Thermal volume expansion as seen by Temperature-modulated optical refractometry, Oscillating dilatometry and Thermo-mechanical analysis

Vitrimer Transition Phenomena from the Perspective of Thermal Volume Expansion and Shape (In)stability

“…At the canonical glass transition ( T g ,1.7mHz ) = 13.5 °C), β drops to ∼2.5 × 10 –4 /K. These values are rather classical for cross-linked thermosets and do not show other anomalies in the investigated temperature interval. , This result in terms of a force-free measurement and a missing signature of an anomaly besides the glass transition is well in agreement with the findings from Kaiser et al…”

“…In order to obtain a better view on the pure flow behavior of the vitrimer system, the idea was to separate the superposition of length changes due to flow or shape changes on one hand and thermal expansion on the other. Thus, the temperaturedependent length changes given in Figure 2 were used to derive a pseudothermal volume expansion parameter γ: According to the mathematical simplicity of eq 1, and because of the independent availability of β(T) by the TMOR method, 28 it is indeed possible to separate the contributions of l sh (T) and l therm (T) in a first approximation. The results are summarized in Figure 3.…”

“…The sample was placed on the measuring prism and softly pressed against the prism using a special pressure device that is screwed on top of the sample unit. 28 Then, the sample was heated to T = 128 °C and kept at that temperature for 30 min to allow for temperature equilibration (128 °C is currently, equipment-related, the upper temperature limit T max of the TMOR device). The actual measurement was performed in cooling mode.…”

“…A method that is perfectly suited to assess these kinds of questions is thermomechanical analysis (TMA). Beyond thermal expansion, TMA couples to reversible and irreversible shape changes of a polymer . Hubbard et al made use of this concept and demonstrated that upon heating a vitrimer sample, the observed pseudothermal expansion signal becomes gradually compensated by shape changes due to the malleability of the vitrimer.…”

Temperature-Controlled Molecular Bonding Hysteresis: Interphase Dynamics of a Nanoparticle-Modified Polymer Network

“…Thus, in accordance with this assumption, the quasi-static and dynamic thermal volume expansion coefficients β stat and β′, respectively, almost coincide with each other and reach values typical for liquid and modified EP [β′( T > T g ) > 5.5 × 10 –4 K –1 ; cf. refs and ] in the whole temperature range from 10 to 85 °C. The accompanying thermal loss factor β″ slightly increases with the temperature.…”