Temperature distribution in polymer samples during DSC-scans

Differential Scanning Calorimetry is frequently used for measurements of thermal properties on all kinds of substances. The temperature lag in the samples depend on the thermal properties and the thermal contact between sample and sample holder. In the paper, we discuss the temperature distribution in samples of comparatively low thermal conductivity, such as polymers. The purpose of this study is to pinpoint the substantial temperature differences that may occur in such bad conducting samples under different conditions. The calculations of the temperature gradients have been carried out by using a finite element software package.     

以阴离子交换纤维素膜作基质室温燐光法测定痕量2,6-二氨基嘌呤的研究

本文对2,6-二氨基嘌呤(DAP)在不同的基质上和不同的重原子微扰剂存在下的室温燐光(RTP)强度进行比较,结果表明,NaI-NaAc是有效的重原子体系。适宜的固体基质为阴离子交换纤维素(二乙氨基乙基纤维素)膜(DEAE)和慢速定量滤纸。前者对酸度的变化具有较好的缓冲能力,本文提出了以DEAE为固体基质,测定痕量DAP的RTP法。     

低温燐光的研究及应用

本文综述了44篇文献,介绍低温燐光的发展概况及其应用。     

Supramolecular Crystallization of Monodispersed Silica Spherical Particles (MSSP) in Concentrated Suspensions

The supramolecular crystallization of MSSP concentrated suspensions in alcohol and ethyl ether with various ammonia concentrations is found to occur as a phase transition, with appearence of a pre-transitional state. The temperature dependence of the time, it takes for this state to be established, evidences for the presence of processes of nucleation and activation character.     

The Development of Gas-flow Modulation for High-frequency MTDSC measurements

The purpose of this study was to investigate the feasibility of modulating the temperature programme of a conventional DSC by use of an alternating gas-flow system. Modulated temperature differential scanning calorimetry (MTDSC) is an important thermal analysis technique but suffers from a limited applicable frequency range due to the mass of the sample and DSC cell leading to the impingement of thermal conductivity effects. We suggest that the frequency limit can be increased by replacing the cell as the source of temperature modulation with an external gaseous source, directed towards the sample and reference pans. In this evaluation, an alternating gas-flow was passed through a line to a forced gas-flow accessory (FGFA). The FGFA consisted of two matched cylinders containing chambers that allowed pre-temperature-equilibration of the stream of gas before it was passed over the sample and reference pans. The development of this device revealed the essential practical requirements of gas-flow modulation for high-frequency temperature modulation. These include the following: an appropriately sealed tunable gas supply to both sample and reference pans, an effective method for high-frequency cycling of the gas-flow rate, a small aperture to deliver the flowing gas directly over the pan and a temperature equilibration chamber. The results from samples of quenched PET and amorphous Saquinavir indicate that gas-flow modulation is indeed feasible, with the FGFA able to raise the attainable temperature modulation frequency by an order of magnitude compared to conventional MTDSC. This revised version was published online in August 2006 with corrections to the Cover Date.     

Crystallization Behavior of Sol-Gel Derived Films by Self-Seeding Process

We propose the novel preparation method, Self-seeding Process, based on the following concept for low temperature crystallization of oxide films. Introduction of desirable inhomogeneity should give lowering of a crystallization temperature through heterogeneous nucleation accompanied with reduced activation energy. We carried out inspection of the above concept through use of PZT films. PZT gel films with the desirable inhomogeneity of microstructure were prepared, and their crystallization behaviors was examined. The PZT film was successfully crystallized at 500°C by the self-seeding process. The single phase (001) oriented PZT film with 0.55 m in thickness was obtained at 550°C for 5 min. The self-seeding process by microstructure control is efficient for the low temperature process of the oxide thin film.     

[13C]Dynamic NMR and Molecular Modeling of 2,4-Bis(N-Pyrrolidinyl)-6-chloro-s-triazine

The room temperature [¹³C]NMR spectrum of 2,4-bis(N-pyrrolidinyl)-6-chloro-s-triazine shows doubled signals for the pyrrolidine rings, which suggests restricted rotation about the Ar-C—N bond. The rotational barrier around this bond was determined by [¹³C]dynamic NMR (DNMR) spectra run at different increasing temperatures and also by the PM3 Hamiltonian contained in the MOPAC package. The values thus obtained, 16.6 and 13.6 kcal mol^–1, respectively, are in good agreement.     

Application of Hot Press Sintering to Na2O-B2O3-SiO2 Gels Containing Quantum Dots for Lowering of Densification Temperature

Na₂O-B₂O₃-SiO₂ (NBS) gels containing a large amount of CdS quantum-dots (10 wt%) were densified using the hot press (HP) sintering method. By HP treatment, full-densification temperature could be lowered by about 40°C than that of the normal non-pressing (NP) heat treatment. Exciton absorption of CdS quantum-dots in HP-sample showed a large blue shift compared with that in the NP sample, and the size-distribution of CdS dots remained very sharp, with a mean particle diameter d = 3.66 nm and a standard deviation of = 0.72. HP pressure had a large effect on the reduction of sintering temperature and time, resulting in the suppression of the aggregation and growth of CdS quantum-dots in NBS glasses.     

Obtaining Modulated Temperature DSC Curves Through a Non-conventional DSC Method

The DSC curve obtained in conventional equipment usually only shows the resultant thermal effect due to simultaneous phenomena, which may occur during isothermal or dynamic analyses. This does not allow one to identify the processes properly and may cause an erroneous interpretation of the resulting curves. Modulated DSC equipment enhances the operating conditions and the analysis capacity of conventional DSC by superimposing a sinusoidal temperature modulation on the linear temperature control. Thus reversing and non-reversing heat flow curves are obtained, which are, respectively, the heat capacity and kinetic components of the DSC curve. Therefore, events that are related to these components can be separately analyzed. A method to obtain curves similar to the MDSC reversing and non-reversing components was developed using conventional DSC equipment in a non-conventional way. It was applied to analyze samples of poly(ethylene terephthalate) (PET) taken from bottles of mineral water. The second PET crystallization step that occurs during its melting was quantified and an apparent initial crystallinity was obtained from the resulting data. This revised version was published online in August 2006 with corrections to the Cover Date.