ARES DETA（介电配件）中材料介电响应、粘弹性检测方案(流变仪)

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APN005e Dielectric Option for ARES A. Franck， TA Instruments Germany Keywords： dielectric option， ARES， SMT， DETA， The ARES DETA (Dielectric Thermal Analyzer)is an accessory which expands the testing capabilitiesof the ARES strain controlled rheometer to includeinvestigations of the dielectric response of materials.This ability to probe the conductive and capacitivenature oftest specimens enlarges the range ofapplications of the ARES rheometer as a universalinstrument in material characterization. FULLYINTEGRATED DIELECTRICMEASUREMENTS The ARES DETA option is an accessory which isreadily engaged or disengaged from the standardARES rheometer. Used with the forced convectionoven， and ARES parallel plate tools，the DETAaccessory measures the dielectric properties of amaterial while the sample is at rest or undergoing adeformation. Other features ofARES testing are nothindered by the addition of the DETA accessory，andchangeover time is under five minutes. PRINCIPALS OFDIELECTRIC ANALYSIS The reorientation of dipoles in an oscillatingelectric field represents the basis of the dielectricthermal analysis (DETA). The ARES rheometerprovides the measuring cell consisting of insulatedparallel plates enclosed by the air convection oven.The gap is set manually or automatically via theAutoTension function (Figure 1). A dielectric bridge(HP4284A)imposes a dielectric signal of preselectedvoltage and frequency (Figure 2). The LCR metermeasures the capacitance and dielectric loss of thesample. From these measurements the permitivity eand the dielectric loss tangent tano are calculated.The capacitance C represents the electrical chargestored across the potential difference of the two Figure 1： Dielectric measuring cell parallel plates. The conductance=1/C is the abilityof a material to pass a charge through the sample.The dielectric constant or permitivity e* is the ratioof a capacitor (the parallel plates of the ARESrheometer) which contains a sample versus one withno sample. The imaginary portion of the signalrepresents the loss factor e“ande“/e ‘the dielectricloss tan 8. The dielectric properties of a materialchange significantly with temperature and frequencyduring transitions in the material， similar to the DMA(Dynamic Mechanica Analysis) measurement. BENEFITS OFDETA Figure 3： Generic behavior of an amorphous polymer and the loss tangent peaks aregenerally broad compared toDMA. The a relaxation isassociated with the polymerchain backbone motion andprovides a dielectricmeasurement of the glasstransition Tg. Above Tg thedipoles are free to orientientaccording to the imposedelectrical field. Tan 8 increasesabovee Tg dduee mto small oac Figure 4： Dielectric and mechanical response for PMMA as function of temperature and frequency Figure 5： PMMA dielectrric 0.1kHz， mechanical 100Hz &Dielec.loss max. ·Mechanicalloss maxiDielec.loss max.一Mech.loss max. The activation energy for the dielectric andmechanical relaxation mechanisms can be extractedfrom the Arrhenius plot shown in figure 6. o and ptransitions shift in the same way for the mechanicaland dielectric testing with the probing frequency. Thisproves， that the same processes are responsible forthe peak maxima in tan 8 for the dielectric and themechanical analysis. Figure 6： Activation energy determined from dielectric andmechanical spectroscopy SPECIFICATIONS Frequency range： 20 Hz to 1 MHz Potential： 0.005 to 20 volts Temperature Range：-150 °℃ to 300 °℃ ORCHESTRATOR POWERED Temperature Stability： ±0.1℃ Powered by TAIOrchestrator software runningunder Windows XP or 2000， the ARES DETAprovides features that simplify testing， ensureaccuracy， and allow unattended operation. Test Modes： Time SweepTemperature rampTemperature step Time sweeps and temperature sweeps at fixedfrequencies over a range from 20 Hz to 1Mz areeasily implemented. The operation menu is fullyintegrated into the rheometer test setup menus. APN The ARES DETA (Dielectric Thermal Analyzer) is an accessory which expands the testing capabilities of the ARES strain controlled rheometer to include investigations of the dielectric response of materials. This ability to probe the conductive and capacitive nature of test specimens enlarges the range of applications of the ARES rheometer as a universal instrument in material characterization.