Combining Fast-Scan DSC with Molecular Simulations
Contents
Combine Flash DSC with molecular simulations
Some applications of Flash DSC
Fast-scan differential scanning calorimeter (DSC)
Principle of DSC
The measured temperature difference between the reference and the sample calorimeters should be proportional to the heat-flow rate (HF=dQ/dt). A linear response of the heat-flow rate to the heating rate (q=dT/dt) can approximately give the sample heat capacity:
Fast-scan chip-calorimeter
By significantly reducing the sample mass and hence the thermal lag, the sample temperature can be more precisely controlled on a chip-sensor. Thus, those fast crystallization behaviors at low temperatures or those fast annealing behaviors at high temperatures can be monitored by this advanced DSC technique.
Flash DSC
First commercialized chip-calorimeter was made by Mettler-Toledo AG.
Sample mass: 10 ng to 1 μg
Heating rates: 30 to 2,400,000 ℃/min
Cooling rates: 6 to 240,000 ℃/min
Temperature range: -95 to 450 ℃
Some references
[1] Zhuravlev E, Schick C. Thermochim Acta, 2010, 505(1-2): 1-13.
[2] Mathot V, Pyda M, Pijpers T, Vanden Poel G, van de Kerkhof E, van Herwaardeng S, van Herwaardeng F, Leenaers A. Thermochim Acta, 2011, 522(1-2): 36 -45.
[3] Iervolino E, van Herwaarden A W, van Herwaarden F G, van de Kerkhof E, van Grinsven P P W, Leenaers A C H I, Mathot V B F, Sarro P M. Thermochim Acta, 2011, 5221-2): 53 -59.
[4] van Herwaarden S, Iervolino E,van Herwaarden F, Wijffels T, Leenaers A, Mathot V B F. Thermochim Acta, 2011, 522(1-2): 46-52.
Combining Flash DSC with molecular simulations
A Review
Jiang, X.-M.; Li, Z.-L.; Gao, H.-H.; Hu, W.-B. Combining fast-scan chip-calorimetry with molecular simulations to investigate polymer crystal melting. Mathot, V. B. F.; Schick, C. (Ed): Fast Scanning Calorimetry, Springer. Book link
[ABSTRACT] Reversible and irreversible melting of lamellar polymer crystals have been studied by means of combining fast-scan chip calorimetry of polymorphic isotactic polypropylenes with dynamic Monte Carlo simulations of polymer chains on a lattice. Different polymorphic phases of polypropylenes are linked to variation of the chain mobility in the crystals of the same species, and this mobility appears as an adjustable parameter in parallel molecular simulations. Such a combination of two different approaches having complemental advantages facilitates a better understanding of the complex phase transition behaviors of lamellar polymer crystals.
Irreversible melting
Gao, H.-H.; Wang, J.; Schick, C.; Toda, A.; Zhou, D.-S.; Hu, W.-B.* Combining fast-scan chip-calorimeter with molecular simulations to investigate superheating behaviors of lamellar polymer crystals. Polymer 55, 4307-4312(2014). Journal Link
[ABSTRACT] We studied the power-law heating-rate dependence of superheating for the melting of alpha- and beta-crystals of isotactic polypropylene by means of chip-calorimeter, and expanded our parallel observation to higher heating rates by means of molecular simulations. We observed that, at low heating rates, the melting of lamellar crystals after thickened via melting-recrystallization exhibits no power-law-dependent superheating; at medium heating rates, the melting of crystals after thickened via chain-sliding diffusion exhibits the power-law-dependent superheating with the power indexes sensitive to chain mobility in the crystals; while at high heating rates, the zero-entropy-production melting of crystals without further thickening maintains the power-law-dependent superheating but with the power indexes uniform at an upper-limit 0.375. We attributed the index 0.375 to a result combining local intramolecular nucleation and global roughening growth at the lateral surface of lamellar crystals, which dominate the kinetics of crystal growth and melting of polymer crystals at high temperatures.
Reversible melting
Jiang, X.-M.; Li, Z.-L.; Wang, J.; Gao, H.-H.; Zhou, D.-S.; Hu, W.-B.* Combining TMDSC measurements between chip-calorimeter and molecular simulation to study reversible melting of polymer crystals. Thermothimica Acta 603, 79-84(2015). Journal Link
[ABSTRACT] Reversible melting is a phenomenon unique to polymer crystals, which raises an excess reversing heat capacity near their melting points. By means of temperature-modulated differential scanning calorimetry (TMDSC) measurements with an expanded frequency range in chip-calorimeter, we studied reversing heat capacities of alpha- and beta-form crystals of isotactic polypropylene. We attributed their differences at high temperatures and low frequencies to variable chain mobility in these two crystals. We further performed parallel dynamic Monte Carlo simulations of lattice polymers with variable chain mobility in the crystals to confirm this attribution. Our observations provide the first evidence on the role of chain mobility in the microscopic mechanism of reversible melting at the fold-end surfaces of lamellar polymer crystals.
Some Applications of Flash DSC
Double melting peaks
Li, Z.-L.; Jiang, X.-M.; Gao, H.-H.; Zhou, D.-S.; Hu, W.-B.* Fast-scan chip-calorimeter measurement on the melting behaviors of melt-crystallized syndiotactic polystyrene. J. Thermal Anal. & Calorimetry 118, 1531-1536(2014). Journal Link
[ABSTRACT] We employed fast-scan chip-calorimeter (FSC) measurement (Flash DSC1) to study the melting of syndiotactic polystyrene after melt-crystallized at various cooling rates as well as after isothermally crystallized at various high temperatures. We attributed the observed double melting peak to a melting-recrystallization process of beta-form crystals upon heating, as evidenced by their variations with different cooling and heating rates. Our experiments demonstrated the advantages of FSC techniques in the investigation of crystallization and melting behaviors of polymer materials.
Comparing cyclic to linear PCL
Wang, J.; Li, Z.-L.; Pérez, R. A.; Müller, A. J.; Zhang, B.; Grayson, S. M.; Hu, W.-B.* Comparing crystallization rates between linear and cyclic poly(epsilon-caprolactones) via fast-scan chip-calorimeter measurements. Polymer 63, 34-40(2015). Journal Link
[ABSTRACT] The vital role of chain ends in the crystallization of linear polymers can be understood by unraveling the mechanisms of crystallization of cyclic polymers. A commercial chip-calorimeter Flash DSC1 was employed to compare the nucleation and overall crystallization rates between linear and cyclic poly(epsilon-caprolactones) (PCL) with similar molar masses of around 2 kg/mol. In the high temperature region, faster overall crystallization of cyclic PCL relative to linear PCL is consistent with previously reported results employing conventional DSC. In the low temperature region, the cyclic PCL exhibits a lower onset temperature of homogenous nucleation when compared to linear PCL analogs. This result was attributed to a higher mobility of free chain ends in the linear PCL as compared to cyclic PCL. A simplified data-treatment method on the nucleation half-time has been proposed.
Li, Z.-L.; Wang, J.; Pérez, R. A.; Müller, A. J.; Zhang, B.; Grayson, S. M.; Hu, W.-B.* Non-monotonic molecular weight dependence of crystallization rates of linear and cyclic poly(epsilon-caprolactone)s in a wide temperature range. Polymer International 65(9), 1074-1079(2016). Journal link
[ABSTRACT] Industrial processing of polymeric materials normally involves fast cooling. We employed a commercial chip calorimeter (Flash DSC) to investigate the crystallization and annealing behaviors of poly(vinylidene fluoride) (PVDF) under fast cooling towards low temperatures. The corresponding polymorphic crystalline phases were identified by wide-angle X-ray diffraction and Fourier transform infrared spectroscopy. The results demonstrated that a cooling process faster than -500 K s-1 results in major thick beta-phase crystallites at high temperatures; in addition, subsequent isothermal annealing at low temperatures slowly generates minor thin beta-phase crystallites rich with trans conformation. Our observations facilitate a better understanding of structural optimization during PVDF processing for its ferroelectric and piezo-response performance in versatile applications.
PVDF-based copolymers
Chen, Y.-X.; Chen, X.; Zhou, D.-S.; Shen, Q.-D.;* Hu, W.-B.* Low-temperature crystallization of P(VDF-TrFE-CFE) studied by Flash DSC. Polymer 84, 319-327(2016). Journal link
[ABSTRACT] We employed commercially available chip-calorimeter Flash DSC1 to investigate the low-temperature crystallization behaviors of random copolymer P(VDF-TrFE-CFE) (poly(vinylidenefluoride-trifluoroethylene-chlorofluoroethylene)), and compared them to the parallel results of P(VDF-TrFE). The resulted ferroelectric crystalline phases were identified by WAXD and FTIR. We found that, although our P(VDF-TrFE-CFE) contains higher content of VDF sequences than our P(VDF-TrFE), it performs crystallization of the ferroelectric phase at low temperatures much slower, and even exhibits cold crystallization upon heating back from fast cooling. We attributed the slowness to the effect of chemical confinement of large CFE comonomers. Our results facilitate better understanding of structural optimization for the electroactive applications of PVDF-based random copolymers.
Chen, Y.-X.; Shen, Q.-D.;* Hu, W.-B.* Primary and secondary crystallization of fast-cooled PVDF studied by Flash DSC, WAXD and FTIR. Polymer International 65(4), 387-392(2016). Journal link
[ABSTRACT] By using a commercial fast-scan chip-calorimeter, the effect of molecular weight on the isothermal crystallization rates of linear and cyclic poly(epsilon-caprolactone) samples (L-PCLs and C-PCLs) is investigated. The results confirm the non-monotonic molecular weight dependence of the crystallization rates of both L-PCLs and C-PCLs over a wide temperature range, previously observed only in the high temperature range, in which the medium molecular weight PCLs exhibit the highest crystallization rate. Chain-end effects of L-PCL with medium molecular weights induce faster crystallization rates in specific low temperature regions, in comparison to that for counterpart C-PCL. This phenomenon no longer exists in high molecular weight samples because of ‘diluted’ chain-end effects in long chain samples.
