Considerations for Measuring Glass Transition Temperature

玻璃化转变温度(Tg)是高分子材料的一个重要特性. 它标志着物质从玻璃态变为橡胶态的点, and influences many other material properties.

Glass transition temperature is characteristic of the type of polymer chain, the amount of crosslinking and chain length or molecular weight. 因为大多数材料都有分子量分布和交联, the Tg is not a discrete temperature, but rather a temperature range. A single temperature is generally reported for convenience, but the material will actually change properties over a range of temperatures.

Because of its close relation to strength and flexibility, 在产品开发生命周期中，理解和应用玻璃化转变温度的概念对于确保聚合物材料的使用至关重要, 组件, and assemblies will function appropriately in the end use environment.

Is there an ideal Glass Transition Temperature (Tg)?

确定理想的玻璃化转变温度取决于所需的材料本身的物理性质, 以及产品或材料将在其中运行的应用和环境. 

When materials like rubbers and 弹性体 need to retain flexibility, 它们应在玻璃化转变温度以上使用和储存(否则, it runs the risk of becoming brittle). However, materials such as rigid plastics and 复合材料 should be used below the glass transition temperature. If used above that point, 热量将使它们具有较低的模量和较高的热膨胀系数. 为 复合材料, this causes lower mechanical resin based properties such as compression, shear and interlaminar tension. 对于电子材料，印刷线路板在装配或使用过程中可能会受到热应力. 这导致在镀通孔，过孔，引线和焊点的机械应力. 为 optimal reliability, a high Tg is important.   

外部因素，如湿度或湿度水平，也可能影响玻璃化转变温度. Because moisture tends to diffuse slowly through a material, 它可以作为增塑剂并使材料达到基于暴露的相对湿度的平衡水分含量. This results in a lower glass transition temperature. 在办公环境中使用的材料在使用寿命期间只会吸收适量的水分, compared to materials outdoors in a humid environment. Because of this, 低温(远低于固化温度)干燥或控制湿度暴露可能是合适的.

How is Glass Transition Temperature 测试 Performed?

In order to determine the glass transition temperature of a material, one of several different test and reporting types may be used. The method used will largely depend on the type of results being sought, and what data is required in the final report. 

测量玻璃化转变温度的经典方法是在预期温度范围内进行一系列机械测试. While there are several options for the test type, flexural strength or shear testing are the standard. 结果报告为弯曲或剪切模量与温度的关系图. 玻璃化转变温度是指材料强度显著下降的地方.

Thanks to modern thermal analysis, 近年来，玻璃化转变温度的测试变得更快、更便宜. 测定转变温度的最标准的热方法是热力学分析(蓝玉)。, Dynamic Mechanical Analysis (直接存储器存取), and Differential Scanning Calorimetry (DSC).

Tg 测试 Methods

Thermomechanical Analysis (蓝玉): 热机械分析使用一小块材料样品，在石英台上加热. 机器内部的一根杆在样品的顶部施加少量的力, 用线性可变差动变压器或LVDT测量杆的运动. 整个仪器以缓慢的速度加热，通常为每分钟5摄氏度. 该数据以曲线形式报告，其中长度变化随温度绘制. 所得曲线的斜率称为线性热膨胀系数(COLTE). 玻璃化转变温度是直线斜率变化的点，如下图所示.

蓝玉 may also be used in flexure or penetrations modes. 在这些方法中，施加更大的力，直到探针明显偏转.  

Differential Scanning Calorimetry (DSC)

在 DSC test method，加热一个小样品，同时测量加热样品所需的能量. This value is then compared to an inert reference material. 因为玻璃化转变温度会使材料的性质发生变化, the polymer chains reorient, requiring a change in energy to heat. This shows as an inflection on the curve. Three points may be selected and reported: the onset, which is the lowest value, the mid-point and end point.  

Dynamic Mechanical Analysis (直接存储器存取)

im体育APP's expertise in glass transition temperature measurement 

As evidenced above, 玻璃化转变温度的测量在技术和计算上有很大的不同，这取决于具体的材料类型, real world application, and many other factors. im体育APP的聚合物科学家拥有所需的知识和专业知识来支持您 material testing program and provide you with accurate and applicable data on your material.

im体育APP 今天来了解更多关于我们的热分析和分析服务.