Acoustic Wave Propagation Across Glassy-Rubbery Polymer Interfaces

Emory University, Atlanta GA

Investigators

Abstract

NON-TECHNICAL SUMMARY Technological applications routinely incorporate multiple components into a device with small-scale structure causing numerous interfaces between the different components. Research has demonstrated that proximity to interfaces can alter the local properties of the material. This has strong implications for predicting the material's performance influencing everything from ion conduction in batteries to a material's overall strength and long-term stability. This project will map the extent, magnitude, and range of local property changes between hard glassy polymer components and soft rubbery polymer components across glassy-rubbery polymer-polymer interfaces testing different interpretations put forward to explain long range coupling of local dynamics across these different polymer domains. Experiments using different techniques will be conducted on simple model systems specifically designed to address which factors impact the observed behavior. The fundamental understanding gained from these studies would have broad implications across a range of different glass-forming systems. Additional activities of the project include a partnership with the art conservation lab at Emory's Carlos Museum to characterize various polymer resins and the application methods used in artwork restoration and conservation, providing both research experiences for undergraduate students and useful information for the art conservation field. Outreach is done as part of the museum's tours for the public and student group activities, as well as other Atlanta-based organizations such as Science.Art.Wonder that pairs artists with scientists to communicate research through art. TECHNICAL SUMMARY Recent efforts have developed a good understanding of local gradients in dynamics near free surfaces spanning 10-20 nm. However new insight is needed to explain outstanding experimental observations of longer-range 100-200 nm perturbations to local dynamics, especially near polymer-polymer interfaces to address the cause of broad, approximately 200 nm, asymmetric local glass-transition temperature gradients that have been observed to emerge upon glassy-rubbery polymer-polymer interface formation. Building on work that identified the glassy-rubbery polymer interfacial width and modulus of the neighboring domain as key parameters controlling this phenomenon, this project will measure the shear wave propagation across glassy-rubbery bilayer samples using a quartz crystal microbalance (QCM) to study how the difference in acoustic impedance between the domains is altered upon polymer interface formation. Information about the depth-dependent gradient in local modulus will be determined using continuum physics layer model analysis. The work aims to test recently proposed mechanisms for the long-range gradients in local dynamics. In addition, efforts will work towards developing perylene dye into a temperature-dependent localized fluorescent probe of polymer vibrational dynamics and so-called dynamic glass transition. . This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.