Glasses of three alkyl phosphates show a range of kinetic stabilities when prepared by physical vapor deposition

Abstract

In situ AC nanocalorimetry was used to characterize vapor-deposited glasses of three phosphates with increasing lengths of alkyl side chains: trimethyl phosphate, triethyl phosphate, and tributyl phosphate. The as-deposited glasses were assessed in terms of their reversing heat capacity, onset temperature, and isothermal transformation time. Glasses with a range of kinetic stabilities were prepared, including kinetically stable glasses, as indicated by high onset temperatures and long transformation times. Trimethyl phosphate forms kinetically stable glasses, similar to many other organic molecules, while triethyl phosphate and tributyl phosphate do not. Triethyl phosphate and tributyl phosphate present the first examples of non-hydrogen bonding systems that are unable to form stable glasses via vapor deposition at 0.2 nm/s. Based on experiments utilizing different deposition rates, we conclude that triethyl phosphate and tributyl phosphate lack the surface mobility required for stable glass formation. This may be related to their high enthalpies of vaporization and the internal structure of the liquid state.

Prediction of Second Melting Temperatures Already Observed in Pure Elements by Molecular Dynamics Simulations

“…Heating the glass through T g breaks the atomic bonds and gives rise to configurons that are always accompanied by a second-order phase transition [ 7 , 8 , 9 , 10 , 11 , 12 ]. The non-classical homogeneous nucleation (NCHM) model predicts the temperatures of glasses, stable and ultrastable glasses [ 13 , 14 , 15 , 16 , 17 , 18 , 19 , 20 , 21 , 22 , 23 , 24 , 25 ], and glacial phases [ 26 , 27 , 28 , 29 , 30 , 31 , 32 , 33 , 34 , 35 ] showing that a new phase called Phase 3 appears after heating the quenched liquids through T g with an enthalpy equal to the difference ∆ε lg between those of liquids 1 and 2. Quenched Liquid 1 has an initial enthalpy, before giving rise to the glass state, equal to ε ls H m, varying with the square of the reduced temperature θ = T−T m )/T m as shown in Equation (1) (H m being the melting heat of crystals) [ 36 ]: …”

Undercooled phase behind the glass phase with superheated medium-range order above glass transition temperature

“…Many new phases with reduced enthalpy have been discovered by vapor deposition below Tg1. The glass transition temperatures Tg2 of these thin films are higher than those of bulk materials [135][136][137][138][139][140][141][142][143][144][145][146]. Cooling these films from above Tg2 does not lead to a glass transition at Tg1.…”