Preparation and studies on properties of porous epoxy composites containing microscale hollow epoxy spheres

• Hollow epoxy spheres were prepared by an amino-modify silica particles templates.
• Hollow epoxy spheres showed good dispersion capability in the polymer matrices.
• The porous epoxy material with 10% HES decreased the thermal conductivity to 49.3%.

In this work, a series of porous epoxy composites containing microscale, hollow epoxy spheres were synthesized and characterized. First, microscale epoxy spheres were produced using amino-modified silica (AMS) particles with diameters of ∼1 μm through a base-catalyzed sol–gel route. The as-synthesized AMS particles were then characterized through Fourier-transform infrared, 13C nuclear magnetic resonance (NMR), and 29Si-NMR spectroscopy. The prepared core–shell particles were immersed into a 1 wt.% of HF solution for 24 h to remove the inner part of the silica core, leading to the formation of hollow spheres of epoxy with a wall thickness of ∼100 nm. These hollow epoxy spheres (HES) were characterized by scanning electron microscopy (SEM), Transmission electron microscopy, and thermogravimetric analysis (TGA). Finally, a series of hybrid materials was synthesized by performing thermal ring-opening polymerization reactions of epoxy resin in the presence of as-synthesized HES. Based on SEM observations on the morphology, the HES showed good dispersion capability in the polymer matrices, which led to a significantly reduced thermal conductivity and slightly decreased dielectric constant based on the transient plane source and LCR measurements, respectively. For example, the thermal conductivity and dielectric constant decreased by 49.3% and 12.6%, respectively, in the porous epoxy material synthesized with a final HES loading of about 10%. One possible reason was the large amount of air present in the material. Other physical characteristics such as the thermal and mechanical properties based on the results of TGA, differential scanning calorimetry, and dynamic mechanical analysis were investigated.

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