Figure 4

Arrhenius plot of the structural (α, filled circles) and secondary β (half-open squares) and γ (open triangles) relaxation times in BrBPh (a) and BPh (b). In (a), the data for all three studied pressures are reported (blue: 0.1 MPa; red, 201 MPa; green: 400 MPa). In (b), α relaxation times above T_g were obtained by our own fits of the loss spectra of Ref.²⁷, and the red dot represents the relaxation time of the fast-β relaxation inferred from analysis of the optical Kerr effect on BPh (Ref.³⁵). In both panels, continuous lines are VFT fits (Eq. 3) of the α relaxations or linear (Arrhenius law) fits of the secondary (β, γ) relaxation times. The dashed horizontal line marks the glass transition temperature T_g, while the dashed vertical line marks the dynamic cross-over temperature at which the VFT temperature dependence of the α relaxation changes in the ambient pressure data. Stars represents the precursor times predicted by the Coupling Model (Eq. 5). Inset to (a): variation of T_g with the applied pressure (markers). The line is a linear fit.