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Relaxation behavior of poly(methyl methacrylate) at a water interface
Yoshihisa Fujii1, Toshihiko Nagamura, Keiji Tanaka
1Department of Applied Chemistry, Kyushu University, Fukuoka 819-0395, Japan.
Abstract:
The relaxation behavior of poly(methyl methacrylate) (PMMA), spin-coated on a silicon wafer, at the water interface was examined by lateral force microscopy as a function of temperature and scanning rate. Even in water, the lateral force peak which was assigned to the segmental motion of PMMA plasticized by water molecules was clearly observed in the temperature domain. The apparent activation energy for the plasticized alpha(a)-relaxation process was much smaller than those for the original alpha(a)-relaxation processes at the intact surface and in the bulk. The depth profile of the glass transition temperature (T(g)) of the PMMA film in water was obtained, showing that T(g) decreases with proximity to the water phase. The T(g) depression observed here was best explained in terms of the water content of the film, rather than a confinement effect.
Insights
Water plasticizes poly(methyl methacrylate) (PMMA) at the interface, lowering its glass transition temperature (Tg). This plasticization effect, driven by water content, impacts PMMA
Area of Science:
- Polymer Science
- Materials Science
- Surface Science
Background:
- Poly(methyl methacrylate) (PMMA) is a widely used polymer.
- Understanding polymer behavior at interfaces is crucial for material applications.
- Water's effect on polymer properties, especially at interfaces, requires detailed investigation.
Purpose of the Study:
- To investigate the relaxation behavior of PMMA at the water interface.
- To determine the influence of water on the glass transition temperature (Tg) of PMMA films.
- To elucidate the mechanisms behind Tg depression in PMMA at the water interface.
Main Methods:
- Spin-coating of PMMA on silicon wafers.
- Lateral Force Microscopy (LFM) for interfacial analysis.
- Variable temperature and scanning rate experiments.
Main Results:
- A distinct lateral force peak, attributed to water-plasticized segmental motion, was observed for PMMA in water.
- The apparent activation energy for the plasticized alpha-relaxation was significantly lower than for bulk or intact surface PMMA.
- A depth profile of Tg revealed a decrease in Tg with proximity to the water phase.
Conclusions:
- Water acts as a plasticizer for PMMA at the water interface.
- The observed Tg depression is primarily due to water content, not confinement effects.
- Interfacial water significantly alters the relaxation dynamics and thermal properties of PMMA.
