Featured Research

from universities, journals, and other organizations

Engineer discovers why particles disperse on liquids

Date:
November 18, 2009
Source:
New Jersey Institute of Technology
Summary:
Even if you are not a cook, you might have wondered why a pinch of flour (or any small particles) thrown into a bowl of water will disperse in a dramatic fashion, radiating outward as if it was exploding. A mechanical engineering professor can now explain why.

NJIT's Pushpendra Singh (right) and his graduate student examine particles in a dish.
Credit: New Jersey Institute of Technology

Even if you are not a cook, you might have wondered why a pinch of flour (or any small particles) thrown into a bowl of water will disperse in a dramatic fashion, radiating outward as if it was exploding. Pushpendra Singh, PhD, a mechanical engineering professor at NJIT who has studied and written about the phenomenon, has not only thought about it, but can explain why.

He says that what's known as the "repulsive hydrodynamic force arising from the oscillation of particles" causes them to disperse. A particle trapped in a liquid surface vibrates up and down from its equilibrium position on the surface, or interface, where air meets water. When many particles do this simultaneously, an explosive dispersion occurs.

Singh says that when small particles, such as flour or pollen, come in contact with a liquid surface, they immediately disperse and form a monolayer. The dispersion occurs so quickly that it appears explosive, especially on the surface of liquids like water.

This explosive dispersion is a consequence of the capillary force pulling particles towards their equilibrium positions in the interface. The capillary force causes the particles to accelerate very rapidly.

"If a particle barely touches the interface, it is pulled onto the surface," said Singh. "For example, if the contact angle for a spherical particle is 90 degrees, it floats in the state of equilibrium so that one-half of it is above the surface and the remaining half is below. If the particle, however, is not in this position, the capillary force will force it to be."

What's interesting is that the smaller the particles, the faster they move. For nanometer-sized particles like viruses and proteins, the velocity or speed on an air-water interface can be as high as 167 kilometers (about 100 miles) per hour.

Singh says the motion of the particles is dominated by inertia because the viscous damping -- which is like friction -- is too small. He compares the situation to a moving pendulum. "The pendulum will oscillate many times before friction makes it stop," he says. "If friction is too great, it won't oscillate."

Eventually, the particles which have been oscillating around their equilibrium point will stop--thanks to viscous drag which causes resistance to the motion.

"Let me explain more about viscous drag," said Singh. "When a body, such as a ball, moves through air or liquid, it will resist the motion. This resistance is caused by viscous drag. Or look at it this way. When a particle is adsorbed at a surface, it acquires a part of the released interfacial energy as kinetic energy," he says. "The particle dissipates this kinetic energy by oscillating from its equilibrium height in the interface. The act gives rise to repulsive hydrodynamic forces, the underlying cause of why particles disperse."

The National Science Foundation has supported this research.



Story Source:

The above story is based on materials provided by New Jersey Institute of Technology. Note: Materials may be edited for content and length.


Journal Reference:

  1. Singh et al. Spontaneous dispersion of particles on liquid surfaces. Proceedings of the National Academy of Sciences, 2009; DOI: 10.1073/pnas.0910343106

Cite This Page:

New Jersey Institute of Technology. "Engineer discovers why particles disperse on liquids." ScienceDaily. ScienceDaily, 18 November 2009. <www.sciencedaily.com/releases/2009/11/091117102042.htm>.
New Jersey Institute of Technology. (2009, November 18). Engineer discovers why particles disperse on liquids. ScienceDaily. Retrieved July 26, 2014 from www.sciencedaily.com/releases/2009/11/091117102042.htm
New Jersey Institute of Technology. "Engineer discovers why particles disperse on liquids." ScienceDaily. www.sciencedaily.com/releases/2009/11/091117102042.htm (accessed July 26, 2014).

Share This




More Matter & Energy News

Saturday, July 26, 2014

Featured Research

from universities, journals, and other organizations


Featured Videos

from AP, Reuters, AFP, and other news services

Europe's Highest Train Turns 80 in French Pyrenees

Europe's Highest Train Turns 80 in French Pyrenees

AFP (July 25, 2014) Europe's highest train, the little train of Artouste in the French Pyrenees, celebrates its 80th birthday. Duration: 01:05 Video provided by AFP
Powered by NewsLook.com
TSA Administrator on Politics and Flight Bans

TSA Administrator on Politics and Flight Bans

AP (July 24, 2014) TSA administrator, John Pistole's took part in the Aspen Security Forum 2014, where he answered questions on lifting of the ban on flights into Israel's Tel Aviv airport and whether politics played a role in lifting the ban. (July 24) Video provided by AP
Powered by NewsLook.com
Creative Makeovers for Ugly Cellphone Towers

Creative Makeovers for Ugly Cellphone Towers

AP (July 24, 2014) Mobile phone companies and communities across the country are going to new lengths to disguise those unsightly cellphone towers. From a church bell tower to a flagpole, even a pencil, some towers are trying to make a point. (July 24) Video provided by AP
Powered by NewsLook.com
Algonquin Power Goes Activist on Its Target Gas Natural

Algonquin Power Goes Activist on Its Target Gas Natural

TheStreet (July 23, 2014) When The Deal's Amanda Levin exclusively reported that Gas Natural had been talking to potential suitors, the Ohio company responded with a flat denial, claiming its board had not talked to anyone about a possible sale. Lo and behold, Canadian utility Algonquin Power and Utilities not only had approached the company, but it did it three times. Its last offer was for $13 per share as Gas Natural's was trading at a 60-day moving average of about $12.50 per share. Now Algonquin, which has a 4.9% stake in Gas Natural, has taken its case to shareholders, calling on them to back its proposals or, possibly, a change in the target's board. Video provided by TheStreet
Powered by NewsLook.com

Search ScienceDaily

Number of stories in archives: 140,361

Find with keyword(s):
Enter a keyword or phrase to search ScienceDaily for related topics and research stories.

Save/Print:
Share:

Breaking News:
from the past week

In Other News

... from NewsDaily.com

Science News

Health News

Environment News

Technology News



Save/Print:
Share:

Free Subscriptions


Get the latest science news with ScienceDaily's free email newsletters, updated daily and weekly. Or view hourly updated newsfeeds in your RSS reader:

Get Social & Mobile


Keep up to date with the latest news from ScienceDaily via social networks and mobile apps:

Have Feedback?


Tell us what you think of ScienceDaily -- we welcome both positive and negative comments. Have any problems using the site? Questions?
Mobile: iPhone Android Web
Follow: Facebook Twitter Google+
Subscribe: RSS Feeds Email Newsletters
Latest Headlines Health & Medicine Mind & Brain Space & Time Matter & Energy Computers & Math Plants & Animals Earth & Climate Fossils & Ruins