# Mussel-Inspired Adhesive Layer Supporting ZnO Nanorod Arrays Combined with Thiol-Ene Click Reaction for Constructing Multi-Level Carbon Fiber/Norbornene-Polyimide Interfaces

## TL;DR

This paper introduces a new method to strengthen carbon fiber composites by using a mussel-inspired adhesive layer and chemical reactions.

## Contribution

A novel multi-level interface reinforcement system using mussel-inspired coatings, ZnO nanorods, and thiol-ene click reactions is proposed.

## Key findings

- The modified carbon fiber composites showed a 39.09% increase in interlaminar shear strength (ILSS).
- Flexural strength improved by 31.16% with the new interface construction method.
- The system enhanced bonding through hydrogen bonding, mechanical interlocking, and covalent bonds.

## Abstract

Due to the non-polar and chemically inert nature of carbon fiber surfaces, the interfacial bonding strength between carbon fibers and norbornene-polyimide (PI-NA) resin matrix is relatively weak. To address this issue, this study constructed a composite coating on the carbon fiber surface and proposed a novel method to build robust interfaces based on multiple interfacial interactions, thereby effectively enhancing the interfacial properties between carbon fibers and PI-NA resin. Inspired by mussel adhesive proteins, this study established a multi-level synergistic interfacial reinforcement system by sequentially constructing a C-PEI@OPDA coating, in situ growing zinc oxide nanorods (ZW) arrays, and grafting 3-mercaptopropyltrimethoxysilane (MPS) onto carbon fiber surfaces. The C-PEI@OPDA coating, rich in amino (–NH2) and hydroxyl groups (–OH), enhanced adhesion to carbon fibers and adsorbed Zn2+ via coordination interactions to provide nucleation sites for ZW growth. Meanwhile, the active hydrogen in the coating promoted the crosslinking of PI-NA resin, thereby increasing the resin crosslinking density in the interfacial region. The vertically aligned ZW significantly increased surface roughness, enhanced mechanical interlocking effects, and provided secondary reaction sites for MPS grafting. The thiol groups (–SH) in MPS formed covalent bonds with PI-NA resin through thiol-ene click reactions, further strengthening interfacial bonding. The results showed that the ILSS, IFSS, and flexural strength of C-PEI@OPDA/ZW/MPS modified carbon fiber composites reached 75.15 MPa, 102.93 MPa, and 1735.56 MPa, representing improvements of 39.09%, 48.79%, and 31.16%, respectively. This study effectively enhanced the carbon fiber-reinforced polymer composites interfacial bonding strength through the synergistic effects of hydrogen bonding, mechanical interlocking, chemical bonding, and increased resin crosslinking density.