Rheology Of Platelets Colloidal Suspension

Research in suspension rheology was mostly focused on the spherical colloids suspensions in the equilibrium, while rheology of platelet suspension in non-equilibrium was seldom reported. The dynamics of the platelet suspensions were rarely involved either. Synthetic hectorite（Laponite XLG） suspension is the typical platelet suspension which platelets dispersed in the Newtonian fluid, and Graphene Oxide /Polyethylene glycol（GO/PEG） suspension is the typical platelet suspension which platelets dispersed in the non-Newtonian fluid. In the present work, the aging process of the two platelet suspensions was studied by kinds of rheological methods in order to relate the suspension structure dynamic variation to their rheological properties, discuss the factors affecting the aging process and illustrate the universal dynamic aging route. The present article was divided as following parts.Firstly, we used multi-wave oscillatory shear time sweep to track the aging process of the synthetic hectorite suspension with different concentration in order to discuss the effects of aging condition. Synthetic hectorite suspensions in 10 “aging-rejuvenation” cycles can be set to a producible situation by preshear（ γ& = 3000 s-1、t = 100 s） after each aging process. We found G’ and G’’ Vs frequency results of synthetic hectorite suspensions at different aging condition obtained by time-resolved viscoelastic spectrum technique can be shifted into a timeaging time superposition master curve, time-temperature superposition master curve and timeaging time-temperature superposition master curve, and this confirmed the universal aging dynamic route for synthetic hectorite suspension in non-equilibrium We calculated the relaxation spectrum of synthetic hectorite suspension on the base of time-aging timetemperature superposition master curve, and found it fitting the power law relaxation spectrum for colloidal system containing both gel and glass proposed by Dannert well. The power exponent of the synthetic hectorite suspension relaxation spectrum n was changed from negative to positive with increasing the hectorite concentration illustrating the variation from gel to glass for synthetic hectorite suspension.Secondly, we prepared GO by modified Hummer’s method and characterized them using FTIR, XPS, TG and so on. The GO was proven having large aspect ratio by rheological method and AFM respectively and its aspect ratio Pa was about 1500. The viscosity abnormal reduction of 0.1 mg/mL GO 5 wt% PEG suspension compared to other GO/PEG suspension might related to the reduction of total hydrogen bonding in GO/PEG suspension resulting from adding moderate GO. The aging process of GO/PEG suspensions was tracked by steady state shearing and small amplitude oscillatory shear. We found that there was no zero-shearing viscosity platform at low shear rate region after GP/PEG suspension aged and G5P5 showed extra transient first normal stress difference after aged. GO platelets in GO/PEG suspension were orientated in the suspension prepare procedure and disorientated when suspension aging. The disorientated GO platelets in aged GO/PEG suspension were orientated again during shearing leading to the extra transient first normal stress difference. Temperature was the main factor determining the velocity of the GO platelets disorientation, and aging time decided degree of the GO platelets disorientation accumulation. For the GO/PEG suspension at the same disorientation degree, shearing at low velocity for a long time is equivalent to shearing at high velocity for a short time to orientate the GO platelets.Thirdly, we characterized the nonlinear viscoelasticity of G5P5, G5P5_preshear, P5, P5_preshear under LAOS controlling the amplitude of the strain rate. Increasing the amplitude of strain rate, all samples showed nonlinear viscoelastic properties more obviously when oscillatory sheared at the same frequency. We found that I3/1, N_1DC, N_1I2 of P5_preshear, G5P5 fell into a muster curve implying strain rate became the deciding factor instead of strain. The nonlinear property parameters of G5P5（G’、I3/1、δ、N_1DC、N₁ I2、δN₁ and Lissajous curve） were different from G5P5_preshear, P5 and P5_preshear, and G5P5 also showed extra transient first normal stress difference under LAOS, suggesting disorientated GO enhance the nonlinear viscoelastic properties. Increasing the strain rate, the nonlinear viscoelastic property parameters of G5P5 approached to G5P5_preshear proving that GO platelets could also be orientated under large amplitude oscillatory shear. Among all kinds of parameters, δN₁ was the most sensitive index to the degree of GO platelets orientation, and Ne could distinguish P5、P5_preshear、G5P5、G5P5_preshear.