测量玻璃化转变温度的注意事项

Glass transition temperature, or Tg is an important characteristic of polymeric materials. It marks the point at which a material changes from a glassy to a rubbery state, 并影响许多其他材料的特性.

玻璃化转变温度是聚合物链类型的特征, 交联量与链长或分子量有关. Since most materials have a distribution of molecular weights and cross-linking, Tg不是一个离散的温度, 而是一个温度范围. 为方便起见，通常报告单一温度, 但这种材料实际上会在一定温度范围内改变性质.

因为它与强度和柔韧性密切相关, it is critical to understand and apply the concepts of glass transition temperature during the product development lifecycle to ensure polymeric materials, 组件, 组件将在最终使用环境中正常工作.

是否存在理想的玻璃化转变温度(Tg) ??

Determining an ideal glass transition temperature depends on the desired physical properties of the material itself, along with the application and environment in which the product or material will operate. 

当橡胶和弹性体等材料需要保持弹性时, they should be used and stored above the glass transition temperature (otherwise, 它冒着变脆的风险). 然而，材料如硬质塑料和 复合材料 是否应在玻璃化转变温度以下使用. 如果在这一点以上使用, the heat will cause them to have lower modulus and a higher coefficient of thermal expansion. 为 复合材料, 这导致较低的机械树脂为基础的性能，如压缩, 剪切和层间张力. 为 electronic materials, printed wiring boards may be thermally stressed during assembly or use. This results in mechanical stresses in plated through holes, vias, leads and solder joints. 为了获得最佳的可靠性，高Tg非常重要.   

External factors, like humidity or moisture level, may also affect glass transition temperature. 因为水分往往会在材料中缓慢扩散, it may act as a plasticizer and causes the material to reach an equilibrium moisture content based on the relative humidly of the exposure. 这导致较低的玻璃化转变温度. Materials used in an office environment will only pickup moderate amounts of moisture during service life, 与室外潮湿环境下的材料相比. 正因为如此, a low temperature (well below the cure temperature) drying or a controlled moisture exposure may be appropriate.

如何进行玻璃化转变温度测试?

为了确定材料的玻璃化转变温度, 可以使用几种不同的测试和报告类型之一. 所使用的方法将在很大程度上取决于所寻求的结果的类型, 最终报告需要哪些数据. 

The classical way of measuring glass transition temperature is to perform a series of mechanical tests over the expected temperature range. 虽然测试类型有几个选项, 抗折强度或剪切试验是标准. Results are reported as a plot of flexural or shear modulus in relation to temperature. The glass transition temperature is indicated where there is a significant drop off in material strength.

多亏了现代热分析, testing for glass transition temperature has become significantly faster and cheaper in recent years. The most standard thermal methods for determining transition temperature are 热力分析(蓝玉), 动态力学分析(直接存储器存取), 差示扫描量热法(DSC).

Tg测试方法

热力分析(蓝玉): A thermomechanical analysis uses a small sample of material, which is heated on a quartz stage. A rod inside the machine places a small amount of force on the top of the sample, and the movement of the rod is measured with a linear variable differential transformer or LVDT. The entire instrument is heated at a slow rate, usually 5 degrees C per minute. This data is reported as a curve, where change in length is plotted versus temperature. The slope of the resulting curve is called the coefficient of linear thermal expansion, or COLTE. The glass transition temperature is the point at which the slope of the line changes, as seen below.

蓝玉也可用于弯曲或穿透模式. 在se approaches a larger force is applied until the probe deflects significantly.  

差示扫描量热法(DSC)

在 DSC试验法, a small sample is heated while measuring the amount of energy required to heat the sample. 然后将该值与惰性参考物质进行比较. Because the glass transition temperature will create a change in the properties of the material, 聚合物链重新定向, 需要能量的变化来加热. 这表现为曲线上的一个拐点. 可选择并报告三点:起病, 哪个是最低值, 中点和终点.  

动态力学分析(直接存储器存取)

im体育APP在玻璃化转变温度测量方面的专业知识 

如上所述, glass transition temperature measurements can vary greatly in technique and calculation based on the specific material type, 实际应用, 还有很多其他因素. im体育APP's polymer scientists have the knowledge and expertise required to support your 材料测试 为您的材料编制程序并提供准确和适用的数据.

im体育APP today to learn more about our thermal analysis and analytical services offering.