# Enhancing Membrane Adhesion to Polymeric Substrates via Plasma Treatment

## TL;DR

Plasma treatment improves adhesion between polymeric membranes and substrates by enhancing chemical bonding and mechanical interlocking.

## Contribution

Demonstrates that plasma treatment effectively enhances adhesion in porous membranes with nanoscale pores.

## Key findings

- Oxygen-containing plasma treatment significantly improves adhesion between PES membranes and PP substrates.
- Adhesion improvements range from 0.12 to 20 times compared to untreated samples.
- Mechanical interlocking due to membrane pore structure plays a key role in adhesion enhancement.

## Abstract

Ensuring strong adhesion
between porous polymeric membranes and
supporting substrates is critical for the reliability and functionality
of membrane devices. However, due to the innate low surface energy
of polymers, achieving strong chemical bonding between such materials
remains challenging. In addition, the small-pore size of membranes
often limits effective pore intrusion (necessary for achieving effective
mechanical interlocking) by polymer adhesives during high-throughput
manufacturing. Plasma treatment is commonly used to modify the surface
energy of polymers to improve adhesion and mechanical properties of
composite systems. However, it remains unexplored whether the method
is effective in improving the adhesion of surfaces containing nanoscale
pores as found in membranes. Herein, we demonstrate that adhesion
between poly­(ethersulfone) (PES) membranes with 20 and 200 nm pore
sizes and polypropylene (PP) substrates is enhanced by low-pressure
plasma treatment (power: 30 W, duration: 60 s, gas flow rate: 30 cm3/min) of the two surfaces. Thermomechanical bonding between
the treated surfaces is performed, and the adhesion behavior is quantified
by a T-peel test and imaging analysis. For the 200 nm PES membranes
and PP substrate, the adhesion after plasma treatment (152–405
N/m), measured by the interfacial fracture toughness, exhibits an
improvement by 0.12 to 2 times in comparison to untreated control
samples (114–156 N/m). For the 20 nm PES membranes and PP substrate,
the adhesion after plasma treatment (14–242 N/m) exhibits an
improvement by 0.13 to 20 times in comparison to that of untreated
control samples (12–96 N/m). Among the different types of plasma
treatment tested, the oxygen-containing plasmas produce the largest
enhancement in adhesion. When benchmarked against the adhesion of
densified, nonporous PES film and PP substrates after plasma treatments
(0–20 N/m), the adhesion is improved by 13 to 37 times for
the 200 nm PES/PP specimens and by 1.5 to 17 times for the 20 nm PES/PP
specimens, showcasing the importance of mechanical interlocking due
to membrane pore structure for adhesion. This study shows that there
is a synergistic effect of chemical bonding and mechanical interlocking
on the interfacial fracture toughness between porous membranes and
thermoplastic substrates, which can be useful in guiding the membrane
bonding process in a variety of applications.