It is well known that pure polymeric materials by themselves cannot be used in various fields for high-performance applications due to their insufficient properties. Therefore surface modification of substrates is essential for many applications. Currently, the common surface modification methods for polymeric substrates can be divided into physical and chemical methods. Physical surface modification can use physical means such as physical adsorption or physical coating to impart a certain surface roughness or pattern on the material surface. The chemical surface modification uses a specific chemical reaction.
Alfa Chemistry offers a variety of chemical surface modification methods to its customers. Chemical grafting is usually more advantageous than physical methods because the graft chains are covalently attached to the substrate surface to avoid desorption and ensure long-term chemical stability. In addition, polymer brushes chemically grafted to the surface have high adhesive strength due to their strong, selective, specific, and easy reactivity.
What Is A Polymer Brush?
A polymer brush is a collection of polymer chains tethered at one end to a surface or interface. The grafting of polymer brushes on the surface of a substrate provides a practical tool for surface modification and functionalization. In order not to affect the mechanical properties of a given substrate, modification of the substrate with grafted polymer brushes can significantly affect surface properties such as friction, adhesion, wettability, and biocompatibility. Furthermore, the real importance of this modification is that it provides a way to enhance the surface properties while maintaining the original substrate properties. However, the approach of grafting polymer brushes still faces some obstacles, for example, the poor robustness has become a bottleneck for large-scale biomedical, industrial or clinical applications of the modified surfaces.
Fig 1. Examples of polymer systems comprising polymer brushes. (Zhao B, et al. 2000)
Alfa Chemistry Chemical Surface Modification Strategies
Surface modification has the advantage in that it is a simple, easy, and versatile process that does not alter the substrate's properties. We can integrate different modification techniques, including physical and chemical modifications, to improve the overall effect. In chemical surface modification techniques, the exposed groups on the material surface can react with the target functional groups to bind the grafting brush to the material surface. It is known that chemical bonds are much stronger than intermolecular interactions, so chemically prepared graft layers can bond more strongly to the material surface.
Our chemical surface modification approaches based on grafting may be split into three categories: "grafting-to," "grafting-from," and "grafting-through," which are commonly utilized for covalent grafting of polymers. The end-transformed polymer chain reacts with the functional group of the substrate to generate the grafted polymer chain in the grafting technique. The polymer chains propagate from the initiator connected to the surface in the grafting process. The polymer chains propagate from the surface-attached double bonds in the grafting technique.
"Grafting to" Approach
"Grafting from" Approach
"Grafting through" Approach
| Strategies | Advantages | Limitations |
|---|
| Grafting to | Polymer brushes with a narrow molecular weight distribution can be characterized prior to grafting;
This method is more mature than other strategies. | It tends to exhibit uneven aggressiveness and low maximum thickness of the layers obtained. |
| Grafting from | The function, density and thickness of polymer brushes can be well controlled with almost molecular precision. | It requires some kind of initiator or active site to be immobilized on the surface. |
| Grafting through | This strategy may be one of the most powerful surface modification processes. | The research and application of its specific mechanism needs further demonstration. |
Reference
- Zhao B, et al. (2000). "Polymer Brushes: Surface-Immobilized Macromolecules." Progress in Polymer Science. 25(5): 677-710.
