Rouse 2D Diffusion of Polymer Chains in Low Density Precursor Films of Polybutadiene Melts

Abstract

We took advantage of pseudopartial wetting to promote the spreading of precursor films whose surface density smoothly decays to zero away from a sessile droplet. By following the spreading dynamics of semidilute precursor films of polybutadiene melts on silicon wafers, we measure molecular diffusion coefficients for different molar masses and temperatures. For homopolymers, chains follow a thermally activated 2D Rouse diffusion mechanism, with an activation energy revealing polymer segment interactions with the surface. This Rouse model is generalized to chains with specific terminal groups.

Morphology and Dynamics of Dense Nanometric Precursor Films of Polymer Melts

“…In this framework, we suggest the friction mechanism at stake for low-mass polymers consists of both monomer/monomer friction and monomer/substrate friction. This hypothesis was verified in a previous study: 29 for non-dense films with effective thickness below b, we showed monomer/substrate interactions were setting the diffusion coefficient of dilute or semi-dilute PBd or PBd-OH polymers on silica. In dense films, low-mass polymers exhibit low film thickness h 2 so that the ratio of the surface friction term to the chain/chain friction term becomes comparatively larger.…”

“…Technical details on these computations are available in a previous paper. 29 Figure 5 presents thickness profiles with time of a secondary film of PBd-OH, and the corresponding D(h) curves. We observe that D increases with h. A temporal dependence of the diffusion coefficient is noted for h ≤ 0.7 × h 2 .…”

“…In the literature, , it is observed that precursor films are composed of two parts: (i) a submolecular part, which connects the uttermost end of the film to the bare substrate, and (ii) a thicker part connected to the droplet, which was sometimes shown to be dense . In a previous work, we studied the submolecular part of precursor films of polybutadiene melts. We showed that polymer molecules are in a non-dense state and that the film spreading dynamics can be described by the sole friction of the polymer segments on the surface, which we measured.…”

“…Hence, experimental efforts have been made to probe the interfacial behavior, and among the methods developed in the past, a promising one is the approach based on wetting experiments of polymer melts on high energy surfaces, characterized by a positive spreading parameter scriptS = γ sv − ( γ + γ sl ) , γ sv , γ, and γ sl being the interfacial tensions of the solid/air, polymer/air, and solid/polymer interfaces, respectively. Indeed, when a polymer melt droplet is deposited on such surfaces, a so-called precursor film spreads around the sessile droplet as recently reviewed by Popescu et al Precursor films have been evidenced a century ago, but they have been precisely measured only over the past 30 years. − Their typical thickness being nanometric, they are extremely interesting systems to probe polymer/substrate interactions. The spreading of such thin films is thought of as an efficient way for the system to lower down its surface energy at early times.…”

Interfacial Friction Controls the Motion of Confined Polymers in the Pores of Nanoparticle Packings

“…Rouse-like motion for diffusive motion of polymer melts has been previously reported for precursor films of poly­(vinyl acetate) spreading on the air–water surface and for PDMS and polybutadiene droplets spreading on silicon wafers; however, such observation has not been made for polymers three dimensionally confined in porous media, to our best knowledge. − Thus, the inverse scaling of D eff with chain size and the increase in dynamics with increasing humidity lead to the conclusion that the interfacial friction arising from strong hydrogen bonding interactions between the silica and PDMS dominates the dynamics of PDMS motion in the disordered SiO 2 nanoparticle packing. The nanoporous domain in the nanoparticle packings is an interconnected network of nanopores of varying sizes.…”