Stability of Thiol-on-Gold Templates under Injection Molding Conditions

James E. Whitten, Chemistry; Joey L. Mead, Plastics Engineering; Carol M. F. Barry, Plastics Engineering 

Self-assembled monolayers (SAMs) of functionalized thiols on gold surfaces are very useful as templates for micro- and nano-scale assembly of polymers and biomaterials from solution. Because of the limited thermal stability of thiol SAMs, the value of these templates for assembly from polymer melts has been questioned. Because of the short duration of the peak temperatures involved, thiol SAM templates may still be viable for polymer assembly using injection molding, and now provide support for the study via direct experimentation and modeling.

In the present work, the stability of PFDT (1H,1H,2H,2H-perfluorodecanethiol) SAMs on gold coated silicon mold inserts, when subject to repeated cycles of injection molding, was studied. The SAMs were characterized using XPS (X-ray Photoelectron Spectroscopy) and water contact angle measurements. PFDT provides high sensitivity for detection by XPS via the F1s transition. Preliminary results indicate that the SAMs were sufficiently intact after 50, 100 or even 500 cycles of injection molding with PMMA (polymethylmethacrylate) at melt temperatures of 460 F (238 C), to serve as potential templates. The thermal histories and temperature profiles of the mold inserts were studied by finite element modeling. These findings are expected to be of considerable value for template based high-rate nanomanufacturing using injection molding.