Shape memory polymers (SMPs) have attracted great interest in recent years. The SMP foams are outstanding, owing to their high shape recovery ratio in compression. They can be used for, for instance, micro foldable vehicles, shape determination, and microtags. This article presents a study on the thermomechanical behavior of a polyurethane SMP foam, associated with these three applications. This includes four types of tests namely, compression test, free recovery test, constrained cooling test, and gripping test.

The behaviour in simple shear of two concentrated and strongly cohesive mineral suspensions showing highly non-monotonic flow curves is described. Two rheometric test modes were employed, controlled stress and controlled shear-rate. In controlled stress mode the materials showed runaway flow above a yield stress, which, for one of the suspensions, varied substantially in value and seemingly at random from one run to the next, such that the up flow-curve appeared to be quite irreproducible. The down-curve was not though, as neither was the curve obtained in controlled rate mode, which turned out to be triple-valued in the region where runaway flow was seen in controlled rising stress. For this first suspension, the total stress could be decomposed into three parts to a good approximation: a viscous component proportional to a plastic viscosity, a constant isostatic contribution, and a third shear-rate dependent contribution associated with the particulate network which decreased with increasing shear-rate raised to the -7/10th power. In the case of the second suspension, the stress could be decomposed along similar lines, although the strain-rate softening of the solid-phase stress was found to be logarithmic and the irreducible isostatic stress was small. The flow curves are discussed in the light of 2 recent simulations and they conform to a very simple but general rule for nonmonotonic behaviour in cohesive suspensions and emulsions, namely that it is caused by strain-rate softening of the solid phase stress.

An experimental system has been found recently, a coagulated CaCO 3 suspension system, which shows very variable yield behaviour depending upon how it is tested and, specifically, at what rate it is sheared. At Péclet numbers Pe > 1 it behaves as a simple Herschel Bulkley liquid, whereas at Pe < 1 highly non-monotonic flow curves are seen. In controlled stress testing it shows hysteresis and shear banding and in the usual type of stress scan, used to measure flow curves in controlled stress mode routinely, it can show very erratic and irreproducible behaviour. All of these features will be attributed here to a dependence of the solid phase, or, yield stress, on the prevailing rate of shear at the yield point. Stress growth curves obtained from step strain-rate testing showed that this rate-dependence was a consequence of Péclet number dependent strain softening. At very low Pe, yield was cooperative and the yield strain was order-one, whereas as Pe approached unity, the yield strain reduced to that needed to break interparticle bonds, causing the yield stress to be greatly reduced. It is suspected that rate-dependent yield could well be the rule rather than the exception for cohesive suspensions more generally. If so, then the Herschel-Bulkley equation can usefully be generalized to readThe proposition that rate-dependent yield might be general for cohesive suspensions is amenable to critical experimental testing by a range of means and along lines suggested.8

The drying of particulate suspensions is important to many industries such as paints, ceramics, minerals processing, and pharmaceuticals. Cakes or films first consolidate due to capillary pressure and, at a critical concentration, stop consolidating and begin to desaturate. Desaturation occurs once the compressive strength of the particulate network is greater than the maximum capillary pressure at the air-liquid interface. This work combines existing descriptions of the compressive strength and the maximum capillary pressure to give the dependencies of volume fraction, particle size, interparticle bond strength, surface tension, and contact angle on the breakthrough pressure and critical concentration. Understanding the interplay of these system parameters explains the point of desaturation in filtration and drying processes, allowing optimization of these processes, including mitigation of cracking. Air-driven filtration results are presented for the direct measurement of breakthrough pressure of coagulated calcium carbonate.

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