Isothermal and isobaric PVT-measurements of anionic polystyrenes

PVT-measurements of anionic polystyrenes on heating have shown that, depending on the mode of operation, specific relaxation zones within the glass transition range are observed. Isothermal PVT curves exhibit always relaxation zones independent whether the pressure is increased or decreased during the scan. The shift of the relaxation zones to higher temperatures is, however, higher for isothermal scans with increasing pressure. These relaxation zones are explained by pressure-dependent changes of the state of the polymeric sample isothermally scanned within the glass transition range. At lower pressures the polymer is actually in the molten state, whereas at higher pressures it may be in the metastable glassy state and the actual state depends on the rate of pressure change. In isobaric PVT curves relaxation zones in heating scans are exhibited only if the pressure applied during glass formation differs from the pressure applied during the heating scan. The observed pressure-dependent shift of the glass temperatures to higher temperatures was higher for the studied polystyrenes of different molecular weight that had a higher glass temperature at normal pressure. But the specific molecular weight influence on the width of the relaxation zone could not be ascertained. An attempt to calculate characteristic volume relaxation times failed because of insufficient precision of the measurements.Dedicated to Professor Bernhard Wunderlich on the occasion of his 65th birthdayAcknowledgement is made to the Deutsche Forschungsgemeinschaft (SFB 60) for financial support of this research.     

Sodium and silver phosphate glasses doped with chlorides of Fe,Mn and Zn

A number of samples of sodium and silver phosphate glasses doped with various compositions of some transition metals viz. iron, manganese and zinc chlorides alongwith undoped samples of sodium and silver phosphate glasses were synthesized and characterized by X-ray diffraction, IR spectral, electrical conductivity and differential scanning calorimetry (DSC). The glass transition temperature (T _g) and crystallization temperature (T _c) values obtained from DSC curves were found to increase with increasing concentration of the dopant Fe/Mn/Zn chlorides in both sodium and silver phosphate glasses and the following sequence is observed: T _g(–FeCl₃)>T _g(–MnCl₂)>T _g(–ZnCl₂) T _c(–FeCl₃)>T _c(–MnCl₂)>T _c(–ZnCl₂) The increase in T _g and T _c values indicate enhanced chemical durability of the doped glasses. The electrical conductivity values and the results of FTIR spectral studies have been correlated with the structural changes in the glass matrix by the addition of different transition metal cations as dopants.     

Thermal Behaviour of Silver-Filled Epoxy Adhesives. Technological implications in microelectronics

One-component silver-filled epoxy adhesives electrically conductive with low extractable ionic content have been used in microelectronics for attach applications. For the specific application described here there was evidence showing that adhesive polymerisation was not complete with negative consequences for the electronic devices. The present study aimed at understanding the causes of such disadvantages and setting up the best conditions to make the epoxy adhesive perfectly suitable for the required applications. The work was carried out mainly by means of differential scanning calorimetry (DSC) and with the help the dynamic mechanical thermal analysis (DMTA) technique. The study succeeded in determining that the technological problems were due to incomplete polymerisation that caused solvent and monomer retention. These residues produced a leakage of the insulating properties of some capacitors present in the devices jeopardising the sensor working. Moreover, the study also showed that it was possible to avoid these difficulties adjusting the polymerisation temperature to 130°C and respecting curing time of 3 h: with these new curing conditions excellent results were achieved. This revised version was published online in July 2006 with corrections to the Cover Date.     

TheT g displacement measurements: A way to foresee the physical behaviour and the use of glassy polymers

The effect of ageing temperature (belowT _g) on physical ageing of glassy PET has been investigated by differential scanning calorimetry. The position of the glass transition endotherm was found to be strongly dependent on the annealing conditions (time, annealing temperature). A single relaxation time model is proposed for the analysis of physical ageing.The variations of the equilibrium relaxation time _iso with annealing temperature allow the determination of the parameters of the model. Finally, using these constants, one can determine the thermal past and foresee the thermal future of unknown samples which are of prime importance in processes using temperatures around the glass transition temperature.

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Zusammenfassung Mittels DSC wurde der Einfluß der Alterungstemperatur (unterhalbT _g) auf das physikalische Altern von glasartigen PET untersucht. Die Lage der Glasumwandlungsendothermen hängt stark von den Temperungsbedingungen (Dauer, Temperungstemperatur) ab. Es wird ein Relaxationszeitmodell für die Analyse physikalischen Alterns vorgeschlagen.Die Parameter dieses Modelles knnen aus der Änderung der Gleichgewichtsrelaxationszeit _iso mit der Temperungstemperatur ermittelt werden. Unter Benutzung dieser Konstanten kann die thermische Vergangenheit unbekannter Proben bestimmt und die thermische Zukunft derselben vorhergesagt werden, was für Vorgänge bei Temperaturen um den Glasumwandlungspunkt von primärer Wichtigkeit ist.

     

A DMA study of the suppression of the Β transition in slightly plasticized PVC blends

A new criterion for evaluating different plasticizers the ability of suppression of the transition in plasticized PVC blends. Accordingly, the suppression ability is proportional to the PVC-plasticizer compatibility, expressed either by the critical solution temperature, CST, or by the interaction parameter related to the difference between the solubility parameters of the blend components. The criterion is, however, valid for low plasticizer contents (<5%w/w) only, as long as the transitions are not overlapped by the transitions, shifted towards lower temperatures due to the effect of the plasticizer. For higher plasticizer contents the transition starts to overlap the transition and the suppression ability of the plasticizer depends increasingly on the efficiency of the plasticizer i.e. on the depression of the glass transition temperature of PVC (related to theT _g of the plasticizer). Accordingly, plasticizers with both good efficiency (lowT _g) and compatibility are more effective in the suppression than plasticizers which have only a higher compatibility but also a highT _g (i.e. reduced efficiency).One of the authors, Tiberiu Vilics, thanks the Konferenz der Deutschen Akademien der Wissenschaften; and Volkswagen Stiftung; for financial support for a research fellowship at the Institut für Makromolekulare Chemie, Freiburg. The financial support of the Deutsche Forschungsgemeinschaft (SFB 60) is greatfully acknowledged.     

Dihydrogen, dihydride and in between: NMR and structural properties of iron group complexes

Tabulating the structures and characteristic NMR properties of 17 iron complexes, 98 ruthenium complexes and 70 osmium complexes that contain dihydrogen or compressed dihydride ligands reveals a variety of trends. The HH bond lengths increase from similar Fe(II) to Ru(II) to Os(II) complexes. Iron(II) displays a narrow range of HH distances for stable complexes. Electronegative atoms Cl and O, when attached on the metal trans to the dihydrogen ligand, result in elongation of the HH bond relative to more electropositive atoms H, C, P and N. The family of cyclopentadienyl ligands also causes this elongating effect. The dihydrogen ligands with short HH distances and weak interactions with the metal, especially on iron and ruthenium are in the fast spinning regime. One exception is the biporphyrin complex of ruthenium with the side-on bridging H₂ ligand which has an HH distance of 118 pm but is in the fast spinning regime. There are some ruthenium complexes with HH distances greater than 110 pm that are in the slow motion regime and several complexes of osmium with HH distances greater than 130 pm that are in this regime. The large J_HH due to quantum mechanical exchange coupling are observable for some of these osmium complexes with HH distances in the range of 140–160 pm. The dihydrogen ligands in many complexes appear to have librational motions or other motions that place them in the intermediate motion regime. New equations to correlate J_HD with HH distances for ruthenium dihydrogen complexes and for osmium dihydrogen complexes are introduced here.     

Thermal induced phase separation of E7/PMMA PDLC system

The phase behaviour of thermoplastic polymer-dispersed liquid crystal system is studied with particular emphasis on the various transitions that occur within the system. The extent of plasticization of the polymer(polymethyl methacrylate) by the low molecular weight liquid crystal(E7) along with the several transitions of theLC(Liquid Crystal) are determined by modulated DSC. Optical microscopy was used to construct the temperature versus composition phase diagram. Our study indicates the existence of a limiting temperature of 40°C around which the PMMA matrix turns glassy irrespective of the initial composition within the phase separated region, suggesting the intersection of the glass transition curve with the coexistence curve. A slight depression of theN-I(Nematic to Isotropic) transition of theLC is observed with increasing composition of PMMA whereas theS-M(Smectic to Nematic) transition and theT _g (Glass transition temperature) of theLC remain unaffected. The one phase mixture remains isotropic until phase separation at a lower temperature where theLC rich domains become nematic. The growth ofLC rich domains is studied as a function of temperature and time.     

Glycosylation States on Intact Proteins Determined by NMR Spectroscopy

Protein glycosylation is important in many organisms for proper protein folding, signaling, cell adhesion, protein-protein interactions, and immune responses. Thus, effectively determining the extent of glycosylation in glycoprotein therapeutics is crucial. Up to now, characterizing protein glycosylation has been carried out mostly by liquid chromatography mass spectrometry (LC-MS), which requires careful sample processing, e.g., glycan removal or protein digestion and glycopeptide enrichment. Herein, we introduce an NMR-based method to better characterize intact glycoproteins in natural abundance. This non-destructive method relies on exploiting differences in nuclear relaxation to suppress the NMR signals of the protein while maintaining glycan signals. Using RNase B Man5 and RNase B Man9, we establish reference spectra that can be used to determine the different glycoforms present in heterogeneously glycosylated commercial RNase B.     

Determination of the net electric charge of a polyacrylamide molecule by Donnan potential measurements

The net electric chargez _pof a polyacrylamide molecule (Praestol, Mol. Wt. 3.4×10⁶) in aqueous solution was determined for two pH values (7.2 and 10.0) by measuring the Donnan e.m.f. as function of the solutions NaCl contentc (2.7 mM<c<74 mM). Taking into account a non-ideal behavior of the counterions (Na⁺) mobility, the numerical values ofz _pturned out to be 3100 and 5500 electric charge units for pH=7.2 and 10.0, respectively. A measurable contribution of the assumed non-ideal model for the Na⁺ ions is found forc<15 mM.     

Single-Sided Portable NMR Investigation to Assess and Monitor Cleaning Action of PVA-Borax Hydrogel in Travertine and Lecce Stone

In this work, we investigated the potential of PVA-borax hydrogel for cleaning limestones and the dependence of the cleaning on the porosity of the rock and on the action time of the hydrogel treatment. Towards this goal, we used a nuclear magnetic resonance (NMR) spectrometer, developed for non-invasive and non-destructive applications on cultural heritage. T₂-NMR parameters were quantified on different samples of Lecce stone and Travertine cut perpendicular (Pe) and parallel (Pa) to the bedding planes under different experimental conditions: untreated samples, treated with Paraloid B72 and cleaned with PVA-PEO-borax hydrogel applied for 4 min and 2 h. The T₂ results suggest that the effectiveness of the cleaning strongly depended on the porosity of the stones. In Lecce stone, the hydrogel seemed to eliminate both the paramagnetic impurities (in equal measure with 4 min and 2 h treatment) and Paraloid B72. In Travertine Pe, characterized by a smaller pore size compared to Lecce stone, no significant effects were found regarding both the cleaning and the treatment with Paraloid B72. In Travertine Pa, characterized by a larger pore size than the other two samples, the hydrogel seemed to clean the paramagnetic agents (it worked better if applied for a longer time) but it did not appear to have any effect on Paraloid B72 removal.     

Thermal explosion and runaway reaction simulation of lauroyl peroxide by DSC tests

Lauroyl peroxide (LPO) is a typical organic peroxide that has caused many thermal runaway reactions and explosions. Differential scanning calorimetry (DSC) was employed to determine the fundamental thermokinetic parameters that involved exothermic onset temperature (T₀), heat of decomposition (ΔH_d), and other safety parameters for loss prevention of runaway reactions and thermal explosions. Frequency factor (A) and activation energy (E_a) were calculated by Kissinger model, Ozawa equation, and thermal safety software (TSS) series via DSC experimental data. Liquid thermal explosion (LTE) by TSS was employed to simulate the thermal explosion development for various types of storage tank. In view of loss prevention, calorimetric application and model analysis to integrate thermal hazard development were necessary and useful for inherently safer design.     

L-malic acid production by entrappedSaccharomyces cerevisiae into polyacrylamide gel beads

The yeastSaccharomyces cerevisiae was entrapped within polyacrylamide gel beads by employing a procedure that uses sodium dodecylsulfate as a detergent to improve the spherical configuration of the beads. The resulting preparation showed a rate of fumarate bioconversion to L-malic acid about 60 times higher than that found for the free cells. Almost all fumarate was converted in 30 min of incubation. The thermal stability of the immobilized cells did not significantly differ from the free cells. An optimal pH of 5.7 was found for the immobilized preparation and no succinic acid was detected as a by-product in the incubation mixture.     

Automatic twin vessel recrystallizer. Effective purification of acetaminophen by successive automatic recrystallization and absolute determination of purity by DSC

I describe an interchangeable twin vessel (J, N) automatic glass recrystallizer that eliminates the time-consuming recovery and recycling of crystals for repeated recrystallization. The sample goes in the dissolution vessel J containing a magnetic stir-bar K; J is clamped to the upper joint H of recrystallizer body D. Empty crystallization vessel N is clamped to the lower joint M. Pure solvent is delivered to the dissolution vessel and the crystallization vessel via the head of the condenser A. Crystallization vessel is heated (P). The dissolution reservoir is stirred and heated by the solvent vapor (F). Continuous outflow of filtrate E out of J keeps N at a stable boiling temperature. This results in efficient dissolution, evaporation and separation of pure crystals Q. Pure solvent in the dissolution reservoir is recovered by suction. Empty dissolution and crystallization vessels are detached. Stirrer magnet is transferred to the crystallization vessel and the role of the vessels are then reversed. Evacuating mother liquor out of the upper twin vessel, the apparatus unit is ready for the next automatic recrystallization by refilling twin vessels with pure solvent. We show successive automatic recrystallization of acetaminophen from diethyl ether obtaining acetaminophen of higher melting temperatures than USP and JP reference standards by 8× automatic recrystallization, 96% yield at each stage. Also, I demonstrate a novel approach to the determination of absolute purity by combining the successive automatic recrystallization with differential scanning calorimetry (DSC) measurement requiring no reference standards. This involves the measurement of the criterial melting temperature T₀ corresponding to the 100% pure material and quantitative ΔT in DSC based on the van’t Hoff law of melting point depression. The purity of six commercial acetaminophen samples and reference standards and an eight times recrystallized product evaluated were 98.8 mol%, 97.9 mol%, 99.1 mol%, 98.3 mol%, 98.4 mol%, 98.5 mol% and 99.3 mol% respectively.     

DSC and NMR Study on the Inclusion Complex of Lappaconitine with β—Cyclodextrin

The inclusion complex of lappaconitine(Lap) with β-cyclodextrin (β-CD) has been studied by the differential scanning calorimetry (DSC) and ^1H-NMR,2D-NMR spectroscopy. The structure of the complex has been deduced.     

Supramolecular fullerene/porphyrin charge transfer interaction studied by absorption spectrophotometric method

A detailed UV–Vis spectrometric and thermodynamic studies were done to look insight into the nature of molecular interactions of the electron donor–acceptor complexes of C₆₀ and C₇₀ with 5,10,15,20-tetrakis(octadecyloxyphenyl)-21H,23H-porphyrin (1) in chloroform and toluene. Charge transfer (CT) absorption bands were located in the visible region and vertical ionization potential of 1 was determined utilizing CT transition energy. Low values of oscillator and transition dipole strengths suggested that the complexes were almost of neutral character in ground states. The high binding constant value for the C₇₀–1 complex indicated high selectivity of 1 molecule towards C₇₀. Experimental as well as theoretically determined of enthalpies of formation value substantiated the trend in K values for fullerene–1 complexes.     

DSC and NMR Study on the Inclusion Complex of Lappaconitine with b-Cyclodextrin

Lappaconitine (Figure 1) is a diterpenoid alkaloid, naturally occurring in roots and rhizomes of Aconitum and delphinium1. Lap reveals bradycardic and hypotensive activity2. But its application is restrained owing to its poor water solubility, toxicity and side effects on humans. In a number of pharmaceutical studies, b-CD has been reported to interact with many drug molecules to form inclusion complexes for improving the water solubility of drugs, and reducing their toxicity3. We have p…     

Vibronic pairwise charge transfer in copper-oxide sheets: A possible approach to high temperature superconductivity theory

Summary To accommodate the number of holes and fractional number of atoms in doped highT _c superconductors, and to produce a periodic structure with given symmetry, we postulate a quadruple cell with four copper atoms on the CuO₂ layer. The quadruple cell structure hasD _2h symmetry which can be distorted toC _2h geometry underB _1g vibration. Such a structure allows the interconversion of different spin angular momenta into paired spins similar to Cooper pairs. It also provides vibronic interactions that lower the energy of the ground state. For electron (hole) pairing, we construct the running wave Bloch sums consisting of linear combination of bonding/antibonding geminals (instead of one-electron atomic orbitals) in these quadruple cells. For bond movement we construct the Bloch sums consisting of linear combination of Covalon waves in quadruple cells related to the movement of conjugate (alternating) bonds. In both cases the pair-wise charge (hole/electron) transfer is coupled with antisymmetric vibrations under a double-well potential related to Peierls distortion. The vibronic mixing of different running bonds with different antisymmetric vibrations at various distances, accounts for the different long-range order of charge transfer. Our formulations represent an alternative view of BCS theory, Bisoliton theory and Resonanting Valence Bond theory by using a quantum chemical, position-space approach to a more tight binding situation.     

Thermal hazard evaluation of carbon nanotubes with sulfuric acid by DSC

Many concerns over unsafe or unknown properties of multi-walled carbon nanotubes (MWNTs) have been raised. The thermal characteristics regarding stability would represent potential hazards during the production or utilization stage and could be determined by calorimetric tests for various thermokinetic parameters. Differential scanning calorimetry (DSC) was employed to evaluate the thermokinetic parameters for MWNTs at various compositions. Thermoanalytical curves showed that the average heat of decomposition (ΔH _d) of the MWNTs samples in a manufacturing process was about 31,723 J g⁻¹, by identifying them as an inherently hazardous material. In this study, significant thermal analysis appeared in the presence of sulfuric acid (H₂SO₄). From the DSC experiments, the purification process of MWNTs could induce an unexpected reaction in the condition of batch addition with reactants of H₂SO₄. The results can be applied for designing emergency relief system and emergency rescue strategies during a perturbed situation or accident.     

Fracture behavior of core-shell rubber-modified crosslinkable epoxy thermoplastics

The fracture behavior of a core-shell rubber (CSR) modified cross-linkable epoxy thermoplastic (CET) system, which exhibits high rigidity, highT _g, and low crosslink density characteristics, is examined. The toughening mechanisms in this modified CET system are found to be cavitation of the CSR particles, followed by formation of extended shear banding around the advancing crack. With an addition of only 5 wt.% CSR, the modified CET possesses a greater than five-fold increase in fracture toughness (G _IC) as well as greatly improved fatigue crack propagation resistance properties, with respect to those of the neat resin equivalents. The fracture mechanisms observed under static loading and under fatigue cyclic loading are compared and discussed.     

An evaluation on thermokinetic parameters for hydrogen peroxide at various concentrations by DSC

Information about the kinetics and thermal decomposition of hydrogen peroxide (H₂O₂) has been required for safety reasons, due to its broad applications in many chemical industries. To determine the inherent hazards during H₂O₂ manufacturing, transportation, disposal, usage, and so on, this study deliberately selected various H₂O₂ concentrations and analyzed them by differential scanning calorimetry (DSC). In addition, thermokinetic parameters were not only established for each of these reactions, but also aimed at comprehensive, kinetic models with various tests conducted at different heating rates. To build up a comprehensive kinetic model, various tests were conducted by heating rates of 1, 2, 4, 10°C min^–1, respectively. According to dynamic DSC tests, the experimental curves show that H₂O₂ decomposition has one exothermic peak and may start to decompose under 47–81°C. The total heat of decomposition is about 192–1079 J g^–1. Not only can these results prevent accidents caused by H₂O₂ during storage and transportation, but also assess its inherent hazards and thereby design procedures for emergency response while runaway reactions occurring.