# Comparison of the slip of a PDMS melt on weakly adsorbing surfaces measured by a new photobleaching-based technique

## TL;DR

This paper introduces a new optical method using photobleaching to measure slip lengths in viscous polymer melts, providing more accurate and detailed insights into slip behavior at various interfaces.

## Contribution

The paper presents a novel photobleaching-based technique for quantifying slip in polymer fluids, improving measurement accuracy over previous methods.

## Key findings

- Slip length varies with shear rate for PDMS melt.
- Different surface treatments significantly affect slip behavior.
- The method accurately measures slip length in the 1 μm to 1 mm range.

## Abstract

We present an experimental method allowing to quantify slip at the wall in viscous polymer fluids, based on the observation of the evolution under simple shear flow of a photobleached pattern within a fluorescent labeled polymer melt. This straightforward method provides access to slip length at top and bottom interfaces in the 1 $\mu$m to 1 mm range and to the actual shear rate experienced by the fluid. Based on simple optical imaging and image analysis techniques, this method affords an improvement compared to previously reported methods in which the photobleached fluorescence intensity profiles before and after shear were compared and measured by scanning a photomultiplier. The present method relies on a direct determination of the displacement profile inside the polymer fluid from an analysis of the 3D evolution of the whole photobleached pattern. We demonstrate the potential of this method with measurements of the slip length for an entangled PDMS melt, as a function of the shear rate, in contact with several weakly surfaces i.e. end-tethered PDMS or polystyrene (PS) chains, a self-assembled monolayer (SAM) of trimethoxy(octadecyl)silane (OTS), and a glassy PS thin-film.