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Unusual Surface MechanicalProperties of Poly(α-methylstyrene):Surface Softening and Stiffening at Different Temperatures.

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Title: Unusual Surface MechanicalProperties of Poly(α-methylstyrene):Surface Softening and Stiffening at Different Temperatures.
Authors: Karim, Taskin B.1, McKenna, Gregory B.1
Source: Macromolecules. Dec2012, Vol. 45 Issue 24, p9697-9706. 10p.
Subjects: Styrene, Mechanical behavior of materials, Surface chemistry, Temperature effect, Atomic force microscopy, Viscoelasticity
Abstract: We report results from experiments based on the spontaneousparticleembedment technique to determine the surface compliance of poly(α-methylstyrene)(PαMS) for temperatures from room temperature to Tg+ 21 °C. Both submicrometer and nanometer diameterparticles were investigated. Atomic force microscopy (AFM) measurementswere used for the particle embedment determination, and the Lee andRadok (LR) model was applied to calculate the surface shear compliancesusing the embedment depth of the particles for the temperatures ofinterest. The adhesion force between the particles and the PαMSwas used as the driving force for the embedment in the LR model calculation.Results were compared with macroscopic viscoelastic data for PαMSobtained from the literature and with new data from the present study.We observed surface softening for the PαMS in the temperaturerange from room temperature to Tg–21 °C. This was followed by a crossover to a surface mechanicalresponse that was stiffer than the macroscopic material for temperaturesfrom Tg– 18 °C to Tg+ 21 °C. These novel findings were observedfor both 199 and 60 nm diameter silica particles. [ABSTRACT FROM AUTHOR]
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Abstract:We report results from experiments based on the spontaneousparticleembedment technique to determine the surface compliance of poly(α-methylstyrene)(PαMS) for temperatures from room temperature to Tg+ 21 °C. Both submicrometer and nanometer diameterparticles were investigated. Atomic force microscopy (AFM) measurementswere used for the particle embedment determination, and the Lee andRadok (LR) model was applied to calculate the surface shear compliancesusing the embedment depth of the particles for the temperatures ofinterest. The adhesion force between the particles and the PαMSwas used as the driving force for the embedment in the LR model calculation.Results were compared with macroscopic viscoelastic data for PαMSobtained from the literature and with new data from the present study.We observed surface softening for the PαMS in the temperaturerange from room temperature to Tg–21 °C. This was followed by a crossover to a surface mechanicalresponse that was stiffer than the macroscopic material for temperaturesfrom Tg– 18 °C to Tg+ 21 °C. These novel findings were observedfor both 199 and 60 nm diameter silica particles. [ABSTRACT FROM AUTHOR]
ISSN:00249297
DOI:10.1021/ma302192b