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Chain dynamics heterogeneity in Plasticized Poly(vinyl butyral)(PVB) as Elucidated by Solid-State NMR

Chinese Journal of Polymer Science 2024年第1期42卷 113-124,I0010页

作者： Jing Lv Xu Chen Zi-Shuo Wu Ya-Hui Li Wei Chen National Synchrotron Radiation Laboratory Anhui Provincial Engineering Laboratory of Advanced Functional Polymer FilmCAS Key Laboratory of Soft Matter ChemistryUniversity of Scienceand Technology of ChinaHefei 230026China

The chain dynamics heterogeneity of the poly(vinyl butyral)(PVB) plasticized by triethylene glycol bis(2-ethylhexa noate)(TEG-EH) was investigated by various solid-state NMR techniques.The plasticized PVB shows two domains in distinct molecular dynamics differences,namely,rigid and soft domains,where the latter is the plasticizer-rich domain.The time domain low field NMR was first used to investigate the dynamics heterogeneity of the plasticized PVB,and the results show the decreasing activated energy of components in the soft domain of plasticized PVB(E_a=20.2 kJ/mol) as compared with that of the pristine one(E_a=24.3 kJ/mol).Detailed dynamics heterogeneity was obtained by high-field NMR with site-specific features.The quadrupole-echo ~2H-NMR was adopted to elucidate the dynamics heterogeneity of the vinyl alcohol(VA) units,where only the hydroxyl group of VA is deuterated.The ~1H-^(13)C WISE NMR spectra show that there is not much difference in the mobility of the VB unit in PVB with and without plasticizer,whereas the glass transition temperature differed by approximately 53℃.This is further supported by Torchia's T_1 relaxation measurements.The origin of such an unusual phenomenon is attributed to the critical role of the remaining VA(~22%) in the soft domain,where the VA units locally aggregate through hydrogen bonding.Also,the existence of a mobility gradient in the VB unit has been demonstrated.Moreover,the mobility difference for VB with different stereo-geometry(meso or racemic conformation) is observed for the first time.This indicates the importance of modulating the ratio of meso over racemic VB for controlling the macroscopic perfo rmance of PVB.

关键词： Poly(vinyl butyral) dynamics heterogeneity Plasticizer Solid state NMR

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Abnormal breakdown of Stokes–Einstein relation in liquid aluminium

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Chinese Physics B 2017年第1期26卷 333-343页

作者：李晨辉韩秀君栾英伟李建国 Laboratory of Advanced Materials Solidification School of Materials Science and Engineering Shanghai Jiao Tong University Shanghai 200240 China

We present the results of systematic molecular dynamics simulations of pure aluminium melt with a well-accepted embedded atom potential. The structure and dynamics were calculated over a wide temperature range, and the calculated results（including the pair correlation function, self-diffusion coefficient, and viscosity） agree well with the available experimental observations. The calculated data were used to examine the Stokes–Einstein relation（SER）. The results indicate that the SER begins to break down at a temperature Tx（-1090 K） which is well above the equilibrium melting point（912.5 K）.This high-temperature breakdown is confirmed by the evolution of dynamics heterogeneity, which is characterised by the non-Gaussian parameter α2（t）. The maximum value of α 2（t）, α（2,max）, increases at an accelerating rate as the temperature falls below Tx. The development of α（2,max） was found to be related to the liquid structure change evidenced by local fivefold symmetry. Accordingly, we suggest that this high-temperature breakdown of SER has a structural origin. The results of this study are expected to make researchers reconsider the applicability of SER and promote greater understanding of the relationship between dynamics and structure.

关键词： diffusion viscosity dynamics heterogeneity local five-fold symmetry

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