IR Heating of CNT-SMP composites

The ability to control mechanical devices remotely by IR light with high speed and spatial precision offers many intriguing possibilities.The low recovery speed (up to several minutes) of thermo-responsive SMPs originates from their intrinsically low thermal conductivity ( 0.3 W m  

The low recovery stress ( 10 MPa) of thermo-responsive SMPs originates from their intrinsically low modulus, in the order of 0.1-1 GPa below the thermal transition temperature. CNTs have proven to enhance the mechanical properties, particularly modulus, of various polymers.  

For example, Koerner et al. ° have found that 8.5 wt% MWNTs could increase the room temperature rubbery modulus of TPU by a factor of 5. In fact, incorporation of 5 wt% of MWNTs into the TPU matrix results in an increase of the recovery stress by 130%. Similarly, Ni et al. have reported that adding 3.3 wt% MWNTs into the TPU matrix leads to an increase in the recovery stress by 100%. The recent study on mechanical properties of CNT-TPU at various nanotube loadings suggests that the reinforcement mechanism is largely due to the immobilization of TPU soft segments by adsorption on to the nanotube surface, which suppresses the glass transition and increases the stress at low strains.  

Chemical functionalization of CNT surfaces could improve their dispersion in the polymer matrix and enhance the nanotube-polymer interfacial interaction and the mechanical load transfer. The effects of nanotube functionalization on the properties of CNT-TPU composites have been investigated in details. Xia and Song have synthesized polycaprolactone polyurethane (PU)-grafted SWNTs (PU-g-SWNTs) and corresponding PU-g-SWNT-PU composites by in-situ polymerization. The results show that PU-g-SWNTs improve the dispersion of SWNTs in the PU matrix and strengthen the interfacial interaction between the PU and SWNTs. Compared with neat PU and pristine SWNT PU composites, PU-g-SWNT-PU composites demonstrate remarkable enhancement on Young s modulus. The Young s modulus of a 0.7 wt /o PU-g-SWNT-PU composite increases by 178% over the blank PU and 88% over the 0.7 wt% pristine SWNT-PU composite, respectively. 

Khan et al. have prepared various composites from a TPU reinforced with two types of chemically functionalized SWNTs water-soluble tubes functionalized with poly(ethylene glycol) (PEG-SWNTs) or poly(amino benzene sulfonic acid) (PASS SWNTs) and tetrahydrafuran-soluble tubes functionalized with octadecylamine (ODA-SWNTs). SWNT-TPU composites prepared with water- or tetrahydrafuran-soluble tubes display markedly different properties. The addition of water-soluble tubes tends to result in crystallization of the PU soft segments, whereas addition of the tetrahydrafuran-soluble tubes promotes crystallization of the PU hard segments. This observation suggests 

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