| Shear thickening (ST) is a non-Newtonian flow behavior sometimes observed in highly concentrated dispersion system, in which the viscosity exhibit an abrupt increase by several orders of magnitude once the shear rate reaches a critical value. Such ST behavior is characteristic of shear thickening fluids (STFs). STFs are concentrated colloidal suspensions composed of non-aggregated micron/nano particles suspended evenly in dispersants such as ethylene glycol, polyethylene and so on. The early investigations in ST behavior were to eliminate its damage in the industrial production. However, the unique mechanical properties of increased energy dissipation combined with increased elastic modulus make STFs ideal for damping and shock-absorption application. In addition, people prepared a new enhanced body armor composed of Kevlar fabrics impregnated with STFs. The new body armor is not only soft and comfortable, but also enhanced the ballistic penetration resistance. In today’s rampant terrorism, the demand for security is increasing. Motivated by this demand, the STFs have been attracted more and more people’s attention. The potential applications of STFs are wide, while the practical systems of STFs are limited. In addition, although the influence of the external macroscopic factors on the ST behavior has been carefully studied in the past decades, there has been comparatively little research into the influence of the suspended particles’inner structure. Finally, in application of damper, physical protection and so on, the STFs with strong ST effect are necessary for the energy absorption. Therefore, the preparation of enhanced STFs is emergent for the development of STFs’application. In this work, we developed a novel kind of STF to broaden the practical STF systems. The particles’structure dependent ST behavior has also been investigated systematically. The STFs enhanced by non-ionic surfactants were prepared and studied to optimize the shear thickening behavior of STFs. The details are as follows:1. A novel kind of STF was developed, and its ST properties were studied. The monodispersed poly(styrene-acrylic acid)(PS-AA) nanospheres with average diameter of about300nm were synthesized through soap-free emulsion polymerization and dispersed into ethylene glycol solvent for preparing a new STF. Its reversibility and stability of were studied. At the same time, the influence of particle concentration, particle dispersion and temperature on the ST behavior was also been researched. In addition, further investigation on dynamic ST behavior was conducted. The results show that the new STF can be applied in the application of moderate intensity energy dissipation and the ST behavior of STF were reversible and stabilized. Its rheological behavior of STF depends on the particle concentration, particle dispersion and temperature. The rheological properties under dynamic test are associated with strain and angular frequency.2. Based on the new STF, the particles’structure dependent ST behavior was investigated systematically. PS-AA nanospheres with different molecular structures were synthesized by varying both the monomer molar ratio of styrene/acrylic acid (St/AA) and cross-linking reagent divinyl benzene (DVB). A series of STFs were prepared by suspended the particles with different structures. The rheological properties of these STFs were measured under steady shear and oscillatory shear by a stress rheometer. The result showed that at high ratio of St/AA, the STF exhibited a better ST effect, while further increasing the ratio was harmful. An optimum St/AA ratio was found (7/1) and the maximum viscosity of the best STF was up to152.2Pa-s as the mass fraction increased to56%. The PS-AA-DVB based STFs exhibited much higher ST effects and the maximum viscosity was up to385Pa-s when the DVB was only increased to0.3%. In combination of the rheological properties and the structure characterization, the influence of the particles’characteristics on the mechanical performance of the PS-AA based STF was carefully analyzed.3. The influence of the various types of non-ionic surfactant on the ST behavior was investigated to optimize the ST performance. The studied non-ionic surfactants included Span20, Tween20, TX100, OP-10, PEG (400,1000,20000). Experimental results showed that Span20, Tween20, TX100and PEG (1000,20000) enhanced the ST effect of STF, while OP-10and PEG400weakened it. Some kinds of non-ionic surfactant have the opposite effect in spite of the similar structure. |
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