Heat Capacity Of Poly Research Articles

Vibrational heat capacity of Poly(N-isopropylacrylamide)

The heat capacity of poly(N-isopropylacrylamide) (PNIPA) has been measured from (1.8–460) K using a quantum design PPMS (Physical Property Measurement System) and differential scanning calorimeters. The low-temperature experimental heat capacity below the glass transition temperature 415 K (141.85 °C) was linked to the vibrational molecular motions of PNIPA to establish the baseline of the solid, vibrational heat capacity. The vibrational heat capacity of PNIPA was computed based on group and skeletal vibrations. The group vibrational heat capacities were calculated based on the chemical structure and molecular vibrational motions derived from infrared and Raman spectroscopy. The skeletal heat capacity was fitted to a general Tarasov equation using sixteen skeletal modes to obtain three Debye characteristic temperatures Θ1 = 650 K and Θ2 = Θ3 = 68.5 K. The fit agreed well with the experimental data (±0.2%) from T = (1.8–250) K, and the vibrational heat capacity, which was extended to higher temperatures, served as a baseline of the solid heat capacity for quantitative thermal analysis of the experimental, apparent heat capacity data of PNIPA. The liquid heat capacity of fully amorphous PNIPA was approximated by a linear regression and expressed as Cpliquid(exp) = 0.3379 ⋅ T + 126.69 in J K−1 mol−1. This was then compared to the estimated linear contributions of polymers that have the same constituent groups. Using estimated parameters of transitions and solid and liquid heat capacities at equilibrium, the integral thermodynamic functions of enthalpy, entropy and free enthalpy as functions of temperature were calculated.

Thermal conductivity and heat capacity of poly(3-octylthiophene-2,5 diyl) and its multi-wall carbon nanotube composites

Poly (3-octylthiophene-2,5-diyl) (P3OT) is one of the most important semiconducting polymer materials used for organic solar cells. Thermal properties data, especially the thermal conductivity of the active material of solar cells, is of fundamental importance. Such data for P3OT are barely available in the literature. The photoacoustic technique is employed to measure thermophysical properties of P3OT including thermal diffusivity, thermal effusivity, specific heat capacity and thermal conductivity. The obtained results are confirmed by many measurements as well as by using more than one method. A remarkable method for thermal effusivity measurements of surface coating as well as bulk samples is introduced. The development of P3OT thermophysical properties with multi-wall carbon nanotube (MWCNT) loading as high as 6% volume fraction is investigated. Continuous enhancement of thermal diffusivity as well as thermal effusivity of P3OT is obtained with increasing MWCNT content. By using the mixed model for the thermal conductivity of a two phase system, we are able to estimate the thermal diffusivity and the thermal effusivity of MWCNTs. A considerable enhancement in thermal conductivity of larger than twice that of neat P3OT at nanotube loading ≈6% volume fraction is obtained. Theoretical analysis of the experimental results generating an interfacial thermal resistance of MWCNTs as Rk = 5.8 × 10−8 m2K W−1.

Vibrational Dynamics and Heat Capacity of Poly(3-methylthiophene): A Conducting Polymer

Using the Urey–Bradley force field and Wilson's GF matrix method as modified by Higgs, normal modes of vibration and their dispersions in poly(3-methylthiophene) have been obtained. They provide a detailed interpretation of its I.R. and Raman spectra. Characteristic features of the dispersion curves, such as regions of high density-of-states, repulsion, and character mixing of dispersive modes, are discussed. Predictive values of the heat capacity as a function of temperature have been calculated.

Thermodynamic characteristics and the temperatures of relaxation transitions of poly(methacrylic acid)

The heat capacity of poly(methacrylic acid) containing 2.5 wt % water was measured in a vacuum adiabatic calorimeter at temperatures between 80 and 325 K. The heat capacity of anhydrous poly(methacrylic acid) was calculated, and its standard enthalpies of combustion and formation were determined. On the basis of the enthalpy of melting of the “free”-water phase, the limit of water solubility in the polymer was found calorimetrically at 273 K. The temperatures of relaxation transitions (the glass transition and the β and γ transitions) of poly(methacrylic acid) mixtures with water were determined via differential thermal analysis in the region 80–550 K. In addition, the determination of the temperatures of transitions of anhydrous poly(methacrylic acid) was performed via extrapolation to zero water content of the concentration dependences of the relaxation-transition temperatures.

Heat capacity of poly(3-hydroxybutyrate)

The heat capacity of poly(3-hydroxybutyrate) (P3HB) has been measured using a quantum design Physical Property Measurement System (PPMS), differential scanning calorimetry (DSC), and temperature-modulated differential scanning calorimetry (TMDSC) over the temperature range of (1.9 to 460)K. The results within the range of (1.9 to 250)K were obtained using the quantum design PPMS, and established the baseline of the solid heat capacity. This experimental low-temperature heat capacity was linked to the vibrational molecular motion of P3HB. The solid heat capacity of P3HB was computed based approximately on groups of vibration and skeletal vibration spectra. The skeletal vibration heat capacity contribution was estimated by a general Tarasov equation with three Debye characteristic temperatures Θ1=549.1K and Θ2=Θ3=71.8K, and ten skeletal modes, Nskeletal=10. The experimental and calculated solid heat capacities agree with an error of ±0.2% over the temperature range from (5 to 250)K. The vibrational, solid heat capacity was extended to higher temperatures to judge additional contributions to the experimental heat capacity from other large-amplitude motion or latent heat during the quantitative thermal analysis of semi-crystalline P3HB. The liquid heat capacity of semi-crystalline P3HB above its melting temperature and of fully amorphous P3HB above the glass transition temperature was approximated by a linear regression and expressed as Cpliquid(exp)=0.1791 T+94.722 in units of J·K−1·mol−1. The calculated solid and liquid heat capacities can serve as equilibrium baselines for the quantitative thermal analysis of semi-crystalline P3HB. Also, the integral thermodynamic functions of enthalpy, entropy and free enthalpy for the equilibrium condition were calculated using estimated parameters of transitions.

Investigation on the Heat Capacity of Water in Poly(Acrylic Acid)/Water Mixtures Through Stepscan Method

The heat capacity of poly(acrylic acid)/water mixtures with low water contents were measured by the stepscan differential scanning colorimetry (DSC) method and the Cp of the bound water in the mixtures were obtained based on simple equations with an assumption that the effect of interaction between polymer and water molecules could be ignored. The results indicated that the water decreased the glass transition temperature of poly(acrylic acid) (PAA), evidently as a plasticizer, and PAA/water mixtures were thermodynamically homogeneous blends. It was found that the Cp of nonfreezable water in PAA/water mixtures was higher than those of glassy water and cubic ice. The Cp increased with the water content, showing that average interactions between polymer and water decreased with water content. The Cp of bound water in the mixtures in the liquid state was lower than that of bulk water and also increased with water concentration, since the water molecules’ regular structures were broken. It showed that the Cp of bound water in the mixtures was lower than that of free water. The Cp of glassy water was calculated based on experimental Cp values of the PAA/water mixtures, which provided an easy way to obtain the Cp values of glassy water through a simple experiment. The values, however, were higher than those obtained by other researchers.

Contribution of surface rayleigh waves to the heat capacity of poly(vinyl chloride)

The method of surface acoustic waves is employed to determine the frequency and temperature dependences of the molar heat capacity of poly(vinyl chloride) on the contribution of Rayleigh local components of the longitudinal and transverse vibrations of structural units of the polymer. The calculated and experimental data are compared in terms of their dependence on the relaxation state of the system.

Reversible melting and crystallization of high‐molar‐mass poly(oxyethylene)

AbstractThe heat capacity of poly(oxyethylene) (POE) with a molar mass of 900,000 Da has been analyzed with differential scanning calorimetry and quasi‐isothermal, temperature‐modulated differential scanning calorimetry. The crystal structure, lattice parameters, and coherently scattering domain sizes have been measured with wide‐angle X‐ray diffraction as a function of temperature. The high‐molar‐mass POE crystals are in a folded‐chain macroconformation and show some locally reversible melting starting already at about 250 K. At 335 K, the thermodynamic heat capacity reaches the level of the melt. The reversible crystallinity depends on the modulation amplitude and has been varied in the melting range from ±0.2 to ±3.0 K. Before melting, there is neither a change in the crystal structure nor a change in the domain size, but the expansivity of the crystals increases at about 320 K. These observations support the interpretation that the monoclinic POE crystals possess a glass transition temperature with a midpoint at about 324 K, whereas the maximum melting temperature is 341 K. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 475–489, 2007

Heat capacity of poly(vinyl methyl ether)

AbstractThe heat capacity of poly(vinyl methyl ether) (PVME) has been measured using adiabatic calorimetry and temperature‐modulated differential scanning calorimetry (TMDSC). The heat capacity of the solid and liquid states of amorphous PVME is reported from 5 to 360 K. The amorphous PVME has a glass transition at 248 K (−25 °C). Below the glass transition, the low‐temperature, experimental heat capacity of solid PVME is linked to the vibrational molecular motion. It can be approximated by a group vibration spectrum and a skeletal vibration spectrum. The skeletal vibrations were described by a general Tarasov equation with three Debye temperatures Θ1 = 647 K, Θ2 = Θ3 = 70 K, and nine skeletal modes. The calculated and experimental heat capacities agree to better than ±1.8% in the temperature range from 5 to 200 K. The experimental heat capacity of the liquid rubbery state of PVME is represented by Cp(liquid) = 72.36 + 0.136 T in J K−1 mol−1 and compared to estimated results from contributions of the same constituent groups of other polymers using the Advanced Thermal AnalysiS (ATHAS) Data Bank. The calculated solid and liquid heat capacities serve as baselines for the quantitative thermal analysis of amorphous PVME with different thermal histories. Also, knowing Cp of the solid and liquid, the integral thermodynamic functions of enthalpy, entropy, and free enthalpy of glassy and amorphous PVME are calculated with help of estimated parameters for the crystal. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 2141–2153, 2005

Heat capacity of poly(butylene terephthalate)

AbstractThe low‐temperature heat capacity of poly(butylene terephthalate) (PBT) was measured from 5 to 330 K. The experimental heat capacity of solid PBT, below the glass transition, was linked to its approximate group and skeletal vibrational spectrum. The 21 skeletal vibrations were estimated with a general Tarasov equation with the parameters Θ1 = 530 K and Θ2 = Θ3 = 55 K. The calculated and experimental heat capacities of solid PBT agreed within better than ±3% between 5 and 200 K. The newly calculated vibrational heat capacity of the solid from this study and the liquid heat capacity from the ATHAS Data Bank were applied as reference values for a quantitative thermal analysis of the apparent heat capacity of semicrystalline PBT between the glass and melting transitions as obtained by differential scanning calorimetry. From these results, the integral thermodynamic functions (enthalpy, entropy, and Gibbs function) of crystalline and amorphous PBT were calculated. Finally, the changes in the crystallinity with the temperature were analyzed. With the crystallinity, a baseline was constructed that separated the thermodynamic heat capacity from cold crystallization, reorganization, annealing, and melting effects contained in the apparent heat capacity. For semicrystalline PBT samples, the mobile‐amorphous and rigid‐amorphous fractions were estimated to complete the thermal analysis. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 4401–4411, 2004

Heat capacity of poly(lactic acid)

The heat capacity of poly(lactic acid) (PLA) is reported from T=(5 to 600) K as obtained by differential scanning calorimetry (d.s.c.) and adiabatic calorimetry. The heat capacity of solid PLA is linked to its group vibrational spectrum and the skeletal vibrations, the latter being described by a Tarasov equation with Θ 1=574 K, Θ 2= Θ 3=52 K, and nine skeletal vibrations. The calculated and experimental heat capacities agree to ±3% between T=(5 and 300) K. The experimental heat capacity of liquid PLA can be expressed by C p(liquid)=(120.17+0.076 T) J · K −1 · mol −1 and has been compared to the ATHAS Data Bank, using contributions of other polymers with the same constituent groups. The glass transition temperature of amorphous PLA occurs at T=332.5 K with a change in heat capacity of 43.8 J · K −1 · mol −1. Depending on thermal history, semi-crystalline PLA has a melting endotherm between T=(418 and 432) K with variable heats of fusion. For 100% crystalline PLA, the heat of fusion is estimated to be (6.55 ± 0.02) kJ · mol −1 at T=480 K. With these results, the enthalpy, entropy, and Gibbs function of crystalline and amorphous PLA were obtained. For semi-crystalline samples, one can check changes of crystallinity with temperature and judge the presence of rigid-amorphous fractions.

Vibrational dynamics and heat capacity of poly(glycolic acid)

Polyglycolic acid (PGA) (–CH 2–COO–) n is the first bioresorbable synthetic polymer which is used to make biomedical and pharmaceutical devices. It has a planar zigzag conformation. A comprehensive study of the normal modes and their dispersion in PGA using Urey Bradley force field is being reported. Characteristic features of the dispersion curves have been reported. The heat capacity derived from the dispersion curves via the density-of-states, is in good agreement with the experimental data of Lebedev and Yevstropov.

Reversible and irreversible heat capacity of poly[carbonyl(ethylene‐co‐propylene)] by temperature‐modulated calorimetry

Reversible and irreversible heat capacity of poly[carbonyl(ethylene‐co‐propylene)] by temperature‐modulated calorimetry

Heat capacity of poly(trimethylene terephthalate)

Thermal analysis of poly(trimethylene terephthalate) (PTT) has been carried out using standard differential scanning calorimetry and temperature-modulated differential scanning calorimetry. Heat capacities of the solid and liquid states of semicrystalline PTT are reported from 190 K to 570 K. The semicrystalline PTT has a glass transition temperature of about 331 K. Between 460 K and 480 K, PTT shows an exothermic ordering. The melting endotherm occurs between 480 K and 505 K with an onset temperature of 489.15 K (216 C). The heat of fusion of typical semicrystalline samples is 13.8 kJ/mol. For 100% crystalline PTT the heat of fusion is estimated to be 28--30 kJ/mol. The heat capacity of solid PTT is linked to an approximate group vibrational spectrum, and the Tarasov equation is used to estimate the skeletal vibrational heat capacity ({Theta}{sub 1} = 542 K and {Theta}{sub 3} = 42 K). A comparison of calculation and experimental heat capacities show agreement of better than {+-}2% between 190--300 K. The experimental heat capacity of liquid PTT can be expressed as a linear function of temperature: C{sub p} {sup L}(exp) = 211.6 + 0.434 T J/(K mol) and compares well with estimations from the ATHAS data bank using groupmore » contributions of other polymers with the same constituent groups ({+-} 0.5%). The change of heat capacity at T{sub g} of amorphous PTT has been estimated from the heat capacities of liquid and solid to be 86.4 J/(K mol). Knowing C{sub p} of the solid, liquid, and the transition parameters, the thermodynamic functions: enthalpy, entropy and Gibbs function were obtained.« less

Vibrational Dynamics and Heat Capacity of Poly(L-lysine)

Poly(L-lysine) is a polypeptide having a bulky hydrophobic side chain. A systematic study of the full vibrational dynamics, including phonon dispersion, for the α-helical form of this biopolymer has been reported using Wilson’s GF matrix method as modified by Higgs for an infinite polymeric chain. The calculated frequencies explain well the IR and Raman spectra. A comparison of the amide modes with other α-helical polypeptides is reported here. Spectral frequencies have been obtained for the N-deuterated species to check the validity of force field and correctness of assignments. Heat capacity has also been calculated from dispersion curves via density-of-states using Debye relation in the temperature range 50–500 K. The calculated values are found to be in close agreement with the recent experimental data of Roles et al. [Biopolymers, 33, 753 (1993)].

Thermal diffusivity and heat capacity of poly(vinylidene fluoride)/poly(methyl methacrylate) blends by flash radiometry

The thermal diffusivity D and the relative heat capacity HC were measured for poly(vinylidene fluoride)/poly(methyl methacrylate) (PVDF/PMMA) blends by flash radiometry. The effect of the crystal form on D of these polymer blends as well as the dependence of D and HC on temperature were discussed. In the PVDF content region between 70 and 80 wt%, the blend samples preferentially form the β crystal phase when they are prepared by melt quenching. The dependence of D on PVDF content for the melt-quenched sample showed a noticeable change in the composition region in which the β crystal phase is formed. D decreased with increasing PVDF content up to 70 wt% and then increased up to 100 wt%, showing a peak between 75 and 80 wt%. From the X-ray diffraction patterns, the crystallinity of the blends monotonically decreases with decrease of PVDF content. The results imply that the peak in D in the melt-quenched 75 25 and 80 20 PVDF/PMMA blends is not related to the crystallinity but to another structural factor. The temperature profile of D showed inflection points corresponding to the glass transition temperature and the melting temperature of the α crystal phase. The temperature profile of HC exhibited changes of HC due to the melting transition of the β and α crystal phases. These points from the temperature profile of D and HC correspond well to those from thermal analysis.

The heat capacity of poly(oxymethylene) as a function of crystailinity

The heat capacity of several poly(oxymethylene) (POM) samples with crystallinities between 50 and 80 per cent are determined by DSC in the solid (−100 to 70°C) and liquid state (170 to 240°C). Linear relationships between heat capacity and crystallinity are found, if premelting phenomena are excluded. The heat capacities of crystalline and liquid POM are obtained by extrapolation. They differ from the hitherto recommended data. Above the glass transition region the extrapolated heat capacity for zero crystallinity agrees with the heat capacity of the melt extrapolated to lower temperatures. This is in contrast to recent results of Suzuki et al., who assume the existence of a rigid amorphous fraction which does not contribute to the glass transition.

Comments on: ?the heat capacity of poly(oxymethylene) as a function of crystallinity?

It is shown that the heat capacities of semicrystalline poly(oxymethylene)s (POM) measured recently by Illers and published in this journal support, rather than refute, the existence of a “rigid, amorphous fraction”. The former was suggested by Illers, the latter was our proposal (Suzuki et al.).

Heat Capacity and Other Thermodynamic Properties of Linear Macromolecules VI. Acrylic Polymers

Heat capacity of poly(methyl methacrylate), polyacrylonitrile, poly(methyl acrylate), poly(ethyl acrylate), poly(n-butyl acrylate), poly(iso-butyl acrylate), poly(octadecyl acrylate), poly(methacrylic acid), poly(ethyl methacrylate), poly(n-butyl methacrylate), poly(iso-butyl methacrylate), poly(hexyl methacrylate), poly(dodecyl methacrylate), poly(octadecyl methacrylate) and polymethacrylamide is reviewed on the basis of measurements on 35 samples reported in the literature. A set of recommended data are derived for each acrylic polymer in the amorphous state. Enthalpy and entropy functions are calculated for poly(methyl methacrylate) and polyacrylonitrile. This is the sixth paper in a series of publications which will ultimately cover all heat capacity measurements on linear macromolecules.

Heat capacity and other thermodynamic properties of linear macromolecules. III. Polyoxides

The heat capacity of poly(oxymethylene), poly(oxyethylene), poly(oxytrimethylene), poly(oxytetramethylene), poly(oxyoctamethylene), poly(oxypropylene), Poly(oxymethyleneoxyethylene), poly(oxymethyleneoxytetramethylene), poly(oxy-1,4-phenylene), poly(oxy-2,6-dimethyl-1,4-phenylene), ploy(oxy-2,6-diphenyl-1,4-phenylene) and poly[oxy-2,2-bis(chloromethyl)trimethylene] is reviewed on the basis of measurements on 35 samples reported in the literature. The crystallinity dependence is critically evaluated and a set of recommended data for each polyoxide is derived. Entropy, enthalpy, and Gibbs energy functions are calculated. The data have been compared to that of polyethylene and the contribution of -O-group has been evaluated. This paper is the third in a series which will ultimately cover all heat capacity measurements on linear macromolecules.