Authors:J. Turner, A. Riga, A. O'Connor, J. Zhang, and J. Collis
Poly-L-lactic acid (PLLA) is an optically active, biocompatible and biodegradable polymer that has been widely investigated as an artificial cell scaffold material. In its most crystalline form, PLLA is highly anisotropic and is one of the most piezoelectric polymers known. Conversely, amorphous PLLA exhibits little, if any, piezoelectric behavior. Compression molded PLLA films can be endowed with varying amounts of crystalline character and piezoelectricity by uniaxially stretching the polymer in a hot air bath. Understanding the precise crystalline architecture of PLLA that results from tensile drawing is important for constructing cell scaffolds that have highly tailored biodegradation and cell guiding properties. In our work here, we investigate the changes in the thermal properties of PLLA at draw ratios between 1.0 and 5.5 using differential scanning calorimetry (DSC). The crystallinity of the compression molded undrawn starting material is characterized using X-ray diffraction. Our DSC results show an increase in percent crystallinity with increasing draw up to a draw ratio of 4.0. At greater draw ratios, there is a decrease in the crystalline character exhibited by PLLA.
Authors:M. Bissengaliyeva, N. Bekturganov, and D. Gogol
The temperature dependence of heat capacity of a natural zinc silicate, hemimorphite Zn4Si2O7(OH)2·H2O, over the temperature range 5–320 K has been investigated by the method of low-temperature adiabatic calorimetry. On the
basis of the experimental data on heat capacity over the whole temperature interval, its thermodynamic functions Cp(T), S(T) and H(T) − H(0) have been calculated. The existence of a phase transition in the area of 90–105 K determined on the basis of vibrational
spectra has been confirmed, and changes of entropy ΔStr. and enthalpy ΔHtr. of the phase transition have been calculated. Hemimorphite heat capacity has also been determined by the calculation methods
according to the valence force field model in LADY program. The values of force constants of valence bonds and angles have
been calculated by semi-empirical method PM5. The calculated IR and Raman spectra concordant with the experimental spectra
have been obtained. The heat capacity values calculated according to the found vibrational states satisfactorily agree with
those experimentally obtained with an accuracy of ±1.7% in the area of 120–200 K, and not more than ±0.8% for the interval
of 200–300 K. This fact testifies that the calculation of thermodynamic characteristics is correct.
Differential scanning calorimetry (DSC) was used to measure the decomposition rates of four commercially used initiators,
2,2′-azobis(isobutyronitrile) 2,2′-azobis(2,4-dimethylvaleronitrile), dilauroyl peroxide and bis(4-t-butylcyclohexyl)peroxydicarbonate,
in dynamic mode, while the courses of methyl methacrylate polymerization with the listed initiators at 65, 75 and 85°C were
measured isothermally. From the DSC curves, the polymerization enthalpies, the overall reaction rate constants and the activation
energies for the initial steady-state polymerization were calculated. It was found that the polymerization enthalpy and the
kinetic parameters depended on the type of the initiator. An initiator with a shorter decomposition half-lifetime shifted
the onset of the gel effect to a higher conversion, intensified it and decreased the average molar mass of the polymer.
The majority of previous studies of the hydration of cements using heat flow calorimetry have been carried out isothermally. However, with oilwell cements the slurry is mixed on the surface at ambient temperature and then gradually increases in temperature as it is pumped down the well. A Setaram C-80 calorimeter has been used to simulate the temperature ramp in API oilwell cement test schedules. This approach has enabled cementing reactions to be studied for the first time under conditions approaching those encountered in the field, and has shown that the results obtained from isothermal experiments may be misleading.
A series of LiMn2O4 samples with nominal Li/Mn molar ratio=1/2 has been synthesized at 700 and 750C by the ceramic procedure from Mn2O3 and several lithium sources. Lattice parameters determined from X-ray diffraction patterns are within a narrow range, from
ac=8.238(1) to ac=8.245(1) , Dac/ac<0.1%. The study by differential scanning calorimetry (DSC) shows that the temperatures of the cubic (Fd3m)↔orthorhombic (Fddd)
phase transition are spread off in a wide range, from -30 to -2C for the exothermic C→O phase transition, and from -21 to
+13C for the endothermic O→C transformation. Relationships between the lattice parameter values, the temperature of the phase
transformation, and the stoichiometry of the LiMn2O4 samples are pointed out. The DSC technique, which reveals more sensitive than X-ray diffraction to very small variations
of composition, is put forward as an essential technique to characterize LiMn2O4 samples.
The thermally stimulated discharge current (TSC) and differential scanning calorimetry (DSC) spectroscopy have been recorded
in 25 μm thick samples of pristine polycarbonate (PC) and zinc oxide nano particle-filled polycarbonate. Polycarbonate (PC)/zinc
oxide (ZnO) nanocomposites of different mass ratio (e.g., 1, 3, and 5%) were prepared by sol–gel method, followed by film
casting. The glass transition temperature of nanocomposite samples increases with increase in concentration of ZnO nano fillers.
It is due to the strong interaction between inorganic and organic components. The TSC peaks of nanocomposite and pristine
PC indicate the multiple relaxation process. It has been observed that the magnitude of TSC decreases with increase in concentration
of nanofillers. The TSC characteristics of 5% filled nanocomposites shows exponential increase of current at higher temperature
region. This increase in current is caused by formation of charge-transfer complex between inorganic phase (e.g., ZnO) and
organic phase (e.g., PC). Thus, the nano material like zinc oxide transfers the charge carriers from inorganic phase to organic
phase rapidly and resultant current increases exponentially. This current is known as leakage current or breakdown current.
TSC peak height is observed as a function of the polarizing field. The height of TSC peak increases as the field increases
in pristine PC, while TSC peak height is suppressed in nanocomposite samples. This indicates the amount of space charge is
smaller in the nanocomposites with a proper addition of ZnO nano fillers than in the pristine PC.
Authors:Lee-Ann Briere, Jan-M. Brandt, and John Medley
Differential scanning calorimetry (DSC) was used to evaluate the thermal transitions associated with protein constituents
of synovial fluid samples from three individuals with osteoarthritis. Analysis of the multi-component DSC curves revealed
that major endothermic transitions of synovial fluid occur between 60 and 80 °C and can be resolved into three peaks, likely
due to the unfolding of human serum albumin and immunoglobulins, and that the enthalpies of these transitions can be quantified
in terms of their relative contribution to the total system enthalpy. DSC was also used to analyze a solution of bovine calf
serum, a lubricant used in simulator wear testing of joint replacement implants, and the resulting endothermic transitions
occurred in a temperature range relevant to that produced by frictional heat during such wear simulator testing. Results of
this study indicate a new application for DSC as a direct method for studying thermal stabilities of both bovine calf serum
and synovial fluid. The use of DSC is proposed as a diagnostic tool to detect altered thermal properties or protein concentrations
indicative of a diseased or injured state, and as a development tool to test the efficacy of additives in controlling protein
denaturation associated with increased wear in joint replacement implants.
Experimental evaluation of the procedures adopted for heat capacity measurements employing differential scanning calorimetry
(DSC) has been carried out by taking nickel and sapphire as test samples. Among the various methodologies reported in literature,
the absolute dual step method was chosen for this purpose due to its simplicity and minimum number of measurements required.
By proper temperature and heat flux calibration employing indium as reference, it was possible to obtain the calibration factor
independent of temperature. This was ascertained by analysing other pure metals namely Sn, Zn, Cd, and Pb and determining
their melting temperatures and heats of melting. Various operator- and sample-dependent parameters such as heating rate, sample
mass, the structure of the sample, reproducibility and repeatability in the measurements were investigated. Heat capacities
of both nickel and sapphire have been determined using the above method. Further, the heat capacity of nickel has also been
using the widely employed three-step method taking sapphire as the heat flux calibration standard. Both methods yielded the
comparable heat capacity values for nickel. Based on the parameters investigated and their influence, it could be concluded
that reasonably precise and accurate heat capacity measurements are possible with DSC. One advantage of this method is the
elimination of a separate calibration run using a reference material of known heat capacity.
Differential scanning calorimetry (DSC) is the most widely used thermal analytical technique in food research and it has a great utility in quality assurance of food. Proteins are the most studied food components by thermal analysis including studies on conformation changes of food proteins as affected by various environmental factors, thermal denaturation of tissue proteins, food enzymes and enzyme preparations for the food industry, as well as effects of various additives on their thermal properties. Freezing-induced denaturation of food proteins and the effect of cryoprotectants are also monitored by DSC. Polymer characterization based on DSC of polysaccharides, gelatinization behaviour of starches and interaction of starch with other food components can be determined, and phase transitions during baking processes can be studied by DSC. Studies on crystallization and melting behaviour of fats observed by DSC indicate changes in lipid composition or help characterizing products. Thermal oxidative decomposition of edible oils examined by DSC can be used for predicting oil stability. Using DSC in the freezing range has a great potential for measuring and modelling frozen food thermal properties, and to estimate the state of water in foods and food ingredients. Research in food microbiology utilizes DSC in better understanding thermoadaptive mechanisms or heat killing of food-borne microorganisms. Isothermic microcalorimetric techniques provide informative data regarding microbial growth and microbial metabolism.
selected papers of SATAC-2011
I am getting immense pleasure in introducing this Special Chapter of Journal of Thermal Analysis and Calorimetry based on papers devoted to the 2011 Symposium on Applications of Thermal Analysis