Neutron reflectivity measurements of the translational motion of tris(naphthylbenzene) at the glass transition temperature

Abstract

The translational dynamics of the low molecular weight glass-former tris(naphthylbenzene) have been studied on the length scale of a few nanometers at the glass transition temperature Tg. Neutron reflectivity was used to measure isotopic interdiffusion of multilayer samples created by physical vapor deposition. Deposition with the substrate held at Tg-6 K allows observation of dynamics characterizing the equilibrium supercooled liquid. The diffusion coefficient measured at q = 0.03 A(-1) was determined to be 1x10(-17) cm2/s at 342 K (Tg). The self-part of the intermediate scattering function I(s)(q,t) decays exponentially. Samples deposited well below Tg show a substantial thermal history effect during subsequent translational motion at Tg.

Molecular view of the isothermal transformation of a stable glass to a liquid

“…When a peak decays completely, it indicates that the protioand deuterio-TNB have become homogeneously mixed on the corresponding length scale. As previously discussed, 12 samples vapor deposited near T g behave as the equilibrium supercooled liquid during annealing. As shown in Fig.…”

“…Evidence supporting these assumptions has been presented elsewhere. 12 Thin films of TNB were prepared by physical vapor deposition. Samples were deposited onto 76 mm diameter, 3 mm thick silicon wafers ͑Wafer World and Virginia Semi-conductor͒.…”

“…Detailed information about the NR data and analysis of these multilayer samples has been previously given. 12 Figure 2 shows the specular NR of a multilayer TNB sample vapor deposited onto a silicon substrate held at 242 K. One can think of the multilayer protio/deuterio structure as a diffraction grating for neutrons. [13][14][15] Because the interfaces are sharp, many Bragg peaks are evident, extending out to the 17th harmonic.…”

Mechanics of Supercooled Liquids

“…In recent decades, however, evidence has accumulated that some supercooled liquids violate the Stokes-Einstein relation [10][11][12][13][14][15][16]. When the temperature drops, such a supercooled…”

Exploring the Dynamics of Glasses Using Beta Detected NMR

“…During deposition, the surface layer is suggested to be in a liquid-like state, and thus the molecules have time to reach a more favourable configuration before freezing. Studies of the diffusion have suggested that the molecular dynamics in the two types of glasses are substantially different [1,6,7]. Glasses have extremely complex relaxational dynamics with timescales varying from picoseconds, for atomic vibrations, to thousands of years, for molecular rearrangements or "aging" [8,9].…”