When dealing with smart polymers, in particular with shape memory polymers, the polymer type and composition specify the overall material properties and in particular the extent of the shape memory effect. Polybenzoxazines as a polymer with high potential for structural applications represent a promising component for materials with both shape memory effect and structurally interesting material properties. This minireview gives insight into how the shape memory effect, in particular the shape recovery event, is influenced by internal factors such as polymer structure, morphology and external factors such as filler addition. 相似文献
We describe an experimental set-up of high resolution thermal analysis (HRTA) activated by Peltier effect and computer-controlled by the signal processing that allows a high resolution programming of the temperature and a reproducibility better than ±0.01 deg.The basic equipment is suitable for studying the behaviour of the shape memory alloys (i.e. Cu based alloys). We also describe the applications of the system, which allows to build up a calorimetric system (heat flux or conduction calorimetry) (resolution 1.5 W) or a stress-strain-temperature system of 20 N of maximum charge (resolution around 1 mN and 0.1 m.CICYT projects MAT89-407-C03-01 and PETRI-90 are gratefully acknowledged. H. T. acknowledges the DGICYT (sabbatic program) for financial aid in international cooperation. The enlightening discussions with Dr. F. C. Lovey (Centro Atomico Bariloche - Argentina) are also acknowledged. 相似文献
In this work, a bilayer shape memory polymer (SMP) composite plate with two-way shape memory behavior is simulated, in which two types of styrene-based SMPs with well-separated glass transition temperatures are assembled in parallel. The finite element (FE) software ABAQUS is selected to exhibit the two-way shape memory effect during the shape recovery step and the Generalized Maxwell Model with the WLF equation is applied to characterize the temperature-dependent properties of the SMP bilayer plates. The effect factors of axial predeformation, thermal expansion coefficient and plate thickness are all considered for the two-way shape memory behavior of the styrene-based bilayer SMP plate. After that, a smart gripper composed of four SMP composite plates is proposed to realize grabbing and releasing functions for one-step and staged heating recovery. The FE results provide some necessary theoretical guidelines for future soft smart structural designs and optimization. 相似文献
Bilayer polymers that consist of two epoxy dual‐shape memory polymers of well‐separated glass transition temperatures have been synthesized. These bilayer epoxy samples exhibit a triple‐shape memory effect (TSME) with shape fixities tailorable by changing the ratio between the two layers. The triple‐shape fixities of the bilayer epoxy polymers can be explained by the balance of stress between the two layers. Based on this work, it is believed that the following three molecular design criterions should be considered in designing triple‐shape memory polymers with optimum TSME: 1) well‐separated thermal transitions, 2) a strong interface, and 3) an appropriate balance of moduli and relative ratios between the layers (or microphases).
Quenching of the eutectoidal composition of the shape memory alloys (SMA’s) allowed us to display the gradual transition of
the martensitic structure as a function of the composition. Indeed, we have verified that for low Al and Ni percentages, the
martensite structure obtained is β′, while, for high Al and Ni (Al<13.3 mass%) contents, the martensite structure is essentially
of β1′ type. Elsewhere, we have observed that a nickel addition (<4.3 mass%) operates simultaneously on the composition of the
eutectoidal pointand the domain of the different martensitic structures types. During reheating of the quenched structure,
the transformation sequences of the martensite to the parent phase (β1), then the decomposition of the later phase into the
equilibrium phases, and finally, the redissolution of all phases to form the β phase at high temperature, are rather similar.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
In this study, high performance shape memory polyurethane (SMPU)/silica nanocomposites with different silica weight fraction including SMPU bulk, 3%, 4.5%, 6%, 7.5%, 10%, were prepared by sol‐gel process initiated by the solid acid catalyst of p‐toluenesulfonic acid (PTSA). Field emission scanning electron microscopy (FE‐SEM) and transmission electron microscopy (TEM) observation show that the silica nanoparticles are dispersed evenly in SMPU/silica nanocomposites. Tensile test and dynamic mechanical analysis (DMA) suggest that the mechanical properties and the glass transition temperature (Tg) of the nanocomposites were significantly influenced by silica weight fraction. Thermogravimetric analysis (TGA) was utilized to evaluate the thermal stability and determine the actual silica weight fraction. The TGA results indicate that the thermal stability can be enhanced with the hybridization of silica nanoparticles. Differential scanning calorimetry (DSC) was conducted to test the melting enthalpy (ΔH) and the results suggest that the ΔH was markedly improved for the SMPU/silica nanocomposites. Thermomechanical test was conducted to investigate the shape memory behavior and the results show that the shape fixity is improved by hybridization of silica and good shape recovery can be obtained with the increasing of cycle number for all the samples. 相似文献