Hi,
I am looking for some insight on what exactly these values are telling me about the material. For example, I have a crosslinked polymer with a CTE Alpha 1 of 47 um/m/°C and an Alpha 2 of 220 um/m/°C. What exactly do these tell me about the material? Is it how many ums this material expands by at 47 °C?
Also, there are typically two alpha values reported for CTE. Wouldn't the material constantly be expanding as the temp increases? Why report only two values? Are they the onset and offset of motion?
Just looking to understand this property a bit more.
Thanks!
Michael Bay ,
the CTE values are reported before the glass transition temperature (Tg) and after the glass transition temperature.
And in your case, your polymer expands less before Tg (because it is in the glassy state) and expands more (higher CTE value after Tg (because it is in the most flexible-rubbery state)
Michelle Costa, thanks for replying. To further help me understand the meaning of the values of CTE I have a follow up question. What do these values actually tell me? For example, my sample has alpha 1 and 2 of 59 and 194 (Tg 78 ), but how do these values compare to another sample with, say, values of 45 and 170 (Tg is 53)? Does the second sample move 'less' before and after the Tg because the numbers are lower? Thanks!
Michael Bay, that's right. To make it easier I will call your sample, sample 1, and the comparative sample, sample 2. The sample 2 has less thermal expansion as function of increase in temperature than your sample 1. That is, it can be said that sample 2 is more thermally stable than sample 1. Generally, in most applications, we do not want samples to expand / contract much as a function of temperature. If this is the case, sample 2 would be more recommended for application in the field. Now if you need higher Tg values your sample 1 would be the most recommended
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