Molecular mobility of amorphous S-flurbiprofen: a dielectric relaxation spectroscopy approach.
Molecular mobility of amorphous S-flurbiprofen: a dielectric relaxation spectroscopy approach.
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无定形 S-氟比洛芬的分子迁移率：介电弛豫光谱方法。
DOI：
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发表时间：
2014
影响因子：
4.9
通讯作者：
N. T. Correia
中科院分区：
文献类型：
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作者：
A. C. Rodrigues;M. T. Viciosa;F. Danède;F. Affouard;N. T. Correia
采用熔体急冷/冷却法制备了S氟比洛芬非晶态制剂。在等时模式、常规和温度调制差示扫描量热仪(TMDSC)研究中进行的介电测量显示了玻璃化转变、重结晶和熔化。在宽温度(183~408K)和频率(10(-1)~10(6)Hz)范围内，用等温介电弛豫谱实验(等温模式)综合表征了表征非晶态S-氟比洛芬复杂分子动力学的不同参数：α松弛宽度(βkww)、α松弛时间(τα)与温度的关系、脆性指数(M)、α松弛与β二次松弛的关系、以及在Tg附近深过冷区结构弛豫时间与直流电导率(σDC)之间的德拜-斯托克斯-爱因斯坦关系的破裂。在玻璃态和过冷态观察到的β驰豫是真正的Johari-Goldstein过程，归因于局域运动，并被认为是耦合模型中所提出的α驰豫的前兆。在Tg处观察到α驰豫和β驰豫之间的间隔约为60年；这种解耦随着温度的升高而减小，这两个过程在Tαβ=295K时合并。α驰豫时间τα的温度依赖于两个Vogel-Fulcher-Tammann-Hesse方程，这两个方程在Tb=290K的交叉温度附近相交，接近α驰豫和β驰豫的分裂温度。从低温VFTH方程估算出的Tg(Drs)=265.2(在τα=100Tg时)与量热值(Tg，起始温度，TMDSC=265.6 K)很好地吻合，并计算出脆性或陡度指数m=113，从而将S-氟比洛芬归类为易碎玻璃体。α弛豫谱具有较大的非指数特征(βkww=0.52)。观察到DSElog10σDc-log10τ关系的破裂，表明随着玻璃化转变温度Tg的升高，平移离子运动比取向分子运动增强。
Amorphous S-flurbiprofen was obtained by the melt quench/cooling method. Dielectric measurements performed in the isochronal mode, conventional and temperature modulated differential scanning calorimetry (TMDSC) studies showed a glass transition, recrystallization, and melting. The different parameters characterizing the complex molecular dynamics of amorphous S-flurbiprofen that can have influence on crystallization and stability were comprehensively characterized by dielectric relaxation spectroscopy experiments (isothermal mode) covering a wide temperature (183 to 408 K) and frequency range (10(-1) to 10(6) Hz): width of the α-relaxation (βKWW), temperature dependence of α-relaxation times (τα), fragility index (m), relation of the α-relaxation with the β-secondary relaxation, and the breakdown of the Debye-Stokes-Einstein (DSE) relationship between the structural relaxation time and dc-conductivity (σdc) at deep undercooling close to Tg. The β-relaxation, observed in the glassy as well as in the supercooled state was identified as the genuine Johari-Goldstein process, attributed to localized motions and regarded as the precursor of the α-relaxation as suggested in the coupling model. A separation of about 6 decades between the α- and β-relaxation was observed at Tg; this decoupling decreased on increasing temperature, and both processes merged at Tαβ = 295 K. The temperature dependence of the α-relaxation time, τα, was described by two Vogel-Fulcher-Tammann-Hesse equations, which intercept at a crossover temperature, TB = 290 K, close to the splitting temperature between the α- and β-relaxation. From the low temperature VFTH equation, a Tg(DRS) = 265.2 was estimated (at τα =100 s) in good agreement with the calorimetric value (Tg,onset,TMDSC = 265.6 K), and a fragility or steepness index m = 113 was calculated allowing to classify S-flurbiprofen as a fragile glass former. The α-relaxation spectra were found to be characterized by a relatively large degree of nonexponentiality (βKWW = 0.52). A breakdown of the DSE log10 σdc - log10 τ relation was observed revealing an enhancement of translational ionic motions in comparison with the orientational molecular motions as the glass transition temperature Tg is approached from above.