A Linear Viscoelastic Study of PEO-based Ionomer and Plasticizer Systems of Varying Composition

Open Access
Author:
Tunic, Tyler Robert
Area of Honors:
Chemical Engineering
Degree:
Bachelor of Science
Document Type:
Thesis
Thesis Supervisors:
  • Ralph H Colby, Thesis Supervisor
  • Darrell Velegol, Honors Advisor
Keywords:
  • polymer
  • ionomer
  • plasticizer
  • glass transition
  • rheology
  • WLF
  • Rouse model
  • KWW equation
Abstract:
In this thesis, a polyethylene oxide oligomer plasticizer was combined in various proportions with a polyethylene oxide based ionomer. The mechanical properties these systems were then studied using a rotational rheometer. Master curves of storage and loss moduli as a function of frequency indicated that a combination of factors was accelerating the terminal relaxation of the polymer as more plasticizer was introduced. Two factors identified as having a large impact on this terminal relaxation acceleration were the decrease in glass transition temperature Tg and increase in the dielectric constant of the medium containing the polymer, both of which are direct results of the plasticizer addition. The goal then became trying to separate the contributions that each of these factors had. In order to quantify the extent of acceleration due to the Tg effect, the WLF equation was initially used. However, further investigation revealed that one of the main assumptions of the WLF equation was invalid for the polymer/plasticizer systems described in this thesis; there is an extra friction corresponding to the change in dielectric constant with changing temperature. The Tg contribution was instead quantified using DSC. The dielectric effect in accelerating the terminal relaxation was approximated using a weighted average mixing law given dielectric data of both the pure polymer and the plasticizer. In the end, it was shown that the increase in the mediums dielectric constant had the greatest effect on the acceleration of the ionomer’s terminal response, and the sum of the Tg and dielectric friction effects approaches that of the measured total friction but that there is still some frictional effect that has not been considered. Each master curve was also fitted with a Rouse model for the (rubbery) low frequency response and the KWW equation for the (glassy) high frequency response. Ionic interactions in the pure ionomer and the 90% ionomer / 10% plasticizer mixture created a very broad glassy response, while mixtures with more plasticizer showed the glassy response narrowing significantly.