Glass transition temperature of thin polycarbonate films measured by flash differential scanning calorimetry

Flash differential scanning calorimetry was used to study the glass transition temperature T_g of polycarbonate ultrathin films. The investigation was made as a function of film thickness from 22 to 350 nm and over a range of cooling rates from 0.1 to 1000 K/s. Polycarbonate spin cast films were floated on a layer of grease on the calorimetric chip. The results show a greatly reduced glass temperature for the thinnest films relative to the macroscopic value. We also observed that the magnitude of the glass temperature reduction decreases as the cooling rate increases with the highest cooling rates showing little thickness dependence of the T_g. Dynamic fragility and activation energy at T_g were found to decrease with decreasing film thickness. The results are discussed in the context of literature reports for supported and freely standing polycarbonate films. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2014 , 52, 1462–1468     

Glass transition temperatures of ABA poly(styrene-b-isoprene) block copolymers by differential scanning calorimetry

The glass transition behavior of two sets of ABA poly(styrene-b-isoprene) block copolymers was examined by differential scanning calorimetry. In one series, the triblock copolymers had different total molecular weights and the same (30 wt %) polyisoprene content, in the other, the molecular weight was constant (30,000 g/mol) and the elastomer content was the variable. For all triblock copolymers studied, the data show an inward shift for the glass transition temperatures T_g of the corresponding homopolymers. This shift increases for the rigid-phase T_g as the polystyrene block length decreases. Depending on their molecular characteristics, two, three, or only one T_g were found. The third T_g was interpreted in terms of the existence of an interphase. Some of these conclusions could be confirmed by transmission electron microscopy.     

Glass transition investigated by a combined protocol using thermostimulated depolarization currents and differential scanning calorimetry

Relaxation times of bisphenol A polycarbonate around the glass transition temperature are estimated using the combination of differential scanning calorimetry (DSC) and thermostimulated depolarization currents (TSDC). These measurements are performed using samples with different thermal histories below and above the vitrification transformation. This protocol enables the extension of the range of equilibrium relaxation times measured by dielectric spectroscopy. By this mean we may recalculate the values of the Kauzmann temperature and fragility index.     

Starch-lipid interactions studied by differential scanning calorimetry

The amylose-lipid complex shows an endothermic transition around 100 °C in excess water. Complexes were prepared by adding lipids to an amylose-solution, and the precipitated complex was studied in the DSC during a heating and cooling sequence. The thermal stability of the complex depends on the lipid part, and the reversibility during cooling depends on presence of excess lipids.The influence of lipids on the gelatinization of starch was studied by adding lipids to wheat and potato starch, respectively, before the DSC-analysis. Depending on the lipid, an earlier as well as a delayed gelatinisation could be obtained.     

Reaction-induced phase separation in polyethersulfone-modified epoxy-amine systems studied by temperature modulated differential scanning calorimetry

In epoxy-amine systems with a thermoplastic additive, the initially homogeneous reaction mixture can change into a multi-phase morphology as a result of the increase in molecular weight or network formation of the curing matrix. Temperature modulated DSC (TMDSC) allows the real-time monitoring of this reaction-induced phase separation. A linear polymerizing epoxy-amine (DGEBA–aniline) and a network-forming epoxy-amine (DGEBA–methylene dianiline), both with an amorphous engineering thermoplastic additive (polyethersulfone, PES), are used to illustrate the effects of phase separation on the signals of the TMDSC experiment. The non-reversing heat flow gives information about the reaction kinetics. The heat capacity signal also contains information about the reaction mechanism in combination with effects induced by the changing morphology and rheology such as phase separation and vitrification. In quasi-isothermal (partial cure) TMDSC experiments, the compositional changes resulting from the proceeding phase separation are shown by distinct stepwise heat capacity decreases. The heat flow phase signal is a sensitive indication of relaxation phenomena accompanying the effects of phase separation and vitrification. Non-isothermal (post-cure) TMDSC experiments provide additional real-time information on further reaction and phase separation, and on the effect of temperature on phase separation, giving support to an LCST phase diagram. They also allow measurement of the thermal properties of the in situ formed multi-phase materials.     

Glass transition of semi-crystalline PLLA with different morphologies as studied by dynamic mechanical analysis

Poly(l-lactic acid) was crystallized from the glassy state at different temperatures to produce fully transformed semi-crystalline specimens exhibiting different lamellar morphologies. The materials were tested by dynamic mechanical analysis, where a T _g decrease was found with an increasing crystallization temperature. Considering a three-phase model, this tendency was related to the corresponding increase in the thickness of the rigid amorphous phase. It is suggested that this phase could, in some extent, accommodate through local translational/rotational motions the cooperative motions taking place within the mobile amorphous phase. This could be due to the non-compact structure of the cooperatively rearranging regions, which can present a string-like or fractal structure in their edges. The width of the loss factor peak associated to the glass transition increases with increasing crystallization temperature, suggesting an increase in the broadness of the distribution of relaxation times. The drop in the storage modulus across T _g varies systematically with the crystallization temperature in the different materials and could be correlated with the crystalline content. Above T _g, the loss factor exhibits a plateau-like behaviour at significantly high values, which seems to be a rather general behaviour in semi-crystalline systems that could be related to the contribution of pure irreversible flow in the overall viscoelastic behaviour.     

Interphase interaction in heterogeneous polymeric systems containing liquid-crystalline component

Some problems of analysis of interphase interactions in heterogeneous polymeric systems containing liquid-crystalline component are considered. Special attention is given to the methods of optical interferometry and dynamic mechanical spectrometry. The formation of interphase layers due to either partial compatibility or chemical interaction causes considerable improvement in mechanical properties of composite materials.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 11, pp. 1862–1878, November, 1994.The authors wish to thank O. V. Vasil'eva for the study of dynamic mechanical properties of melts of polysulfone-LC polyester Ultrax blends.     

Hydration of thermally denatured lysozyme studied by sorption calorimetry and differential scanning calorimetry

We have studied hydration (and dehydration) of thermally denatured hen egg lysozyme using sorption calorimetry. Two different procedures of thermal denaturation of lysozyme were used. In the first procedure the protein was denatured in an aqueous solution at 90 degrees C, in the other procedure a sample that contained 20% of water was denatured at 150 degrees C. The protein denatured at 90 degrees C showed very similar sorption behavior to that of the native protein. The lysozyme samples denatured at 150 degrees C were studied at several temperatures in the range of 25-60 degrees C. In the beginning of sorption, the sorption isotherms of native and denatured lysozyme are almost identical. At higher water contents, however, the denatured lysozyme can absorb a greater amount of water than the native protein due to the larger number of available sorption sites. Desorption experiments did not reveal a pronounced hysteresis in the sorption isotherm of denatured lysozyme (such hysteresis is typical for native lysozyme). Despite the unfolded structure, the denatured lysozyme binds less water than does the native lysozyme in the desorption experiments at water contents up to 34 wt %. Glass transitions in the denatured lysozyme were observed using both differential scanning calorimetry and sorption calorimetry. Partial molar enthalpy of mixing of water in the glassy state is strongly exothermic, which gives rise to a positive temperature dependence of the water activity. The changes of the free energy of the protein induced by the hydration stabilize the denatured form of lysozyme with respect to the native form.     

Equilibrium and non-equilibrium transitions studied by adiabatic calorimetry

The principle and recent technical development of adiabatic low temperature calorimetry are described with experimental results taken mostly from the authors' laboratory. Topics on the equilibrium and quasi-equilibrium heat capacities include the separation of the Schottky heat capacity from the experimental data on bromo-hydroxyphenalenone and non-Debye excess heat capacity of a glassy hydrocarbon. Relaxation of glassy crystals of rubidium cyanide and C₆₀ and stabilization of a supercooled phase of methylammonium hexachlorotellurate are discussed. A unique adiabatic calorimeter of top-loading construction recently completed in the authors' laboratory is described along with an experimental result on a glassy liquid prepared at a cooling rate 100 times greater than was possible with a calorimeter of the conventional design.     

Oxidation of lipios studied by isothermal heat flux calorimetry

The exothermic reaction of the autoxidation of lipids has been studied by isothermal heat flux calorimetry at temperatures between 80°C and 160°C. A number of lipid samples have been kept in the calorimeter under excess of oxygen for 1 or 2 hours. The capabilities of the method are illustrated by examples exhibiting different thermal behaviour, where the influence of temperature and the role of unsaturation and of antioxidants are presented for selected lipids.     

Thermal behaviour of carbohydrates studied by heat flow calorimetry

The technique of heat flow calorimetry was used to study the thermal behaviour of different carbohydrates between 20°C and 270°C. The samples were analyzed by heating in sealed cells. The temperature range in which exothermic reactions, due to thermal decomposition, occurred varied widely depending on the type of carbohydrate investigated. Reaction enthalpies of 44 sugars and polysaccharides are given. Endothermic phenomena, such as fusion or vaporization of crystallized water, were also observed: fusion temperatures and enthalpies of 34 sugars and sugar alcohols are listed. Calorimetric curves showing crystallization of amorphous sucrose, cellobiose and lactose are also presented.

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Zusammenfassung Die Technik der Wärmeleitungs-Kalorimetrie wurde zur Untersuchung des thermischen Verhaltens von verschiedenen Kohlenhydraten zwischen 20°C und 270°C eingesetzt. Die Muster wurden in dicht verschlossenen Kapseln erhitzt. Der Temperaturbereich, in welchem exotherme Reaktionen infolge thermischer Zersetzung abliefen, änderte sich stark in Abhängigkeit vom untersuchten Kohlenhydrattyp. Reaktionsenthalpien von 44 Zuckern und Polysacchariden wurden ermittelt. Endotherme Phänomene, wie das Schmelzen oder das Verdampfen von Kristallwasser wurden auch beobachtet. Schmelztemperaturen und Schmelzenthalpien von 34 Zuckern und Zuckeralkoholen sind tabelliert. Kalorimetrische Daten der Kristallisation amorpher Saccharose, Cellobiose und Lactose werden diskutiert.

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20 270°C. . , . 44 . , . 34 . , , .

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The authors greatly acknowledge many discussions with P. Würsch, R. F. Hurrell and J. Löliger and the technical assistance of F. Michel, Ph. Roulet and S. Reimann.     

Thermal behaviour of emulsions studied by differential scanning calorimetry

This article is a review about the ways in which solidification and the melting may occur within emulsions submitted to steady cooling and heating performed in a differential scanning calorimeter. Simple, multiple and mixed emulsions are considered. Due to nucleation phenomena creating supercooled and supersaturated liquids, the DSC curves obtained during cooling and heating are quite different. The influence of a solute in the disperse phase is described in detail. Some implications about the instabilities of emulsions due to mass transfer phenomena are described.     

Equilibrium and non-equilibrium phase transitions studied by adiabatic calorimetry

An adiabatic calorimetry was used for some investigations of equilibrium and non-equilibrium phase transitions. For one of the substances studied (4,4′-di-n-heptyloxyazoxybenzene) it was possible to determine temperature dependence of an order parameter and number of clusters of high temperature phase in a region of a phase transition. For another substance (liquid 3,4 dimethylpiridine) an anomaly on the specific heat curves was interpreted as being responsible for a decay of molecules’ clusters. Non-equilibrium phase transitions were investigated for some liquid crystal substances. The process of transformation between metastable and stable phases was described quantitatively. The conclusions obtained concern the stability of metastable phases.     

Thermal stability of whey proteins studied by differential scanning calorimetry

The thermal stability of the bovine whey proteins.; β-lactoglobulin (β-1g), α-lactalbumin (α-1a) and serum albumin (BSA) was studied individually and in mixtures in the temperature range 25–140°C by differential scanning calorimetry. The thermal denaturation temperature (T_D) and the transition enthalpies (ΔH_app) were determined at different pH-values (3.0–10.0) in simulated milk ultrafil-trate (SMUF).β-Lg was, except at pH 9.0 and 10.0, the most thermostable protein at all pH-values. At acidic pH-values BSA was the least thermostable. At alkaline pH-values, however, α-la had lower thermal stability than BSA. α-La exhibited double peak behaviour at acidic pH-values and ΔH_app was dependent on Ca-content. Mixtures of the proteins were studied at pH 4.0, 5.0 and 6.6. In general, when mixed, the proteins seemed to denaturate independently of each other.     

On the transition between a heterogeneous and homogeneous corona in mixed polymeric micelles

Two-dimensional NMR and small-angle neutron scattering experiments were performed on comicelles of poly(N-methyl-2-vinyl pyridinium iodide)-block-poly(ethylene oxide), P2MVP-b-PEO, and poly(acrylic acid)-block-poly(acryl amide), PAA-b-PAAm, in aqueous solutions to study whether a transition between a heterogeneous (Janus-type) and homogeneous corona can be observed upon a variation of parameters that are anticipated to affect the miscibility of the PEO and PAAm coronal blocks. Investigated were the effect of a salt-induced decrease in micellar aggregation number, P agg for 1相似文献   

Nucleotide coordination with 14 lanthanides studied by isothermal titration calorimetry

ITC reveals the increasingly importance of entropy for heavier lanthanides binding to nucleotides. The phosphate group forming chelating effect with purine bases but not with pyrimidines.     

Spectrophotometric determination of thermal transition of polymeric systems using photochromic probes

Mercury-dithizone complex both free and bonded to a polymeric system has been synthesized and used to measure the thermal transition of polystyrene, poly(vinyl acetate), and some other polymers. The thermal relaxation rate of the activated complex in dark has been found to be dependent on the free volume of a polymer matrix. The rate goes through a maximum above T_g of a polymer. A very sensitive method, based on thermal recovery of activated photochromic probe chromophore has been devised to measure the thermal transition of both single and multicomponent polymer matrices. © 1995 John Wiley & Sons, Inc.     

Polymorphism in alternating polyketones studied by x-ray diffraction and calorimetry

Differential scanning calorimetry and high temperature x-ray diffraction were used to study the perfectly alternating copolymer of ethene and carbon monoxide (polyketone; POKC2). It was found that oriented POK-C2 fibers show a crystalline phase transition at a temperature between 110–125°C with a 10% change in crystalline density. At this temperature, the crystal structure reported recently (POK-α) is transformed to a crystal structure that was reported in the past for room temperature imperfectly alternating polyketone. The latter structure will be designated as POK-β. The influence of chain defects on the crystal structure was studied by synthesizing terpolymers (POK-C2/C3), in which small amounts of propylene-CO units are incorporated into the polymer backbone. The resulting terpolymers differ from the copolymer by the presence of methyl groups randomly distributed along the polyketone backbone chain. Evidence is presented that indicates that the methyl groups are built into the crystal lattice as defects. With more than 5 mole-% propene the terpolymer fibers crystallize exclusively in the β-modification. Below this level the α/β ratio (at room temperature) increases with decreasing amounts of propene. Both as-synthesized and as-spun POK-C2 were found to consist of both POK-α and POK-β; the α/β ratio depends on the method of preparation. Because the drawn POK-C2 fibers studied here consist exclusively of POK-α, the process of spinning and drawing leads to the transformation of unoriented β-rich material into oriented POK-α. © 1995 John Wiley & Sons, Inc.