Dynamic temperature ramps

Fig. Z4 (a) Temperature ramp at a frequency a> = lOrads (strain amplitude A = 2%) for a nearly symmetric PEP-PEE diblock with Mn = 8.1 X 104gmol l, heating from the lamellar phase into the disordered phase. The order-disorder transition occurs at 291 1 °C, the grey band indicates the experimental uncertainty on the ODT (Rosedale and Bates 1990). (b) Dynamic elastic shear modulus as a function of reduced frequency (here aT is the time-temperature superposition shift factor) for a nearly symmetric PEP-PEE diblock with Mn = 5.0 X 1O g mol A Shift factors were determined by concurrently superimposing G and G"for w > and w > " respectively. The filled and open symbols correspond to the ordered and disordered states respectively. The temperature dependence of G (m < oi c) for 96 < T/°C 135 derives from the effects of composition fluctuations in the disordered state (Rosedale and Bates 1990). (c) G vs. G"for a PS-PI diblock with /PS = 0.83 (forming a BCC phase) (O) 110°C (A) 115°C ( ) 120°C (V) 125°C ( ) 130°C (A) 135°C ( ) 140°C ( ) 145°C. The ODT occurs at about 130°C (Han et at. 1995).

Figure 11.5 Complex dynamic viscosity as a function of temperature for a main-chain polyether consisting of a methyl stilbene mesogen and a mixture of seven-and nine-carbon aliphatic spacers. The polymer has a molecular weight of 36,000. The diamonds and squares are for temperature ramp rates of 0.1 °C and 2.0°C/min, respectively the open and closed symbols are for heating and cooling, respectively. The dashed line marks the isotropic-nematic transition. (From Gillmor et al. 1994, with permission from the Journal of Rheology.)...

As mentioned in the previous section, the apparatus is able to work in non-isother-mal conditions. This is a useful feature since in the chemical industry very often the reactions are initiated on a temperature ramp. A first series of experiments was carried out by successive injections of Q with the temperature ranging from 75 to 130 °C and a scanning rate of 0.12 °C min (see Figure 12). The first portion of Cl was injected just after the stable dynamic base line was reached all other injections were initiated after the heat evolution of the previous step had ceased. As expected, the shape of the curves representing the heat evolution with polymerization changes from two peaks at low temperatures (up to 95 °C) to one peak with a small shoulder at the highest injection temperature (about 105 °C). The intensity of the first peak is not influenced by temperature, but the intensity of the second one strongly increases with temperature, and consequently the monomer conversion also increases. 

The work of several authors (Peters et al, 1993, Halley et al, 1994) has demonstrated the use of non-isothermal dynamic sweep tests to examine the combined effects of shear rate and curing on the chemoviscosity of a highly filled epoxy resin simultaneously. These tests use a selected temperature ramp with repeated dynamic rate sweeps to investigate the effects on the chemoviscosity. The advantage of these tests is that the effects of shear rate and cure are not separated, which is similar to processing conditions. 

A method for determining kinetic parameters from dynamic infrared data was developed to overcome the problems listed above (A). Through the use of constant temperature ramps, appropriate instrument software (6) (Sheen, C. W. Snyder, R. W. Computers Chemistry, in press) and spreadsheet techniques the activation energy and pre-exponential factor for any reacting system can be obtained in a few hours. When performing this dynamic kinetic analysis however there are some effects which must be accounted for... 

Dynamic torsional shear experiments were conducted on a Rheometric Scientific ARES rheometer. The samples were cut 6.35 cm in length strips, 0.30 cm thick. The single frequency temperature ramp test was taken at 1 Hz from -100°C to 150°C at 2°C/min in the linear strain regime (0.01 to 2.00%). 

Such calibrations can also be performed on temperature ramps or while chemical reactions are still in progress, provided that the correct, generally valid unsteady-state heat balance corresponding to the mode of operation is used for their evaluation. In these cases, however, it becomes crucial that in the period of time shortly before and shortly after the calibration heater is in use no significant dynamic effects occur, as these times are used to determine initial and final state of the system. The course of a typical experiment including the calibration phases is shown in Figure 4-68. 

Fig. 24 (a) Molecular structure of poly(thymine acrylate-i>-n-butyl acetate-b-adenine acrylate) triblock copolymers (PTBA). (b) Dynamic mechanical temperature ramp of PTBA and copolymer controls. Reproduced from [141] with permission of The Royal Society of Chemistry. Copyright 2014... 

FIGURE 19 The thermal stability of a cross-linked DEC chromophore containing NLO polymer is assayed both by the dynamic thermal stability (temperature ramping) method of Fig. 18 and by measuring the electro-optic coefficient for a sample maintained at a temperature of 100°C for 1000 h. 

Thermal dynamic mechanical analysis (TDMA) was done on a Rheometric Scientific RSA II Solids Analyzer (Piscataway, NJ) using a film testing fixture (5, 6). A nominal strain of 0.1% was us in all cases, with an applied frequency of 10 rad/sec (1.59 Hz). A temperature ramp of 10°C/min was used in all cases. Nominal dimensions of the samples were 6.4 mm x 38.1 mm. The gap between the jaws at the beginning of each test was 23.0 mm. Data analyses were carried out using Rheometrics RHIOS and Orchestrator software. 

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