Authors:M. Matthews, I. Atkinson, Lubaina Presswala, O. Najjar, Nadine Gerhardstein, R. Wei, Elizabeth Rye, and A. Riga
Dielectric analysis (DEA), supported by thermogravimetric analysis (TG), differential scanning calorimetry (DSC), powder X-ray
diffraction analysis (PXRD) and photomicrography, reveal the chiral difference in the amino acids. The acids are classified
as dielectric materials based on their structure, relating chirality to the vector sum of the average dipole moment, composed
of the constant optical (electronic) and infra-red (atomic) polarizabilities, as well as dipole orientation. This study encompasses
14 L-and D-amino acid isomers. Physical properties recorded include AC electrical conductivity, charge transfer complexes, melting,
recrystallization, amorphous and crystalline phases, and relaxation spectra, activation energies and polarization times for
the electrical charging process.
Authors:P. Di Martino, P. Conflant, M. Drache, J. -P. Huvenne, and A. -M. Guyot-Hermann
The polymorphic forms II and III of paracetamol were obtained by melting the marketed form I. Under the melting and cooling conditions used, it was possible to obtain forms I, II and III. The recrystallization conditions and the physical properties of forms II and III were investigated by means of various techniques: thermomicroscopy, DSC analysis, infrared microspectrometry and X-ray powder diffraction at room temperature and as a function of temperature. Form III was found to be very unstable. However, its formation seems to be an important intermediate step in the preparation of form II.
The multiple melting behaviour of isothermally crystallized bulk poly(trimethylene
terephthalate) (PTT) observed using DSC has been correlated to the total depolarized
light intensity (DLI) of thin films using hot-stage polarized light optical
microscopy. The observation of partial melting, recrystallization and final
melting in the DSC is correlated to the observation of the partial decrease,
sudden increase and final decrease in DLI under the same heating conditions.
Integration of real-time visible spectra of the transmitted light was used
to separate the effects of retardation from pure birefringence of the colorful
spherulitic thin-film PTT samples. The correlation of the results from these
two methods has demonstrated clearly that the observed DSC multiple melting
behaviour of this particular polymer is the illustrated effect of a process
of continuous partial melting/recrystallization/final melting in the material
during thermal analysis. The observed thermal behaviour of these metastable
spherulitic materials is a complex function of their thermal history including
crystallization temperature and anneal conditions, including scanning rate
during thermal analysis.
The characteristics of crystallization, melting and spherulitic growth of a random propylene copolymer (PRC) containing small amount of ethylene were studied in the presence of a selective Β-nucleating agent (calcium pimelate). It was established that the products of isothermal and non-isothermal crystallization are very rich in Β-modification but have mixed polymorphic composition. The formation of α-modification may be attributed to Βα-transition on the surface of growing Β-spherulites resulting in αΒ-twin-spherulites. During melting of PRC of Β-modification, the characteristics observed with Β-nucleated propylene homopolymers, namely, a Βα-recrystallization of recooled samples and separated melting of non-recooled samples (i.e. the melting memory effect), as well as a ΒΒ-recrystallization leading to a perfection of the structure within the Β-modification, are also demonstrated. The disturbance of regularity of the polymer chain highly reduces the tendency to Β-crystallization. In contrast to the observations with propylene homopolymers, the growth rate of α-modification (Gα) is higher than that of Β-modification (Gβ) and no critical crossover temperature can be found (T(Βα)=413 K) below whichGα>Gβ. The experimental results show that a partial disturbance of chain regularity by incorporation of comonomer units considerably reduces the tendency to Β-crystallization.
Authors:F. Giordano, A. Rossi, R. Bettini, A. Savioli, A. Gazzaniga, and Cs. Novák
The thermal behavior of binary mixtures of paracetamol and a polymeric excipient (microcrystalline cellulose, hydroxypropylmethylcellulose
and cross-linked poly(vinylpyrrolidone)) was investigated. The physical mixtures, ranging from 50 to 90% by mass of drug,
were submitted to a heating-cooling-heating program in the 35–180C temperature range. Solid-state analysis was performed
by means of differential scanning calorimetry (DSC), hot stage microscopy (HSM), micro-Fourier transformed infrared spectroscopy
(MFTIR), and scanning electron microscopy (SEM).
The polymeric excipients were found to address in a reproducible manner the recrystallization of molten paracetamol within
the binary mixture into Form II or Form III. The degree of crystallinity of paracetamol in the binary mixtures, evaluated
from fusion enthalpies during the first and second heating scans, was influenced by the composition of the mixture, the nature
of the excipient and the thermal history. In particular, DSC on mixtures with cross-linked poly(vinylpyrrolidone) and hydroxypropylmethylcellulose
with drug contents below 65 and75%, respectively, evidenced the presence only of amorphous paracetamol after the cooling phase.
Microcrystalline cellulose was very effective in directing the recrystallization of molten paracetamol as Form II.
Authors:A. Fave, M. Bouchaour, A. Kaminski, S. Begrger, A. Ould-Abbas, and N. Chabane Sari
The fabrication of solar cells based on the transfer of a thin silicon film on a foreign substrate is an attractive way to
realise cheap and efficient photovoltaic devices. The aim of this work is to realise a
thin mono-crystalline silicon film on a double porous silicon layer in order to detach and transfer it on mullite. The first
step is the fabrication of a double porous silicon layer by electrochemical
anodisation using two different current densities. The low current leads to a low porosity layer and during annealing, the
recrystallisation of this layer allows epitaxial growth. The second current leads
to a high porosity which permits the transfer on to a low cost substrate. Liquid Phase Epitaxy (LPE) performed with indium
(or In+Ga) in the temperature range of 950–1050C leads to almost homogeneous
layers. Growth rate is about 0.35 μm min−1. Crystallinity of the grown epilayer is similar on porous silicon and on single crystal silicon. In this paper, we focus
on the realisation of porous silicon
sacrificial layer and subsequent LPE growth.
Authors:H. Enginar, P. Ünak, F. Yurt, and F. Zümrüt Biber
An oestrogen derivative 3,17-a-oestradiolyl propyl 1,4,8,11-tetraazacyclotetradecanyl-1-(4-methylbenzoic acid)ester (ESTCPTA) that is 3,17-a-oestradiolyl propinol coupled to 1-(4-methylbenzoic acid)1,4,8,11-tetraazacyclotetradecane (CPTA) was synthesized in five steps. The product was purified by recrystallization in ethyl alcohol, and analysed by NMR and IR spectroscopy. ESTCPTA was labeled with 99mTc and radio thin layer chromatography (RTLC) and radio-paper electrophoresis were used to determine the radiochemical yields. Specific activity was approximately 23.7 GBq/mmol and the labeling yield was over 95%. The biodistribution studies were performed on female Albino Wistar rats. The rats were sacricified by ether narcotization at certain time intervals and the activity of the organs was counted by a gamma counter. The activity per gram tissue was calculated and time activity curves were generated.
Carrier-free strontium and cesium isotopes were used to study the heterogeneous exchange of the systems strontium/strontium
carbonate and cesium/cesium tetraphenylborate. The elements under consideration are among the long-lived isotopes most desired
to be removed from waste solutions and consequently the use of heterogeneous exchange as an applied phenomenon for selective
fixation is possible. The results obtained show that the above two systems are unstable ones (i. e., undergoing either formation
or dissolution of the precipitated solid phase). New modified equations were proposed for quantitative calculation of the
fraction of exchange, using only radiometric data and avoiding the use of microanalytical data. The equations are useful for
all unstable systems, especially if no precise microquentitative method of analysis is known for the element under consideration.
Recrystallization and self-diffusion were proposed to explain the two parts characterizing the exchange curves.
A survey is given on the basic factor affecting the determination of90Sr in milk and bones by removal of the excess calcium by precipitation. Strong co-precipitation of calcium and strontium takes
place using fuming nitric acid, potassium hexacyano-ferrate, EDTA, ethanol-ether mixture and butanol-(1) due to partial precipitation,
recrystallization and adhesion processes where thepH value of the environment plays an improtant role. The obtained results show very limited applicability of these agents for
the determination of90Sr in biological materials because of low accuracy and reproducibility. This conclusion is especially valid for the method
of rapid determination of90Sr with EDTA according toWelford andSutton. In this work a method is given for the determination of90Sr in milk and bones using potassium hexacyanoferrate.
Authors:J. L. Pérez-Rodríguez, F. Franco, V. Ramírez-Valle, and L. A. Pérez-Maqueda
The differences on the thermal behaviour (DTG-DTA) of antigorite sample measured before and after sonication have been studied.
Sonication treatment produces negligible changes in the structure of the material but substantial textural modifications.
These modifications produce changes in the thermal behaviour of antigorite sample. Thus, it has been observed a decrease in
the dehydroxylation temperature as measured by DTG and DTA effects. For sonication treatments longer than 20 h, two new effects
of dehydroxylation are observed, the intensity of these two new effects increases with the sonication time showing a modification
in the release of structural OH. It has been also observed that the formation of forsterite takes place simultaneously with
the dehydroxylation of the antigorite. The high temperature exothermic effect is due to the recrystallization of forsterite
and not to the formation of forsterite as traditionally assumed. Modifications in the thermal dehydroxylation of antigorite
observed in this study are related to the pronounced decrease in particle size obtained by sonication.