Above,below, and in‐between the two glass transitions of ultrathin free‐standing polystyrene films: Thermal expansion coefficient and physical aging

In previous work we observed two simultaneous transitions in high molecular weight (MW) free‐standing polystyrene films that were interpreted as two thickness‐dependent reduced glass transition temperatures (T_gs). The weaker lower transition agreed well with the MW‐dependent T_g(h) previously reported, while the much stronger upper transition matched the MW‐independent T_g(h) previously observed in low‐MW free‐standing films. Here, we investigate the nature of these two transitions by inspecting the temperature dependence of the films' thermal coefficient of expansion (TCE) and present physical aging measurements using ellipsometry both below and in‐between the two transitions. TCE values indicate approximately 80 to 90% of the film solidifies at the upper transition, while only 10 to 20% remains mobile to lower temperatures, freezing out at the lower transition. Physical aging is observed at a temperature below the upper transition, but above the lower transition, indicative of the upper transition being an actual glass transition associated with the α‐relaxation. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2015 , 53, 64–75     

Pressure‐volume‐temperature and glass transition behavior of silica/polystyrene nanocomposite

The pressure‐volume‐temperature (PVT) behavior and glass transition behavior of a 10 wt % silica nanoparticle‐filled polystyrene (PS) nanocomposite sample are measured using a custom‐built pressurizable dilatometer. The PVT data are fitted to the Tait equation in both liquid and glassy states; the coefficient of thermal expansion α, bulk modulus K, and thermal pressure coefficient γ are examined as a function of pressure and compared to the values of neat PS. The glass transition temperature (T_g) is reported as a function of pressure, and the limiting fictive temperature (T_f′) from calorimetric measurements is reported as a function of cooling rate. Comparison with data for neat PS indicates that the nanocomposite has a slightly higher T_g at elevated pressures, higher bulk moduli at all pressures studied, and its relaxation dynamics are more sensitive to volume. The results for the glassy γ values suggest that thermal residual stresses would not be reduced for the nanocomposite sample studied. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2015 , 53, 1131–1138     

Rheology of polystyrene/poly(vinyl methyl ether)blends near the phase transition

Mixtures are expected to show anomalous behavior in their viscoelastic properties close to a critical point. In this study, the reheological behavior of blends of polystyrene and poly (vinyl methyl ether) below, close to, and above the phase separation temperature T_s was investigated. Rheological measurements were carried out at three different compositions in the melt. Below and far from T_s, a satisfactory superposition of the storage and loss moduli G' and G″ was observed at all temperatures and frequencies. Close to T_s deviations were observed for G' at low frequencies (the so-called terminal zone). Above T_s G″ values was still observed over the whole range of frequencies and temperatures. The deviations observed for G' near T_s can be interpreted as due to the presence of significant concentration fluctuations. Plots of log (G'/G″²) as a function of temperature were shown to be sensitive to this anomalous behavior.     

Dynamic light scattering from bulk poly(n-hexylmethacrylate) near and above the glass transition

Photon correlation spectra of polarized scattered light from poly(n-hexylmethacrylate) PHMA (M_w = 1.6·10⁵, T_g = ?5°C) have been studied in the temperature range of ?2–25°C. The experimental time correlation functions over the time range 10^?6?10² s were represented by the Kohlrausch-Williams-Watts (KWW) function exp{?(t/τ)^β} with a virtually temperature-independent distribution parameter β = 0.27 ± 0.02. The observed relaxation functions were also analyzed in terms of a continuous distribution of retardation times L(τ) by means of a direct inverse Laplace transformation. The computed L(τ) distributions reveal a broad single peak structure in agreement with the results of the single KWW fit. The temperature dependence of τ is very similar to that of the shift factors obtained from measurements of the shear modulus and the stress relaxation modulus in the glass-rubber region. Conversely, the values of τ compare well with those extracted from the experimental dielectric loss peaks consistently represented in the time domain by the KWW function. These findings suggest that the slow density fluctuations in bulk PHMA are associated with the primary glass-rubber or α-relaxation, which, however, displays an unusual low apparent Arrhenius activation energy and a rather low β value. PHMA exhibits significant dynamic light scattering with correlation times faster than 10^?6 s near T_g. © 1992 John Wiley & Sons, Inc.     

Volumetric coefficients,internal pressure,and cohesion energy density of <Emphasis Type="Italic">n</Emphasis>-alcohols

Changes in the thermal expansion coefficient and isothermal compressibility in homological series of n-alcohols at 298 K are discussed. It is shown that only methanol exhibits abnormal behavior. Volumetric coefficients of hypothetical solvents such as pseudo-water and pseudo-methanol are determined. Internal pressure values of liquids are calculated. The internal pressure of pseudo-water exceeds that of water, whereas the situation is opposite for the cohesion energy density.     

Effect of nanoscale confinement on the glass transition temperature of free-standing polymer films: Novel,self-referencing fluorescence method

The effect of nanoscale confinement on the glass transition temperature, T_g, of freely standing polystyrene (PS) films was determined using the temperature dependence of a fluorescence intensity ratio associated with pyrene dye labeled to the polymer. The ratio of the intensity of the third fluorescence peak to that of the first fluorescence peak in 1-pyrenylmethyl methacrylate-labeled PS (MApyrene-labeled PS) decreased with decreasing temperature, and the intersection of the linear temperature dependences in the rubbery and glassy states yielded the measurement of T_g. The sensitivity of this method to T_g was also shown in bulk, supported PS and poly(isobutyl methacrylate) films. With free-standing PS films, a strong effect of confinement on T_g was evident at thicknesses less than 80–90 nm. For MApyrene-labeled PS with M_n = 701 kg mol⁻¹, a 41-nm-thick film exhibited a 47 K reduction in T_g relative to bulk PS. A strong molecular weight dependence of the T_g-confinement effect was also observed, with a 65-nm-thick free-standing film exhibiting a reduction in T_g relative to bulk PS of 19 K with M_n = 701 kg mol⁻¹ and 31 K with M_n = 1460 kg mol⁻¹. The data are in reasonable agreement with results of Forrest, Dalnoki-Veress, and Dutcher who performed the seminal studies on T_g-confinement effects in free-standing PS films. The utility of self-referencing fluorescence for novel studies of confinement effects in free-standing films is discussed. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 2754–2764, 2008     

Equations of state for polyamide‐6 and its nanocomposites. II. Effects of clay

The pressure‐volume‐temperature (PVT) dependencies of polyamide‐6 and its nanocomposites (polymeric nanocomposites) were measured at temperatures T = 300–600 K and pressures P = 0.1–190 MPa, thus spanning the range of molten and “solid” phases. The Simha‐Somcynsky (S‐S) cell‐hole equation of state (EOS) was used for describing the molten region. At T_g(P) ≤ T ≤ T_m(P), the “solid” phase is a mixture of the liquid polyamide‐6 with dispersion of crystals. Accordingly, the PVT behavior in this region was described as a combination of the S‐S EOS for the liquid phase and the Midha‐Nanda‐Simha‐Jain (MNSJ) EOS for the crystalline one. These two theories based on different models yielded two sets of the characteristic reducing parameters, P^*, T^*, V^* and the segmental molecular weight, M_s. Incorporation of 2 and 5 wt % clay increased P^* and reduced T^* and V^*, but the effects were small. Fitting the combination of S‐S and MNSJ EOS' to isobaric “solid” phase data yielded the total crystallinity, X_cryst, and the correcting excess specific volume, ΔV_m,c. Both parameters were sensitive to pressure, P, and the clay content, w—the former increased with P and w, whereas the latter decreased. The raw PVT data were numerically differentiated to obtain the thermal expansion and compressibility coefficients, α and κ, respectively. At T < T_m, addition of clay reduced their relative magnitude, whereas at T > T_m, the opposite effect was observed, most likely owing to the excess of intercalant in the polymeric nanocomposites samples. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 966–980, 2009     

Continuous Miscibility from Dilute Solution to Fused Salt: Volumetric Properties of Binary Solutions of Nitrobenzene, 1-Butanol, and Anisole with Tetra-n-Butylammonium Picrate from 298.15 to 371.1 K

The densities and speeds of sound of binary solutions of nitrobenzene, 1-butanol, and anisole with tetra-n-butylammonium picrate have been measured over the full composition range from 298.15 to 371.1 K, in order to study the volumetric behavior of continuously miscible systems, made from an organic fused salt and a molecular organic liquid, at just above the melting point of the salt. The calculated apparent molar volumes and compressibilities are analyzed by using the equations of Petrenko and Pitzer. The thermal expansion coefficients of the above systems are also reported.     

Equation of state of hexagonal hydroxylapatite (P63) as obtained from density functional theory simulations

Hydroxylapatite is an important calcium phosphate phase whose knowledge is useful in different fields, for instance in bone biology, development of biomaterials and even cultural heritage. In this work, the equation of state of this mineral was calculated by using the quasi‐harmonic approximation, also including for the first time the temperature effect. In athermal conditions (0 K), we found that the pressure dependence of the hydroxylapatite unit cell volume is well described by a third‐order Birch–Murnaghan formulation, with parameters K₀ = 115.9(1), K' = 4.47(6), and V₀ = 524.323(27). The inclusion of temperature led to a lower bulk modulus, for example, KT₀ = 109.55 GPa at 300 K. The thermal expansion coefficient between 0 and 1000 K was also reported. The results are in good agreement with the few available experimental data reported in literature and further extend the knowledge of the mechanical and thermal behavior of this important mineral.     

Isobaric thermal expansivities of polyethylenes with various crystallinities over the pressure range from 0.1 to 300 MPa and over the temperature range from 303 to 393 K

A pressure-controlled scanning calorimeter (PCSC) has been applied for measuring the isobaric volume thermal expansivities (α_p) of crystalline polymers as a function of pressure up to 300 MPa at various temperatures. The measurements have been performed for several well-defined polyethylenes with various degrees of crystallinity at 302.6, 333.0, 362.6, and 393.0 K. The results are reported as values of coefficients in a correlation equation, which facilitates the use of reported data over large ranges of temperature and pressure. The general pressure-temperature behavior of α_p for all polyethylenes under study is such that α_p increases with temperature and decreases with pressure. The increase with temperature is smaller at high pressures and the isotherms of α_p have a tendency to converge at high pressures; α_p decreases linearly with the crystallinity of the polyethylene over the whole range of pressure and temperature under investigation. From the linear approximation of experimental data for polyethylenes with various crystallinities the estimated α_p for both crystal and amorphous phases of polyethylenes have been determined as a function of pressure up to 300 MPa at 302.6, 333.0, and 362.5 K. The obtained results have been compared with available literature crystallographic data and with the values derived from the Pastine theoretical equation of state for both crystalline and amorphous phases. © 1996 John Wiley & Sons, Inc.     

Pressure–volume–temperature properties and free volume parameters of PEO/PMMA blends

Melt-miscible polymer blends of poly(ethylene oxide)/atactic poly(methyl methacrylate (PEO/a-PMMA)) were prepared by melt-mixing and characterized by pressure–volume–temperature (PVT) dilatometry in the pressure and temperature range of 0 to 200 MPa and 20 to 200°C, respectively. The PVT data were analyzed in terms of two equations of state (EOS). The empirical Tait EOS was applied in the glassy, semicrystalline, and equilibrium melt state, and the Simha-Somcynsky EOS theory was applied in the equilibrium melt and glassy state. The Simha-Somcynsky EOS theory contains a free volume function. The temperature, pressure, and composition dependence of the free volume fraction h calculated from the Simha-Somcynsky EOS theory was studied. As a function of blend composition we observe that the free volume fraction, thermal expansivity, and compressibility all deviate mainly positively from linearity while the specific volume deviates mainly negatively from linearity. These findings are reconciled with composition-dependent free volume parameters, the free volume and cell volume as well as with self- and cross-interaction parameters derived from the Simha-Somcynsky EOS theory as applied to polymer mixtures. Moreover, the pressure dependence of glass and melting transitions as well as crystallization kinetics have been investigated. © 1998 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 36: 1061–1080, 1998     

Studies on the MxiH Protein in T3SS Needles Using DNP‐Enhanced ssNMR Spectroscopy

Bacterial T3SS needles formed by the protein MxiH are studied using DNP‐enhanced ssNMR spectroscopy at 14.1 T (600 MHz). This technique provides spectra of good resolution, allowing us to draw conclusions about the protein dynamics. With the obtained signal enhancement, samples of limited quantity now get within reach of ssNMR studies.     

Chemical Bonding Effects and Physical Properties of Noncentrosymmetric Hexagonal Fluorocarbonates ABCO3F (A: K,Rb, Cs; B: Mg,Ca, Sr,Zn, Cd)

The present work applied the methods of density functional theory and the van der Waals interaction PBE + D3(BJ) on the basis of localized orbitals of the CRYSTAL17 package. It featured the effect of interactions between structural elements of fluorocarbonates ABCO₃F (A: K, Rb, Cs; B: Mg, Ca, Sr, Zn, Cd) on their elastic and vibrational properties. The hexagonal structures proved to consist of alternating ···B-CO₃··· and ···A-F··· layers in planes ab, interconnected along axis c by infinite chains ···F-B-F···, where cations formed polyhedra AO_nF₃ and BO_mF₂. The calculations included the band energy structure, the total and partial density of electron states, the energy and band widths of the upper ns- and np-states of alkali and alkaline-earth metals, as well as nd-zinc and nd-cadmium. For hydrostatic compression, we calculated the parameters of the Birch–Murnaghan equation of state and the linear compressibility moduli along the crystal axes and bond lines. We also defined the elastic constants of single crystals to obtain the Voigt–Reuss–Hill approximations for the elastic moduli of polycrystalline materials. The study also revealed the relationship between the elastic properties and the nature of the chemical bond. Hybrid functional B3LYP made it possible to calculate the modes of normal long-wavelength oscillations, which provided the spectra of infrared absorption and Raman scattering. Intramolecular modes ν1 and ν4 with one or two maxima were found to be intense, and their relative positions depended on the lengths of nonequivalent C–O bonds.     

Unsaturated polyester resins cure: Kinetic,rheologic, and mechanical dynamical analysis. II. The glass transition in the mechanical dynamical spectrum of polyester networks

Unsaturated polyester networks with various structures built from an orthophtalic polyester, with methyl ethyl ketone peroxide as an initiator and cobalt octoate as a promoter, were studied with dynamic mechanical thermal analysis from −50 to 200 °C to characterize changes in the mechanical properties as a function of the temperature. From these measurements, the glass‐transition temperatures of the different networks were determined, their dependence on conversion being fitted to an equation related to the Couchman and DiBenedetto equations. Finally, the different transitions were analyzed as a function of the cure conditions. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 39: 146–152, 2001     

Energies,fine structures,and transition rates of the core‐excited states in BeII

The energies and fine structures of some doubly excited resonances of lithiumlike beryllium are calculated using the saddle‐point variational method. A restricted variational method is used to extrapolate a better nonrelativistic energy. Relativistic and mass polarization corrections are included. Oscillator strengths, transition rates, and wavelengths are also calculated. The results are compared with other theoretical and experiment data in the literature. © 2000 John Wiley & Sons, Inc. Int J Quant Chem 76: 656–661, 2000     

Determination of the glass transition temperature of polystyrene,poly(vinyl chloride) and poly(methyl methacrylate) using gas chromatography

The glass transition temperatures, Tg, of polystyrene, poly (vinyl chloride) and poly(methyI methacrylate) have been determined from gas chromatographic measurements using n-hexane, n-heptane, meta-xylene and para-xylene solvents. The glass transition temperatures were detected on the z-shaped retention diagrams which were produced from the plot of the logarithm of the specific retention volumes of the above-mentioned solvents against the reciprocal of temperature, i.e. log V${}_{\text{g}}^{\text{º}}$ vs. 1/T. The glass transition temperature is specified by the temperature where the slope of log V${}_{\text{g}}^{\text{º}}$ vs. 1/T changes abruptly. The observed glass transition temperature of polystyrene produced by this technique was found to be in good agreement with those produced by other techniques such as the differential scanning colorimeter. The industrial importance of the glass transition temperature, T_g, might be due to the dramatic changes in the physical properties of the polymer, such as hardness and elasticity, which take place in the vicinity of this temperature. However, perfectly crystalline polymers do not exhibit glass transitions, because their chains are incorporated in regions of three-dimensional order, called crystallites. Completely amorphous polymers and semi-crystalline polymers usually exhibit both glass transition and melting.     

Use of a recently developed thermal modulator within the context of comprehensive two‐dimensional gas chromatography combined with time‐of‐flight mass spectrometry: Gas flow optimization aspects

The present research is based on the use of a recently developed comprehensive two‐dimensional gas chromatography thermal modulator, which is defined as solid‐state modulator. The transfer device was installed on top of a single gas chromatography oven, while benchtop low‐resolution time‐of‐flight mass spectrometry was used to monitor the compounds exiting the second analytical column. The solid‐state modulator was first described by Luong et al. in 2016, and it is a moving modulator that does not require heating and cooling gases to generate comprehensive two‐dimensional gas chromatography data. The accumulation and remobilization steps occur on a trapping capillary, this being subjected to thermoelectric cooling and micathermic heating. In this study, the effects of the gas linear velocity on the modulation performance were evaluated by using two different uncoated trapping capillaries, viz., 0.8 m × 0.25 mm id and 0.8 m × 0.20 mm id. Solid‐state modulator applications were carried out on a standard solution containing n‐alkanes (C_9, C_10, C₁₂), and on a sample of diesel fuel. The results indicated that the type of trapping capillary and gas velocity have a profound effect on modulation efficiency.     

Dielectric relaxations of chitosan: The effect of water on the α‐relaxation and the glass transition temperature

In this work thermal relaxations of chitosan are reported by using a novel methodology that includes subtraction of the dc conductivity contribution, the exclusion of contact and interfacial polarization effects, and obtaining a condition of minimum moisture content. When all these aspects are taken into account, two relaxations are clearly revealed in the low frequency side of the impedance data. We focus on the molecular motions in neutralized and non‐neutralized chitosan analyzed by dielectric spectroscopy in the temperature range from 25 to 250 °C. Low and high frequency relaxations were fitted with the Havriliak and Negami model in the 10^?1 to 108 Hz frequency range. For the first time, the low frequency α‐relaxation associated with the glass‐rubber transition has been detected by this technique in both chitosan forms for moisture contents in the range 0.05 to 3 wt % (ca. 18–62 °C). A strong plasticizing effect of water on this primary α‐relaxation is observed by dielectric spectroscopy and is supported by dynamic mechanical analysis measurements. In the absence of water (<0.05 wt %) the α‐relaxation is obscured in the 20–70 °C temperature range by a superposition of two low frequency relaxation processes. The activation energy for the σ‐relaxation is about 80.0–89.0 kJ/mol and for β‐relaxation is about 46.0–48.5 kJ/mol and those values are in agreement with that previously reported by other authors. The non‐neutralized chitosan possess higher ion mobility than the neutralized one as determined by the frequency location of the σ‐relaxation. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 2259–2271, 2009