Short chains enhance slip of highly entangled polystyrenes during thin film dewetting

Abstract

We investigate the effect of short chains on slip of highly entangled polystyrenes (PS) during thin film dewetting from non-wetting fluorinated surfaces. Binary and ternary mixtures were prepared from monodisperse PS with weight average molecular weights 5 < Mw < 490 kg/mol. Flow dynamics and rim morphology of dewetting holes were captured using optical and atomic force microscopy. Slip properties are assessed in the framework of hydrodynamic models describing the rim height profile of dewetting holes. We show that short chains with Mw below the polymer critical molecular weight for entanglements, Mc, can play an important role in slip of highly entangled polymers. Among mixtures of the same Mw, those containing chains with M < Mc exhibit larger slip lengths as the number average molecular weight, Mn, decreases. The slip enhancement effect is only applicable when chains with M < Mc are mixed with highly entangled chains such that the content of the long chain component, φL, is dominant (φL < 0.5). These results suggest that short chains affect slip of highly entangled polymers on non-wetting surfaces due to the physical or chemical disparities of end groups, and any associated dynamical effect their presence may have, as compared to the backbone units. The enhanced slip in this regard is attributed to the impact of chain end groups or short chain enrichment on the effective interfacial friction coefficient. Accordingly, for entangled PS, a higher concentration of end groups or short chains at the interface results in a lower effective friction coefficient which consequently enhances the slip length.

Detection of Surface Enrichment Driven by Molecular Weight Disparity in Virtually Monodisperse Polymers

“…Chain length disparity is a ubiquitous driver of surface enrichment. − The enrichment of shorter chains affects properties such as surface tension, , wall slip, , and glass transition of thin films. , This entropically driven enrichment has been studied experimentally for systems in which the disparity in chain sizes is large. ,,, Hariharan et al first described such segregation theoretically for two lengths using lattice self-consistent field theory (SCFT). Van der Gucht et al extended that approach to melts with several chain lengths.…”

“…Chain length disparity is a ubiquitous driver of surface enrichment. 18−28 The enrichment of shorter chains affects properties such as surface tension, 21,24 wall slip, 22,23 and glass transition of thin films. 25,26 This entropically driven enrichment has been studied experimentally for systems in which the disparity in chain sizes is large.…”

Entropic segregation of short polymers to the surface of a polydisperse melt

“…This has a wide range of implications in regards to surface tension [15,16], wall slip [17,18], the glass transition of thin films [19,20], and the effective force between polymer surfaces [21], to name a few. The phenomenon also has similar implications for mixtures of chemically identical molecules of different architecture [22][23][24][25][26].…”

Influence of Polymer Molecular Weight on Chain Conformation at the Polystyrene/Silver Interface

“…Polymer/solid interfaces regulate many critical processes and properties such as adsorption, adhesion, , wall-slip, and wettability . For example, in the aerospace industry, polymer coatings are applied to metallic substrates to improve their corrosion resistance, while in biomedical applications they can be applied to implants to reduce their failure rate .…”