Phenomenological Theory of First-Order Prefreezing

Abstract

Prefreezing is the prewetting of the crystalline phase at the interface of a melt to a solid substrate via a first-order phase transition. We present a phenomenological theory of prefreezing and analyze thermodynamic properties of the prefrozen crystalline layer. The theory enables a clear thermodynamic explanation of the abrupt formation of a mesoscopically thick crystalline layer during cooling and defines the corresponding transition temperature as a function of the interfacial free energies. It is shown that the interfacial energy difference γ sm – (γ sc + γ cm) acts as a driving force for prefreezing. The analytical results are congruent with recent experimental outcomes for poly­(ε-caprolactone) crystallized on graphite via prefreezing. The calculated interfacial free energies take reasonable values being close to the experimental estimates.

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

“…The glass transition temperature of polycaprolactone is Tg1 = 213 K [ ( 45)] and the melting temperature Tm = 335 K [ ( 14) (19)]. The enthalpy coefficients ls of Liquid 1, gs of Liquid 2, and lg of Liquid 3 are determined using (4-9) and given in (18)(19)(20):…”

Roughening Transition and Quasi-continuous Melting of Monolayers of Ultra-long Alkanes: Why Bulk Polymer Melting Is Strongly First-Order

“…Previous studies on adsorbed shorter alkanes, mainly in the length range 20 < n < 40, − have found that monolayers on graphite melt at temperatures somewhat above the bulk melting point T m bulk , with additional phase transitions in the ordered state . A ″prefreezing″ effect was also found in PE and PCL thin layers on graphite and other substrates, where a thin layer of polymer is found to crystallize above its bulk melting point T m bulk (by 47 K for PE on MoS 2 ) at the substrate–melt interface. − The effect is attributed to the reduced overall interface energy when a semicrystalline thin layer is sandwiched between the substrate and melt compared to that of a direct substrate–melt interface. Most notably, the melting of multilayers of n -C 60 H 122 and n -C 390 H 782 was reported to occur, respectively, 45 and 55 K above T m bulk , prior to our study on C 390 H 782 .…”

Heterogeneous Crystal Nucleation from the Melt in Polyethylene Oxide Droplets on Graphite: Kinetics and Microscopic Structure

“…Note that when γ sm > γ sc + γ cm , the contact angle θ becomes zero and f (0) = 0 (Equation (4)), implying that the energy barrier for heterogeneous nucleation (∆G * het ) vanishes. Under this condition, crystallization can even take place above T m via prefreezing [3,[5][6][7][8][9], the other phenomenon of interface-induced crystallization, which is beyond the framework of classical nucleation theory. For heterogeneous nucleation, θ has a value 0 < θ < 180°and the function 0 < f (θ) < 1.…”

“…In general, a solid substrate can induce the crystallization of liquids either by heterogeneous nucleation [1,2] or by prefreezing [3,4]. Prefreezing, i.e., the formation of a stable crystalline layer at the substrate interface above the melting temperature (T m ) of the material, is an equilibrium phenomenon and does not require a nucleation event [5][6][7][8][9]. By contrast, heterogeneous nucleation is an activated process taking place at a finite supercooling below T m [10].…”