Ultrathin Polymer Films: Viscoelasticity, Physical Aging and Failure

Texas Tech University, Lubbock TX

Investigators

Abstract

TECHNICAL SUMMARY: The behavior of ultrathin polymer films below the glass temperature is not well understood despite its importance in micro- and nano-scale engineering of polymeric structures. Research is to be performed to understand the physical aging response of ultrathin polymer films as a function of temperature and of film thickness for several different polymeric materials. The approach includes making measurements using a novel bubble inflation method of measurement developed in the labs of Texas Tech University (TTU) to perform equi-biaxial and nonequibiaxial deformation geometries. These will be the first physical aging measurements on freely standing ultrathin polymer films. In addition, the work adapts a unique dewetting method in order to perform physical aging experiments below but near to the glass transition for polystyrene films. These dewetting experiments provide completely different film constraint than do the nanobubbles and comparison of the results between the two methods provides a strong challenge to both techniques that are nominally similar, but in the literature have given different and, to-date, unreconciled results. The work also directly probes the dynamics of confined polymers and addresses unreconciled mesoscale vs. nanoscale aging responses that have been reported in the literature. Finally, material failure at the nanometer size scale has been little investigated and the TTU bubble inflation technique will be exploited to examine the rupture behavior of ultrathin polymer films. NON-TECHNICAL SUMMARY: Polymers are widely used in micro-, now becoming nano-, electronics applications. Because it is observed that polymer material properties change when feature sizes are smaller than 100 nm, this makes design and prediction of the polymer behavior at the nanoscale difficult for the electronics developer and designer. Similar effects occur in nanocomposites and other futuristic applications of polymers at the nanoscale. The present work is designed to put two different methods of measurement of nanoscale properties into direct confrontation in order to reconcile differences of nanoscale properties that have been reported in the literature. One method is the TTU nanobubble inflation test developed by the principal investigator in Lubbock, TX and the other is a nanofilm dewetting method developed by researchers at the E.S.P.C.I. in Paris, FR. The outcome of the work will provide highly important insights into the reasons for similarities and differences in reported material behaviors at the nanometer size scale. In addition to the technical work the research is to be carried out by graduate students in the Chemical Engineering Laboratories at TTU and will provide opportunities for two students to be trained and to achieve the bulk the research education to obtain their Ph.D. degrees. Finally, the results of the research will be widely disseminated through journal publication and presentations by the PI and students at national meetings.