<br/>The properties of polymer glasses have been studied classically due to their importance for a wide range of technologies; however, there is increasing need and demand to use these materials in geometries where dimensions approach the length scale of an individual polymer chain. Although significant efforts over the past few decades have provided insight into how physical properties, especially the glass transition temperature, can change as a function of dimensional confinement, there has been significantly less development with regards to other properties, including mechanical properties, which are critical for their performance. One reason for this dearth of understanding is the lack of quantitative measurement methods. We present results using a recently-developed experimental method, called The Uniaxial Tensile Tester for Ultra-Thin films (TUTTUT), which allows for the direct measurement of the complete stress-strain relationship for uniaxial stretching of ultra-thin polymer films. We provide quantitative measurement of changes in the low strain properties, e.g. elastic modulus, as well as changes in the yielding and fracture processes as molecules within the polymer glass are dimensionally confined. We present results on a variety of polymer glasses and blends across a range of thickness, from 15nm to 300nm. In particular, our results reveal a new, thickness-controlled transition from craze deformation processes to shear deformation zones, surprisingly accompanied with extreme embrittlement, for films that are less than 30nm in thickness. We relate this deformation mechanism transition to other property changes in bulk and thin film polymer glasses. This method and these results not only provide fundamental insight into the physics of polymer materials but also new opportunities for designing ultra-thin film materials with enhanced performance.

Deformation mechanisms in ultra-thin polymer glasses

2019 Spring National Meeting

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