Direct observation of desorption of a melt of long polymer chains

Abstract

Tuning the thermodynamic state of a material has a tremendous impact on its performance. In the case of polymers placed in proximity of a solid wall, this is possible by annealing above the glass transition temperature, T g , which induces the formation of an adsorbed layer. Whether heating to higher temperatures would result in desorption, thereby reverting the thermodynamic state of the interface, has so far remained elusive, due to the interference of degradation. Here, we employ fast scanning calorimetry, allowing to investigate the thermodynamics of the interface while heating at 10 4 K s −1. We show that applying such rate to adsorbed polymer layers permits avoiding degradation and, therefore, we provide clear-cut evidence of desorption of a polymer melt. We found that the enthalpy and temperature of desorption are independent of the annealing temperature, which, in analogy to crystallization/melting, indicates that adsorption/desorption is a first order thermodynamic transition.

Physical Aging Behavior of a Glassy Polyether

“…This has been, for instance, put forward in the shape recovery kinetics of shape memory polymers (SMP) [75]. Other examples where the kinetic of equilibration may be triggered by either the α relaxation or another mechanisms with milder activation energy are polymers adsorbed on an substrate [45,76] and polymer films dewetting [77].…”

“…Furthermore, samples heated at high rates are less amenable to chemical degradation, since the time spent at high temperatures is very short. This allows investigating phenomena, including glass transition [42,43], melting [44], and polymer adsorption [45], otherwise impossible to study by standard calorimetry. The choice of an amorphous polyether rests on his chemical difference with previously employed polymers [18], which were either vinyl polymers or presenting an aromatic ring in the backbone.…”

Direct observation of morphological transition for an adsorbed single polymer chain

“…The reversibility of the chain adsorption onto the substrate surface is still controversial and, of course, should be dependent on the time/spatial scale as well as temperature 25 , 51 , 52 . Although it seems accepted that the adsorption of chains is practically irreversible because the desorption rate is so slow, when the thermal energy associated with rising temperature much increases, adsorbed segments could start to decrease in number 53 . Under experimental conditions in the current study, the adsorption of chains onto the substrate surface could be regarded as an irreversible process.…”

Secondary nucleation in polymer crystallization: A kinetic view

“…Recently, the force‐induced melting in polymer single crystals was studied by single‐molecule force spectroscopy 126 . A direct observation of desorption of a melt of long polymer chains was given by employing fast scanning calorimetry 127 . We may expect that these new methods will provide a technological breakthrough to establish links between crystallization mechanism and melting.…”