Studying dispersoid systems

Summary Measurements of energy transformation in mitochondria are done on a capillary differential titration calorimeter CTD2156. It is important to mention that a sediment is quickly formed by the mitochondria suspension without mixing by means of a vibrating needle. During the measurements, the vibrating needle is located inside the working volume of the chamber. The design of the calorimeter is substantiated theoretically. It provides a new mode of a reagent input in the measuring volume of the calorimetric chambers. It expands the spectrum of tasks that can be solved using this instrument. In the capillary calorimeter the calorimetric chambers unit is simple and small in size. These advantages of capillary chambers provide an opportunity to unite 20 capillary calorimetric chambers in one calorimetric block. It allows designing a multi-channel titration calorimeter. There are obvious advantages of such a calorimeter over other instruments in screening researches and in researches of objects maintaining stability only for a short time.     

New Isothermal Titration Calorimeter for Investigations on Very Small Samples. Theoretical and experimental studies

A new isothermal titration calorimeter with 78.5 μL volume capillary chambers has been developed. It is based on the theory of mixing reagents in a capillary chamber of a titration calorimeter and separation of the sensitive volume of chambers in a differential calorimeter. The evaluation of the efficiency of diffusion mixing is described by means of an oscillating dispensing needle. The calorimeter was tested by the reactions: Ba²⁺– 18-Crown-6 and Rnase-2’CMP. The main advantages of the new titration calorimeter are the use of very small amounts of reagents, the high accuracy of separating the sensitive volume of calorimetric chambers and the minimization of power input while mixing reagents in a horizontally located capillary chamber. This revised version was published online in August 2006 with corrections to the Cover Date.     

Fully integrated PCR-capillary electrophoresis microsystem for DNA analysis

A fully integrated genomic analysis microsystem including microfabricated heaters, temperature sensors, and PCR chambers directly connected to capillary electrophoretic separation channels has been constructed. Valves and hydrophobic vents provide controlled and sensorless sample positioning and immobilization into 200 nL PCR chambers. The use of microfabricated heating and temperature sensing elements improves the heating and cooling rates for the PCR reaction to 20 degree C s(-1). The amplified PCR product, labeled on-column with an intercalating fluorescent dye, is injected into the gel-filled capillary for electrophoretic analysis. Successful sex determination using a multiplex PCR reaction from human genomic DNA is demonstrated in less than 15 min. This device is an important step toward a microfabricated genomic microprocessor for use in forensics and point-of-care molecular medical diagnostics.     

Method of Separating the Sensitive Volume of Calorimetric Cells in a Differential Titration Calorimeter

A scientific and technical solution of capillary calorimetric unit design is described based on a method of separating the sensitive volume of calorimetric cells with a heat-conducting bridge in a differential titration calorimeter. The design of the calorimetric cells as thin capillary tubes allowed to minimize the dimension of the heat-conducting bridges and to separate with high accuracy the sensitive volume of the calorimetric cells which is of 78.5 μl. Due to high calorimeter power sensitivity (10 nW) a modern level of requirements for measuring minimum specific heat of processes is provided. The adopted design of the calorimetric cells permits to possess the cells located horizontally and to simplify the solution of the problem of equalizing components concentration along the volume of the calorimetric cells. This revised version was published online in July 2006 with corrections to the Cover Date.     

Crystallization and melting of isotactic polypropylene in response to temperature modulation

Isotactic polypropylene (iPP) was crystallized using temperature modulation in a differential scanning calorimeter (DSC) to thicken the crystals formed on cooling from the melt. A cool-heat modulation method was adopted for the preparation of the samples under a series of conditions. The effect of modulation parameters, such as temperature amplitude and period was monitored with the heating rate that followed. Thickening of the lamellae as a result of the crystallization treatment enabled by the cool-heat method lead to an increase in the peak melting temperature and the final traces of melting. For instance, iPP melting peak shifted by up to 3.5°C with temperature amplitude of 1.0°C while the crystallinity was increased from 0.45 (linearly cooled) to 0.53. Multiple melting endotherms were also observed in some cases, but this was sensitive to the temperature changes experienced on cooling. Even with a slower underlying cooling rate and small temperature amplitudes, some recrystallization and reorganization occurred during the subsequent heating scan. The crystallinity was increased significantly and this was attributed to the crystal perfection that occurred at the crystal growth surface. In addition, temperature modulated differential scanning calorimetry (TMDSC) has been used to study the melting of iPP for various crystallization treatments. The reversing and non-reversing contribution under the experimental time scale was modified by the relative crystal stability formed during crystallization. Much of the melting of iPP was found to be irreversible.This revised version was published online in November 2005 with corrections to the Cover Date.     

Signal processing and uncertainty in an isothermal titration calorimeter

In this paper, it is made a study of the accuracy of an isothermal titration calorimeter in the operating mode of ‘continuous injection’. The experimental equipment has been a TAM2277-201/2250 by Thermometric AB and the liquid mixtures used in the calibration have been the mixture cyclohexane+benzene and the mixture water+ethanol. The calibration contemplates different effects that affect the uncertainty in the determination of the sensitivity, the effect of the liquid injection, the treatment of the calorimetric signal, the variation of the experimental baseline and the different noises included in the calorimetric signal.     

Thermophysical Properties of Cholesteryl Oleyl Carbonate Determined with Microscopic Ftir/Dsc System

A microscopic Fourier transform infrared spectrometer (Micro FTIR) equipped for differential scanning calorimetry (DSC) was used to measure simultaneously the chemical structural variation and the thermal response of phase transition of cholesteryl oleyl carbonate (COC). The differential scanning calorimeter served also to determine the phase transitions of COC during heating or cooling. Two endothermic features due to phase transition were found in the thermogram: 18. 3 °C for a smectic-cholesteric transition and 37.5 °C for a cholesteric-isotropic transition during heating; 35.1 °C for an isotropic-cholesteric transition and 15.8 °C for a cholesteric-smectic transition during cooling. The breadth of the feature indicated sluggish phase transitions. The three-dimensional plot indicated that the intensities of lines due to the C-H stretching and scissoring deformation modes and C=O stretching mode of COC decreased suddenly near the temperature of phase transition during heating but the intensity of the line dues to the C-O stretching mode of carbonate ester of COC increased. Lattice vibrations or coupling of vibrational modes might be responsible for the result. These intensities in the cooling process varied inversely to those in heating process.     

Chip calorimetry for fast cooling and thin films: a review

Here we review on the thin-film chip calorimeter with controllable cooling as well as heating rates up to 10⁶ K·s⁻¹ developed in the last 5 years at the Institute of Physics, Rostock University. The calorimeter has been successfully used for fast thermal processing and simultaneous calorimetric measurements of many polymer samples, the physical properties of which are generally dependent strongly on their thermal history. Besides, owing to the very small addenda heat capacity, the calorimeter is very sensitive to study samples of only several tenths of nanograms. With differential alternating current (AC) design, the sensitivity of the calorimeter increased to a few tenths of pico-Joules per Kelvin. Therefore, it can be used to study glass transition of polymers confined in ultra-thin films down to several nanometers thickness. After the discussion of the strategy to realize fast cooling, we describe the static and dynamic thermal properties of the sensors used for the setup of the calorimeter. Finally, we present examples to show the performance of the calorimeter in different measurement modes.     

Temperature Control Modes in Thermal Analysis

Now we can use several temperature control modes, i.e., the isothermal run including stepwise heating and cooling, constant rate heating (or cooling), temperature control for sample thermal history, sample controlled thermal analysis (SCTA or controlled-rate thermal analysis, CRTA), temperature jump, rate jump, temperature modulation and repeated temperature scanning. Their advantages and drawbacks are reviewed with some illustrative examples, especially for application to kinetic analysis. The combined use of these varieties of temperature control mode is recommended by showing examples. Temperature modulation and repeated temperature scanning are discussed in comparison with temperature modulated DSC, and common and analogous points are elucidated. In relation to this, the possibility that an imaginary part of overall reaction rate constant in complex reaction is postulated. Finally,these modes are classified and tabulated from two viewpoints and other possible modes are shown. This revised version was published online in July 2006 with corrections to the Cover Date.     

RheoDSC: design and validation of a new hybrid measurement technique

A newly developed hyphenated technique is presented that combines an existing rheometer and differential scanning calorimeter (DSC) into a single experimental setup. Through the development of a fixation accessory inside the cell of the calorimeter and the introduction of an add-on unit for the rheometer, the simultaneous calorimetric and rheological measurement inside the well-controlled thermal environment of a Tzero™ DSC cell opens new experimental possibilities. The evolution of thermal and flow properties of a material can be simultaneously monitored during steady or oscillatory shear flow and regular or modulated temperature DSC measurements. The technique offers interesting opportunities for the investigation of flow-induced transitions, such as crystallization or phase separation, and provides a possibility for high-throughput screening of materials. The signal quality of the novel technique in comparison to the stand-alone techniques is demonstrated by the evaluation of the calibration factors and by measurements on standard materials. Finally, combined rheological and calorimetric melting and crystallization experiments on polycaprolacton are performed.     

精密滴定量热计的改进及联机

LKB8700精密量热系统的滴定量热计是用于常量的量热测定,反应器是进口的玻璃容器。加热器、温度计、滴定管均装在反应器内,不便装样和清洗,滴定液进口只有一个,三种液体的混合只能分步滴定,热敏电阻随温度的变化用惠斯登电桥测量。针对快速反应手动跟踪较为困难这一情况,特别是为了研究油田应用的油-水-表面活性剂三元体系或多元体系,我们设计和建立了图1所示不锈钢制反应器,并在桥路输出中与微机相联接(图2),实     

Thermodynamic and morphological studies of the solid-state transition in copolymers of vinylidene fluoride and trifluoroethylene

Copolymers of vinylidene fluoride and trifluroethylene are presently being considered for many piezoelectric applications. In contrast to the poly(vinylidene fluoride) homopolymer, a transition from the room temperature ferroelectric phase to a paraelectric phase has been observed in these copolymers. The temperature of this transition was determined by measuring the position of the endothermic peak observed in the differential scanning calorimeter. The rate of cooling from the paraelectric to ferroelectric phase was found to affect the temperature at which the transition occurred on subsequent heating. Changing the conditions under which molten polymer initially crystallized into the paraelectric phase had an even greater effect on the resultant transition temperature. In addition to the DSC studies, wide-angle x-ray measurements were performed on samples subjected to different thermal treatments. No significant differences were found in the x-ray scans of these copolymers.     

Thermophysical property determination of high temperature alloys by thermal analysis

Differential scanning calorimetric measurements to determine solidus and liquidus temperatures and latent heat of fusion of two high temperature materials, PWA1484 and an experimental gamma titanium aluminide alloy, are presented. The solidus and liquidus temperatures of PWA1484 are 1340 and 1404°C. The solidus and liquidus temperatures of the titanium aluminide alloy are 1453 and 1522°C. Solidus and liquidus temperatures determined from actual heating and cooling curves, which were measured using imbedded thermocouples and analyzed by a pseudo-differential thermal analysis technique are found to be in good agreement with the differential scanning calorimetric measurements. This revised version was published online in July 2006 with corrections to the Cover Date.     

Thermodynamic insights into the binding of Triton X-100 to globular proteins: a calorimetric and spectroscopic investigation

The interaction of the nonionic surfactant Triton X-100 (TX-100) with two proteins (bovine serum albumin (BSA) and alpha-lactalbumin (alpha-LA)) has been investigated by using a combination of differential scanning calorimetry, isothermal titration calorimetry, and fluorescence and circular dichroism spectroscopies. All of the calorimetric transitions in BSA were partially reversible, while being two-state and reversible in the case of alpha-LA. TX-100 molecules do not reduce the thermal stability of the protein in the monomeric form. However, in the micellar form the protein might become thermally destabilized by the micelles depending upon the nature of the protein. Isothermal titration calorimetry has been used to demonstrate that TX-100 binds to BSA at two sets of sites with 4:1 stoichiometry in each case. The van't Hoff enthalpy calculated from the temperature dependence of the binding constant did not match with the calorimetric enthalpy indicating conformational change in the protein upon surfactant binding. The surfactant binds to alpha-LA with one class of binding site, and the thermal unfolding results indicate it to be a stronger destabilizer than BSA. The fluorescence, circular dichroism, and differential scanning calorimetric results corroborate well with each other. The effect of ionic strength on the binding parameters suggests that TX-100 can bind to the protein surface via both hydrophobic and polar interactions depending upon the nature of the protein. The physical chemistry underlying the interactions between TX-100 and proteins has been presented. The mode of interaction of TX-100 with proteins is via direct binding, which has been discussed quantitatively in this work.     

The Application of Modulated Temperature Power Compensation DSC to the Characterisation of Polymer Blends

A modulated temperature power compensated differential scanning calorimeter, MTDSC, has been built from a standard Perkin-Elmer DSC model-2 such that a computer generated voltage has been applied to induce a sinusoidal change in sample temperature superimposed on a linear heating rate. The effect of amplitude of the temperature fluctuation, modulation period and block temperature on the reversibility has been assessed from the Lissajous diagram of heat flow vs. sample temperature. From their reproducibility and symmetry the most effective conditions for operating the MTDSC has been deduced. The specific heat of sapphire has been measured using these operational conditions for comparison with conventional DSC. Phase separated blends of polycarbonate (PC) and polyethylene terephthalate (PET) have been analysed. This revised version was published online in August 2006 with corrections to the Cover Date.     

A direct isoperibol aneroid calorimeter

An aneroid isoperibol calorimetric apparatus is described which is particularly suitable for measurement of the reaction heat among solids. Such an apparatus contains four calorimeters and allows to carry out differential measurements. Each calorimeter includes two small electric furnaces employed for heating the solid mixture until the reaction begins and for the successive electric calibrations, respectively. The temperature trend of each calorimeter is followed by 80 thermocouples in series. The instrument characteristics are briefly discussed. Examples of its employment in the alloy thermochemistry are given.     

Recent Developments in Integrated Circuit Calorimetry

In the present paper the properties of a new class of calorimeters, so called integrated circuit calorimeters (IC calorimeters) are discussed. IC calorimeters are constructed on the basis of micro-sized silicon chips with integrated thermopile and heater. The applicability of integrated circuits for calorimetric purposes strongly depends on their sensitivity and on an optimized area of the sensitive sphere. Thus the sensitivity has to be much higher than that of the heat power transducers of conventional calorimeters. The parameters of different integrated circuits are compared corresponding to their use in calorimeters. Different constructions of IC calorimeters are possible: batch and flow-through calorimeters operating at isoperibol or temperature scanning mode. As an example a batch type IC calorimeter for liquid samples with a resolution in heat measurement of >100µJ is described in more detail. The applications of this calorimeter are represented in the paper with the investigation of enzyme catalysed reactions, i.e. the hydrolysis of urea and the oxidation of glucose catalysed by the enzymes glucose oxidase and catalase.This revised version was published online in November 2005 with corrections to the Cover Date.     

The integration of an ultraviolet-visible spectrometer and a reaction calorimeter

A small ultraviolet-visible absorption spectrometer which uses fibre optic coupled immersion probes has been incorporated into a laboratory scale reaction calorimeter. The combined instrument has been tried out using the hydrolysis of acetic anhydride as a test reaction. With the calorimeter operating in the isoperibolic mode good agreement is found for the pseudo-first order reaction rate constant as determined from spectroscopic and calorimetric measurements. Experiments have been made in order to follow the reaction indirectly using optical pH measurements with acid-base indicators. The possibility of determining the temperature dependence of the rate constant in a single experiment has also been investigated. This revised version was published online in July 2006 with corrections to the Cover Date.     

Improved calorimetric procedure for monitoring the approach to thermodynamic equilibrium in glassy polymers

Techniques for measuring the enthalpy change during isothermal aging of polymer glasses are discussed. Critical analysis of conventional scanning calorimetry reveals that its accuracy may be suspect under certain circumstances due to the thermal lag inherent in a temperature scanning experiment. An additional problem is that the conventional technique is restricted to certain kinds of paths for reaching the aging temperature. It is proposed that both problems can be overcome by analyzing the output of a scanning calorimeter not only during steady heating but also during the transients at the beginning and end of a heating scan. This data analysis method represents an extension of a method used previously by others in accurate measurements of the much larger heat of fusion of crystalline polymers. Practical feasibility of the improved technique is demonstrated by preliminary measurements of enthalpy relaxation during aging of well-characterized polystyrene at 80°C. In particular, the initial departure from equilibrium of a glass prepared by 5°C/min cooling from the liquid state is found to be 6.9 ± 0.6 J/g. This measured value agrees with a value calculated on the basis of the glass transition temperature corresponding to 5°C/min cooling and heat-capacity data from the literature.