This paper presents experimental investigation of nanoscale indentation formation in shape
memory polymers. The polymers were synthesized by photopolymerizing a tert-butyl
acrylate (tBA) monomer with a poly(ethylene glycol dimethacrylate) (PEGDMA)
crosslinker. The concentration and the molecular weight of the crosslinker were varied
to produce five polymers with tailored properties. Nanoscale indentations were
formed on the polymer surfaces by using a heated atomic force microscope (AFM)
cantilever at various temperatures near or above the glass transition (between 84 and
215 °C) and a range of
heating durations from 100 µs
to 8 ms. The images of the indents were obtained with the same probe tip at room
temperature. The contact pressure, a measure of transient hardness, was derived from the
indentation height data as a function of time and temperature for different polymers. With
increasing crosslinker molecular weight and decreasing crosslinker concentration, the
contact pressures decreased at a fixed maximum load due to increased crosslink spacing in
the polymer system. The results provide insight into the nanoscale response of these novel
materials.
This paper investigates the thermomechanical formation and recovery of nanometer-scale indents in a shape memory polymer (SMP), studied using a heated atomic force microscope (AFM) tip and hot-stage atomic force microscopy. The material tested is a tert-butyl acrylate (tBA)-based polymer, which has a glass transition temperature of 60 degrees C. The AFM tip forms indents in the polymer in the temperature range 25-250 degrees C. The shape recovery of the indents is studied while the polymer is heated up to 100 degrees C. The temperature required for complete annealing of the indents depends upon the indentation formation conditions, with higher temperature formation corresponding to higher temperature recovery.
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