The Experts below are selected from a list of 360 Experts worldwide ranked by ideXlab platform
Lynne S Taylor - One of the best experts on this subject based on the ideXlab platform.
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impact of polymers on the melt Crystal Growth Rate of indomethacin polymorphs
Crystal Growth & Design, 2017Co-Authors: Bin Tian, Wei Gao, Xiaoguang Tao, Xing Tang, Lynne S TaylorAbstract:Crystal Growth from amorphous drugs is of interest in the context of solubility enhancing formulations. Herein, the impact of polymers on the Crystal Growth of different polymorphs from the undercooled liquid was investigated using indomethacin (IDM) as a model compound and hydroxypropyl methylcellulose (HPMC), hydroxypropyl methylcellulose acetate succinate (HPMCAS) and polyvinylpyrrolidone (PVP) as polymeric inhibitors. Samples sandwiched between two coverslips were prepared by melt quenching and polymorphs were identified using Raman spectroscopy, hot stage microscopy and X-ray diffraction. Crystal Growth Rates of δ, α and γ polymorphs were measured in the absence and presence of polymers. Polymorphs grown from pure IDM melt showed different Crystal Growth Rates at a given temperature, that persisted when differences in the extent of undercooling were accounted for. The Crystal Growth Rates of IDM Crystals were reduced by the three polymers. At lower temperatures, the effectiveness of the polymers in i...
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impact of bile salts on solution Crystal Growth Rate and residual supersaturation of an active pharmaceutical ingredient
Crystal Growth & Design, 2017Co-Authors: James D Ormes, Michael Lowinger, Amanda K P Mann, Sanjaykumar Patel, J D Litster, Lynne S TaylorAbstract:Supersaturating formulations have become a popular approach to address the issue of inadequate aqueous solubility for small molecules. Given that prevention of nucleation may not be always possible, it is of particular interest to control Crystal Growth from supersatuRated solutions in order to maximize the extent of oral absorption of therapeutic agents. Bile salts are endogenous surfactants that are present in biorelevant dissolution media and can have direct impact on the in vivo performance of therapeutic agents due to their presence in the gastrointestinal tract. In this study, an in situ common history seeding method was implemented to provide seeds that better mimic Crystals formed from aqueous supersatuRated solutions. By forming seeds in situ and then regenerating supersaturation, we were able to probe the influence of biorelevant bile salts on telaprevir Crystal Growth Rates and secondary nucleation. The extent of Growth inhibition was found to vary with bile salt chemistry and aggregation level...
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acceleration of the Crystal Growth Rate of low molecular weight organic compounds in supercooled liquids in the presence of polyhydroxybutyRate
CrystEngComm, 2017Co-Authors: Takafumi Sato, Lynne S TaylorAbstract:Modification of the Crystallization kinetics of amorphous systems is an important topic, in particular in the area of drug delivery. Herein, we studied the impact of polyhydroxybutyRate (PHB), a biocompatible polymer with a low glass transition temperature (Tg), on Crystal Growth Rates from the supercooled liquid phase of a variety of organic compounds. Low levels of PHB were mixed with the supercooled liquid and Growth Rates were monitored using optical microscopy at several temperatures above the Tg of the mixture. Growth Rates were determined from a plot of Crystal size as a function of time. It was found that PHB inhibited the Growth of low Tg compounds, while acceleRated Crystal Growth was observed for compounds that had a much higher Tg (>50 °C) than the polymer. The observations were rationalized based on the extent of mobility differences between the Crystallizing compound and the polymer. This is the first reported example of a polymer having compound specific inhibitory or accelerator effects on Crystal Growth.
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influence of polymers on the Crystal Growth Rate of felodipine correlating adsorbed polymer surface coverage to solution Crystal Growth inhibition
Langmuir, 2015Co-Authors: Caitlin J Schram, Lynne S Taylor, Stephen P BeaudoinAbstract:The bioavailability of orally administered drugs that exhibit poor aqueous solubility can be enhanced with the use of supersaturating dosage forms. Stabilization of these forms by preventing or inhibiting Crystallization in solution is an important area of study. Polymers can be used to stabilize supersatuRated systems; however, the properties that impact their effectiveness as Crystal Growth Rate inhibitors are not yet fully understood. In this study, the impact of various polymers on the Crystal Growth Rate of felodipine and the conformation of these polymers adsorbed to Crystalline felodipine was investigated in order to gain a mechanistic understanding of Crystal Growth inhibition. It was determined that polymer hydrophobicity impacted polymer adsorption as well as adsorbed polymer conformation. Polymer conformation impacts its surface coverage, which was shown to directly correlate to the polymer's effectiveness as a Growth Rate inhibitor. By modeling this correlation, it is possible to predict polymer effectiveness given the surface coverage of the polymer.
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evaluation of the Crystal Growth Rate of felodipine polymorphs in the presence and absence of additives as a function of temperature
Crystal Growth & Design, 2013Co-Authors: Umesh S Kestur, Lynne S TaylorAbstract:The purpose of the present study was to compare the effect of temperature and a polymeric additive, poly(vinyl pyrrolidone) (PVP), on the Crystal Growth Rate of two polymorphs of felodipine from amorphous samples. Comparing the Growth Rates of the two polymorphs in the presence of PVP should provide mechanistic information on whether PVP inhibits Crystal Growth of felodipine by interacting at the Crystal surface of felodipine or in the amorphous regions. Optical microscopy was used to measure the Growth Rates at various temperatures in the range of 18–100 °C for the form I polymorph and 40–100 °C for the form II polymorph. Both surface and bulk Growth Rates for the form I polymorph were evaluated, while for the form II polymorph, only the bulk Growth Rate could be studied. No difference in the Growth Rate between surface and bulk Crystals of form I was observed at higher temperatures (>70 °C). However, below 65 °C the surface Crystal Growth Rate was faster than the bulk Crystal Growth Rate. Another mode o...
Tiefeng Xu - One of the best experts on this subject based on the ideXlab platform.
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Crystallization kinetics with fragile to strong crossover in zn sb te supercooled phase change liquids
Applied Physics Letters, 2019Co-Authors: Jierong Gu, Yimin Chen, Qian Zhang, Guoxiang Wang, Rongping Wang, Xiang Shen, Junqiang Wang, Tiefeng XuAbstract:Understanding Crystallization kinetics is essential to select the high-performance materials for phase-change memory. By ultrafast differential scanning calorimetry, we found the distinct fragile-to-strong crossover Crystallization kinetics in ZnSb and Zn28Sb54Te18 supercooled liquids. Zn28Sb54Te18 inherits the excellent thermal stability around glass transition from ZnSb and exhibits faster Crystal Growth Rate close to melting temperature (Umax is 9.1 m s−1) and larger crossover magnitude f (2.3), compared to the typical fragile-to-strong crossover material Ag-In-Sb2Te. Such a material with a distinct fragile-to-strong crossover is helpful to improve their thermal stability nearby glass transition temperature and acceleRate the phase transition speed close to melting temperature.
Lijun Liu - One of the best experts on this subject based on the ideXlab platform.
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influence of an insulation partition on a seeded directional solidification process for quasi single Crystalline silicon ingot for high efficiency solar cells
Solar Energy Materials and Solar Cells, 2012Co-Authors: Genxiang Zhong, Xinming Huang, Lei Sun, Lijun LiuAbstract:Abstract An insulation partition was designed in a seeded directional solidification (DS) furnace of industrial-size to produce quasi-single Crystalline silicon ingot for solar cells of high efficiency. We used a transient global model to study the effects of the insulation partition block on the temperature and thermal stress fields in the solidified silicon ingot during the solidification process. We validated the transient global model by comparing the calculations with the experimental measurements. Simulation results show that an insulation partition block can significantly reduce the total heating power consumption and influence the temperature and velocity fields in the silicon melt. We also found that the melt-Crystal interface (m–c interface) shape changes from concave to convex to the melt with a larger Crystal Growth Rate with an insulation partition, while it always remains flat with a smaller Crystal Growth Rate without a partition block. The axial temperature gradient and thermal stress in the grown silicon Crystal increased with a partition block. The solar cells from the grown quasi-single Crystalline silicon ingot exhibited higher short-circuit current (Isc) and open-circuit voltage (Voc). The average conversion efficiency of solar cells is increased to 17.8% and about 1.2% more than that based on mc-Si ingot from the conventional furnace.
Norimasa Okui - One of the best experts on this subject based on the ideXlab platform.
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temperature dependence of Crystal Growth Rate for α and β forms of isotactic polypropylene
Polymer Journal, 2008Co-Authors: Kayo Nakamura, Satoko Shimizu, Susume Umemoto, Annette Thierry, Bernard Lotz, Norimasa OkuiAbstract:The Crystal Growth Rate of the α1, α2 and β forms of isotactic polypropylene (iPP) and their morphological changes were studied in a wide range of Crystallization temperatures. The temperature dependence of the Crystal Growth Rate of the α1 form showed a bell-shaped curve with the maximum Growth Rate (Gmax) at 70 °C. The Crystal Growth Rate of the β form induced by calcium pimelate also showed a bell-shaped curve with Gmax at 79 °C. Two crossover points on the Growth Rate curve from the α1 form to the β form or vice versa were observed at 90 °C and 133 °C, respectively. Tear-drop shaped spherulites were observed at temperatures between the two crossover points. Electron diffraction patterns showed the high ordered structure of the α2 form for thin films Crystallized at 140 °C. The α2 fraction became detectable in X-ray diffraction pattern for temperatures above 110 °C. The α2 fraction increased with Crystallization temperature and satuRated to 100% at about 140 °C. In the temperature region from 110 °C to 140 °C, several Crystal Growth Rates were found at the same Crystallization temperature. The Growth Rate variations could be associated with the co-Crystallization of the α1 and α2 forms. Above 140 °C, the Growth Rate variations disappeared, since the fraction of the α2 reached to 100%. The extrapolated Gmax of the α2 showed at 72 °C.
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master curve of Crystal Growth Rate and its corresponding state in polymeric materials
Polymer, 2002Co-Authors: Sususmu Umemoto, Norimasa OkuiAbstract:Abstract The temperature dependence of linear Crystal Growth Rate (G) for various polymers shows a bell shape with the maximum Growth Rate (Gmax). The Gmax shows remarkable molecular weight dependence. The Gmax was formulated on the basis of a Crystallization theory, both for Arrhenius and WLF expressions in the molecular transport term. The plots of the reduced Growth Rate (G/Gmax) against the reduced temperature (T/Tcmax) for a given polymer showed a single master curve without molecular weight dependence. The ratio of G0/Gmax gave a constant value for each polymer, indicating a material constant. On the basis of Gmax for many polymers, a universal master curve was observed when the ratio of ln(G/Gmax)/ln(G0/Gmax) was plotted against the reduced temperature (T/Tcmax).
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molecular weight dependence of Crystal Growth Rate and its degree of supercooling effect
Journal of Macromolecular Science Part B, 2002Co-Authors: Susumu Umemoto, N Kobayashi, Norimasa OkuiAbstract:The molecular weight (MW) dependence of the linear Crystal Growth Rate (G) and the influence of the supercooling on the relationship between MW and G at a given supercooling were studied for poly(ethylene succinate). The spherulite Growth Rate was measured over a wide range of temperature. It had a bell-shape with a maximum Growth Rate (G max) that showed a remarkable MW dependence. The MW dependence of G max was mainly a consequence of the MW dependence of G o (pre-exponential factor of the Crystal Growth Rate). The G max increased first with MW up to 3000 and then decreased. The maximum of G max at 3000 was attributed to the transition from extended chain Crystallization (ECC) to folded chain Crystallization (FCC). The MW dependence of G max was expressed as α was a constant depending on the morphological features of the Crystallization. The value of α was nearly unity for ECC below MW of 3000 and α was about −0.5 for FCC above MW of 3000. However, the value of α was strongly dependent on the degree of ...
Jierong Gu - One of the best experts on this subject based on the ideXlab platform.
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Crystallization kinetics with fragile to strong crossover in zn sb te supercooled phase change liquids
Applied Physics Letters, 2019Co-Authors: Jierong Gu, Yimin Chen, Qian Zhang, Guoxiang Wang, Rongping Wang, Xiang Shen, Junqiang Wang, Tiefeng XuAbstract:Understanding Crystallization kinetics is essential to select the high-performance materials for phase-change memory. By ultrafast differential scanning calorimetry, we found the distinct fragile-to-strong crossover Crystallization kinetics in ZnSb and Zn28Sb54Te18 supercooled liquids. Zn28Sb54Te18 inherits the excellent thermal stability around glass transition from ZnSb and exhibits faster Crystal Growth Rate close to melting temperature (Umax is 9.1 m s−1) and larger crossover magnitude f (2.3), compared to the typical fragile-to-strong crossover material Ag-In-Sb2Te. Such a material with a distinct fragile-to-strong crossover is helpful to improve their thermal stability nearby glass transition temperature and acceleRate the phase transition speed close to melting temperature.