Stimuli responsive materials based on cellulosic fibers.

摘要

Cellulose is the most abundant polymeric material in nature. In this study, the application of cellulose and its synthetic derivatives in electrorheological (ER) or magnetorheological (MR) materials has been investigated. For ER fluids based on underivatized cellulose, the mobility of water adsorbed onto cellulose was shown to strongly influence performance. The maximum ER response for a water-activated fluid at 25°C was observed at a moisture content near the transition of "less mobile" (LM) "liquid-like" water to "more mobile" (MM) "liquid-like" non-freezing water. Diethylaminoethyl (DEAE) cellulose and cellulose sulfate were prepared from microcrystalline cellulose through heterogeneous reactions and characterized for particle size, the degree of substitution (DS) of ionic groups, thermal stability, etc. For DEAE cellulose containing ER fluids, trace water and ionized DEAE groups may enhance the polarization of particles producing improved ER response. These fluids can be categorized into two types (i) water-activated or (ii) operationally anhydrous depending on the particle water content. For water-activated DEAE cellulose-based fluids, water deteriorated ER strength with increasing temperature. For operationally anhydrous DEAE cellulose-based ER fluids, residual moisture enhanced ER response with increasing temperature and yield stress reached around 1000 Pa at 80°C suggesting that DEAE cellulose has excellent potential as a particulate phase for high temperature ER fluids. Cellulose sulfate (DS = 0.9) coated on a hollow glass bead surface significantly improved the ER effect of fluids compared with the effect of uncoated beads, providing a prototype "buoyant" particulate phase. For pre-aligned DEAE cellulose containing ER elastomers, storage moduli were enhanced over 300% at 2.5 kV/mm compared with storage moduli in the absence of a field. Cellulose/ferrite composites containing 26%--32% ferrites in silicone oil showed a very weak MR response compared to a commercial available fluid Lord MRF-132AD.