Complex fluids

Complex fluids

Complex fluids are binary mixtures that have a coexistence between two phases: solid–liquid (suspensions or solutions of macromolecules such as polymers), solid–gas (granular), liquid–gas (foams) and liquid–liquid (emulsions). They exhibit unusual mechanical responses to applied stress or strain due to the geometrical constraints that the phase coexistence imposes. The mechanical response includes transitions between solid-like and fluid-like behavior as well as fluctuations. Their mechanical properties can be attributed to characteristics such as high disorder, caging, and clustering on multiple length scales.

Example

Shaving cream is an example of a complex fluid. Without stress, the foam appears to be a solid: it does not flow and can support (very) light loads. However, when adequate stress is applied, shaving cream flows easily like a fluid. On the level of individual bubbles, the flow is due to rearrangements of small collections of bubbles. On this scale, the flow is not smooth, but instead consists of fluctuations due to rearrangements of the bubbles and releases of stress. These fluctuations are similar to the fluctuations that are studied in earthquakes.

Dynamics

The dynamics of the particles in complex fluids are an area of current research. Energy lost due to friction may be a nonlinear 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.

Although many materials found in nature can fit into to the class of complex fluids, very little is well understood about them. Inconsistent and controversial conclusions concerning their material properties still persists. 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.

External links


Wikimedia Foundation. 2010.

Игры ⚽ Поможем написать курсовую

Look at other dictionaries:

  • Migrating motor complex — Migrating motor complexes (or migrating myoelectric complex) are waves of activity that sweep through the intestines in a regular cycle during fasting state. These motor complexes help trigger peristaltic waves which facilitate transportation of… …   Wikipedia

  • Kennedy Space Center Launch Complex 39 — Launch Complex 39 redirects here. For the Proton launch complex at Baikonur, see Baikonur Cosmodrome Site 200. Launch Complex 39 An aerial view of Launch Complex 39 Launch site Kennedy Space Center Locat …   Wikipedia

  • Major Histocompatibility Complex and Sexual Selection — A pathogen is any agent that causes disease. The body has two defense mechanisms for dealing with pathogenic microorganisms and other harmful substances: the inflammatory reaction and the development of an acquired immunity. Acquired immunity… …   Wikipedia

  • Oceanic core complex — An oceanic core complex (OCC), or megamullion, is a seabed geologic feature that forms a long ridge perpendicular to a mid ocean ridge. It contains smooth domes that are lined with transverse ridges like a corrugated roof. They can vary in size… …   Wikipedia

  • immune complex diseases — Diseases characterized by the presence of immune complexes in body fluids. Hypersensitivity of the Arthus type and serum sickness are examples …   Dictionary of molecular biology

  • Max Planck Institute for Dynamics and Self-Organization — The Max Planck Institute for Dynamics and Self organisation in Göttingen, Germany, is a research institute for investigations of complex non equilibrium systems, particularly in physics and biology. Its founding history goes back to Ludwig… …   Wikipedia

  • Polymer field theory — A polymer field theory within the framework of statistical mechanics is a statistical field theory, describing the statistical behavior of a neutral or charged polymer system within the field theoretic approach.It can be derived by transforming… …   Wikipedia

  • Raghunath Anant Mashelkar — Infobox Scientist name = Raghunath Anant Mashelkar box width = image width = 200px caption = World renowned scientist birth date = January 1, 1943 birth place = Mashel, Goa death date = death place = residence = Pune citizenship = nationality =… …   Wikipedia

  • Dissipative particle dynamics — (DPD) is a stochastic simulation technique for simulating the dynamic and rheological properties of simple and complex fluids. It was initially devised by Hoogerbrugge and Koelman [1][2] to avoid the lattice artifacts of the so called lattice gas …   Wikipedia

  • David A. Weitz — Born October 3, 1951(1951 10 03) Ottawa, Ontario, Canada Residence U.S …   Wikipedia

Share the article and excerpts

Direct link
Do a right-click on the link above
and select “Copy Link”