Session D40 - Poster Session I.
POSTER session, Monday afternoon, March 12
Exhibit Hall, Washington State Convention Center
Mechanical properties of polymers, such as silk, are influenced by the fundamental properties: crystallinity, orientation, and crystal modulus. X-ray diffraction with the assumption of uniform stress has been used frequently to determine the crystal modulus. The values for silk fibers have been previously reported to be about an order of magnitude lower than those obtained by computational modeling. This difference is outside the limit of experimental and computational error and probably reflects some conceptual error. The moduli of silk have been reexamined, both experimentally and computationally, in an improved manner. For the X-ray method, this includes making measurements of samples with various degrees of crystallinity and orientation obtained along the cocoon. The measurements yielded crystal moduli in the range of 20-28 GPa, depending on crystallinity and orientation. For the computation, molecular dynamics are used with periodic boundary conditions. The three-dimensional fluctuations analysis performed on the data yields a modulus of approximately 16 GPa. The calculated and experimentally obtained moduli, agree reasonably with those of polymers having similar conformations.