Phonon dispersion and heat capacity in poly(ε-caprolactone)

Normal mode of vibration and their dispersion for poly(ε-caprolactone) (PCL) chain have been obtained by using Urey-Bradley force field and the Wilson's GF matrix method as modified by Higgs. Characteristic features of the dispersion curves such as crossing, repulsion and regions of high density-of-states have been explained. Heat capacity measurements have been interpreted and the limitations of the present work discussed.     

Phonon dispersion in polycytidilic acid

A study of the normal modes of vibration and their dispersion in polycytidilic acid based on the Urey–Bradley force field and Raman and Fourier transform infrared spectroscopy is reported. Characteristic features of dispersion curves such as regions of high density of states, repulsion, and character mixing of dispersive modes are discussed. The predictive value of the heat capacity as a function of temperature is reported. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 504–516, 2006     

Phonon dispersion and heat capacity of polydichlorobutadiene

Normal modes and their dispersion have been obtained for trans polydichlorobutadiene (PDCB) in the reduced zone scheme using Wilson’s G F matrix method as modified by Higg’s for an infinite polymeric chain. The Urey Bradley potential field is obtained by least square fitting of the observed infrared and Raman bands. The obtained results agree well with the experimental values. Because of the presence of centre of symmetry, the PDCB molecule obeys the mutual exclusion principle. Several new assignments which are missing in the earlier work are reported. The characteristic features of dispersion curves such as repulsion and exchange of character have been discussed and possible explanation has been given. Heat capacity has been calculated via density-of-states using Debye relation in the temperature range 10–450 K.     

Dispersion of normal modes in cis 1,4 polybutadiene

Among the synthetic polymers of commercial potential, poly-butadiene is an important rubbery material and it encompasses the bulk elastomers in use. To the best of our knowledge, a complete normal coordinate analysis with full phonon dispersion curves for cis 1,4 polybutadiene (CPBD) have not been reported so far. In the present communication, we report a complete normal coordinate analysis with full dispersion curves, density-of-states and calculation of heat capacity. The normal coordinate analysis has been carried out using the Urey-Bradley force field and the Wilson's GF matrix method as modified by Higgs. A comparison has been made with trans 1,4 polybutadiene (TPBD). The prominent features of the dispersion curves like crossing over and regions of zero-slope away from the zone centre are discussed. To check the validity of the force field used and the assignments, normal mode calculations are also performed for unsaturated C-deuterated and fully deuterated CPBD.     

A comparative study of vibrational dynamics of α- and β-forms of poly(β-hydroxybutyrate)

Normal modes and their dispersion are obtained for planar zig-zag form of poly(β-hydroxybutyrate) using Urey-Bradley force field. A comparison is made with the spectra of its helical form. Apart from detailed assignment of modes, various characteristic features of dispersion curves have been explained as arising due to internal symmetry in energy momentum space. The density-of-states have been used to calculate heat capacity in the temperature range 10-450 K using Debye's formalism.     

Phonon dispersion treatment for the heat capacities of vitreous and crystalline phases

Based upon the Barker and Martin treatment developed for the analysis of vitreous phases, an analysis of both polycrystalline and crystalline phases of various complexity is described. Primarily, cryogenic heat-capacity measurements and spectroscopic vibrational analysis are involved. Some history of the development of the phonon dispersion equations is incorporated. The applicability of the phonon velocity dispersion to polycrystalline and single-crystal copper are used as convenient examples to illustrate the application of the theory. They emphasize the complications occasioned by anisotropies in single crystals even in polycrystalline aggregates, where they are only partially obscured by the macroscopic isotropy of aggregates. Copper does involve the treatment of the electronic terms and demonstrates a competence of critical relevance to other types of crystalline and vitreous materials.     

Phonon dispersion in poly(dimethylsilane)

In the present communication we report normal modes and their dispersion in polydimethylsilane (PDMS) [-Si(CH₃)₂-]_n using Urey-Bradley force field, which in addition to valence force field accounts for the non-bonded interactions in the gem and cis configurations and tension terms. The partially deuterated PDMS (PDMS-d₃), i.e., (SiCH₃CD₃)_n and fully deuterated PDMS (PDMS-d₆), i.e., (SiCD₃CD₃)_n are also studied to check the assignments and validity of the force field. Dispersion curves show two interesting features: (1) a divergence of dispersion curves following repulsion of species belonging to the same symmetry; (2) crossing between the two modes. In addition, heat capacity as a function of temperature via density-of-states is evaluated and some of the modes left unassigned by the earlier workers have been assigned.     

Heat capacity and glass transition of ethylene oxide clathrate hydrate

The heat capacity of structure I ethylene oxide clathrate hydrate EO-6.86 H₂O was measured in the temperature range 6–300 K with an adiabatic calorimeter. The temperature and enthalpy of congruent melting were determined to be (284.11 ± 0.02) K and 48.26 kJ mol^–1, respectively. A glass transition related to the proton configurational mode in the hydrogen-bonded host was observed around 90 K. This glass transition was similar to the one observed previously for the structure II tetrahydrofuran hydrate but showed a wider distribution of relaxation times. The anomalous heat capacity and activation enthalpy associated with the glass transition were almost the same as those for THF-hydrate.Dedicated to Dr D. W. Davidson in honor of his great contributions to the sciences of inclusion phenomena.Author for correspondence.     

High temperature enthalpy and heat capacity of GaN

The heat capacity and the heat content of gallium nitride were measured by calvet calorimetry (320-570 K) and by drop calorimetry (670-1270 K), respectively. The temperature dependence of the heat capacity in the form C_pm=49.552+5.440×10⁻³T−2.190×10⁶T⁻²+2.460×10⁸T⁻³ was derived by the least squares method. Furthermore, thermodynamic functions calculated on the basis of our experimental results and literature data on the molar entropy and the heat of formation of GaN are given.     

Heat balances and heat capacity calculations

We present enthalpy and heat capacity calculations under reversible conditions in which a system is allowed to reach equilibrium after incremental steps in temperature. We focus on the binary systems Ag–Cu and 1,3,5 tri-bromo-benzene and 1,3,5 tri-chloro-benzene and show that due to the compositional effect, thermodynamic properties differ up to an order of magnitude in two-phase regions relative to values in single-phase regions. We demonstrate that Planck’s definition of heat capacity needs a minor extension to include the change of phase assemblages due to phase transitions. Dedicated to Professor Su-II Pyun on the occasion of his 65th birthday     

Zeolite 4A: heat capacity and thermodynamic properties

The heat capacity of zeolite 4A (also known as LTA, Linde Type A and sodium zeolite A), in the temperature range from 37 to 311 K, is reported. The heat capacity shows no anomalies in this temperature range. Thermodynamic parameters, H, S and G, relative to their values at T=0 K were derived. From these data, we find that zeolite 4A is stabilized by strong enthalpic interactions. Furthermore, its thermodynamic stability results from the strong Si---O and Al---O bonds in the primary building units, with bond strengths very close to those in other similar materials.     

Anomalously high heat capacity of core-softened liquids

Heat capacity is among the most important thermodynamic characteristics of a substance. The behaviour of the heat capacity is well understood in gases and crystals, but not in liquids. A common view on the heat capacity of liquids is that it should be close to the solid-like values close to the melting line and it should approach the gas values in the limit of high temperatures. However, some liquids can show anomalously high magnitudes of isochoric heat capacity. In the present paper, I show that core-softened liquids can demonstrate unusually high magnitude of the heat capacity induced by a structural crossover of the liquid.     

Importance of heat capacity determination in homogeneous nucleation: application to progesterone

Progesterone is known to exist under different crystallographic forms in the solid state. The thermodynamic stable form (I), melts at 129.2 °C (402.35 K) under atmospheric pressure. After melting and cooling a metastable form (II) can be obtained which melts at 122 °C (395.15 K). This uncommon behaviour can be explained with the theory of nucleation, only if heat capacity of the different forms are known.     

Influence of surface modification adopting thermal treatments on dispersion of detonation nanodiamond

In order to improve the dispersion of detonation nanodiamonds (ND) in aqueous and non-aqueous media, a series of thermal treatments have been conducted in air ambient to modify ND surface. Small angle X-ray scattering (SAXS) technique and high resolution transmission electron microscopy (HRTEM) were introduced to observe the primary size of ND. Differential thermal analysis (DTA), X-ray diffraction (XRD) methodology, X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared (FTIR) spectroscopy were adopted to analyze the structure, bonds at surfaces of the treated ND. Malvern instrument Zetasizer3000HS was used for measuring the surface electric potential and the size distribution of ND. As thermal treatments can cause graphitization and oxidization of functional groups at the surface, ND treated at high temperature is correspondingly more negatively charged in an aqueous medium, and the increased absolute value of zeta potential ensures the electrostatic stability of ND particles. Specially, after being treated at a temperature more than 850 K, ND can be well dispersed in various media.     

Isobaric specific heat capacity of typical lithium chloride liquid desiccants using scanning calorimetry

Three kinds of lithium chloride desiccants were selected, which are considered to be potential and interesting working fluids for a desiccant/dehumidification or absorption refrigeration system, and their isobaric specific heat capacities were determined in this context. Experiments were conducted at a high accuracy twin-cell scanning calorimeter. The temperature accuracy and heat flux resolution of the calorimeter are ±0.05 K and 0.1 μW respectively. The data of lithium chloride + water and lithium chloride + triethylene glycol (TEG)/propylene glycol (PG) + water systems were achieved at temperatures from 308.15 K to 343.15 K and atmospheric pressure. The mass fraction of LiCl ranged from 15% to 45% in the LiCl + H₂O system, and the mass fraction of LiCl and glycol ranged from 10% to 23.3% and 20% to 46.7% in the ternary systems respectively. Based on the experimental heat capacity data, a universal empirical formula was correlated as a function of temperature and solute mass fraction. In the experimental mass fractions and temperatures range, the average absolute deviation (AAD) between experiment results and calculated values is no more than 0.15%, and maximum absolute deviation (MAD) is within 0.38%. These thermodynamic data of lithium chloride solutions can be effectively used for analysis and design of desiccant/dehumidification systems and absorption refrigeration systems in both refrigeration and chemical industry.     

Some elements in specific heat capacity measurement and numerical simulation of temperature modulated DSC (TMDSC) with R/C network

One important application of temperature modulated DSC (TMDSC) is the measurement of specific heat of materials. In this paper, a thermal resistance/capacitance (R/C) numerical model is used to analyze the effects of experimental parameters and calibration on the measurement of specific heat in TMDSC under isothermal conditions. The actual TMDSC experiments were conducted with sapphire and pure copper samples, respectively. Both simulation and experiments showed that in TMDSC, the measured sample specific heat is a non-linear function of many factors such as sample mass, the heat transfer properties of the TMDSC instrument, temperature modulation period, the heat capacity difference between calibration material and the test material, but modulation amplitude has very little effect on the results. The typical behavior of a heat flux type TMDSC can be described as a low pass filter in terms of specific heat capacity measurement when the instrument heat transfer properties are taken into account. At least for metallic materials, where the temperature gradient inside the sample can normally be ignored, the sample should be chosen in such a way that its total heat capacity (mass times specific heat) is close to that of the calibration material in order to get a more accurate result. Also, a large modulation period is beneficial to improving the test accuracy.     

Specific heat capacity and Debye temperature of zirconia and its solid solution

Specific heat C_P of zirconia and yttria stabilized zirconia doped or not with erbia and ceria was measured from 128 to 823 K and of yttria stabilized zirconia doped with erbia and plutonia from 443 to 1573 K. The new determined data were modelled using Debye theory. Data for the tetravalent oxide and for the studied solid solutions show that the extended Dulong and Petit law in Neumann-Kopp rule is verified for zirconia and the quaternary compounds. The Debye temperature of zirconia (590 K) and its yttria, erbia and ceria doped solid solutions (575-625 K) derived from these C_P measurements between 150 and 823 K is discussed and compared with that reported for other tetravalent metal oxides.     

Assessment of nanoparticle loading and dispersion in polymeric materials using optical wavefront correlation

Small concentrations (≤5 wt. %) of nanoparticles in polymeric materials can potentially result in improvements in material properties and functionality. However, poor or non-uniform particle dispersion resulting in clustering (agglomeration) in polymer nanocomposites (PNCs) limits the potential for property enhancement. Achieving good dispersion is considered essential for large-scale production and commercialization of PNCs. New and effective measurement techniques capable of quantitatively characterizing particle loading and dispersion would significantly contribute towards understanding and optimizing the material performance of PNCs and, consequently, play a pivotal role in product development. This paper presents the results of a study using a static light scattering technique, optical wavefront correlation (OWC), for discriminating between different particle loadings and levels of dispersion. The technique has been applied to a range of PNCs, including epoxy resins reinforced with nanoclay platelets or silica microspheres, and zinc oxide and lithium aluminate reinforced polypropylene.     

Assessment of nanoparticle loading and dispersion in polymeric materials using optical coherence tomography

The inclusion of small concentrations of nanoparticles can significantly enhance the thermal and electrical properties, and to a lesser degree the mechanical performance, of polymers. Dispersion of nanoparticles during mixing is problematic, with poor mixing resulting in particle agglomeration (i.e. particle clustering), which subsequently limits the potential for property enhancement. Achieving good dispersion is considered key to large-scale production and commercialization of polymer nanocomposites (PNCs), and a measurement technique capable of quantitatively characterizing particle loading and dispersion would significantly enhance product development. This paper presents the results of a study using a static light scattering technique, Fourier domain optical coherence tomography (FD-OCT), for discriminating between different particle loadings and levels of dispersion. The technique has been applied to a range of PNCs including epoxy resins reinforced with nanoclay platelets, silica microspheres or multi-walled carbon nanotubes (MWCNTs), and zinc oxide and lithium aluminate reinforced polypropylene.