This document discusses complex fluids, which exhibit both liquid-like and solid-like properties. Complex fluids include polymeric solutions, gels, foams, and granular materials. They have heterogeneous structures with fluctuations across different length and time scales. When molecules in a polymeric solution or melt become sufficiently crosslinked, a gel transition occurs where a macroscopic cluster forms, localizing the molecules. The dynamics of particles in complex fluids are highly nonlinear and irregular, alternating between solid-like arrested states and fluid-like behavior depending on factors like density, temperature, and external forces inducing flow. While complex fluids are common in nature, their material properties are not fully understood and more research is still needed.

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).
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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.
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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.
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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
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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.
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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.
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