Dewetting temperatures of prefrozen and grafted layers in solid ultrathin films viewed as melt-memory effects

Abstract

Undercooled phase exists behind glass phase with superheated medium-range order between Tg and Tn+ > Tm. The ordered volume fraction stays equal to the percolation threshold F  0.15 of broken bonds up to Tn+. The difference Tg between Tg(bulk) of films with thickness (h > h0) and Tg(h) of ultrathin films of thickness (h < h0) is a linear function of (h-ho). Dense layer with minimum thickness hr is grafted against substrate by isothermal annealing, rinsed to reduce film thickness below hr/F, and finally dewetted at Tg. Similar thickness prepared and annealed near Tm and heated above Tm contains residual crystallized layer dewetting at Tn+. The prefrozen layer reproduces the glassy grafted layer in a crystallized state up to Tn+. Melting heat and melting temperature Tm are linear functions of h for h < h0. Prefrozen layers are due to meltmemories leading to new scenarios of crystallization.

The Modified Random Network (MRN) Model within the Configuron Percolation Theory (CPT) of Glass Transition

“…where T g (bulk) is the glass transition temperature for large-size samples when L >> ξ(T), α cpt = ξ 0 [7.843RT g (bulk)/H d ] ν , δ = 1/ν, and ν = 0.88 is the critical exponent. This equation conforms well with experiments and theory [46] and are also applicable to thin polymeric films [47].…”

Building and Breaking Bonds by Homogenous Nucleation in Glass-Forming Melts Leading to Transitions in Three Liquid States

“…Our new publication here was devoted to the simplest case where ultrastable glass and glacial phase are not formed. The value of θ n+ was maximum in this case because all transformations below T g and T m modified the liquid state and decrease θ n+ [ 19 ].…”

“…A quench from T m < T < T n+ along q3 led to the enthalpy of phase 3 with crystallized nuclei being the skeleton of this phase after percolation at T g , as shown for plastic crystals. A slow cooling led to crystallization at T m without undercooling [ 19 ].…”

“…The crystallization temperature occurred at the reentrant formation temperature of ultrastable glass with its enthalpy equal to −Δε lg0 . This nucleation temperature opened the door to crystallization [ 19 ].…”

“…This paper is devoted to phase transitions above T m completing our recent work, showing that the dewetting temperatures of prefrozen and grafted layers in ultrathin films are equal to T n+ [ 19 ]. The latent heats are exothermic or endothermic without knowing the explanation.…”