Determinative scrolling and folding of membranes through shrinking channels.

Flat membranes ubiquitously transform into mysterious complex shapes in nature and artificial worlds. Behind the complexity, clear determinative deformation modes have been continuously found to serve as basic application rules but remain unfulfilled. Here, we decipher two elemental deformation modes of thin membranes, spontaneous scrolling and folding as passing through shrinking channels. We validate that these two modes rule the deformation of membranes of a wide thickness range from micrometer to atomic scale. Their occurrence and the determinative fold number quantitatively correlate with the Föppl-von Kármán number and shrinkage ratio. The unveiled determinative deformation modes can guide fabricating foldable designer microrobots and delicate structures of two-dimensional sheets and provide another mechanical principle beyond genetic determinism in biological morphogens.

Falling-Leaves Stacking Aggregation of Two-Dimensional Macromolecular Graphene Oxide in Solution.

Understanding the dynamical behaviors of two-dimensional (2D) macromolecules is of fundamental importance for the precise modulation of their assembled structures and material performances. However, considerably less is known about how discrete macromolecular sheets aggregate into extended macroscopic assemblies in solutions. The absence of a quantitative description of the assembly process limits the precise structural control of assemblies. Here, we investigated the aggregation thermodynamic transition and kinetic behavior of 2D macromolecules in the model of single layer graphene oxide (GO). Combining Flory-Huggins theory with experimental observations, we unveiled the critical thermodynamic transition of GO to correlate with the solvent property. We proposed a theoretical falling-leaf model to quantitatively describe the kinetic aggregation process of 2D GO sheets. Experimental analysis validated the theoretical prediction that the thickness of GO aggregates has a power law relation with the poor solvent content. Our work provides a fundamental understanding of phase separation of 2D macromolecules and offers an insight into modulating the aggregated structures of their assembled materials.

High-Performance Nonisocyanate Thermoplastic Polythiourethane with High Hydrogen Bond Content.

Nonisocyanate polyurethane (NIPU) has been extensively studied because of its sustainability potential. However, the low reactivity of five-membered cyclocarbonates with amines and the side reactions at higher temperatures always sacrifice the performance of NIPUs. In this work, a bisphenol-S cyclic thiocarbonate and different amino-terminated dimer-acid polyamides (DAPAs) were used to prepare nonisocyanate polythiourethanes (SPTU-DAs). Wherein bisphenol-S acts as a hard segment due to a π-π package, plentiful hydrogen bonds introduced by DAPA units induce crystallization and nanophase separation. They both endow the NIPUs with high mechanical performance. Meanwhile, active cyclic thiocarbonate, instead of cyclic carbonate, ensures rapid synthesis under mild conditions without side reactions. The experimental results of DSC, WAXD, and DMA confirmed the existence of crystallization of SPTU-DAs. The as-prepared thermoplastic polythiourethane has a maximum strength of more than 10 MPa, which is stronger than those of the cross-linked nonisocyanate polythiourethanes reported. It is of key significance to obtain the high performance of nonisocyanate polythiourethanes.