<p>Halloysite nanotubes (HNTs)-reinforced epoxy composites are commonly utilized in a multitude of applications due to their excellent mechanical properties. However, the development of epoxy composites with high interfacial strength remains a significant challenge. In this work, polyetheramine-grafted halloysite nanotubes (PEA-HNTs) were prepared to fabricate strong and tough epoxy composites. The influence of polyethylene amine-functionalized halloysite nanotubes (PEA-HNTs) incorporation on both the mechanical performance and free volume holes in epoxy matrix composites was systematically investigated through positron annihilation lifetime spectroscopy (PALS). The results demonstrated that PEA-HNTs were uniformly dispersed in the epoxy matrix, forming strong interfacial interaction. The nanoscale dispersion architecture effectively decreased the free volume hole size (<InlineEquation ID="IEq1"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="289_2025_5890_Article_IEq1.gif" Format="GIF" Height="19" Rendition="HTML" Resolution="72" Type="Linedraw" Width="19" /> </InlineMediaObject> <EquationSource Format="TEX">\(V_{f}\)</EquationSource> <EquationSource Format="MATHML"><math> <msub> <mi>V</mi> <mi>f</mi> </msub> </math></EquationSource> </InlineEquation>) and relative free volume <InlineEquation ID="IEq2"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="289_2025_5890_Article_IEq2.gif" Format="GIF" Height="19" Rendition="HTML" Resolution="72" Type="Linedraw" Width="28" /> </InlineMediaObject> <EquationSource Format="TEX">\((f_{r} )\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mo stretchy="false">(</mo> <msub> <mi>f</mi> <mi>r</mi> </msub> <mo stretchy="false">)</mo> </mrow> </math></EquationSource> </InlineEquation>, resulting in the improved mechanical properties. This work presents a novel and scalable strategy for developing high-performance epoxy composites through rational nanotube functionalization and interfacial engineering.</p> Graphical abstract <p></p>