Fast Differential Scanning Calorimetry Research Articles

Kinetics of nucleation and crystallization in poly(ɛ-caprolactone) (PCL)

The recently developed differential fast scanning calorimetry (DFSC) is used for a new look at the crystal growth of poly(ɛ-caprolactone) (PCL) from 185 K, below the glass transition temperature, to 330 K, close to the equilibrium melting temperature. The DFSC allows temperature control of the sample and determination of its heat capacity using heating rates from 50 to 50,000 K/s. The crystal nucleation and crystallization halftimes were determined simultaneously. The obtained halftimes cover a range from 3 × 10 −2 s (nucleation at 215 K) to 3 × 10 9 s (crystallization at 185 K). After attempting to analyze the experiments with the classical nucleation and growth model, developed for systems consisting of small molecules, a new methodology is described which addresses the specific problems of crystallization of flexible linear macromolecules. The key problems which are attempted to be resolved concern the differences between the structures of the various entities identified and their specific role in the mechanism of growth. The structures range from configurations having practically unmeasurable latent heats of ordering (nuclei) to being clearly-recognizable, ordered species with rather sharp disordering endotherms in the temperature range from the glass transition to equilibrium melting for increasingly perfect and larger crystals. The mechanisms and kinetics of growth involve also a detailed understanding of the interaction with the surrounding rigid-amorphous fraction (RAF) in dependence of crystal size and perfection.

An investigation into the crystallisation behaviour of an amorphous cryomilled pharmaceutical material above and below the glass transition temperature

The aim of this study was to evaluate the glass transition and recrystallisation of a cryomilled drug, TMC125 (Etravirine), with particular emphasis on assessing the physical stability of the drug above and below the glass transition temperature. DSC (conventional, fast and modulated temperature) and variable temperature ATR–FTIR spectroscopy were employed to monitor the glass transition and crystallisation behaviour of the material. The isothermal crystallisation behaviour was investigated at temperatures below Tg. The humidity-induced crystallisation behaviour of the material was evaluated using dynamic vapour sorption (DVS). The glass transition (99°C) was measured in isolation from the crystallisation process using fast DSC, while ATR–FTIR allowed identification of the polymorph formed on recrystallisation. At a heating rate of 0.2°C/min, the onset temperature of the crystallisation exotherm (67°C) was 32°C below Tg. Evidence is presented for incomplete crystallisation under isothermal conditions. In conclusion, the study has ascertained the crystallisation profile of cryomilled Etravirine under both isothermal and scanning conditions, with the material showing marked physical instability below the measured Tg. © 2009 Wiley-Liss, Inc. and the American Pharmacists Association J Pharm Sci 99:196–208, 2010

Nickel silicides and germanides: Phases formation, kinetics and thermal expansion

Thin film germanide reactions are often declared to be the same as silicides reactions which were far more studied. In this paper, we present a comparative study of the phase formation and kinetics of nickel silicides and nickel germanides by several experimental techniques. The samples, composed of a nanometric nickel film (50 nm) deposited on silicon or germanium substrates, have been examined by several “ in situ” real time measurements: X-ray diffraction (XRD), and differential scanning calorimetry (DSC). These original DSC and “ in situ” XRD measurements have allowed us to determine the interfacial reaction rate for Ni 2Si using a linear-parabolic law. During the relatively fast DSC ramp, the growth is mainly controlled by the interface while isothermal heat treatments lead to a mainly diffusion control. In contrary to what is usually found for nickel silicide and germanides, a simultaneous growth of Ni 5Ge 3 and NiGe has been found during “ in situ” XRD measurements. The different behavior between the Ni–Si system (sequential formation) and the Ni–Ge system (simultaneous formation) is interpreted in term of diffusion and interface controlled growth. In addition, in devices, the film stability and the stress of the silicides or the germanides can be affected by an important physical characteristic that is the anisotropy of dilatation coefficient. In this work, the lattice parameters and linear thermal expansion coefficients ( γ a , γ b and γ c ) of the orthorhombic Ni(Si 1 − X Ge X ) compounds with 0 ≤ X ≤ 1 were determined from high temperature X-ray diffraction data (298–1073 K). A negative thermal expansion coefficient of the b lattice parameter of Ni(Si 1 − X Ge X ) for all the studied Ge concentration was observed: the magnitude of this negative thermal expansion coefficient is decreasing with increasing Ge concentration.

Fast Scan Differential Scanning Calorimetry Distinguishes Melting, Melting-Degradation/Sublimation and Thermal Stability of Drugs

Abstract In order to establish a structure and property (melting and oxidative or thermal degradation, or both) relationship for a United States Pharmacopeias (USP) set of standard drugs, they were evaluated by fast scan differential scanning calorimetry. A critical problem in characterizing the endothermic melting of a drug is to determine the melting range and if a chemical melts and immediately degrades. The stability of standard drugs is based on a comparison of their thermal properties at widely varying ramp or heating rates from 10 to 100°C/min. A stable crystalline drug has an obvious melting endotherm followed by a stable baseline. An unstable crystalline drug melts and immediately degrades as viewed by a shifting melt endotherm with heating rate. The USP thermally stable standards evaluated in this study include vanillin (melt temperature, Tm, 80.4°C), acetanilide (Tm, 114°C), acetophenetidin (Tm, 135°C), sulfanilamide (Tm, 165°C), sulfapyridine (Tm, 191°C), and caffeine (Tm, 235°C and Tsublimation, <220°C). In addition to the USP samples a number of commercial and model drugs, like benzoic acid (Tm, 122°C and Tsublimation, <120°C), lidocaine.HCl and procaine.HCl were also examined. Their melt profiles were ranked as stable or unstable post fusion by the fast scan DSC technique and are reported.

Gelatinization of Starch in Excess Water: Beyond the Melting of Lamellar Crystallites. A Combined Wide- and Small-Angle X-ray Scattering Study

The gelatinization of waxy rice, regular rice, and potato starch suspensions (66% w/w moisture) was investigated by real-time small-angle X-ray scattering (SAXS) and wide-angle X-ray diffraction (WAXD) during heating and by fast ramp differential scanning calorimetry (DSC). The high-angle tail of the SAXS patterns suggested the transition from surface to mass fractal structures in the DSC gelatinization range. Amylose plays a major role in determining the dimensions of the self-similar structures that develop during this process as the characteristic power-law scattering behavior extends to lower scattering angles for regular than for waxy starches. Crystallinity of A-type starches is lost in the temperature region roughly corresponding to the DSC gelatinization range. At the end of the gelatinization endotherm, the B-type potato starch showed residual crystallinity (WAXD), while SAXS-patterns exhibited features of remaining lamellar stacks. Results indicate that the melting of amylopectin crystallites during gelatinization is accompanied by the (exothermic) formation of amorphous networks.

Crystallization and melting behavior of three biodegradable poly(alkylene succinates). A comparative study

Polyesters based on succinic acid and respective aliphatic diols, with 2–4 methylene groups were synthesized by melt polycondensation. Crystallization and melting behaviour of samples having the same molecular weight were studied. The odd–even effect was observed for the melting temperatures of these polymers. Poly(propylene succinate) exhibited the slower crystallization rates and lower degree of crystallinity, among these polyesters. In contrast poly(butylene succinate) showed the faster crystallization rates and higher degree of crystallinity. Multiple melting of the isothermally crystallized samples was attributed to partial melting re-crystallization and re-melting, as was revealed by MTDSC measurements and observations at fast DSC heating scans. The equilibrium melting points were found to be 114, 133.5 and 58 °C for PESu, PBSu and PPSu respectively. Also, the corresponding values for enthalpy of fusion were 180, 210 and 140 J/g. Spherulitic growth rates were analysed and the regime transition of PESu and PBSu was studied.

Probing Glass Transition of Ultrathin Polymer Films at a Time Scale of Seconds Using Fast Differential Scanning Calorimetry

Ultrasensitive, thin-film, differential scanning calorimetry is used to determine the glass-transition temperature of 3−400 nm thick, spin-cast films of polystyrene, poly (2-vinyl pyridine), and poly (methyl methacrylate) on a platinum surface. The technique used here is modified to characterize the glass transition over a time scale of seconds rather than milliseconds. No appreciable dependence of the glass-transition temperature on thickness is observed over the entire range used. The results are discussed in comparison with previous calorimetric measurements, characterized by the glass-transition time scale of milliseconds.

Synthesis and structural characterization of nonanuclear lanthanide complexes.

A series of nonanuclear lanthanide oxo-hydroxo complexes of the general formula [Ln(9)(mu(4)-O)(2)(mu(3)-OH)(8)(mu-BA)(8)(BA)(8)](-)[HN(CH(2)CH(3))(3)](+).(CH(3)OH)(2)(CHCl(3)) (BA = benzoylacetone; Ln = Sm, 1; Eu, 2; Gd, 3; Dy, 4; Er, 5) were prepared by the reaction of hydrous lanthanide trichlorides with benzoylacetone in the presence of triethylamine in methanol and recrystallized from chloroform/methanol (1:10) at room temperature. These five compounds are isomorphous. Crystal data for 1: cubic, Pn3n; T = 180 K; a = 33.8652(4) A; V = 38838.4(8) A(3); Z = 6; D(calcd) = 1.125 g cm(-)(3); R1 = 3.37%. Crystal data for 2: cubic, Pn3n; T = 180 K; a = 33.8252(8) A; V = 38700.9(16) A(3); Z = 6; D(calcd) = 1.133 g cm(-)(3); R1 = 4.97%. Crystal data for 3: cubic, Pn3n; T = 180 K; a = 33.7061(6) A; V = 38293.5(12) A(3); Z = 6; D(calcd) = 1.157 g cm(-)(3); R1 = 5.13%. Crystal data for 4: cubic, Pn3n; T = 180 K; a = 33.5900(7) A; V = 37899.2(14) A(3); Z = 6; D(calcd) = 1.182 g cm(-)(3); R1 = 4.03%. Crystal data for 5: cubic, Pn3n; T = 180 K; a = 33.5054(8) A; V = 37613.6(16) A(3); Z = 6; D(calcd) = 1.202 g cm(-)(3); R1 = 4.86%. The core of the anionic cluster comprises two vertex-sharing square-pyramidal [Ln(5)(mu(4)-O)(mu(3)-OH)(4)](9+) units. The compounds were characterized by elemental analysis, IR, fast atom bombardment mass spectra, thermogravimetry, and differential scanning calorimetry. The thermal analysis indicated that the nonanuclear species were stable up to 150 degrees C. Luminescence spectra of 2 and magnetic properties of 1-5 were also studied.

Thermal and Dynamic-Mechanical Characterization of Uni- and Biaxially Oriented Polypropylene Films

The effect of uni- and biaxial orientation in the morphology of polypropylene films has been investigated by thermal, dynamic-mechanical, X-ray pole figure and diffraction patterns. In uniaxial oriented films the level of damping is roughly three times higher in the MD direction than it is in the TD direction. The stretching always produces crystals of the α form independently of the starting type. Fast DSC scans show two melting peaks indicative of two crystalline species. The Fujiyama et al. model for the crystalline structure can be also applied to the uniaxially stretched films. Upon biaxially orienting, the folded lamellae crystals (kebabs) are the ones to support all the force applied, and when their maximum level of stress slippage is reached they deform following the Peterlin's model, forming a new shish structure. These new shishes are aligned to the TD direction and by linking the original shishes in the MD direction produce a planar orthogonal net of linked shish structures. The space among the shishes is filled with small and imperfect folded lamellae with c-axis in the film plane and preferentially oriented in the MD and TD directions, keeping constant crystallinity density throughout.

Polymorphism of the fast ionic conductor Li 2MnBr 4-neutron diffraction and differential scanning calorimetry

The trimorphic Li 2MnBr 4 has been studied by neutron powder diffraction and differential scanning calorimetry (DSC) in order to prove the nature of the high lithium ion conductivity of this compound. The room temperature polymorph ( oI 28) crystallizes in a hitherto unknown ordered NaCl defect structure, whilst the high-temperature phases exhibit a modified Zr 3S 4 (space group Fd3m, z = 8) and a disordered deficient NaCl type structure, respectively. The structural data of the high temperature polymorphs at 350 and 500 °C are communicated (a = 1123.72(5) and 567.31(7) pm, u = 0.2540(3) (HTM I), R I - 4.41 and 4.26 %, respectively). The phase transitions at 545 K (first order) and 758 K (second order) (heat of transition 3 and 2.7 J g −1, entropy changes 2 and 1.4 J mol −1 K −1) and the ionic conductivities (as compared to the larger ones of Li 2MnCl 4) are discussed.

Fast DSC applied to the crystallization of polypropylene

In an effort to find the limit of crystallization of polypropylene, a series of quantitative and semiquantitative DSC experiments at rates up to 10,000 deg/min are described. Even at these fast rates polypropylene crystallized on cooling between 350±15 K and 280±6 K. No “fully amorphous” polypropylene was produced. No initial stage crystallization to the condis state could be proven by quenching after partial crystallization.