Optimizing the mechanical properties of polymer resists for strong and light-weight micro-truss structures

Abstract

Cellular materials with specific three-dimensional microarchitectures achieve outstanding strength-to-weight ratios due to the mechanical size effect and their optimized architecture. By applying 3D direct laser writing and different coating techniques the materials can be fabricated as polymer nanocomposites. So far, mainly coating materials and techniques have been investigated to enhance the mechanical properties. It is the aim of this study to improve the strength of polymer lattice materials by applying specific annealing treatments to the polymer after the laser writing step. We present push-to-pull tensile tests of single struts as well as compression tests of entire truss structures after different annealing temperature–time combinations. Depending on the specific heat treatment, strength, stiffness and engineering toughness of the polymer can be optimized for the use in architected materials. We show that the tensile strength of single struts can be increased by a factor of 10 compared to samples without heat treatment. Simultaneously, the compressive strength of entire truss structures was improved by a factor of 2.5. Here, failure is induced at lower compressive stresses due to stress concentrations at the truss nodes, and, thus, the observed strength gain cannot be fully exploited.