Classic Ubbelöhde Intrinsic Viscosity Laboratory Exercise Made Simple and Fast

Intrinsic viscosity is a foundational concept in a student’s
understanding of macromolecular structures and solution behavior.
Its measurement through simple laboratory techniques can teach undergraduate
students the importance of accuracy and precision while learning concepts
in polymer science such as hydrodynamic volume and the dependence
of viscosity on concentration, density, and mass as well as mathematical
principles such as the Taylor series and l’Hopital’s
rule. Only simple and inexpensive equipment is required, but the measurements
consume much time and can frustrate both students and instructors.
We propose a faster method for conducting intrinsic viscosity measurements
for polystyrene in toluene without forfeiting any of the valuable
lessons provided in a traditional intrinsic viscosity experiment.
Splitting students into teams where each use their own viscometer
to measure flow times of a single solution concentration allows for
the measurement of multiple concentrations at once. This practice
also eliminates the need for long-term and precise temperature control
and diluting (or cleaning and purging) of viscometers between different
concentrations. Results from each team can be combined, allowing students
to analyze one another’s data and make decisions on exclusion
of erroneous measurements, data fitting, and uncertainty analyses.
Choosing a polymer in pellet form reduces congestion at the analytical
balance and provides valuable lessons in refractive index matching
and the torpid diffusion/dissolution of entangled macromolecules.
In this method, students can learn the same fundamental concepts in
polymer science and critical data analysis in a much faster and less
frustrating manner.

特性黏度（intrinsic viscosity）是学生理解高分子（macromolecule）结构与溶液行为的核心概念。通过简易实验技术开展其测量，可让本科生在学习高分子科学相关概念（如流体力学体积、黏度对浓度、密度与质量的依赖关系）以及泰勒级数、洛必达法则等数学原理的同时，领会准确度与精密度的重要性。该实验仅需简易且低成本的设备，但测量过程耗时较长，易使学生与实验指导教师产生挫败感。我们提出了一种用于甲苯中聚苯乙烯特性黏度测量的快速方法，且不会舍弃传统特性黏度实验中所有极具教学价值的内容。将学生划分为若干小组，每组使用各自的黏度计（viscometer）测量单一溶液浓度的流出时间，即可同时完成多个浓度的测量。该操作模式还可省去长期精准控温的需求，以及不同浓度测量间对黏度计的稀释（或清洗与吹扫）步骤。可将各小组的实验结果进行合并，让学生能够相互分析彼此的数据，并对异常测量值的剔除、数据拟合以及不确定度分析做出决策。选用粒状聚合物可减少分析天平前的拥堵情况，同时让学生在折射率匹配以及缠结高分子的缓慢扩散/溶解过程中获得极具教学价值的实践经验。通过该方法，学生能够以更高效、更不易产生挫败感的方式，掌握高分子科学的核心概念与关键数据分析技能。