A computer assisted heat capacity measuring system has been designed from commercial components. A differential scanning calorimeter of type Perkin-Elmer DSC-2 forms the basis for measurements from 100 to 1000 K. A Hewlett-Packard calculator (minicomputer) of type 9821 is the data handling system. The data are collected and permanently stored on teletape. The program has been written to govern measurement and final computation, tabulation, plotting, and curve fitting. Calibration is done by comparison with benzoic acid or aluminium oxide (sapphire). Zinc heat capacities have been measured as an example and for evaluation of accuracy. Accuracies of better than ± 0.5% have been achieved, an improvement of approximately a factor 3 to 5 over a similar system without computer assist. The system will be used mainly for heat capacities of linear macromolecules.
Authors:B. Gaur, B. Lochab, V. Choudhary, and I. Varma
The paper describes the synthesis of low molecular mass poly(allyl chloride) (PAC) (Mn= 856-3834 g mol-1) using Lewis acid (ALCL3, FeCL3, TiCL4) and al powder. Branching in PAC was indicated on the basis of elemental analysis and 1H-NMR spectroscopy. azidation of pac could be carried out at 100°C by using NaN3 and DMSO as solvent. Curing of poly(allyl azide) (PAA) by cyclic dipolar addition reaction with EGDMA (ethylene glycol dimethacrylate,
5-45 phr) was investigated by differential scanning calorimetry and structure of cured polymer was confirmed by FTIR. A two-step
mass loss was exhibited by uncured and cured PAA in nitrogen atmosphere. A mass loss of 20-28% (155-274°C) and 50-61% (330-550°C)
Authors:Umesh Gaur, Miao -Yong Cao, R. Pan, and B. Wunderlich
It is shown that heat capacities of linear macromolecules consisting of all-carbon single-bonded backbones can be calculated from the appropriate contributions of substituted carbon atoms to a precision of about − 0.2±2.5% (155 data points), which is similar to the experimental precision. Heat capacity contributions of 42 groups are given over the full range of measurement and reasonable extrapolation. The quality of the addition scheme is tested on 16 series of measurements on homopolymers, copolymers and blends. The addition scheme works for all these different states of aggregation of the constituent groups. The basis of the addition scheme is discussed.
Authors:R. C. Bopp, U. Gaur, R. P. Kambour, and B. Wunderlich
The thermal behavior of poly(2,6-dimethyl-1,4-phenyiene oxide) (PPO R resin), poly(3-bromo-2,6-dimethyl-1,4-phenylene oxide), and a series of their statistical copolymers with identical average molecular lengths has been characterized by thermogravimetry and computer-interfaced differential scanning calorimetry. The heat capacities are found to be additive with respect to the concentrations of the two components. The change in heat capacity at the glass transition (Δ Cp) is independent of composition for bromination of up to 75% of the repeat units. At higher bromine levelsΔ Cp decreases abruptly. This behavior is attributed to the temperature dependence ofΔ Cp for the two components. The glass transition temperature (Tg) of the copolymers varies nearly linearly with composition. A comparison of the experimental values ofTg is made with various equations derived for statistical copolymers and homogeneous polymer blends. A modification of the Couchman equation is presented taking into account the temperature dependence ofΔCp.
Authors:U. Gaur, G. Pultz, H. Wiedemeier, and B. Wunderlich
The low temperature heat capacities of 13 group IV chalcogenides are examined. The heat capacity of crystals with largely isotropic structure (GeTe, SnSe, SnTe, PbS, PbSe, PbTe) can be represented within ±3% by a three-dimensional Debye function (θ3=205, 230, 175, 225, 150 and 130, respectively). The heat capacity of crystals with anisotropic structures (GeS, GeSe, SnS, GeS2 and SnS2) could only be represented by pairs of two-dimensional Debye functions for the longitudinal and transverse lattice vibrations (error ±0.5 to 3%;θ2(l)=505, 345, 400, 705, 480 and 570, respectively, andθ2(t)=200, 185, 160, 175, 100 and 265, respectively).
Authors:E. Sapi, K. Gupta, K. Wawrzeniak, G. Gaur, J. Torres, K. Filush, A. Melillo, and B. Zelger
Our research group has recently shown that Borrelia burgdorferi, the Lyme disease bacterium, is capable of forming biofilms in Borrelia-infected human skin lesions called Borrelia lymphocytoma (BL). Biofilm structures often contain multiple organisms in a symbiotic relationship, with the goal of providing shelter from environmental stressors such as antimicrobial agents. Because multiple co-infections are common in Lyme disease, the main questions of this study were whether BL tissues contained other pathogenic species and/or whether there is any co-existence with Borrelia biofilms. Recent reports suggested Chlamydia-like organisms in ticks and Borrelia-infected human skin tissues; therefore, Chlamydia-specific polymerase chain reaction (PCR) analyses were performed in Borrelia-positive BL tissues. Analyses of the sequence of the positive PCR bands revealed that Chlamydia spp. DNAs are indeed present in these tissues, and their sequences have the best identity match to Chlamydophila pneumoniae and Chlamydia trachomatis. Fluorescent immunohistochemical and in situ hybridization methods demonstrated the presence of Chlamydia antigen and DNA in 84% of Borrelia biofilms. Confocal microscopy revealed that Chlamydia locates in the center of Borrelia biofilms, and together, they form a well-organized mixed pathogenic structure. In summary, our study is the first to show Borrelia–Chlamydia mixed biofilms in infected human skin tissues, which raises the questions of whether these human pathogens have developed a symbiotic relationship for their mutual survival.