Talk:Glass transition temperature
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I think that article should note that in spin glass physics the word glass transition is used to describe a second order phase transition. Furthermore the term ideal glass transition refers to a hypothetical low temperature second order phase transition in supercooled liquids.
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[edit] Introduction
I still think the introduction is going into far too much detail. I'm a 3rd year Pharmacy student and am studying it at the moment, but it lost me after about 2 lines. I think someone with a really good understanding of the basics needs to concentrate on the intro.
Angel delicia 13:41, 16 May 2007 (UTC)
[edit] Hanging Clause
The clause "nor melting" in the following sentence seems to hang in the air for me: "But such behavior is not exhibited by crosslinked thermosetting plastics which, oncecured, are set for life and will shatter rather than deform, never becoming plastic again when heated, nor melting." GeneCallahan
[edit] Correction
I changed the word in the article 'Below' to 'Above' (See History). It was somewhat of a big error. --rolandog 17:38, 15 November 2005 (UTC)
- Oops, that was my mistake. Thanks. Nathaniel 01:35, 16 November 2005 (UTC)
[edit] Values
Is the value for isotactic PP correct? Reference? I only found the overall value of -15°C for PP and DSC-Analyses of iPP fibers in the range of 0°C to 250°C do not show a glas transition.
[edit] Small Molecules
"Small molecular weight pure substances such as water have just one such condensed-phase temperature, below which they are solid crystals and above which they are liquids." - This statement is not entirely true. There are many small moecules which can be made amorphous by very rapid cooling e.g.water, tert-butanol etc.Rvlaw 19:54, 15 January 2006 (UTC)
- Furthermore the glass transition temperature for a molecular glass cannot be calculated from the energy necesary to break a bond. (I believe that this is also true for polymers)
[edit] Thermoplastics
The second paragraph states that "But such behavior is not exhibited by crosslinked thermosetting plastics which, once cured, are set for life and will shatter rather than deform, never becoming plastic again when heated, nor melting". How accurate is this statement? In the case of thermoset plastics there is a glass transition stage on the cured film. In fact, they become rubbery above this stage, even though not reaching elastic stage. A best example is a Fusion Bonded Epoxy coating film, which shows a clear glass transition area on thermal analysis scans. 213.42.2.23 08:38, 7 June 2006 (UTC)spj June 7, 2006
[edit] Confusing introduction
The introduction contains a lot of infrmation about supercooling and the kauzmann paradox. This stuff is not real necesary for introducing the glass transition temperature. I propose that we replace it with a link. How about writing the folllowing instead:
The viscosity of liquids depend strongly on temperature. The lower you cool a sample the more viscous it becomes. The glass transition temperature is usually defined as the temperature at which the sample has a viscosity of 10^12 Pa*s. Below this temperature the sample is said to be solid-like rather than liquid-like. Many liquids have a glass transition temperature which is lower than the melting point. Therefore one has to supercool the sample in order to reach the glass transition temperature.
Experimentalists frequently use a different definitions of the glass transition temperature. In general the word glass transition temperature is used to denote a temperature in which the internal relaxation time of a sample is larger than a given experimental timescale. As an example you can define the glass transition temperature of an experiment in which a liquid sample is cooled at a constant rate. At high temperature the internal relaxation time of the sample is so fast that the cooling is virtually reversible, and thus the sample is virtually at equilibrium. However at the glass transition temperature the internal relaxation becomes so slow that the sample leaves equilibrium. A similar definition can be applied to [[[DSC]] experiments. It is worth noting that this definition makes the glass transition temperature depend on the cooling rate.
The definition of the glass transition is general, but the article should distinguish between different compounds.
- The glass transition polymers depends on chain length (and polymers have a rubber plateau).
- The glass transition of simple supercooled organic liquids is often believed to depend on the configurational entropy, theough the Adam Gibbs-relation, but this is still open to debate.
- The article mentions that the glass transition temperature of metallic glasses depend on the number of convalent bonds. I am not an expert on this.
—Preceding unsigned comment added by 203.200.55.101 (talk • contribs) 0947, 30 September, 2006
- I'm not familiar with the definition where the glass transition occurs when the viscosity of the sample is 1E12 Pa.s. My normal understanding of Tg is the second - that the internal relaxation time of the strands is longer than the timescale of the experiment. I think a cite would be helpful at this point.
Secondly, by convention, the title is usually mentioned in the first part of the first sentence. Perhaps you can rewrite it thus.
Other than that, I think the new intro is fine. Do be bold and change it! --Rifleman 82 10:35, 30 September 2006 (UTC)
- Debenedetti & Stillinger, Supercooled Liquids and the Glass Transition, Nature, vol 410, 8 march 2001 give the definition of Tg as 10^13 poise (10^12 Pa.s) User A1 03:35, 11 October 2006 (UTC)
