Two roles of guest and crosslinked degree on hydrosoluble β-cyclodextrin polymer electrorheological fluids

As a potential candidate for the development of well-controlled electrorheological (ER) materials, five hydrosoluble β-cyclodextrin polymer (2–6)/3-hydroxy-2-naphthoic acid particles (2′–6′) were synthesized. Fluorescence analysis conformed that all the polymers can form 1:1 type supramolecular complex with the guest. The ER properties of suspensions of these particles in silicon oil have been investigated under DC electric field. The yield stress of the typical supramolecular complex (5′) ER fluid was 9.23 kPa at 4 kV/mm. It was much higher than that of pure β-cyclodextrin polymer 5, pure 3-hydroxy-2-naphthoic acid (guest) as well as the mixture of the host and the guest (5+guest). Just because of the formation of supramolecular complex, the improvement of dielectric constant, conductivity and loss tangent of 5 resulted in the enhancement of 5′ ER effect. Meanwhile, the measurement of 2′–6′ dielectric properties was given the evidence that the molar crosslinked degree (m) of the polymer has strong influence on the supramolecular complex ER behavior as well as the host. It was found that the yield stress of the supramolecular complex ER fluid increases initially with m, reaches the maximum at m=7.53 and finally appears a decline at m=8.89, while that of the host has an enhancement trend with the increase of m.