Polystyrene Glasses under Compression: Ductile and Brittle Responses

Glassy gels toughened by solvent

Glassy polymers are generally stiff and strong yet have limited extensibility1. By swelling with solvent, glassy polymers can become gels that are soft and weak yet have enhanced extensibility1-3. The marked changes in properties arise from the solvent increasing free volume between chains while weakening polymer-polymer interactions. Here we show that solvating polar polymers with ionic liquids (that is, ionogels4,5) at appropriate concentrations can produce a unique class of materials called glassy gels with desirable properties of both glasses and gels. The ionic liquid increases free volume and therefore extensibility despite the absence of conventional solvent (for example, water). Yet, the ionic liquid forms strong and abundant non-covalent crosslinks between polymer chains to render a stiff, tough, glassy, and homogeneous network (that is, no phase separation)6, at room temperature. Despite being more than 54 wt% liquid, the glassy gels exhibit enormous fracture strength (42 MPa), toughness (110 MJ m-3), yield strength (73 MPa) and Young's modulus (1 GPa). These values are similar to those of thermoplastics such as polyethylene, yet unlike thermoplastics, the glassy gels can be deformed up to 670% strain with full and rapid recovery on heating. These transparent materials form by a one-step polymerization and have impressive adhesive, self-healing and shape-memory properties.

Compression-induced anti-nematic order in glassy and semicrystalline polymers

We provide new insights into the molecular origin of the asymmetry between uniaxial tensile and compressive deformation of glassy and semicrystalline polymers using molecular dynamics simulations. The difference between the two responses strongly depends on the chain length and is the largest at intermediate chain lengths. Irrespective of chain length, the intra- and interchain organization of polymers under extension and compression are remarkably distinct. The chains align along the tensile axis leading to a global nematic order of the bonds and end-to-end vectors, whereas compression reorganizes polymers to lie in planes perpendicular to the compressive axis resulting in the emergence of an anti-nematic order and destruction of crystallinity. Regardless of the initial glassy or semicrystalline structure, the deformed state of polymers at large strains converge towards the same kind of structure that only depends on the deformation mode.

The Microscopic Structure-Property Relationship of Metal-Organic Polyhedron Nanocomposites

Monodispersed hairy nanocomposites with typical 2 nm (isophthalic acid)₂₄ Cu₂₄ metal-organic polyhedra (MOP) as a core protected by 24 polymer chains with controlled narrow molecular weight distribution has been probed by imaging and scattering studies for the heterogeneity of polymers in the nanocomposites and the confinement effect the MOPs imposing on anchored polymers. Typical confined-extending surrounded by one entanglement area is proposed to describe the physical states of the polymer chains. This model dictates the counterintuitive thermal and rheological properties and prohibited solvent exchange properties of the nanocomposites, whilst those polymer chain states are tunable and deterministic based on their component inputs. From the relationship between the structure and behavior of the MOP nanocomposites, a MOP-composited thermoplastic elastomer was obtained, providing practical solutions to improve mechanical/rheological performances and processabilities of inorganic MOPs.