Measurement of size‐dependent glass transition temperature in electrospun polymer fibers using AFM nanomechanical testing

Abstract

The glass transition temperature (T g ) of individual electrospun polymer polyvinyl alcohol fibers of varying diameter was measured using atomic force microscopy (AFM) based nanomechanical thermal analysis. Indentation and bending of individual electrospun fibers using AFM allowed the calculation of the elastic modulus of the polyvinyl alcohol (PVA) fibers across a range of different temperatures. The elastic modulus of electrospun PVA fibers was observed to decrease significantly when passing through T g , which allowed accurate deter-mination of T g . The T g of electrospun PVA fibers was shown to decrease for smaller fiber diameters especially for fiber diameters below 250 nm. This size-dependent glass transition behavior of electrospun PVA fibers is indicated as being due to polymer chain confinement.

Nano-scale temperature dependent visco-elastic properties of polyethylene terephthalate (PET) using atomic force microscope (AFM)

“…The glass transition temperature is identified as the point of inflection on the sigmoidal shape within the heat flow data. At this point the entangled polymer molecules become more mobile and undergo a reversible transition from a glassy to a rubbery state, leading to enhanced polymer chain mobility (Wang and Barber, 2012). The visco-elasticity of PET was recently examined using dynamic mechanical analysis (DMA) at a range of temperatures and with varying crystallinity: low crystallinity (0 and 17%) PET was more viscous around T g when compared to highly crystalline (24 and 35%) samples (Bédoui and Guigon, 2010).…”

“…Further, as the cantilever probe assembly can be treated as a spring, it can be used to measure surface stiffness and adhesive properties. Previous studies have explored the visco-elastic and nano-mechanical properties of polymer films (Bliznyuk et al, 2002;Cappella et al, 2005;Kaliappan and Cappella, 2005;Torres et al, 2009;Tsui et al, 2000;Yang et al, 2006), polymer electrospun fibres (Wang and Barber, 2012) and rubber (Tranchida et al, 2009) using AFM with increasing temperature. However, AFM based nanoindentation analysis on polymeric materials can become problematic * Corresponding author.…”

Effect of cyano dipolar groups on the performance of lithium-ion battery electrospun polyimide gel electrolyte membranes

“…On the other hand, a strong decrease of T g is observed in the 0CN/2CN (50/50 w/w) copolymer sample, which can be related to polymer chain [35] and amorphous regions confinement [37] in the copolymer due to the different nature of the polymer phases with and without CN-dipolar groups.…”

“…(table 2), which is lower than the one reported in [33] for polymer films. It was reported that the high electric field used to obtain electrospun fibers can lead to polymer chain alignment along the longitudinal direction of the polymer fiber [34], which in turn can influence the glass transition temperature of the polymer, as demonstrated for poly(vinyl alcohol) (PVA) [35].…”

Tensile testing of individual glassy, rubbery and hydrogel electrospun polymer nanofibres to high strain using the atomic force microscope

“…Consequently, there are many methods for measuring mechanical properties by AFM. The most common approach is to move the cantilever perpendicular to the plane of the substrate with the measured cantilever deflection providing normal force such as nanoindentation 42,43 or bending of a horizontally suspended nanofibre [44][45][46][47][48][49] to determine the material's Young's modulus or yield strength. Breaking strength and elongation at break are usually not measurable when using this geometry because the vertical range of motion for most AFM's is limited to a few micrometres.…”