No abstract

Auto-programmable shape memory polymers (AP-SMPs) can deform automatically without external manipulation, exhibiting either a free-standing temporary shape or a permanent shape. The unique shape memory behaviors derive mainly from control by two factors, water and temperature. However, the control mechanism is unknown. This study analyzes and demonstrates the dual-control mechanism of water and temperature in the three shape-changing processes of AP-SMPs. First, the AP-SMP is immersed in warm water (50 °C). Asymmetric swelling of bilayer films provides the driving force for the shape auto-programming of the AP-SMP. The solvent effect of water reduces the glass transition temperature (T g ) of the AP-SMP, which becomes lower than the medium temperature in warm water. AP-SMP can be programmed automatically. Then, the AP-SMP is removed from water and placed in air at room temperature. The T g value of the matrix film increases notably in air and exceeds the medium temperature. The temporary shape of the AP-SMP can thus be fixed. Finally, the AP-SMP can quickly return to its permanent shape when the medium temperature exceeds the matrix film T g in air. The dual control shape memory mechanism provides insights into the design and development of AP-SMPs.

Two novel bridged silsesquioxane (BSQ) precursors, 1,4-bis(trimethoxysilylpropylthioethenylphenoxy)benzene and 1,3-bis(trimethoxysilylpropylthioethenyl)benzene, were synthesized from arylacetylenes and 3-mercaptopropyltrimethoxysilane through the thiol-yne click reaction. Then, bridged polysilsesquioxane aerogels were prepared from BSQ precursors alone or together with tetramethoxysilane (TMOS) as a co-precursor through the sol–gel method. The resulted aerogels were characterized by scanning electron microscopy, mercury intrusion porosimetry, thermogravimetric analysis, transient hot-wire method, and water contact angle tests. Their mechanical properties were evaluated by unidirectional compression tests. The properties of the aerogels are strongly affected by precursor content, mass ratio of BSQ to TMOS, and the structures of BSQ. The obtained aerogels do not break even when compressive strain is up to 55% and show high compressive modulus (≥2.46 MPa) and hydrophobicity (water contact angle ≥130°).