration are discussed.     

Investigation of the atom-atom and structural relaxation in liquid alkali metals by means of the memory function formalism

An attempt is made to systematize the data on the relaxation characteristics of liquid alkali metals (Li, Na, and K), which were investigated based on neutron-scattering data with the application of the two-time memory function formalism.     

The crystal and solution structure of 2,4-dinitrophenyl phenylsulfide determined by X-ray crystallography and13C-NMR spin-lattice relaxation measurements

The crystal structure of 2,4-dinitrophenyl phenylsulfide, C₁₂H₈N₂O₄S, has been determined by single crystal X-ray diffraction. The crystals are monoclinic, space groupP2 _{1/n, Z} = 8, witha = 10.670(2),b = 8.381(4),c = 27.998(18) Å, and = 100.44(4) °. There are two crystallographically independent molecules per asymmetric unit. All intensity measurements were made at room temperature on an Enraf-Nonius CAD-4 automatic diffractometer using monochromatized MoK radiation. The structure was solved by direct methods and refined to a finalR value of 0.032. The two independent molecules have nearly identical geometries, with the most notable difference being the torsion angles involving the sulfur atoms. Thepara-nitro groups are more nearly in the planes of the central phenyl rings than are theortho-nitro groups although there may be nonbonded attractions between the latter. The two phenyls of each molecule are nearly at right angles to each other, as necessitated by steric forces involvingortho hydrogens. The characteristic distortions of the central phenyl rings caused by differing substituent electronegativities and degrees of conjugation are noted. The¹³C-NMR spectrum of the compound was assigned by comparison of calculated with observed chemical shift data. Calculated chemical shifts were obtained by incrementation of the chemical shifts of diphenylsulfide with standard nitro group additivities which were adjusted for the sulfur-nitro group interaction. Where necessary, assignments were confirmed with selective excitation spin-coupled subspectra. Solution behavior of the molecule was determined from spin-lattice (T ₁) relaxation measurements which showed the unsubstituted ring to reorient anisotropically about the C(21)-C(24) bond axis while the substituted ring appears to be governed by the overall isotropic reorientation of the molecular framework, indicating that the sulfur-nitro group interaction restricts anisotropic reorientation about the C(11)-C(14) bond axis.     

Growth and energy band gap of CaSeS thin films prepared by hot-wall epitaxy

This paper investigates preparation of CaSeS thin films using hot-wall epitaxy. These films can be grown epitaxially on cleaved BaF₂(1 1 1) at a substrate temperature of 873 K by tailoring the VI/II flux ratio vaporized from Ca and SeS resources. The optical absorption edge of these films thus tailored can be observed clearly, shifting toward higher photon energy with increasing S content. In particular, the energy band gap of CaSe_0.66S_0.34, capable of lattice-matching to InP was found to be 4.69 eV, producing considerably large band gap difference of 3.34 eV between the CaSe_0.66S_0.34 and InP.     

Crystal growth of progesterone metastable and stable polymorphs by polymer induced herteronucleation (PIHn) method

The selective crystallization of progesterone polymorphs prepared by Polymer‐Induced Heteronucleation (PIHn) method was investigated. Polyvinyl alcohol (PVA), hydroxypropyl methylcellulose (HPMC), dextran, gelatin, polyisoprene (PI), and acrylonitrile/butadiene copolymer (NBR) were used as heteronucleants. Crystallizations were conducted from 0.5, 10 and 40 mg mL⁻¹ solutions in chloroform at room temperature by solvent evaporation. The samples were characterized by X‐ray powder diffraction, differential scanning calorimetry, infrared spectroscopy and scanning electron microscopy. Form 2 was obtained from 0.5 mg mL⁻¹ solution in almost all polymers. A mixture of both polymorphs crystallized from the three concentrations on gelatine; from 10 and 40mg mL⁻¹ on PVA and HPMC and, from 10 mg mL⁻¹ solutions on NBR. Form 2 crystallized on HPMC was stable for three months under ambient stress conditions (40ºC and 75% RH). These results are good evidence that the tailoring of new formulations and devices with progesterone the metastable and more soluble form 2 is possible.     

Investigation of lignin models of the biphenyl type by X-ray crystallography and NMR spectroscopy

Lignin models of the biphenyl type have been synthesized and crystal structures of two of them have been determined. The tetraacetate of 5,5-bis(hydroxymethyl)-3,3-dimethoxy-2,2-biphenyldiol crystallizes in space group witha=11.319(2),b=12.232(6),c=9.242(3) Å, =101.66(3)°, =108.14(2)°, =79.08(2)° andZ=2.R=0.036 (2720 observed [I>3(I)] reflections). The acetate of 5,5-di-tert-butyl-2,3,3-trimethoxy-2-biphenylol crystallizes in space group witha=11.972(2),b=21.621(3),c=9.834(1) Å, =91.18(1)°, =113.13(1)°. =98.42(1)°, andZ=4.R=0.050 (8129 observed [I>3(I)] reflections).¹H NMR and¹³C NMR data for the above-mentioned compounds and a third model, the diacetate of 5,5-bis(1-hydroxyethyl)-2,2,3,3-tetramethoxybiphenyl, are reported. Observed signal positions are compared with those calculated on the basis of crystal structure data. The possibilities to obtain structural information about biphenyl structures in lignins from NMR spectra are discussed.