The lifetime of the deviations from bulk behaviour in polymers confined at the nanoscale

Abstract

monitoring the impact of annealing on the dynamic glass transition of nanometres-thick polymer layers provides new insights into the mechanisms behind the tremendous changes in the performance of macromolecular materials in close proximity to an interface. Here we present results revealing a correlation between deviations from bulk behaviour, manifesting in changes to the glass transition temperature, the reduction of dielectric strength and the growth of an irreversibly adsorbed layer (Guiselin brushes). The non-universal behaviour of polymers under confinement could be explained in terms of a dimensionless number given by the ratio between the timescale of adsorption and the annealing time. In particular, in the case of slow adsorption kinetics, such as for polystyrene on aluminium, deviations from bulk behaviour correspond to metastable states with an extremely long lifetime.

Supercooled liquids with enhanced orientational order

“…To discern the impact of the interface-induced ordering caused by steric effects from the possible impact of molecular interactions with the substrate 36 , we investigated MROL glycerol films grown on OL layers of the same material, previously deposited well above T g (see Supplementary Methods for further details). We obtained quantitative agreement with the values measured in the single-layer films of comparable thickness, proving that the interactions between the polyols and the substrate of the interdigitated electrodes (IDE) do not influence the structure of the MROL phase.…”

Calorimetric evidence for a mobile surface layer in ultrathin polymeric films: poly(2-vinyl pyridine)

“…However, the corresponding point for polysulfone is located far away from the correlation line between the polymer-substrate interaction energy and the change in the glass transition temperature. However, by taking the Vogel temperature, T 0 , as a measure for the thermal glass transition temperature, the correlation between the change in the glass transition temperature and the polymer-substrate interaction energy 31,35 seems to be fulfilled.…”

“…For polymers having a strong interaction with the substrate, T g may increase with the reduction of the film thickness. [31][32][33] These experimental results were explained by the formation of an adsorbed boundary layer, in which the polymer segments have a lower molecular mobility; hence a higher glass transition temperature. 34 For that reason, attempts are made to correlate depression or increase of the glass transition temperature with the interaction energy between the surface of the substrate and the polymer g SP .…”

Confinement enhances dispersion in nanoparticle–polymer blend films

“…On the other hand, very little is known or understood about the nature of dispersion of nanoparticles in thin polymer films [5][6][7]9,10,12 . This is a bit surprising since, a vast amount of research has been devoted to understanding of structure and properties of thin polymer films, especially those related to the perturbation of chain conformation [17][18][19][20][21] and glass transition due to confinement [5][6][7][8]11,[22][23][24][25] . Although there is significant progress in understanding the chain conformation with confinement, some conflicting reports still exist [18][19][20]26,27 .…”

“…Although there is significant progress in understanding the chain conformation with confinement, some conflicting reports still exist [18][19][20]26,27 . Similarly, in the case of glass transition of thin polymer films, contradictory reports on finite size effects on T g in polymer thin films have emerged [5][6][7][8][22][23][24] . If polymer chain conformations do get perturbed due to confinement, does it affect the state of dispersion and other physical properties in thin films of PNCs?…”