Analyzing and Modeling Mechanical Properties of Aging Photothermally Cured Polydimethylsiloxane (PDMS)

open_access
Open Access
Author:
Mc Queen, Duncan
Area of Honors:
Chemistry
Degree:
Bachelor of Science
Document Type:
Thesis
Thesis Supervisors:
Benjamin James Lear, Thesis Supervisor
Timothy Charles Meredith, Thesis Honors Advisor
Joseph D Houck, Faculty Reader
Keywords:
PDMS
Aging
Photothermal Effect
Abstract:
Photothermal curing of polymers using nanoparticles shows great potential for substantially reducing the curing time of polymerization reactions. One crucial metric for understanding how well these polymers work its tensile properties, which indicates how the polymer acts from an applied force. Laser-irradiated polymer samples perform comparably to traditionally oven-cured polymers, but these samples are typically tested immediately after curing occurred. The long-term aging behavior on the tensile properties of such photothermally cured polymers has not been thoroughly investigated—until now. In this study, films (0.1-0.2 mm thick) of polydimethylsiloxane (PDMS) were cured using three methods: oven curing (at 100 °C for 30 minutes), ambient room-temperature (at 25 °C for 24 hours), and laser irradiation under 808 nm near infrared light for 75 passovers of the laser. Carbon black nanoparticles were used for photothermal curing due to their cost efficiency and were used across all samples at 0.1 weight percent for consistency. After curing, dynamic mechanical analysis (DMA) was performed using constant-force stress-strain tests to evaluate the key mechanical properties of Young’s modulus, toughness, and ultimate tensile strength (UTS). Five samples from each curing method were tested weekly, excluding any that snapped. Results showed a significant increase in the Young’s Modulus over time for all curing methods, indicating an increase in sample stiffness as it ages. This trend is hypothesized to result from changing crosslink density as the samples age. Conversely to the modulus results, neither toughness nor UTS exhibited notable changes over time. Soxhlet tests were employed to measure the change in crosslink density for the polymer samples to determine if extent of crosslinking is the reason for observed changes in tensile properties. These changing values of crosslink density over time are used to model the aging process in PDMS, enabling a more accurate understanding of the mechanical behavior of polymers cured through photothermal and traditional methods.