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1.
Summary A double endothermic peak appears in the DSC curve of a PTHF oligomer. In order to investigate this phenomenon, a two-component blend of PTHF was prepared with a number average molecular mass of M=1400, and the double endothermic phenomena were investigated by TM-DSC. The larger the amount of the long chain component in the PTHF blend, the smaller the difference between the Cp-T curve and the normal DSC curve. The amounts of endothermic energy Hendo,1, Hendo,2 and exothermic energy Hexo,1, Hexo,2 in each peak at infinite modulation frequency were estimated. 相似文献
2.
Iwona Zięborak-Tomaszkiewicz P. Gierycz 《Journal of Thermal Analysis and Calorimetry》2008,93(3):693-699
The change of thermal functions (ΔH
0(T), ΔS
0(T), ΔG
0(T)) and formation functions (ΔH
f0(T), ΔG
f0(T), K
f(T)) with temperature for gallium nitride and indium nitride have been formulated based on the reliable experimental data obtained
by the use the same equipment in one laboratory. 相似文献
3.
Differential
scanning calorimetry (DSC) is a thermal analytical tool for preformulation
studies. Extrapolated melting temperature (TP)
and heat of fusion (ΔHf)
can be used as parameters for optimizing the DSC performance. Two model pharmaceuticals
acetaminophen and nicotinamide are used in this study. Using a factorial design
for the experimental model and matrix analysis the results, the effect of
sample mass, heating rate and the nitrogen flow rate were evaluated on the
ΔHf values
and TP values. Two
levels for each of the procedural variables were used as a balanced experimental
design with two sample sizes, two heating rates and two nitrogen flow rates.
It was found that the change in the heating rate caused significant changes
in the ΔHf
values but not the Tp
values for acetaminophen. However, no significant effect was found for the Tp value but ΔHf value was affected to a
certain extent for nicotinamide. 相似文献
4.
Lebedev B. V. Kulagina T. G. Smirnova N. N. Shifrina Z. B. Averina M. S. Rusanov A. L. 《Journal of Thermal Analysis and Calorimetry》2003,74(3):735-748
In an adiabatic vacuum calorimeter, the temperature dependence of the heat capacity C
p of phenylated polyphenylene and initial comonomer 1,4-bis(2,4,5-triphenylcyclopentadienone-3-yl)benzene was studied between
6 and 340 K with an uncertainty of about 0.2%. In a calorimeter with a static bomb and an isothermal shield their energies
of combustion DUcomb were measured. From the experimental data, the thermodynamic functions C
p
0 (T), H
0(T)-H
0(0), S
0(T)-S0(0), G
0(T)-H
0(0) were calculated from 0 to 340 K, and standard enthalpies of combustion ΔH
comb
0 and thermodynamic parameters of formation-enthalpies ΔH
f
0, entropies ΔH
f
0, Gibbs functions ΔG
f
0 - of the substances studied were estimated at T=298.15 K at standard pressure. The results were used to calculate the thermodynamic characteristics (ΔH
f
0 ,ΔS
f
0, ΔG
f
0) of phenylated polyphenylene synthesis in the range from 0 to 340 K.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
5.
The physical ageing characteristics of glucose, fructose, and their mixtures were studied using standard differential scanning calorimetry (DSC). The inflection, onset, midpoint,half-height, and endpoint glass transition temperature (T
g), fictive temperature (T
f), and relaxation enthalpy (H) were measured as a function of ageing time. The relationship between H and T
f was evaluated. The time dependence of H was fit using the Cowie and Ferguson model. The ageing rate was expressed in terms of the average relaxation time (<>) and the entropy production (P). It was found that the fructose component decreased the rate of ageing of the mixtures.This revised version was published online in November 2005 with corrections to the Cover Date. 相似文献
6.
N. N. Smirnova T. A. Bykova V. N. Larina T. G. Kulagina A. D. Pomogailo G. I. Dzhardimalieva 《Polymer Science Series A》2010,52(4):349-355
The temperature dependences of the heat capacities of hydrated acrylamide and poly(acrylamide) complexes of cobalt nitrate
are studied via high-precision adiabatic calorimetry at 6 to 300–380 K. The energy of combustion is estimated via isothermic
calorimetry. This evidence makes it possible to calculate thermodynamic functions C
p
ℴ(T), H
ℴ(T) − H
ℴ(0), S
ℴ(T), G
ℴ(T) − H
ℴ(0) at 0 to 300–380 K; the standard enthalpy of combustion, ΔcH
ℴ; and the thermodynamic parameters of formation, Δ
f
H
ℴ, Δ
f
S
ℴ, and Δ
f
G
ℴ, of monomer and polymer complexes composed of simple compounds at 298.15 K. The results are used for the estimation of enthalpy
Δpol
H
ℴ, entropy Δpol
S
ℴ, and Gibbs function Δpol
G
ℴ of bulk polymerization for hydrated acrylamide complexes of cobalt nitrate at 0–300 K. 相似文献
7.
The temperature dependence of the Gibbs free energy difference (ΔG), enthalpy difference (ΔH) and entropy difference (ΔS) between the undercooled meltand the corresponding equilibrium solid has been analysed for glass forming polymeric materials
by calculating ΔG, ΔH and ΔS within the framework of the hole theory of liquids. The study is made for nine samples of glass forming polymeric melts;
polypropylene oxide (PPO), polyamid-6 (PA-6), polytetramethylene oxide (PTMO), polyethylene oxide (PEO), polystyrene (PS),
polypropylene (PP), polyethylene (PE), polyethylene terephthalate (PET) and polybutadiene (PB) and three simple organic liquids:
tri-α-naphthyl benzene (tri-α-NB), o-terphenyl (o-ter) and phenyl salicylate (salol) in the entire temperature range T
m (melting temperature) to T
g (glass transition temperature). The ideal glass transition temperature (T
K) and the residual entropy (ΔS
R) of these samples have also been studied due to their important role in the study of the glass forming ability of materials.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
8.
T. G. Kulagina Ya. S. Samosudova I. A. Letyanina E. V. Sevast’yanov N. N. Smirnova L. A. Smirnova A. E. Mochalova 《Russian Journal of Physical Chemistry A, Focus on Chemistry》2012,86(5):747-751
The temperature dependence of the heat capacity C
p
o= f(T) 2 of 2-ethylhexyl acrylate was studied in an adiabatic vacuum calorimeter over the temperature range 6–350 K. Measurement
errors were mainly of 0.2%. Glass formation and vitreous state parameters were determined. An isothermic shell calorimeter
with a static bomb was used to measure the energy of combustion of 2-ethylhexyl acrylate. The experimental data were used
to calculate the standard thermodynamic functions C
p
o(T), H
o(T)-H
o(0), S
o(T)-S
o(0), and G
o(T)-H
o(0) of the compound in the vitreous and liquid states over the temperature range from T → 0 to 350 K, the standard enthalpies of combustion Δc
H
o, and the thermodynamic characteristics of formation Δf
H
o, Δf
S
o, and Δf
G
o at 298.15 K and p = 0.1 MPa. 相似文献
9.
The non-radiative processes of deactivation from the lowest singlet excited state of aminoanthraquinones have been studied
using steady-state and time-resolved methods. The fluorescence decay rate constant, kf correlates well with the solvent polarity parameter, ET(30), in nonhydrogen bonding solvents. Large deuterium isotope effects in fluorescence lifetimes (τf) and quantum yields (ϕf) are observed in the case of 1-amino (AAQ) and 1-methylaminoanthraquinones (MAQ), where the S1 state is mainly deactivated through internal conversion to the ground state. The temperature-dependence of the fluorescence
quantum yields of various aminoanthraquinones was also investigated. The ϕf and τf exhibited strong temperature-dependence in the case of 1-acetylaminoanthraquinone (ACAQ). In the case of ACAQ, the intersystem
crossing to the triplet state is a major deactivation channel from the S1 and in this derivative a close-lying T2 state seems to be responsible for the high kisc rate.
The fluorescence properties of 1,5-diaminoanthraquinone (DAQ) are affected by intermolecular hydrogen bonding with alcohols.
Increasingn-alkyl chain length in the case of l-(n-alkyl)aminoanthraquinones from methyl to butyl does not produce any change in the fluorescence properties, whereas a hydroxypropyl
substitution results in a small decrease of ϕf and τf in these compounds, indicating an interaction of the hydroxyl group with the carbonyl group of the aminoanthraquinones. 相似文献
10.
The temperature dependence of heat capacity of C70 fullerene was studied by calorimetry in the range between 6 and 390 K. Phase transitions were established and their thermodynamic
characteristics were determined. From the experimental data obtained, the thermodynamic functionsH
o
(T)-H
o(0),S
o(T),G
o(T)-H
o(0) for temperatures between 0 and 390 K were calculated. The results were used to calculate the standard values of Δf
S
o, Δf
G
o, and logK
f
o
for the formation of C70 from graphite.
Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 4, pp. 647–650, April, 1998. 相似文献
11.
J. Ahmed J. -X. Zhang Z. Song S. K. Varshney 《Journal of Thermal Analysis and Calorimetry》2009,95(3):957-964
A thermal analysis of a series of polylactides (PLA) was carried out based on the number of average molecular mass (M
n), and the nature of isomer (D, L and DL). It is confirmed that the glass transition temperature (T
g) of PLA increased as a function of molecular mass irrespective of isomer type except sample with a high polydispersity index.
The melting temperature (T
m) and enthalpy of crystal fusion (ΔH
f) of L-isomer increased as the M
n was increased from 1100 to 27500. The degree of crystallinity (χc%) increased as a function of molecular mass. However no crystallization peak was detected in the lower molecular mass range
(550–1400). The non-isothermal crystallization behavior of the PLA melt was significantly influenced by the cooling rate.
Both D and L isomers exhibited insignificant difference in thermal properties and DL lactides exhibited amorphous behavior at identical molecular masses. Change in microstructure showed significant difference
between two isomers. Analysis of the FTIR spectra of these PLA samples in the range of 1200–1230 cm−1 supported DSC observation on crystallinity. 相似文献
12.
DTA and DSC were used to study the thermal behaviour of Ca(NO3)2·4H2O, Cd(NO3)2·4H2O, Mg(NO3)2·6H2O and their deuterated analogues. Evidence was found concerning the process of melting of the initial hydrates and deuterates,
followed by a one-stage dehydration of the melt to vield the respective anhydrous salt.
T
m, ΔH
m
o
, ΔS
m
o
and ΔH
deh
o
were determined and the ΔH
f
o
values for the investigated hydrates were calculated from the ΔH
deh
o
data.
Zusammenfassung DTA und DSC wurden zur Untersuchung des thermischen Verhaltens von Ca(NO3)2·4H2O, Cd(NO3)2·4H2O, Mg(NO3)2·6H2O und ihrer deuterierten Analoge eingesetzt. Man fand Aussagen bezüglich des Schmelzvorganges der Ausgangshydrate und Deuterate, gefolgt von einer Einschritt-Dehydratation der Schmelze unter Bildung der entsprechenden wasserfreien Salze. T m, ΔH m o , ΔS m o und ΔH deh o wurden ermittelt und die ΔH f o Werte für die untersuchten Hydrate wurden anhand der ΔH deh o berechnet.相似文献
13.
Molar heat capacity and thermodynamic properties of 1,2-cyclohexane dicarboxylic anhydride [C8H10O3]
X. -C. Lv X. -H. Gao Z. -C. Tan Y. -S. Li L. -X. Sun 《Journal of Thermal Analysis and Calorimetry》2008,92(2):523-527
The molar heat capacity C
p,m of 1,2-cyclohexane dicarboxylic anhydride was measured in the temperature range from T=80 to 390 K with a small sample automated adiabatic calorimeter. The melting point T
m, the molar enthalpy Δfus
H
m and the entropy Δfus
S
m of fusion for the compound were determined to be 303.80 K, 14.71 kJ mol−1 and 48.43 J K−1 mol−1, respectively. The thermodynamic functions [H
T-H
273.15] and [S
T-S
273.15] were derived in the temperature range from T=80 to 385 K with temperature interval of 5 K. The thermal stability of the compound was investigated by differential scanning
calorimeter (DSC) and thermogravimetry (TG), when the process of the mass-loss was due to the evaporation, instead of its
thermal decomposition. 相似文献
14.
Quasielastic light scattering measurements are reported for experiments performed on mixtures of gelatin and glutaraldehyde
(GA) in the aqueous phase, where the gelatin concentration was fixed at 5 (w/v) and the GA concentration was varied from 1×10−5 to 1×10−3 (w/v). The dynamic structure factor, S(q,t), was deduced from the measured intensity autocorrelation function, g
2(τ), with appropriate allowance for heterodyning detection in the gel phase. The S(q,t) data could be fitted to S(q,t)=Aexp(−D
f
q
2
t)+Bexp(−t/τc)β, both in the sol (50 and 60 ∘C) and gel states (25 and 40 ∘C). The fast-mode diffusion coefficient, D
f showed almost negligible dependence on the concentration of the crosslinker GA; however, the resultant mesh size, ξ, of the
crosslinked network exhibited strong temperature dependence, ξ∼(0.5−χ)1/5exp(−A/RT) implying shrinkage of the network as the gel phase was approached. The slow-mode relaxation was characterized by the stretched
exponential factor exp(−t/τc)β. β was found to be independent of GA concentration but strongly dependent on the temperature as β=β0+β1
T+β2
T
2. The slow-mode relaxation time, τc, exhibited a maximum GA concentration dependence in the gel phase and at a given temperature we found τc(c)=τ0+τ1
c+τ2
c
2. Our results agree with the predictions of the Zimm model in the gel case but differ significantly for the sol state.
Received: 25 May 1999 /Accepted in revised form: 27 July 1999 相似文献
15.
Elena Blanco J. M. Ruso J. Sabín G. Prieto F. Sarmiento 《Journal of Thermal Analysis and Calorimetry》2007,87(1):211-215
The interactions of lysozyme and myoglobin with anionic surfactants
(hydrogenated and fluorinated), at surfactant concentrations below the critical
micelle concentration, in aqueous solution were studied using spectroscopic
techniques. The temperature conformational transition of globular proteins
by anionic surfactants was analysed as a function of denaturant concentration
through absorbance measurements at 280 nm. Changes in absorbance of protein-surfactant
system with temperature were used to determine the unfolding thermodynamics
parameters, melting temperature, T
m,
enthalpy, ΔH
m,
entropy, ΔS
m
and the heat capacity change, ΔC
p,
between the native and denatured states. 相似文献
16.
We continue our use of “simple” energetic patterns, where simple means the use of parameters derived only from the stoichiometry
of these species in our studies of the entropy of formation (TΔf
S
o) of aqueous anions. Relationships between the entropy of formation and different parameters such as the number of oxygen
atoms, the natural logarithm of the molecular weight and the total number of atoms are explored. The charge of the species,
z− continues to be explicitly considered where we now explore various choices of p and use of z
p as a parameter. 相似文献
17.
N. N. Smirnova T. A. Bykova N. A. Polotnyanko N. D. Shikina I. L. Khodakovskii 《Russian Journal of Physical Chemistry A, Focus on Chemistry》2010,84(11):1851-1855
The temperature dependence of the heat capacity C
p
o = f(T) of palladium oxide PdO(cr.) was studied for the first time in an adiabatic vacuum calorimeter in the range of 6.48–328.86
K. Standard thermodynamic functions C
p
o(T), H
o(T) — H
o(0), S
o(T), and G
o(T) — H
o(0) in the range of T → 0 to 330 K (key quantities in different thermodynamic calculations with the participation of palladium compounds) were
calculated on the basis of the experimental data. Based on an analysis of studies on determining the thermodynamic properties
of PdO(cr.), the following values of absolute entropy, standard enthalpy, and Gibbs function of the formation of palladium
oxide are recommended: S
o(298.15) = 39.58 ± 0.15 J/(K mol), Δf
H
o(298.15) = −112.69 ± 0.32 kJ/mol, Δf
G
o(298.15) = −82.68 ± 0.35 kJ/mol. The stability of Pd(OH)2 (amorph.) with respect to PdO(cr.) was estimated. 相似文献
18.
Photon transmission technique was used to monitor the evolution of transparency during film formation from poly(vinyl acetate) (PVAc) latex particles. The latex films were prepared below the glass transition temperature (T
g) of PVAc. These films were annealed at elevated temperatures in various time intervals above the T
g of PVAc. It is observed that transmitted photon intensity (I
tr) from these films increased as the annealing temperature is increased. It is seen from I
tr curves that there are two film formation stages. These successive stages are named void closure (viscous flow) and interdiffusion. The activation energies for viscous flow (ΔH) and backbone motion (ΔE
b) were obtained by using well-defined models. The averaged values of the backbone (ΔE
b) and the viscous flow activation energies (ΔH) were found to be 188.6 and 5.6 kcal/mol, respectively. The minimum film formation (τ
M,T
M) and healing points (τ
H,T
H) were determined. Minimum film formation (ΔE
M) and healing activation energies (ΔE
H) were measured using these time–temperature pairs. ΔE
M and ΔE
H were found to be 32.5 and 28.3 kcal/mol, respectively. 相似文献
19.
Viscosity, ultrasonic velocity and density measurements have been carried out for glycylglycine in aqueous FeCl3 solution as a function of molality at T=288.15 K, 298.15 K and 308.15 K. The experimental data have been used to derive properties such as isentropic compressibility
(κ
S
), change in isentropic compressibility (Δκ
S
), relative change in isentropic compressibility (Δκ
S
/κ
0), apparent molar compressibility, volume and their limiting apparent molar quantities along with the constants S
K
, S
V
and viscosity B-coefficient. The obtained thermodynamic properties have been discussed in terms of molecular interactions. 相似文献
20.
M.-H. Wang Z.-C. Tan Q. Shi L.-X. Sun T. Zhang 《Journal of Thermal Analysis and Calorimetry》2006,84(2):413-418
The
heat capacities of 2-benzoylpyridine were measured with an automated adiabatic
calorimeter over the temperature range from 80 to 340 K. The melting point,
molar enthalpy, ΔfusHm,
and entropy, ΔfusSm,
of fusion of this compound were determined to be 316.49±0.04 K, 20.91±0.03
kJ mol–1 and 66.07±0.05 J mol–1
K–1, respectively. The purity of the compound
was calculated to be 99.60 mol% by using the fractional melting technique.
The thermodynamic functions (HT–H298.15) and (ST–S298.15) were calculated based
on the heat capacity measurements in the temperature range of 80–340
K with an interval of 5 K. The thermal properties of the compound were further
investigated by differential scanning calorimetry (DSC). From the DSC curve,
the temperature corresponding to the maximum evaporation rate, the molar enthalpy
and entropy of evaporation were determined to be 556.3±0.1 K, 51.3±0.2
kJ mol–1 and 92.2±0.4 J K–1
mol–1, respectively, under the experimental
conditions. 相似文献