Rheology Of Physical Aging Dynamic Of Physical Gel Under Steady Shear Rate

Glassy material will undergo physical aging with time.The internal structure of the material will relax with time,and have a characteristic of dynamic slowing down,and the relaxation time will increase with the aging time.Shear melting is considered as one of the important tools to quench the colloidal gel system.Orthogonal superposition method is the superposition of the steady shear field in the horizontal direction and the small oscillation shear field in the vertical direction,so that the viscoelastic information of the material changing with time under the shear condition can be realized.The physical gel involved in this paper is synthetic hectorite suspension with a concentration of 3.0 wt%.The present article was divided as following parts:1.After preshear and equilibrate for 800 s,a relatively stable gel was subjected to orthogonal frequency sweeps at different shear rates.The time-shear superposition could be realized and obtain a master curve which has a unique"dual-mode"shape indicates that the shear may induce some new microstructure that not present under natural aging conditions.The master curve obtained from constant strain rate sweep experiment(SRFS)has a single mode shape.Since some strains in SRFS have been in the nonlinear viscoelastic region,its viscoelastic spectrum is not completely linear.As a result,the orthogonal experiment results is the true dynamic viscoelastic spectra of the sample under shear.2.The time-resolved viscoelastic spectrum is obtained by multiple repeated sweeps.The time-shear superposition at any time can be achieved indicates that the material follows a universe structural relaxation at different shear rates.the relationship of horizontal shift factor against the shear rate is_??.We cannot achieve the superposition of the time-aging time at the same shear rate,which means that under the shear,the relaxation spectrum is changed.The shift factors by the time-aging time indicates that the sample will reach different steady state of aging under different shear rates.The larger the shear rate,the sooner it will reach the final steady state.3.Compare to Kovacs temperature jump tests,we design a series of shear rate experiments for the physical aging of the physical gel system.It was found that the first and the second signature under shear still make sense:intrinsic iso-shear rate and asymmetry approach.However,we did not observe memory effect.We also compare the effect of temperature and stress on the physical aging system.It was found that steady shear-rate effect is more like temperature effect..