NR/GE composites were prepared by an ultrasonically‐assisted latex mixing and in situ reduction process. Graphene oxide was dispersed in NRL using an ultrasonic field and was then reduced in situ, followed by latex coagulation to obtain the NR/GE masterbatch. The results show that the process produces a much better dispersion and exfoliation of GE in the matrix and contributes to an increase in the tensile strength compared to conventional direct mixing. Compared to pure rubber, the tensile strength and tear strength for NR/(2 wt.‐%)GE composites were increased by ≈47 and 50%, respectively. With increasing GE content, the maximum torque, crosslink density, elastic modulus, and thermal conductivity of NR/GE composites were found to increase. magnified image
Physically cross-linked isotropic and anisotropic poly(vinyl alcohol) (PVA) hydrogels containing micron-sized carbonyl iron particles were prepared through a cyclic freezing-thawing process. The PVA hydrogel can respond to a magnetic field and shows a magnetorheological (MR) effect, i.e., the modulus of the PVA hydrogel can be adjusted under a magnetic field. The chain-like structures of carbonyl iron are formed in the PVA hydrogel after orientation under a magnetic field of 1.5 T. Also some magnetic field induced oriented pores with a tunable diameter are observed in the dried PVA gel. The MR effect can be adjusted by changing the carbonyl iron content, the initial concentration of PVA solution and test frequency. The formation of aligned chain-like structures of carbonyl iron in the anisotropic PVA MR hydrogel improves the compression properties and the MR effect. At a carbonyl iron content of 70 wt%, the maximum absolute and relative MR effect of anisotropic PVA MR hydrogels are $1.24 MPa and $230%, respectively. The PVA hydrogels with good MR effects and moderate mechanical strength have potential applications in artificial muscle, soft actuators and drug release.
Highly filled polytetramethylene ether glycol (PTMEG)-based polyurethane (PU) magnetorheological elastomers (MREs) with anisotropic structure and good mechanical properties were prepared. The difficulty in dispersion and orientation of iron particles in the PU elastomer was overcome by ball milling mixing and further in situ one-step polycondensation under a magnetic field. The microstructure and properties of the composite were characterized in detail. Scanning electron microscopy (SEM) showed that a chain-like structure of carbonyl iron was formed in the PU matrix after orientation under a magnetic field of 1.2 T. The aligned chain-like structure of carbonyl iron in PU greatly enhanced the thermal conductivity, the compression properties and the magnetorheological (MR) effect of anisotropic PU MREs compared to that of the isotropic one. When the test frequency is 1 Hz, the maximum absolute and relative MR effect of anisotropic PU MREs with 26 wt% hard segment and 70 wt% carbonyl iron were ∼1.3 MPa and ∼ 21%, respectively.
ABSTRACT:The highly filled isotropic polyurethane (PU) elastomer with a magnetorheological (MR) effect was prepared through an in situ polycondensation method. The carbonyl iron particles were treated by coupling agents and then the dispersions of polyol/carbonyl iron particles was prepared by a ball milling process. The dispersion problem of magnetizable particles at a high content in PU matrix was tried to overcome by the combination of surface modification, ball milling, and in situ polymerization. The microstructure and properties of the composite were examined in detail. With increasing the content of carbonyl iron particles, the degree of phase separation of PU increased and the glass transition temperature (T g ) of PU soft segment decreased. Highly filled carbonyl iron particles led to the decrease in the thermal stability of PU matrix, especially in the heating air atmosphere. The MR effect appeared when the content of carbonyl iron particles was higher than 50 wt %, and became relatively pronounced at a 70 wt % of carbonyl iron content. The mechanical properties of PU MR elastomers were deteriorated significantly at a high content of carbonyl iron. Surface modification of carbonyl iron particles can improve the mechanical properties to some extent; however, it was also found that surface modification led to a decrease in the MR effect because of the improved interfacial adhesion. The MR test showed that the maximum absolute MR effect and relative MR effect of PU composite were $ 0.31 MPa and $ 8.1% at 1 Hz and 400 mT with 70 wt % of carbonyl iron, respectively.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.