# Electrorheological fluids

1. Jan 17, 2005

ive been reading up a little bit, (a very little bit actually, i have really bad science info sources lol) about electrorheological fluids, now as i understand it, these fluids increse in viscosity as voltage increses. doesnt this meen taht density or mass should increece also? couldnt that meen taht the volume of this substance would increese, but then, how could the substance be getting more dence if the mollecules themselves were getting farther apart? i have a fealing that there are quite a few things i am missing. anyone care to help?

P.S. im still trying to figure out how to pronounce electrorheological fluids without cracking up so i can ask my teachers lol

2. Jan 18, 2005

### Gokul43201

Staff Emeritus
No, the mass and density remain the same. Changing the mass would violate a basic conservation law, so that's definitely not allowed. But you are on the right track.

When you apply an electric (or magnetic - in which case you'd need a magnetorheological fluid) field along some direction, the molecules in the fluid line up along that direction. As a result, the linear density (mass per unit length) increases along this direction locally, but decreases elsewhere, so as to keep the overall density the same. This is a simplified explanation, and the actual mechanism is more complex and can vary from one fluid to another.

Electrorheological (pronunciation) = electro + rio (as in Rio de Janeiro) + logical

You only have to say this word the first time. For subsequent usage in the same conversation, you can simply say ER Fluid. That's a commonly used abbreviation, and your teachers will know what you mean.

Maybe this picture might help : http://img143.exs.cx/my.php?loc=img143ℑ=er18jl.png It shows what happens to the molecules/particles of the ER Fluid, when you apply a field along some (in this case the vertical) direction.

Hope that helps.

Last edited: Jan 18, 2005
3. Jan 18, 2005

ok then

wow looks like you answered most of my questions, so am i to understand that if you somthing like a cube of this liquid and then had the 2 electrodes or however it works on two sides, well it would become viscous virtically but it would remain as a liquid horizontally? i couldnt open the link, right now im using a linux system and its either that, the school internet blocks, or that its a bad link lol. anyway, so if i shot a bullet straight down through this stuff it would be slowed down more than if i shot it through the sides...i dont think that was worded very well...if i had more time i could draw a little text graphic but i hav about 20 minutes left lol.

P.S. is an examle of the ER fluid that works on magnetic force ferro fluid by any chance? just wondering

4. Jan 18, 2005

### Gokul43201

Staff Emeritus
I guess it is a Linux thing. I uploaded the picture at home, from Windows, but can't open it here from Linux. :grumpy:

But it sounds like you get the idea. The viscosity will be highly anisotropic, peaking sharply along the plane normal to the applied field.

Code (Text):

__________________________     ____________________________
|   *      *        *    |     |   *         *         *   |       |
| *            *         |     |   *         *         *   |       | E
|        *              *|     |   *         *         *   |       V
| *  *       **    *     |     |   *         *         *   |
--------------------------     -----------------------------

In the second box, the particles can move vertically along each line, but not horizontally, from one to the other.
Yes, a fluid that responds similarly to a magnetic field is called a megnetorheological (MR) fluid. Ferrofluid (not sure if that's a brand name or a common name) is one type of MR Fluid.

5. Jan 21, 2005

very cool, well scrach my old invenion ideas for this lol but ill come up with somthin elce for it lol, i tlked to my physics teach and he sed that these types of things are used a lot in joints becasue its like a stack of cards, if you push straight down on em, they hold, but if you push to the side, it moves with you...kinda lol, snyway, is this effect on the liquid instantanios? i meen if you just started shooting electic jolts ithrough it it would loose and gain viscosity just as fast?

6. Jan 21, 2005

also, i tried the link again, it wont work, it just brings me to the sites home page

7. Jan 21, 2005

### Gokul43201

Staff Emeritus
Yeah, that link's busted, but the picture is almost identical to what I've drawn up in post #4.

ER and MR fluids have been a hot topic of research since the 80s, and over these couple of decades, hundreds of possible applications have been proposed and some implemented. The most wide use of these materials is in vibration dampers.

The field has grown so moch over the last few years, that there are reasonably large conferences dedicated entirely to EMR (electro- magneto- rheology) research.

Check this one out : http://ermr04.iphy.ac.cn/Presentation%20schedule.htm [Broken]

Last edited by a moderator: May 1, 2017