Yong Zhu

Bio: Yong Zhu is an academic researcher from Hong Kong Polytechnic University. The author has contributed to research in topics: Shape-memory polymer & Fiber. The author has an hindex of 25, co-authored 45 publications receiving 2579 citations.

Rapidly switchable water-sensitive shape-memory cellulose/elastomer nano-composites

Abstract: We report a new phenomenon in which the reversible formation and disruption of a cellulose nano-whisker (CNW) percolation network in an elastomeric thermoplastic polyurethane (TPU) matrix leads to an unprecedentedly rapidly switchable shape-memory effect (SME) that may be activated by water The materials have been fully characterized to investigate the SME phenomenon using a number of different experimental techniques including cyclic tensile deformation, dynamic mechanical analysis, FTIR and polarized Raman spectroscopy A model is developed in which it is shown that exposure to water allows breakup of the CNW percolation network so that the flexible elastomer matrix can be deformed to the desired shape The CNW percolation network reforms after drying to provide a fixing force for the temporary shape The entropy elasticity of the TPU matrix then enables rapid shape recovery when the CNW percolation network is disrupted again during wetting This completely athermal water-sensitive SME mechanism is totally different from traditional ones, in which the water or other solvents are used as plasticizers to lower the glass transition temperature of shape memory polymers, so as to allow triggering of the shape recovery at room temperature or lower The reported work provides a novel and effective strategy to achieve rapidly switchable shape recovery in a material by a simple wetting process and fixing through an easily applicable programmed drying process

Smart polymer fibers with shape memory effect

Abstract: In this study, a series of smart polymer fibers with a shape memory effect were developed. Firstly, a set of shape memory polyurethanes with varying hard-segment content were synthesized. Then, the solutions of the shape memory polyurethanes were spun into fibers through wet spinning. The thin films of the polyurethanes were considered to represent the nature of the polyurethanes. Differential scanning calorimetry tests were performed on both the thin films and the fibers to compare their thermal properties. Wide angle x-ray diffraction and small angle x-ray scattering techniques were applied to investigate the structure of the thin films and the fibers, and the structure change taking place in the spinning process was therefore revealed. The spinning process resulted in the polyurethane molecules being partially oriented in the direction of the fiber axis. The molecular orientation prompted the aggregation of the hard segments and the formation of hard-segment microdomains. The mechanical properties of the fibers were examined through tensile tests. The shape memory effect of the thin films and the fibers was investigated through a series of thermomechanical cyclic tensile tests. It was found that the fibers showed less shape fixity but more shape recovery compared with the thin films. Further investigations revealed that the recovery stress of the fibers was higher than that of the thin films. The smart fibers may exert the recovery force of shape memory polymers to an extreme extent in the direction of the fiber axis and therefore provide a possibility for producing high-performance actuators.

Development of shape memory polyurethane fiber with complete shape recoverability

Abstract: To illustrate the shape memory properties of shape memory polyurethane (SMPU) fiber and the difference of thermal/mechanical properties between SMPU fiber and other various man-made fibers, series of shape memory polyurethane having various hard segment content were synthesized with the pre-polymerization method and spun with the wet spinning process. Differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA), and mechanical testing were conducted to study the particular thermal/mechanical properties of shape memory polyurethane fiber in comparison with other man-made fibers such as nylon6, polyester, Lycra and XLA. In addition, in the preparation of shape memory polyurethane fiber, the effect of thermal setting temperature was systematically investigated by mechanical properties testing, DMA and cyclic tensile testing, suggesting that the thermal setting temperature has a huge influence on the mechanical properties and shape memory property due to the elimination of internal stress. Thermal setting with a higher temperature will give rise to a lower tensile modulus and tenacity and a higher elongation ratio at break. Through employing the optimal thermal setting treatment, the complete heating responsive recovery in SMPU fiber can be achieved because of the counteracting effect of the irreversible strain and thermal shrinkage.

Aggregation-Induced Emission: Together We Shine, United We Soar!

Abstract: Ju Mei,†,‡,∥ Nelson L. C. Leung,†,‡,∥ Ryan T. K. Kwok,†,‡ Jacky W. Y. Lam,†,‡ and Ben Zhong Tang*,†,‡,§ †HKUST-Shenzhen Research Institute, Hi-Tech Park, Nanshan, Shenzhen 518057, China ‡Department of Chemistry, HKUST Jockey Club Institute for Advanced Study, Institute of Molecular Functional Materials, Division of Biomedical Engineering, State Key Laboratory of Molecular Neuroscience, Division of Life Science, The Hong Kong University of Science and Technology, Clear Water Bay, Kowloon, Hong Kong, China Guangdong Innovative Research Team, SCUT-HKUST Joint Research Laboratory, State Key Laboratory of Luminescent Materials and Devices, South China University of Technology, Guangzhou 510640, China