TA仪器Discovery流变仪

Linear viscoelastic measurements are often taken for granted. Many users are not aware that systematic errors such as instrument compliance may significantly corrupt the test results, especially at high frequency when the sample becomes stiff in comparison to the instrument itself. Instrument compliance effects can be demonstrated, when running high modulus materials in different size plate geometries. Figure 1 shows the complex modulus of PIB measured at -20°C using 8mm and 25mm plates. With increasing frequency, the complex modulus of the test run with 25mm plate geometry deviates significantly from the result obtained with the 8mm plate geometry. In the same graph, the measured sample deformation is plotted versus frequency. While the strain amplitude for the test performed with 8mm parallel plates is virtually constant and close to the 2% command value, does the actual sample strain for the tests performed with 25mm plates, decrease with frequency. This shows that for these tests, the deformation amplitude applied by the actuator is not fully transferred onto the sample. The smaller the sample strain in relation to the command strain, the higher the compliance effect of the instrument.

在当今日益激烈的竞争环境下，高性能先进材料的开发尤为重要。许多材料制造商不在专注于单一产品领域，而是越来越趋向于多元化。以至于现在开发研究实验室经常研究一系列有明显的不同物理和化学性质的材料。因为这个原因，分析仪器必须非常灵活，它必须能够容纳存在各种各样的物理状态的样品且不影响其灵敏度和重现性。动态力学分析（DMA）也不例外，本文将讨论使用DMA测量系列材料的粘弹性特征，包括液体、聚脂薄膜、乳胶、预浸料坯和复合材料。

从1970到1980，美国对塑料的需求从200亿磅增加到了500亿磅。塑料的成功主要是由于其广泛的应用，由于其广泛的性能，塑料可以替代金属、玻璃、陶瓷、纸张、天然纤维、包装材料、消费产品、管道、家具，等等…… 塑料最重要的性能在于其重量轻，耐破损，能巩固功能部件，想对便宜，易于自动化生产，生产成本较低……

Creep recovery measurements on anionically polymerized polystyrenes and commercial low density polyethylene have been performed with a new magnetic bearing rheometer. Due to the very small residual torque, a key feature of the magnetic bearing rheometer, small recoverable compliance values in the linear viscoelastic regime could be accurately measured. The equilibrium compliance Je obtained is compared to the ratio of G’/G’’2, evaluated from oscillation measurements in the terminal region (low frequency). Excellent agreement could be found for the narrow distributed PS with a molecular weight from 13,000 to 330,000 g/mol. Finally the shear compliance of a commercial PS was converted to the dynamic moduli G’ and G’’ using approximation formulas by Schwarzl to extend the frequency range, large enough to fully describe the viscous and elastic behavior of the material.

It is well known that there is an equivalence of the effects of time and temperature on the rheological properties of viscoelastic materials1. At low temperatures a material will behave in the same fashion as at high frequency, and at high temperature the material will behave as it would at low frequency. Data in a range of temperatures over modest frequency ranges( see figure 1) can be collected and arranged to predict the behavior over a wider frequency range than possible in practical testing. Bear in mind that very low frequencies can take days or weeks for measurements, and ultra high frequencies cannot be measured by existing instruments. The modulus data can then be shifted horizontally along the abscissa to overlap forming a smooth curve. This approach allows the generation of master curves of modulus data spanning considerably wider ranges of time (frequency) and/or temperature than the range of the original data (see figure 2).

由于巨大仪器惯性原因能够破坏通过旋转流变仪得出的震荡测试，这与电机轴的周期性加速和减速造成的。在一台流变仪上，电机的扭矩输出是由所需克服仪器惯性的扭矩组成的且扭矩变形进行示例。扭矩惯性的增加与所施加的功率频率相关，通常在低粘度测试的样品中起到主导地位。配备独立传感器的旋转流变仪受惯性影响要小得多，主要因为样品扭矩是由电机扭矩单独决定的。

一个医药公司想比较两种洗液的扩散速度，以确定不同配方的作用效果。可是两种洗液的量非常少，难以用合适的方法进行表征。