Liquid complexes

Complex fluids

1. LIQUID COMPLEX OR COMPLEX FLUIDS Presented by: Mahewash Sana A. Pathan

2. LIQUID COMPLEX OR COMPLEX FLUIDS “Complex fluids and soft matter are materials intermediate between conventional liquids and solids, displaying fluid‐like as well as solid‐like behavior”. OR “Complex fluids are binary mixtures that have a coexistance between two phases: solid- liquid (suspensions or solutions of macromolecules such as polymers), solid-gas (granular), liquid-gas (foams) & liquid- liquid ( emulsions). 2

3. Examples are polymeric melts or solutions, glasses, gels, foams and granular matter. Many of these systems are inherently disordered and strongly heterogeneous with large fluctuations on a wide range of length‐ and time‐scales. Furthermore many complex fluids, such as glasses or gels, never relax to equilibrium, which makes a theoretical analysis difficult. Complex systems are distinguished by a rather general common feature: their behavior is determined by competing processes of self-organization (ordering) and self disorganization (disordering) creating a hierarchical adaptive structure. 3

4. A notion of complexity is also used in amorphous materials exhibiting slow and non-exponential relaxation , in particular in glass-forming liquids and glasses . Not every liquid becomes complex on cooling. Three-dimensional ( 3D) liquids with simple two-particle interactions (molten metals and salts, liquefied noble gases, and also computer liquids of Lennard -Jones ( LJ), soft core, Morse particles) aggressively crystallize on cooling before they show any significant signs of complexity. 4

5. Gels and glasses: If the molecules in a polymeric melt or dense solution are sufficiently crosslinked, a gel transition is observed, when a macroscopic cluster of connected molecules forms for the first time. Whereas in the fluid or sol phase at low crosslinking the molecules explore all the available volume, in the gel or amorphous solid phase the particles are localized a random positions and perform finite thermal excursions. Fig. 1: Spanning cluster (green) of crosslinked molecules 5

6. DYNAMICS Dynamics of particles in complex fluids are an area of current research. Energy lost due to friction may be a non linear function of the velocity and normal forces. The topological inhibition to flow by the crowding of constituent particles is a key element in these systems. Under certain conditions, including high  densities  and low  temperatures, when externally driven to induce flow, complex fluids are characterized by irregular intervals of solid-like behavior followed by stress relaxations due to particle rearrangements . The dynamics of these systems are highly nonlinear in nature . The increase in stress by an infinitesimal amount or a small displacement of a single particle can result in the difference between an arrested state and fluid-like behavior . 6

7. Although many materials found in nature can fit into the class of complex fluids, very little is well understood about them. Inconsistent and controversial conclusions concerning their material properties still persist. The careful study of these systems may lead to "new physics" and new states of matter. For example, it has been suggested that these systems can jam and a "jamming phase diagram" can be used to consider how these systems can jam and unjam . It is not known whether further research will demonstrate these findings, or whether such a theoretical framework will prove useful. As yet this large body of theoretical work has been poorly supported with experiments. 7

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