Transitions from solid to liquid in isotactic polystyrene studied by thermal analysis and X-ray scattering

The rigid amorphous fraction in isotactic polypropylene is comprehensively analyzed as a function of the history of crystallization. The crystallinity, crystal morphology, and superstructure were independently and precisely controlled by the rate of cooling on melt crystallization and by the temperature/time of subsequent annealing. Formation of lamellae and spherulites on slow cooling and formation of nodular domains on rapid cooling are observed. Annealing allowed an increase of the crystallinity and perfection/growth of crystals, without affecting their habit and higher order organization. Analysis of the glass transition of the amorphous phase in preparations with a crystallinity between 40% and 75% proves coexistence of differently mobile amorphous structures. The rigid amorphous fraction and the ratio between rigid and mobile amorphous fractions decrease with increasing crystallinity, which is due to reduced covalent coupling of crystals and amorphous phase in preparations of high crystallinity. Analysis of the effect of the crystal habit on the rigid amorphous fraction allows identification of the structure at the basal planes of crystals as a major source of the immobilization of the amorphous phase. The mobile amorphous fraction cannot primarily be related to interspherulitic or interlamellar stack regions of the semicrystalline superstructure. The presence of crystals in semicrystalline isotactic polypropylene also affects the properties of the mobile amorphous fraction, which is detected by a distinct decrease of its glass transition temperature in samples of high crystallinity, which contain crystals of high stability. This confirms increasing decoupling of the crystalline and amorphous phases in preparations of high crystallinity, as was independently derived by the analysis of the rigid amorphous fraction.

Graphene of two differentaspect ratios, Af, was melt mixed withpoly(ethylene terephthalate) (PET) toform amorphous PET/graphene composites with less than 5% crystallinity.The higher-order structure and mechanical properties of poly(ethyleneterephthalate) (PET) in these composites were investigated using techniquessuch as differential scanning calorimetry and dynamic mechanical analysis,whereas transmission electron microscopy, melt rheology, and electricalconductivity were used to study the graphene dispersion. A decreasein heat capacity changes, ΔCp, ofPET in nanocomposites at the glass transition temperature, Tg, without Tg changesuggests that a rigid amorphous fraction (RAF) of PET was formed atthe PET/graphene interface. The stiffening effect of graphene below1 wt % loading is quite small in the glassy state region and independentof the Af of graphene. Above 2 wt %, grapheneforms a mechanical percolation network with the RAF of PET and thePET chains are geometrically restricted by the incorporation of graphenewith a high Af, resulting in an unexpectedlyhigher modulus of nanocomposites both below and above Tg.

Insight into the annealing peak and microstructural changes of poly(l-lactic acid) by annealing at elevated temperatures

The characteristic length of cooperative rearranging region for uniaxial drawn poly(ethylene terephthalate) films

Glass transition behavior and dynamic fragility in polylactides containing mobile and rigid amorphous fractions

Glass transition temperatures and rigid amorphous fraction of poly(ether ether ketone) and poly(ether imide) blends

Isothermal crystallization of cis-1.4-polybutadiene at low temperatures

Chapter 9 - Thermal characterization of materials using differential scanning calorimeter

A three-phase model, comprising crystalline, mobile amorphous, and rigid amorphous fractions (χ c, χ MA, χ RA, respectively) has been applied in the study of semicrystalline Nylon-6. The samples studied were Nylon-6 alpha phase prepared by subsequent annealing of a parent sample slowly cooled from the melt. The treated samples were annealed at 110°C, then briefly heated to 136°C, then re-annealed at 110°C. Temperature-modulated differential scanning calorimetry (TMDSC) measurements allow the devitrification of the rigid amorphous fraction to be examined.

Heat capacity and enthalpy of indapamide

Advanced characterization of the structuration of ionic liquids in a copolyester

Poly(L‐lactide) (PLLA) on poly(2‐hydroxyethyl methacrylate) (PHEMA) backbone was prepared by a combination of atom transfer radical polymerization (ATRP) and ring‐opening polymerization (ROP). The structure of the comb polymer was analyzed by wide angle X‐ray diffraction (WAXD), small angle X‐ray scattering (SAXS), and differential scanning calorimetry (DSC). WAXD result indicates that the comb polymer has α crystalline modification with a 103helical conformation. Lamellar parameters of the crystalline structure were obtained by one‐dimension correlation function (1DCF) calculated from SAXS results. The calculations show that the thickness of crystalline layer is controlled by annealing temperature and comb structure. DSC was applied to study kinetics of the crystallization and melting behavior. Two melting peaks on melting curves of the comb polymer at different crystallization temperature were detected, and the peak at higher temperature is attributed to the melt‐recrystallization. The equilibrium melting temperature is found to be influenced by the comb structure. In this article the effects of the comb structure on Avrami exponent, equilibrium melting point and melting peak of the comb polymer were discussed. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 589–598, 2008

Quantitative thermal analysis was carried out for poly‐(pivalolactone) (PPVL), including heat capacity determinations from 140 to 550 K. The experimental Cp below the glass transition temperature was fitted to an approximate vibrational spectrum and the ATHAS computation scheme was used to compute the “vibration only” heat capacities from 0.1 to 1000 K. The liquid Cp was derived from an empirical addition scheme and found to agree with the experimental Cp with an RMS of ±2.8% from 240 K to 550 K. A glass transition, Tg, could be detected at 260 K, and the change in heat capacity for 100% amorphous PPVL was calculated to be 38.8 J/(K mol). Above Tg, semicrystalline samples seem to show a rigid amorphous fraction that does not contribute to the increase in heat capacity at Tg. Using the ATHAS recommended heat capacities, the various thermodynamic functions (enthalpy, entropy, and Gibbs function) were derived. The residual entropy at 0 K for the amorphous PPVL was calculated to be 5.2 J/(K mol) per mobile bead, and was comparable to that obtained for a series of linear, aliphatic polyesters analyzed earlier.

The main challenge for electric vehicles, smaller portable devices and high capacity stationary storage facilities is their safety behaviour under normal and abusive operation conditions. The most commonly used cathodes in lithium-ion batteries (LIB) for portable applications contain lithium cobalt oxide (LiCoO2) as active material. The susceptibility of LiCoO2 cathodes to thermal runaway was previously reported in the framework of safety studies for energy storage systems [1]. The partial substitution of Co by other transition metals was much exploited. One of the main benefits of cells containing electrodes with new chemistries, such as lithium nickel manganese cobalt oxide (Li(NiMnCo)O2, isostructural with the layered LiCoO2), is the improved thermal stability in the fully charged state (delithiated cathodes). LIB with cathodes containing Li(NiMnCo)O2 perform better during thermal runaway tests than those with LiCoO2 [2,3]. Understanding the heat balance between the amounts of heat generated and dissipated in LIB during operation, when the concentration of Li in the electrode varies, is a critical issue. To improve battery safety, thermal management systems (TMS) were introduced to control the operation of high energy and high power batteries. Therefore, knowledge of bulk electrode thermal properties such as thermal conductivity, thermal diffusivity and specific heat capacity are required to optimize TMS design models and for increasing the predictability of multiscale simulations [4]. The thermodynamic properties of LiMeO2 (Me=Ni+Mn+Co) materials for LIB with layered structure were measured by calorimetry up to 973 K. Heat increment and specific heat capacity of samples with Ni:Mn:Co ratio of 1:1:1 and 4:4:2 were determined by transposed drop calorimetry and differential scanning calorimetry. These studies on active materials were extended to cathode level for samples with 1:1:1 stoichiometry. The cathodes under investigation were tape-casted composite thick films, both containing LiMeO2 active material mixed with additives (binder and carbon black), deposited on aluminium current collector foils. To compare the currently studied alternative material (Me=Ni+Mn+Co and Ni:Mn:Co=1:1:1) with the traditional LiCoO2, cathodes with Me=Co were also prepared using the same method and additionally investigated. Due to the presence of the additives, the thermophysical properties of the cathodes were studied as a function of temperature up to 573 K [5]. Thermal diffusivity was measured directly on cathode samples by laser flash analysis, whereas specific heat capacity measurements were performed using differential scanning calorimetry on samples prepared from the composite contained in the cathode sheet. These heat capacity data, together with those for aluminium, were used to predict the cathodes respective heat capacities. Furthermore, the transport properties were also studied as a function of lithium concentration x in the Li x MeO2 cathodes (0≤x≤1). The compositions, which were investigated in this work, were produced by electrochemical titration. The values of x were determined by laser induced breakdown spectroscopy through surface and bulk analysis for homogeneity in lithium concentration [6]. All cathode samples for the laser flash measurements were used in a dry state, without liquid electrolyte in the pores of the composite. Since most of the cell and battery pack models consider a homogeneously distributed mixture of liquid electrolyte in the porous electrodes, data provided in this study could contribute to the improvement of such models through the implementation of dry areas which coexist within cell layers [7]. These areas represent sources of ageing and degradation and lead to thermal gradients across the cells which are up to now neglected in the state of the art of the TMS. The results presented in this work are the first experimental data of this kind which combine application oriented and fundamental research. Furthermore, our temperature and concentration dependent data are critical for significantly improving simulation studies of the thermal behaviour of LIB, including thermal runaway, since current approaches assume bulk properties to be independent of temperature and lithiation degree due to lack of measured data.

One of the goals of the Saltstone variability study is to identify (and quantify the impact of) the operational and compositional variables that control or influence the important processing and performance properties of Saltstone grout mixtures. The heat capacity of the Saltstone waste form is one of the important properties of Saltstone mixes that was last measured at SRNL in 1997. It is therefore important to develop a core competency for rapid and accurate analysis of the specific heat capacity of the Saltstone mixes in order to quantify the impact of compositional and operational variations on this property as part of the variability study. The heat capacity, coupled with the heat of hydration data obtained from isothermal calorimetry for a given Saltstone mix, can be used to predict the maximum temperature increase in the cells within the vaults of the Saltstone Disposal Facility (SDF). The temperature increase controls the processing rate and the pour schedule. The maximum temperature is also important to the performance properties of the Saltstone. For example, in mass pours of concrete or grout of which Saltstone is an example, the maximum temperature increase and the maximum temperature difference (between the surface and the hottest location) are controlled to ensure durability of the product and prevent or limit the cracking caused by the thermal gradients produced during curing. This report details the development and implementation of a method for the measurement of the heat capacities of Saltstone mixes as well as the heat capacities of the cementitious materials of the premix and the simulated salt solutions used to batch the mixes. The developed method utilizes the TAM Air isothermal calorimeter and takes advantage of the sophisticated heat flow measurement capabilities of the instrument. Standards and reference materials were identified and used to validate the procedure and ensure accuracy of testing. Heat capacities of Saltstone mixes were {approx} 55% higher than the previous measurement of specific heat capacity on a reference Saltstone mix in 1997. Values of mixes prepared using Deliquification, Dissolution and Adjustment (DDA), Modular Caustic Side Solvent Extraction Unit (MCU) and Salt Waste Processing Facility (SWPF) simulants and premix at 0.60 w/cm ratio were {approx} 1.95 J/g/{sup o}C and were equivalent within experimental error. The simple law of mixtures was used to predict the heat capacities of the Saltstone and the results were in excellent agreement with experimental data. This simple law of mixtures can therefore be used to predict the heat capacities of Saltstone mixes in those cases where measurements have not been made. The time dependence of the heat capacity is important as an input to the modeling of temperature increase in Saltstone vaults. The heat capacity of a mix of MCU and premix at 0.60 w/cm ratio was measured immediately after initial mixing and then periodically up to times greater than 100 days. Within experimental error, the heat capacity did not change with time. Therefore, the modeling is not complicated by requiring a time dependent function for specific heat capacity. The water to cementitious material (w/cm) ratio plays a key role in determining the value of the heat capacity. Both experimental and predictive values for SWPF mixes as function of the w/cm ratio were obtained and presented in this report. Predictions of the maximum temperatures of the Saltstone mixes were made using the heat of hydration data from previous isothermal measurements and the newly measured heat capacities for DDA, MCU and SWPF mixes. The maximum temperature increase ranged from 37 to 48 C for these mixes. The presence of aluminate at 0.33 M produced a temperature increase of 68 C which is close to the adiabatic temperature rise of 74 C observed by Steimke and Fowler in 1997 for a mix containing 0.35 M aluminate. Aluminum dissolution of the sludge will increase the aluminate in the DSS which in turn will result in a larger temperature increase in the Saltstone vaults during the curing period. The initial temperature of the Saltstone mixes in the Saltstone Production Facility (SPF) can be predicted using the specific heat capacities of Decontaminated Salt Solutions (DSS), the specific heat capacities of cementitious materials, and the initial temperatures of the DSS and the premix. This initial mix temperature is dominated by the DSS temperature due to its high heat capacity relative to the cementitious materials. Therefore, controlling the initial temperature of the DSS to lower temperatures will lead to lower maximum temperatures in the vault for a given batch of Saltstone.