Liquid-like at rest, dense suspensions of hard particles can undergo striking transformations in behaviour when agitated or sheared. These phenomena include solidification during rapid impact, as well as strong shear thickening characterized by discontinuous, orders-of-magnitude increases in suspension viscosity. Much of this highly non-Newtonian behaviour has recently been interpreted within the framework of a jamming transition. However, although jamming indeed induces solid-like rigidity, even a strongly shear-thickened state still flows and thus cannot be fully jammed. Furthermore, although suspensions are incompressible, the onset of rigidity in the standard jamming scenario requires an increase in particle density. Finally, whereas shear thickening occurs in the steady state, impact-induced solidification is transient. As a result, it has remained unclear how these dense suspension phenomena are related and how they are connected to jamming. Here we resolve this by systematically exploring both the steady-state and transient regimes with the same experimental system. We demonstrate that a fully jammed, solid-like state can be reached without compression and instead purely with shear, as recently proposed for dry granular systems. This state is created by transient shear-jamming fronts, which we track directly. We also show that shear stress, rather than shear rate, is the key control parameter. From these findings we map out a state diagram with particle density and shear stress as variables. We identify discontinuous shear thickening with a marginally jammed regime just below the onset of full, solid-like jamming. This state diagram provides a unifying framework, compatible with prior experimental and simulation results on dense suspensions, that connects steady-state and transient behaviour in terms of a dynamic shear-jamming process.

Unlike dry granular materials, a dense granular suspension like cornstarch in water can strongly resist extensional flows. At low extension rates, such a suspension behaves like a viscous fluid, but rapid extension results in a response where stresses far exceed the predictions of lubrication hydrodynamics and capillarity. To understand this remarkable mechanical response, we experimentally measure the normal force imparted by a large bulk of the suspension on a plate moving vertically upward at controlled velocity. We observe that, above a velocity threshold, the peak force increases by orders of magnitude. Using fast ultrasound imaging we map out the local velocity profiles inside the suspension, which reveal the formation of a growing jammed region under rapid extension. This region interacts with the rigid boundaries of the container through strong velocity gradients, suggesting a direct connection to the recently proposed shear-jamming mechanism.

We show that the shear rate at a fixed shear stress in a micellar gel in a jammed state exhibits large fluctuations, showing positive and negative values, with the mean shear rate being positive. The resulting probability distribution functions (PDF's) of the global power flux to the system vary from Gaussian to non-Gaussian, depending on the driving stress and in all cases show similar symmetry properties as predicted by Gallavotti-Cohen steady state fluctuation relation. The fluctuation relation allows us to determine an effective temperature related to the structural constraints of the jammed state. We have measured the stress dependence of the effective temperature. Further, experiments reveal that the effective temperature and the standard deviation of the shear rate fluctuations increase with the decrease of the system size. with Σ = 1. Here, s τ = 1 τ t+τ t s(t ) dt and s(t) is the rate of entropy production in the non-equilibrium steady state. P (+s τ ) is the probability of observing a fluctuation of magnitude s τ over a phase space trajectory of duration τ which is larger than any microscopic time scale of the system. Naturally, P (−s τ ) gives the probability of transient violation of second law of thermodynamics for the time τ , as the entropy decreases over this time.The physical implication of Eq (1) is that, if the value of s τ and τ is large, as in case of macroscopic systems and time scales, P (+s τ ) >> P (−s τ ), i.e. the probability of observing entropy increasing fluctuations are overwhelmingly large compared to those in which entropy decreases. Thus, in classical thermodynamics we never see the decrease in entropy in any physical process. Extension of steady state fluctuation theorem for finite times is discussed in [6]. The experiments on Fluctuation Relation (FR) reported so far can be broadly divided into two classes. Experiments on systems with small number of degrees of freedom include dragging of a Brownian particle in an optical trap [7,8], electrical circuits [9], RNA stretching [10,11] where RNA free energy between folded and unfolded states were estimated using Crook's Relation and Jarzynski Equality and stochastic harmonic oscillators [12,13]. The second class of experiments which is of relevance here, includes macroscopic systems with large number of degrees of freedom such as, Rayleigh-Benard convection [14,15], pressure fluctuations on a surface kept in turbulent flows [4], vertically shaken granular beads [5], Lagrangian turbulence on a free surface [16] and liquid crystal electro-convection [17]. To our knowledge no experimental evidence exists for the FR in large volume sheared fluids. In this Letter we address, for the first time, instance of the FR in case of a macroscopic sized sheared micellar gel in a jammed state. In our context s(t) =, where P(t) is the instantaneous power flux into the system and T ef f is the effective temperature of the system. We show that the nature of PDF's of global power flux for the same system can be Gaussian or non-Gaussian, depending on t...

We report the interfacial properties of monolayers of Ag nanoparticles 10-50 nm in diameter formed at the toluene-water interface under steady as well as oscillatory shear. Strain amplitude sweep measurements carried out on the film reveal a shear thickening peak in the loss moduli (G") at large amplitudes followed by a power law decay of the storage (G') and loss moduli with exponents in the ratio 2:1. In the frequency sweep measurements at low frequencies, the storage modulus remains nearly independent of the angular frequency, whereas G" reveals a power law dependence with a negative slope, a behavior reminiscent of soft glassy systems. Under steady shear, a finite yield stress is observed in the limit of shear rate .gamma going to zero. However, for .gamma > 1 s-1, the shear stress increases gradually. In addition, a significant deviation from the Cox-Merz rule confirms that the monolayer of Ag nanoparticles at the toluene-water interface forms a soft two-dimensional colloidal glass.