期刊
ACS NANO
卷 3, 期 9, 页码 2677-2685出版社
AMER CHEMICAL SOC
DOI: 10.1021/nn9006847
关键词
thin films; elastic modulus; wrinkling; glass transition; polymers; confinement
类别
资金
- National Science Foundation [0653989-CMMI]
Understanding the mechanical properties of polymers at the nanoscale is critical innumerous emerging applications, While it has been widely shown that the glass transition temperature (T-g) in thin polymer films generally decreases due to confinement effects in the absence of strong favorable interactions between the polymer and substrate, there is little known about the modulus of sub-100 nm polymer films and features. Thus, one might use this depressed T-g as a surrogate to estimate how the modulus of nanoconfined polymeric materials deviates from the bulk, based on constructs such as Williams-Landel-Ferry (WLF) time-temperature superposition principles. However, such relationships have not been thoroughly examined at the nanoscale where surface and interface effects can dramatically impact the physical properties of a material. Here, we measure the elastic modulus of a series of poly(methacrylate) films with widely varying bulk T-g's as a function of thickness at ambient temperature, exploiting a wrinkling instability of a thin, stiff film on an thick, elastic substrate. A decrease in the modulus is found for all polymers in ultrathin films (<30 nm) with the onset of confinement effects shifting to larger film thicknesses as the quench depth (T-g,(bulk) - T) decreases. We show that the decrease in modulus of ultrathin films is not correlated with the observed T-g decrease in films of the same thickness.
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