What additives would be used for epoxy adhesive flow stopper？

In epoxy adhesive formulations, flow stoppers are additives used to control the flow characteristics of the adhesive, preventing it from flowing excessively or dripping during application or curing. Several types of additives can be used for this purpose:

1. Thickeners or rheology modifiers: These additives increase the viscosity of the epoxy adhesive, making it more viscous and less prone to flowing. Common thickeners include fumed silica, clays (such as bentonite or montmorillonite), cellulose derivatives, and acrylic polymers. They help to control the flow of the adhesive and improve its sag resistance.
2. Microspheres or hollow glass spheres: Microspheres are lightweight, hollow particles that can be added to epoxy adhesives to increase viscosity without significantly adding weight. They help to thicken the adhesive while maintaining its lightweight properties. Microspheres are particularly useful for applications where weight is a concern, such as in aerospace or automotive applications.
3. Fiber additives: Fibers, such as glass fibers or aramid fibers, can be incorporated into epoxy adhesives to increase viscosity and provide reinforcement. These fibers help to improve the mechanical properties of the adhesive while also reducing flow and preventing sagging.
4. Thixotropic agents: Thixotropic agents are additives that change the viscosity of the adhesive depending on shear stress. They increase viscosity under static conditions, preventing flow, but decrease viscosity under shear, allowing for easy application. Examples of thixotropic agents include organically modified clays and associative thickeners.
5. Gelling agents: Gelling agents are chemicals that promote the formation of a gel structure within the adhesive, effectively immobilizing the adhesive and preventing flow. Common gelling agents include amine-based compounds and certain metal salts.

The choice of flow stopper additive depends on factors such as desired viscosity, application method, curing conditions, and specific performance requirements of the epoxy adhesive. Formulators may use a combination of these additives to achieve the desired flow characteristics and performance properties