Chain Entanglement in Thin Freestanding Polymer Films

Direct Observation of Confined Single Chain Dynamics by Neutron Scattering

“…Possibly similar arguments hold as compared to the flow experiments. We also mention that the distinction between self-chain and interchain entanglements in confined polymers was an essential ingredient to interpret the extensional strain results in thin polymer films by Si et al [10]. Their model based on chain packing assumed that the total entanglement density is constant when applied to systems with R e & 2h (h, film thickness).…”

“…Performing very delicate studies on the extension ratio of nanoscopic polymer films under shear, Si et al also conjectured on a reduced density of interchain entanglements which, according to them, should be compensated by a corresponding increase of intrachain entanglements [10]. Similarly, from dewetting experiments a significantly reduced entanglement density in thin polymer films was conjectured [11].…”

“…The dominant motional mechanisms in this model are (i) a curvilinear version of the Rouse motion (local reptation) followed by (ii) the escape of the whole molecule from the tube at long times, the reptation process (see, e.g., [6,7]). The important question that is addressed now both by simulations [2,3,8,9] as well as by a variety of experiments on a macroscopic level [4,[10][11][12] is how these dynamics change under confinement.Basically all simulations available indicate that confinement reduces chain mobility independent of the adhesive potential of the wall. An analysis of the Rouse modes of unentangled chains under confinement reveals a uniform slowing down of all modes which was interpreted by an effective increase of monomeric friction [8].…”

Onset of Plasticity in Thin Polystyrene Films

“…Polystyrene is often used as a model polymeric material because thin films are easily produced and manipulated, they are relatively rigid, and polystyrene is a comprehensively studied glassforming polymer with well known bulk material properties. However, as the thickness of a polymer film is reduced to nanoscopic dimensions it is now well established that the glass transition is altered [9][10][11][12][13][14][15], the number of entanglements between chains are reduced [1,2], and mechanical properties can change [16,17]. Remarkably few studies have considered how failure processes might be altered in thin films, or how plasticity might alter a films response to other stimuli.…”

“…Thin polymer films are materials that are uniquely suited for countless goals, finding use in studies ranging from fundamental polymer physics [1,2], to elasticity [3][4][5][6][7][8], and glass-phase physics [9][10][11][12][13][14][15]. Polystyrene is often used as a model polymeric material because thin films are easily produced and manipulated, they are relatively rigid, and polystyrene is a comprehensively studied glassforming polymer with well known bulk material properties.…”