Direct Evidence of Relaxation Anisotropy Resolved by High Pressure in a Rigid and Planar Glass Former

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Direct Evidence of Relaxation Anisotropy Resolved by

High Pressure in a Rigid and Planar Glass Former

Wenkang Tu1, Sofia Valenti2, Kia Ling Ngai1,3, Simone Capaccioli2,3, Ying Dan Liu1, and Li-Min Wang1,*

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State Key Lab of Metastable Materials Science and Technology, and College of Materials Science and Engineering, Yanshan University, Qinhuangdao, Hebei, 066004 China

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Dipartimento di Fisica, Università di Pisa, I-56127 Pisa, Italy

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CNR-IPCF, Largo B. Pontecorvo 3, I-56127, Pisa, Italy

Supporting Information

1-methylindole (1MID, 97+%) was purchased from Sigma-Aldrich and used without further purification. The high pressure dielectric measurements are performed by using a Novocontrol Alfa-Analyzer equipped with a Unipress system, which allows pressurization up to 500 MPa by a hydraulic pump. The scanning frequency spans from 0.01 Hz to 10 MHz. A parallel plate capacitor separated by thin Teflon spacers was used with samples in the liquid state held between the two electrodes. The sample cell was then well wrapped by Teflon membranes to ensure the complete isolation from the pressurizing liquid (silicon oil) before it was placed in the high pressure chamber. Pressure was measured by a Nova Swiss tensor metric pressure meter with an accuracy of 1 MPa, and the temperature of the cell was controlled in the range of 195-360 K within 0.1 K by means of a thermostatic bath.

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(ii) Resolution of the slower secondary relaxation at sufficiently high pressures in isothermal data at 221 K.

Figure S1. Separation of two secondary relaxations at high pressures for isothermal

dielectric loss data at 221 K. Isothermal measurements at T = 221 K. The data at P = 348 MPa are shifted vertically by a factor of 1.5.

(iii) Pressure dependence of Tg

Figure S2. Pressure dependence of the glass transition temperature. The solid line

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(iv) Demonstration of the enhanced resolution of the β-relaxation with pressure.

Figure S3. Dielectric loss data of 1MID measured at various temperature and pressure

combinations to demonstrate the enhanced resolution of the β-relaxation with pressure. The high-pressure and ambient-pressure data are under the condition of the same α-loss peak frequency fα. The black dashed line represents the KWW fits to the data with the

βKWW value of 0.53. The black vertical arrows indicate the estimated JG β-relaxation

frequency f0 by CM. The blue open squares are the total ambient-pressure ββ′-relaxation

peaks shifted vertically by multiplying a factor of 1.71. The magenta and blue vertical dashed arrows mark the positions for the ambient-pressure ββ′-loss peaks and the high pressure ones. The horizontal black dashed arrow represents the shift of the faster β′-relaxation to lower frequency.