Final answer:
Nanotechnology is the field of study most closely associated with the technological development of flexible displays for e-books.
Step-by-step explanation:
The field of study most closely associated with the technological development of flexible displays for e-books is Nanotechnology. Nanotechnology refers to the development of products and components that are between 1 and 100 nanometers in size. These extremely small sizes allow for the creation of flexible, lightweight, and high-resolution displays that are used in e-books.