Large amplitude oscillatory shear flow: Microstructural assessment of polymeric systems

Nonlinear oscillatory shear tests of pressure-sensitive adhesives (PSAs) designed for transdermal therapeutic systems (TTS)

“…This is already indicated by the 4 rad/s curve of the AC compound with 𝑣 𝐹 = 49.1 %. Similar cross-linking dependent findings were reported by Kamkar (2020) for a gelatin methacryloyl hydrogel, and explained intermediate shear thickening (T>0) followed with shear thinning behavior (T<0) at higher amplitudes by shear induced gelation processes through physical crosslinks being destroyed by increasing amplitudes. Du et al (2018) found a filler dependent behavior for T showing a transition from intra-cycle shear thickening (T >0) to intra-cycle (T <0) shear thinning with increasing filler content for polydimethylsiloxane nanocomposites and Kádár et al (2020) for 3D hierarchical graphene nanocomposites; both attributed this effect to the destruction of a weakly interconnected filler network, or (given the high strain amplitudes) to the distortion of partially interconnected filler network patches.…”

“…In addition, S and T analyses gave a deeper insight into the behavior of molecular segments of the PSAs by comparing them with findings from literature for gelled networks or particle filled systems. Firstly, the onset of the inter-cycle nonlinearity of S and T decreases with increasing resin content due to a lower chain mobility, which was also found by Du et al (2018), Kamkar et al (2018), Kamkar (2020), Gaska and Kádár (2019), Goudoulas and Germann (2018), Kádár et al (2020) and Alibadian et al (2018).…”

“…This quadratic dependence can be inferred theoretically considering the similitude between the Taylor series expansion of the shear viscosity and the corresponding Fourier series, combined with symmetry arguments (Hyun and Wilhelm 2009). However, rather recently, this has been shown not to be a universal scaling for numerous examples of material systems exhibiting non-quadratic scaling behavior (Natalia et al 2020), including polymer melts (Hyun et al 2007) and filled polymer systems (Gaska and Kádár 2019, Kádár et al 2017, 2020. It should be noted that based solely on 𝐼 3/1 for non-quadratic scaling cases, it is rather difficult to ascertain the noise-MAOS transition.…”

“…Hyun et al (2006) correlated the deformation behavior of hard gels in the nonlinear region to the destruction of the layer interactions and the breakdown of initial microstructures. Other researchers (Khandavalli and Rothstein 2015, Du et al 2018, Kamkar 2020, Kádár et al 2020) reported about interconnected filler networks or shear induced gelation at medium amplitudes being destroyed by higher amplitudes (𝛾 0 < 10 %) and resulting in oriented polymer chains and slippage of the particles or stretching of the network junctions, respectively.…”

“…Khandavalli and Rothstein (2015) related high S values to the yielding of the microstructures in polyethylenoxide dispersions with hydrophobic fumed silica particles. However, Kamkar (2020) explained positive S values of gelatin methacryloyl hydrogel at the highest strain amplitude with the stretching of the chains between two polymer junctions, which would react stiffer if the chains were already stretched to large deformations.…”