Enhancing fracture toughness of polydimethylsiloxane with cyclosiloxane hybrid polymer microspheres

Abstract

Polydimethylsiloxane (PDMS) offers many unique advantages, but the poor fracture toughness (300–500 J/m2) limits its applications. Conventional methods of toughening PDMS through chain modification or inorganic fillers may negatively impact other properties, such as increase in hysteresis, stiffness, or viscosity. To address this problem, we introduce organic cyclosiloxane hybrid polymer (CHP) microspheres to toughen PDMS. These microspheres are synthesized by emulsion polymerization of two cyclosiloxane monomers and can be regarded as an extremely crosslinked PDMS. The interpenetration of polymer chains between CHP and matrix increases the interface adhesion to transfer the stress while the high modulus contrast can prevent the propagation of cracks, resulting in a high toughness without a sharp increase in stiffness. At the same time, the low friction between the filler and matrix reduces viscosity and hysteresis. Moreover, by incorporating magnetically responsive Fe3O4 nanoparticles, the CHP microspheres can be aligned. Aligned-CHP/PDMS composites exhibit a fracture toughness of 4223 J/m2, three times higher than SiO2 reinforced composites and nearly an order of magnitude higher than pure PDMS. These composites also have a lower modulus (3.3 MPa), lower hysteresis (0.167), and a viscosity two orders of magnitude lower compared to SiO2-filled counterparts. This method offers a new pathway for toughening siloxane elastomers without affecting other properties.