Theory and applications of ultrasonic soft materials and surface analyzer (USMASA).

摘要

High-frequency linear viscoelastic properties of soft materials are essential for material designing and engineering applications. Traditionally, the high-frequency properties are estimated through the time-temperature superposition (WLF equation) of low-frequency data, which are questionable because the existence of multi-phase in elastomer compounds. Until now, no reliable data at high frequencies over MHz are available.;Ultrasonic measurement techniques are most cost-effective for measuring high-frequency properties. In order to fully characterize high-frequency mechanical properties of materials, both ultrasonic longitudinal and shear properties are necessary. Ultrasonic pulse echo method can measure longitudinal properties precisely, while shear properties can only be determined by ultrasonic impedance method due to high shear attenuation of soft materials. However, currently there are still some major difficulties in determination of high-frequency shear properties of soft materials using this technique.;One of the challenges for ultrasonic impedance technique is that the adhesion between the specimens and measurement device has never been perfect and repeatable, which is influenced by applied load, location, composition (carbon black loadings, etc.), and processing conditions, etc. However, at present, studies of high-frequency properties using ultrasonic impedance technique are almost based on the assumption of perfect contact. A new evaluation approach considering the effects of adhesion needs to be developed.;In this dissertation, a device of ultrasonic soft material and surface analyzer (USMASA) is established based on ultrasonic impedance technique. The device can determine both high frequency longitudinal and shear properties by one measurement. The reliability of USMASA is demonstrated through the characterization of water and sillyputtyRTM that have almost perfect contact with the device.;USMASA is a valuable tool of monitoring adhesion dynamics. The adhesions between filled elastomers and fused silica plate, including the effects of pressure, specimen surface treatments with solvents, and composition of materials, were studied with USMASA.;Furthermore, a new evaluation scheme including adhesion effects is presented. The high-frequency shear properties of carbon black filled rubbers were characterized by USMASA. The effects of filler loading level, filler type, filler dispersion, base polymer, and temperature on high-frequency shear properties were discussed. The effects of different compound preparation techniques could be evaluated effectively by USMASA.