Predicting the Rubbery Response of Polymer Liquids

Melts and solutions of long polymers flow very differently from simple fluids.  Polymer fluids behave much like rubber; a flowing stream “snaps back” when the flow stops.  This behavior is crucial for polymer processing.  Its origin is entanglement:  polymer chains deformed by flow cannot easily recover their usual random-walk configurations, because neighboring chains get in the way.  A given chain moves as if it is confined to a tube.  

The tube diameter determines how rubbery is the fluid response.  The tube diameter depends on the type of polymer and its concentration in solution.  Predicting the tube diameter from structure has been a longstanding challenge.  Our work describes how different kinds of polymer entangle.  The key insight is simple to state intuitively:  polymer chains entangle as often as they can, limited only by how often they can closely approach each other.  We turn this deceptively simple statement into a unified scaling theory for different kinds of polymer fluids.

The Milner research group actively mentors research undergraduates, through a variety of programs at Penn State, including the WISER (Women In Science and Engineering Research) program, the Chemical Engineering REU,  and the Schreyer Honors College.  In the past decade, I have worked with 21 research undergraduates, leading to 7 honors theses and 8 publications with undergraduate first authors. 

I am currently working with four research undergraduates.  Colin Gillespie is completing his honors thesis and will enter the PhD program at Penn this fall. 
Lindsay Jones is a WISER student, working on simulations related to the work presented here, simulating for polymers of different structure the “packing length”, which governs how closely different polymer strands can approach each other.