Characterizing bound rubber of additively manufactured silicone rubber at an expanded scale: A contrast variation spin-echo small-angle neutron scattering investigation

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Current work investigates the multi-scale microstructures and mechanical properties of additively manufactured silicone rubber filled with silica at two concentrations (11.57% and 16.76%), designated as S30 and S45. Hierarchical structures were characterized by combining contrast variation (CV) and spin-echo small angle neutron scattering (SESANS) techniques, as well as utilizing scanning electron microscopy (SEM), low-field 1 H-NMR, and CV small angle neutron scattering (CV-SANS). The CV-SESANS technique extended the observational scale window to several micrometers, revealing a linearly decreasing trend in the normalized SESANS signal that reflects high polydispersity of filler aggregates/agglomerates at the micrometer scale. Furthermore, the CV-SESANS signal − [ d l n [ P ( Z ) / P ( 0 ) ] d z ] / [ λ 2 t ( Δ ρ ) 2 ] in ΦD=0.6 highlights the contribution of bound rubber acting as a pseudo-single scatterer within the matrix. It provides direct evidence of the existence of bound rubber structure on the micrometer-scale filler network. At the 10 to 100 nm scale, CV-SANS and low-field 1 H-NMR measurements identified aggregation sizes of approximately 125 nm (S30) and 105 nm (S45). CV-SANS further determined bound rubber thicknesses of 8.7 nm and 9.1 nm for S30 and S45, respectively. While low-field 1 H-NMR indicated the mobile bound rubber layer thicknesses of 7.9 nm and 8.1 nm. The mechanical properties of 3D-printed silicone rubber were influenced by temperature modulation and structural parameters, including print geometry controllability and filler content.

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