The innovation engine for new materials

Zugui Peng

Zugui Peng


Tokyo Institute of Technology


Mechanical Engineering


Sarah Innes-Gold

Faculty Sponsor(s): 

Omar Saleh

Faculty Sponsor's Department: 


Project Title: 

Measurement of Temperature Effects on the Elasticity of Single Polymers Using Magnetic Tweezers

Project Description: 

Studies of polymer physics are essential to a range of fields, including drug discovery, physics of disease, and materials development. Single-molecule measurements are a useful means of studying the elastic and conformational properties of individual polymers. Magnetic tweezers are a powerful tool which can be used in polymer elasticity measurements to apply stable and low forces on the order of 0.01 pN up to forces on the order of 10 pN to single polymers. Since high forces (~100 pN or greater) would give information about short-length-scale, sub-nanometer structural features, applying low forces to polymers is good for learning about long-range structure. Theory predicts that polymers under tension will behave like springs. Pulling the polymer decreases the number of configurations that the polymer can be in, so the force applied to stretch the chain is doing work against entropy. The force response of such polymers is characterized by an entropic spring" constant which is proportional to temperature. Polyethylene glycol (PEG) is a chemically inert water-soluble polymer that is a useful model system due to its simple structure. Previous theoretical and experimental work has shown that under large stretching forces, PEG elasticity is dominated by enthalpic effects and chain entropy does not contribute. However, under the low stretching forces of a magnetic tweezers experiment, configurational entropy of the polymer chain is expected to be more important. Here, we use magnetic tweezers force spectroscopy to measure changes in the low-force elasticity of PEG between 25℃ and 50℃. We also use magnetic tweezers to investigate the temperature-dependence of the elasticity of biopolymers such as DNA and hyaluronic acid.