Tg ptfe
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The document discusses the complexity of measuring the glass transition temperature of polytetrafluoroethylene (PTFE), also known as Teflon. Using dynamic mechanical analysis, the authors found three transitions labeled α, β, and γ. The β-transition was identified as a crystalline rearrangement. Both the α- and γ-transitions showed sensitivity to the rate of measurement, indicating they were glass transitions. The authors propose PTFE has two amorphous phases, one mobile and one rigid, corresponding to the γ- and α- transitions respectively. However, the explanation is still beyond current understanding. Ultimately, the γ- transition is believed to be the true glass transition temperature, but questions
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![The Glass Transition of Teflon
It's a simple enough question raised by a new research article (European Polymer Journal ($)):
"What is the glass transition temperature of PTFE"?, but like so many measurements of PTFE,
the answer always starts with "it's complicated".
Even after 24 years in the polymer industry, the complexity of PTFE (polytetrafluorethylene) but
better known as Teflon [1] still baffles me. It's not as if the underlying molecular structure is
complicated. It is simply a perfluorinated analog of polyethylene, and polyethylene is about as
well behaved as any polymer out there. But with PTFE, the material that is prone to incredibly
simple questions with extremely difficult answers. Try these for starters: At what temperature
does it melt? [2] If nothing sticks to Teflon, how does Teflon stick to the fry pan? [3].
Given all that, plus making measurements of the glass transition, which by itself is already a
heated subject, the title are guarantees you a head-scratcher. You may come up with an answer,
but it will be quickly followed by "it's complicated".
Being a very simple macromolecule, PTFE crystallizes, so it may seem odd that PTFE shows a
glass transition at all, as the transition is normally associated with amorphous materials.
However, as is the case with all crystalline polymers, any given non-microscopic sample is only
semi-crystalline. Because of the chain lengths and entanglements that arise from them, it is
impossible for the polymer to completely crystallize. As a result, there is a significant amount of
amorphous material trapped in the sample and this material is what exhibits the glass transition.
Using dynamic mechanical analysis, the authors found three transitions which they labeled, α, β
and γ. The β-transition they quickly identified as a crystalline rearrangement based on existing](https://image.slidesharecdn.com/tgptfe-220102073532/85/Tg-ptfe-1-320.jpg)
![research. Sadly, both temperatures for both the α- and γ-transitions showed strain rate sensitivity.
I say sadly, as one of the unofficial, non-theoretically-derived observations of the glass-transition
is that it is always sensitive to the rate of measurement. If either the α- or γ-transitions had NOT
shown this sensitivity, one would have to believe that it was not the glass transition.
Ultimately the authors propose the existence of 2 amorphous phases as shown in this illustration.
One is mobile (labeled as "(1)") and one is rigid (labeled as "(2)" with the crystalline regions
labeled as "(3)"). These are believed to correspond to the γ- and α-transitions respectively. The
authors ultimately then decide that the γ-transition is the "real" glass transition.
This is all a little too much hand-waving for me. This is just a souped-up version of the fringed
micelle explanation for polymer crystallization, something we seen discussed here before. The
boundary between the mobile and rigid phases is visually clear in this drawing, but how can that
be objectively stated?
Ultimately I do feel that the γ-transition is the glass transition for a number of subjective reasons
(the temperature range, and that is it below the crystalline transitions), but the explanation of it is
still beyond our current understanding, and I certainly don't buy what is being sold here. So what
is the mysterious α-transition? Well, it's complicated...
[1] Teflon is actually the Trademark from Dupont for their PTFE. Other companies have their
own trademarks for their own PTFE.
[2] 327 oC, but take that with a grain of salt. Even molten, PTFE doesn't flow like normal
polymers, and adding more heat only degrades it that much faster. It's not surprising that
LinkedIn had a recent discussion on whether PTFE is a thermoplastic or a thermoset. "Melting"
PTFE is not like melting most other polymers.
[3] A fluid will wet a surface if it has a lower surface energy than the surface. PTFE has the](data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7)
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considered crystalline. The opposite is an amorphous polymer. Almost
all amorphous polymers possess a temperature boundary. Above this
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it is soft is called the glass transition temperature.
For example:-
When an ordinary natural rubber ball if cooled below -70oC becomes so
hard and brittle that it will break into several pieces like a glass ball falling on a
hard surface.
This happens because there is a temperature boundary for amorphous.
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The hard, glassy, brittle state is known as the glassy state and the soft,
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This document summarizes a laboratory experiment to determine the bulk density and void ratio of fine and coarse aggregates. The experiment involves weighing an empty metal cylinder, filling it with dry aggregate in layers and tamping it, weighing it again to find the compacted bulk density. It also involves filling the cylinder loosely with aggregate and weighing it to find the loose bulk density. The purpose is to find these properties which are important for converting aggregate proportions by weight to volume. The procedure, materials used like the cylinder and tamping rod, and calculations to derive bulk density and void ratio are described.
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Tg ptfe
- 1. The Glass Transition of Teflon It's a simple enough question raised by a new research article (European Polymer Journal ($)): "What is the glass transition temperature of PTFE"?, but like so many measurements of PTFE, the answer always starts with "it's complicated". Even after 24 years in the polymer industry, the complexity of PTFE (polytetrafluorethylene) but better known as Teflon [1] still baffles me. It's not as if the underlying molecular structure is complicated. It is simply a perfluorinated analog of polyethylene, and polyethylene is about as well behaved as any polymer out there. But with PTFE, the material that is prone to incredibly simple questions with extremely difficult answers. Try these for starters: At what temperature does it melt? [2] If nothing sticks to Teflon, how does Teflon stick to the fry pan? [3]. Given all that, plus making measurements of the glass transition, which by itself is already a heated subject, the title are guarantees you a head-scratcher. You may come up with an answer, but it will be quickly followed by "it's complicated". Being a very simple macromolecule, PTFE crystallizes, so it may seem odd that PTFE shows a glass transition at all, as the transition is normally associated with amorphous materials. However, as is the case with all crystalline polymers, any given non-microscopic sample is only semi-crystalline. Because of the chain lengths and entanglements that arise from them, it is impossible for the polymer to completely crystallize. As a result, there is a significant amount of amorphous material trapped in the sample and this material is what exhibits the glass transition. Using dynamic mechanical analysis, the authors found three transitions which they labeled, α, β and γ. The β-transition they quickly identified as a crystalline rearrangement based on existing
- 2. research. Sadly, both temperatures for both the α- and γ-transitions showed strain rate sensitivity. I say sadly, as one of the unofficial, non-theoretically-derived observations of the glass-transition is that it is always sensitive to the rate of measurement. If either the α- or γ-transitions had NOT shown this sensitivity, one would have to believe that it was not the glass transition. Ultimately the authors propose the existence of 2 amorphous phases as shown in this illustration. One is mobile (labeled as "(1)") and one is rigid (labeled as "(2)" with the crystalline regions labeled as "(3)"). These are believed to correspond to the γ- and α-transitions respectively. The authors ultimately then decide that the γ-transition is the "real" glass transition. This is all a little too much hand-waving for me. This is just a souped-up version of the fringed micelle explanation for polymer crystallization, something we seen discussed here before. The boundary between the mobile and rigid phases is visually clear in this drawing, but how can that be objectively stated? Ultimately I do feel that the γ-transition is the glass transition for a number of subjective reasons (the temperature range, and that is it below the crystalline transitions), but the explanation of it is still beyond our current understanding, and I certainly don't buy what is being sold here. So what is the mysterious α-transition? Well, it's complicated... [1] Teflon is actually the Trademark from Dupont for their PTFE. Other companies have their own trademarks for their own PTFE. [2] 327 oC, but take that with a grain of salt. Even molten, PTFE doesn't flow like normal polymers, and adding more heat only degrades it that much faster. It's not surprising that LinkedIn had a recent discussion on whether PTFE is a thermoplastic or a thermoset. "Melting" PTFE is not like melting most other polymers. [3] A fluid will wet a surface if it has a lower surface energy than the surface. PTFE has the
- 3. lowest surface energies of all polymers (~ 19 dynes/cm2), while the metals of the fry pan are hundreds if not thousands of dynes/cm2. In other words, the PTFE can't help but stick to the metal. That also explains why nothing else sticks to the PTFE - practically anything else has a higher surface energy. (There is more to adhesion than just wettability, but that is a critical starting point - no wetting, no adhesion.) http://www.rheothing.com/2013/05/the-glass-transition-of-teflon.html