Self-diffusion and spatially heterogeneous dynamics in supercooled liquids near Tg

威斯康星州麦迪逊大学的Mark Ediger在实验物理化学计划的支持下进行实验，测量低分子量过冷液体中平移运动的基本方面。 在使用热程序解吸和前向反冲光谱法的实验中，四种不同脆性的过冷液体的自扩散系数将在非常接近玻璃化转变温度的情况下测量，在这个范围内，目前很少有实验结果。 选择用于研究的系统是甘油、salol、邻三联苯和十氢化萘，范围从文献中确定的最不脆弱的单组分有机玻璃形成剂之一到最脆弱的单组分有机玻璃形成剂之一。这些系统的自扩散结果将与PI最近的三萘基苯（TNB）数据相结合。 对于TNB，中子反射率将用于确定分子在平移运动变得扩散之前必须移动的距离。 小角中子散射技术将用于直接探测非均匀动力学区域并确定其大小。 此外，中子反射率将被用来确定附近的界面对玻璃化转变温度附近的动力学的影响。 所有这些实验都将使用气相沉积来制备正常和氘代玻璃形成剂的薄双层。 实验结果将对玻璃化转变温度附近的分子运动模型施加强有力的约束，并将用于测试这些模型。 这些结果也将增加对动力学中空间不均匀性起源的理解。了解玻璃化转变温度附近的输运性质对于聚合物和其他技术上重要的无序或无定形材料是重要的。 结果预计将提高能力，以操纵聚合物和金属玻璃的性能，提供基本的见解，通过光刻制备的小聚合物结构的崩溃，并为实际的纳米结构和涉及非晶材料的设备的发展至关重要。 同样，蛋白质、泡沫和颗粒材料都表现出玻璃态动力学，这些对过冷液体的研究将增强对它们的理解。

Mark Ediger of the University of Wisconsin Madison is supported by the Experimental Physical Chemistry Program to carry out experiments that will measure fundamental aspects of translational motion in low molecular weight supercooled liquids. In experiments using thermally programmed desorption and forward recoil spectrometry, the self-diffusion coefficients of four supercooled liquids of varying fragility will be measured very near the glass transition temperature, a range in which there are currently very few experimental results. The systems selected for study are glycerol, salol, ortho-terphenyl, and decalin, ranging from one of the least fragile to one of the most fragile single component organic glass formers identified in the literature. Self-diffusion outcomes on these systems will be combined with the PI's recent data for tris-naphthylbenzene (TNB). For TNB, neutron reflectivity will be used to determine the distance over which molecules must move before translational motion becomes diffusive. The technique of small angle neutron scattering will be used to directly detect regions of heterogeneous dynamics and to determine their size. As well, neutron reflectivity will be used to determine the influence of nearby interfaces on dynamics near the glass transition temperature. All of these experiments will be performed using vapor deposition to prepare thin bilayers of normal and deuterated glass formers. Experimental outcomes will place strong constraints on models of molecular motion near the glass transition temperature, and will be used to test these models. The results will also increase understanding of the origin of spatial heterogeneities in dynamics.Understanding transport properties near the glass transition temperature is important for polymers and other technologically important materials that are disordered, or amorphous. Outcomes are expected to advance the ability to manipulate properties of polymers and metallic glasses, to provide fundamental insights into the collapse of small polymer structures prepared by lithography, and to be essential for the development of practical nanoscale structures and devices involving amorphous materials. As well, proteins, foams, and granular materials all exhibit glassy dynamics whose understanding will be enhanced by these studies on supercooled liquids.