= Keller four-roller polymer experiment
{c}
<Pierre-Gilles de Gennes>'s 1991 lecture describes <Andrew Keller> and collaborators using four rollers to deform a dilute <polymer solution>. A well-chosen exit trajectory kept coils under sustained extension. Above a threshold flow rate the solution became <birefringent>, revealing a change in chain orientation and conformation. The experiment connected an optical readout to a mechanically driven molecular response.<Soft Matter by Pierre-Gilles de Gennes>[Printed p. 9: four-roller experiment and coil-stretch interpretation; text inspected in the Columbia reproduction]{ref}
\Image[/four-roll-polymer-stretch-functional-experiment.png]
{title=Four rollers create a region of sustained extension}
This original functional diagram shows a central flow idealization, rather than historical dimensions or a photograph. A probe of <birefringence> detects different optical responses along different directions; it does not directly photograph a chain or establish its extension without an optical model. Comparing a flowing solution with its quiescent state and controlling <temperature> and <concentration> are useful proposed checks, not an assertion that this is the complete historical protocol.
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