Why does the glass transition temperature increases with increase in frequency in dynamic mechanical analysis?
When characterizing a material by DMA, the time of the deformation is the frequency(ies) as frequency is the inverse of time (frequency = 1/time). Therefore, high
frequencies are analogous to short times and low frequencies to long times.The glass transition is a molecular relaxation that involves cooperative segmental
motion whose rate will depend on temperature. Therefore,as the frequency of the test increases, the molecular relaxations can only occur at higher temperatures and, as a
consequence, the Tg will increase with increasing frequency.
hello, Time=1/frequency, Short Time => molecular mobility is decreased, material is brittle and glass transition shift to higher temperature, so=> There is a direct relationship between glass transition and requency
Dr. Rao has explained the phenomenon rightly. I like to add that the segmental mobility depends on frequency as well as temperature. At high frequency most of the segments may pose as stiff as by the time next frequency arrives the segments will not be able to relax back. Only few segments will respond, thus delaying the glass transition and the Tg.
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