TY - JOUR
T1 - Impact of molecular mass on the elastic modulus of thin polystyrene films
AU - Torres, Jessica M.
AU - Stafford, Christopher M.
AU - Vogt, Bryan D.
N1 - Funding Information:
This work was financially supported by the National Science Foundation under grant # 0653989-CMMI . We gratefully acknowledge the use of facilities within the LeRoy Eyring Center for Solid State Science at Arizona State University. We thank Dr. Dallas Kingsbury for assistance with Instron measurements, Dr. Chad R. Snyder for DSC measurements, and Ms. Kathy M. Flynn for GPC measurements.
PY - 2010/8
Y1 - 2010/8
N2 - Surface wrinkling was used to determine the elastic modulus at ambient temperature of polystyrene (PS) films of varying thickness and relative molecular mass (Mn). A range of Mn from 1.2 kg/mol to 990 kg/mol was examined to determine if the molecular size impacts the mechanical properties at the nanoscale. Ultrathin films exhibited a decrease in modulus for all molecular masses studied here compared to the bulk value. For Mn > 3.2 kg/mol, the fractional change in modulus was statistically independent of molecular mass and the modulus began to deviate from the bulk as the thickness is decreased below ≈50 nm. An order of magnitude decrease in the elastic modulus was found when the film thickness was ≈15 nm, irrespective of Mn. However, an increase in the length scale for nanoconfinement was observed as the molecular mass was decreased below this threshold. The modulus of thin PS films with a molecular mass of 1.2 kg/mol deviated from bulk behavior when the film thickness was decreased below ≈100 nm. This result illustrates that the modulus of thin PS films does not scale with molecular size. Rather, the quench depth into the glass appears to correlate well with the length scale at which the modulus of the films deviates from the bulk, in agreement with molecular simulations from de Pablo and coworkers [31] and recent experimental work [35].
AB - Surface wrinkling was used to determine the elastic modulus at ambient temperature of polystyrene (PS) films of varying thickness and relative molecular mass (Mn). A range of Mn from 1.2 kg/mol to 990 kg/mol was examined to determine if the molecular size impacts the mechanical properties at the nanoscale. Ultrathin films exhibited a decrease in modulus for all molecular masses studied here compared to the bulk value. For Mn > 3.2 kg/mol, the fractional change in modulus was statistically independent of molecular mass and the modulus began to deviate from the bulk as the thickness is decreased below ≈50 nm. An order of magnitude decrease in the elastic modulus was found when the film thickness was ≈15 nm, irrespective of Mn. However, an increase in the length scale for nanoconfinement was observed as the molecular mass was decreased below this threshold. The modulus of thin PS films with a molecular mass of 1.2 kg/mol deviated from bulk behavior when the film thickness was decreased below ≈100 nm. This result illustrates that the modulus of thin PS films does not scale with molecular size. Rather, the quench depth into the glass appears to correlate well with the length scale at which the modulus of the films deviates from the bulk, in agreement with molecular simulations from de Pablo and coworkers [31] and recent experimental work [35].
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U2 - 10.1016/j.polymer.2010.07.003
DO - 10.1016/j.polymer.2010.07.003
M3 - Article
AN - SCOPUS:77955555442
SN - 0032-3861
VL - 51
SP - 4211
EP - 4217
JO - Polymer
JF - Polymer
IS - 18
ER -