iMechanica - nanomechanics - Comments

Poster presentation at MRS Fall Meeting, Boston

Sandip Basu — Fri, 23 Nov 2007 14:01:03 -0500

I'll be presenting a poster on my research at the MRS Fall Meeting at Boston next week (Tuesday Nov 27, poster number AA5.4).

Thanks,

Sandip

time-temperature equivalence for a viscouselastic material

Henry Tan — Sat, 08 Sep 2007 15:59:24 -0400

How does the time-temperature equivalence for a viscouselastic material be viewed at molecular scale?

How temperature affects the viscoelastic behaviour?

Henry Tan — Sat, 08 Sep 2007 15:56:04 -0400

How temperature affects the viscoelastic behaviour? especially viewed from the behaviour of molecular movements?

Mr Tan, But it

Aneet — Tue, 15 May 2007 10:38:47 -0400

Mr Tan,

But it should make sense, as the molecules/atoms vibrate or move around, they do so because they have velocity. And when we talk about molecular dynamics wont we say KE = (1/2)mv2 where KE = (3/2)NkT (for a 3D system, K - Boltzmann's constant?)

Then we do have energy and thus 'temperature'.

Aneet

How to interpret the nanoindentation data for composites

Rohit Khanna — Sat, 12 May 2007 11:58:50 -0400

Hi all,

I wish to discuss on interpreting the nanoindentation data for
viscoelastic-plastic composite materials say polymer based composites.
I have experienced that if the microsructure is not homogeneous, it is
very difficult to meangingful data and normally, spread in elastic
modulus is very large depending on the load.

Second point for discussion is that does modulus mapping technique holds good for viscoelastic-elastic composites?

Can anybody comment on this?

Regards,

Rohit Khanna

Julia, please nominate a paper of interest

Xiaodong Li — Fri, 20 Apr 2007 21:24:36 -0400

Thanks, Julia. Can you please nominate a paper about micro/nano pillar compression for May issue of J-Club? I think that pillar compression test has attracted much attention.

Experimental Nanomechanics is a VERY useful topic!

Julia R. Greer — Tue, 17 Apr 2007 13:40:17 -0400

As someone who is very interested in investigating plasticity at nano-scale by pillar compression (and otherwise), of course it would be great to see more experimental nanomechanics topics. As most experiments at that scale are difficult to perform and there is a lot of controversy in modeling, it would be very helpful to start a discussion club.

Julia Rosolovsky Greer

Ortwin Hess

Henry Tan — Sun, 15 Apr 2007 23:18:11 -0400

Professor Ortwin Hess
Department of Physics
University of Surrey

His recent interests include nano-thermodynamics.
http://www.ph.surrey.ac.uk/profiles?s_name=Ortwin_Hess

Thermodynamics and nanotechnology

Henry Tan — Fri, 13 Apr 2007 15:56:23 -0400

Thermodynamics, largely driven into being by the steam engine, should be pushed into a further mature stage, driven by the nanotechnology that controls matter on the atomic scale.

temperature at the tip of the nano-indenter

Henry Tan — Fri, 13 Apr 2007 01:36:15 -0400

Nanoindentation is a fundamental, evolving, and complementary discipline (Michelle, http://imechanica.org/node/1237).

It iis an interesting topic among imechanicians from many different backgrounds:
Experimental Nanomechanics (Xiaodong, http://imechanica.org/node/606);
Viscoelastic Contacts (Michelle, http://imechanica.org/node/842);
On the uniqueness of measuring elastoplasticproperties from indentation (Xiaodong, http://imechanica.org/node/1222).

The nanoindentation measurements can be even more interesting, when accounting for the temperature at the tip of the nano-indenter.

Nanotubes may have no 'temperature'

Henry Tan — Fri, 13 Apr 2007 00:56:28 -0400

An interesting news headline in nanotechwire.com
http://www.nanotechwire.com/news.asp?nid=1064&ntid=133&pg=9

Physicists have made a bizarre discovery: the concept of temperature is meaningless in some tiny objects. Although the concept of temperature is known to break down on the scale of individual atoms, research now suggests that it may also fail to apply in rather larger entities, such as carbon nanotubes.

The blossoming field of nanotechnology relies on being able to manipulate materials that are made from just a few thousand atoms. Carbon nanotubes, for example, are tiny cylinders that could be used to make miniature electronic devices.

Ortwin Hess from the University of Surrey, Guildford, UK and colleagues say that if you took the temperature at one end of a 10-micrometre nanotube, it would not necessarily have the same temperature as the other end, no matter how long it was left to reach a thermal equilibrium. Such a nanotube is about as long as a sheet of paper is thick.

quotation by Thomas Jefferson

Henry Tan — Fri, 23 Mar 2007 12:53:00 -0400

Dear Cetin:

The quotation by Thomas Jefferson was not on “American approach on getting things done”, but on his views of mathematics (he was enthusiastic about mathematics).

A complete quotation should be:

"…… Having to conduct my grandson through his course of mathematics, I have resumed that study with great avidity. It was ever my favorite one. We have no theories there, no uncertainties remain on the mind; all is demonstration and satisfaction."

nanoscale thermodynamics

Henry Tan — Thu, 22 Mar 2007 23:33:22 -0400

Many thanks to Sukumar for bringing Tsallis's non-extensive statistics into our attention.

As the size of systems becomes smaller to nanoscale, effects of ﬂuctuations and contributions from surface play more important roles.

I searched the literature, there are currently three approaches for nanoscale thermodyamics:

(1) generalizing the Boltzmann-Gibbs statistics as to take account of the non-extensive feature of such systems, e.g., Tsallis statistics (http://en.wikipedia.org/wiki/Tsallis_entropy);

(2) a modiﬁcation of the Boltzmann-Gibbs statistics by adding subdivision energy;

(3) non-equilibrium thermodynamics including work ﬂuctuations.

Boltzmann distribution

Henry Tan — Thu, 22 Mar 2007 21:36:47 -0400

In the derivation of the Boltzmann distribution for a small system, the system and the reservoir are in thermal contact, exchanging energy. All other modes of interactions between the system and the reservoir are blocked: no exchange of molecules, of volume, or anything else.

This block requirement works fine for macroscopic system.

However, for a nanoscale system the energy changes are associated with volume change which cannot be ignored as in macroscopic systems.

Therefore, the Boltzmann distribution needs to be modified to characterize nanoscale systems.

one has to learn at least three times

Henry Tan — Thu, 22 Mar 2007 17:00:49 -0400

Sommerfeld's words remind me of Zhigang's comment (http://imechanica.org/node/207):

"...... As many people say, thermodynamics is a subject that one has to learn at least three times."