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This study investigated the non-linear rheological behaviors of silver nanowire (AgNW) suspensions containing silica nanoparticles (SiNPs) dispersed in aqueous polyvinyl alcohol (PVA) solutions under large amplitude oscillatory shear (LAOS) flows with various methods including LAOS moduli, Fourier-transform (FT) rheology, and the sequence of physical processes (SPP). The microstructures of the suspensions depended on the ratio of SiNP and AgNW concentrations (φSi/φAg). Lower φSi/φAg ratios yielded entangled AgNWs, whereas high φSi/φAg ratios induced AgNW–SiNP bundle formation due to strong attraction between SiNPs and AgNWs. Non-linear rheological behaviors were classified into three new LAOS types (A, B, and C) based on distinct microstructures including entangled networks of individual AgNWs, stiff AgNW–SiNP bundles, and a combination of both. Type A, with dominant entangled AgNWs, displayed two-step strain thinning attributed to flocculated network formation. Network disruption aggravated the non-linearities due to strain-induced structure formations, followed by the appearance of minima in FT intensities due to disentangled and aligned AgNWs. Type B, comprising AgNW entangled networks and AgNW–SiNP bundles owing to higher SiNP contents, exhibited broad one-step strain thinning. Type C, with dominant stiff bundles, presented the simplest network structures, resulting in one-step strain thinning. Furthermore, intracycle structural changes during LAOS flows were examined using two SPP parameters: instantaneously recoverable elasticity G t , max ′ and internal area of SPP moduli. The SPP analysis also exhibited different behaviors depending on the LAOS types. Thus, employing FT rheology and SPP methods, complex microstructures containing PVA, AgNWs, and SiNPs and their structural changes during LAOS flows were investigated. [ABSTRACT FROM AUTHOR]

In the medium amplitude oscillatory shear (MAOS) test, intrinsic nonlinearity Q0(ω) derived from Fourier-transform (FT)-rheology is an important material function for investigating the nonlinear responses of complex fluids. However, Q0 consists of elastic and viscous components without phase information, such as complex modulus |G*| obtained from the small amplitude oscillatory shear (SAOS) test. In this study, we decomposed Q0 into Q 0 ′ (ω) and Q 0 ″ (ω), as done for storage modulus G′ and loss modulus G″ in the SAOS test. Furthermore, intrinsic-nonlinear tan δ (≡tan δ3,0), which provides third-harmonic phase information, was calculated by dividing Q 0 ″ by Q 0 ′ . First, we defined mathematically elastic nonlinearity Q 0 ′ and viscous nonlinearity Q 0 ″ , and then investigated the physical meanings of Q 0 ′ and Q 0 ″ . Second, we applied the intrinsic parameters Q 0 ′ and Q 0 ″ to monodisperse polystyrene solutions. All intrinsic-nonlinear master curves of Q 0 ′ (ω) and Q 0 ″ (ω) for model solutions showed similar behavior in the terminal regime (at low frequencies). Unentangled polymer solutions had the same intrinsic-nonlinear master curves. However, although the intrinsic-nonlinear master curves of entangled polymer solutions superimposed well at low De (near the terminal regime), they deviated at high De due to different entanglement densities. Therefore, two characteristic times, MAOS relaxation time and inflection time (τN and τinf), were determined from intrinsic-nonlinear master curves by comparing with terminal relaxation time and Rouse time (τL and τR) obtained from linear master curves. The results showed that intrinsic nonlinearities from the MAOS test are sensitive to relaxation processes (terminal and Rouse) of polymer chains. Finally, master curves were compared with predictions by the molecular stress function (MSF) model and the Pom-Pom model. The single-mode predictions of these two models described behavior changes qualitatively. However, both failed to achieve quantitative predictions of Q 0 ′ (ω) and Q 0 ″ (ω). On the other hand, the multimode MSF model agreed well with experimental data from the terminal regime to the inflection time scale under the terminal relaxation mode assumption. [ABSTRACT FROM AUTHOR]

Effects of silica nanoparticles withdifferent natures (hydrophilicityand hydrophobicity) on (80/20) PP/PS blends were investigated vialinear and nonlinear rheological properties. The hydrophilic silicananoparticle was fumed silica OX50 while the two hydrophobic oneswere precipitated silica D17 and fumed silica R202. SEM images revealedthat hydrophilic OX50 could not improve morphological properties ofthe blends. On the other hand, the two hydrophobic silica nanoparticles(R202 and D17) improved morphological properties. TEM examinationshowed that OX50 silica nanoparticles aggregated inside PS droplets,thereby making breakup of PS (dispersed) phase into smaller sizesmore difficult. D17 and R202 improved morphological properties regardlessof the different droplet size reduction mechanisms, and rheologicalproperties improved as a result. Both linear rheological propertiesfrom SAOS (small-amplitude oscillatory shear) tests and nonlinearrheological properties from LAOS (large-amplitude oscillatory shear)tests were obtained. The nonlinear–linear viscoelastic ratio(NLR ≡ normalized nonlinear rheological properties/normalizedlinear rheological properties) was used to quantify the degree ofdroplet dispersion and distinguish the effects of silica particleson the morphology of PP/PS blends. Previous research has observedan inverse correlation between NLR and droplet size. PP/PS/OX50 blendswith no alteration of droplet size showed constant NLR values (≅1)with increasing concentration of OX50 (hydrophilic silica). However,NLR values of PP/PS blends with hydrophobic silica nanoparticles (D17and R202) were much larger than 1 (NLR > 1) and increased withsilicaconcentration, which is consistent with morphological evolution, i.e.,reducing droplet size. However, NLR values of PP/PS/R202 blends wererelatively larger than those of PP/PS/D17 blends despite smaller dropletsizes. This can be attributed to a different morphology microstructure,i.e., R202 located in PP matrix phase and D17 at interface betweenPP and PS. Therefore, the NLR value of PP/PS/silica blend could bedue to the combined effects of the interface between droplets (PP/PSblend) and particle–polymer interactions (PP/silica nanocomposites).Especially, R202 showed larger NLR values due to PP/R202 nanocomposites.Based on these findings, relative NLR (= NLRPP/PS/silica/NLRPP/silica) is proposed as an effective measurementof droplet size information in PP/PS blends by eliminating the effectsof PP/silica nanocomposites. Relative NLR matched well with dropletsize evolution from the SEM results. [ABSTRACT FROM AUTHOR]