Bulk And Micro-Viscoelastic Spectra Of The Liquid-to-Solid Transition Of Complex Fluids

Complex fluids respond as soft solids under certain conditions and can be altered between liquid and solid states by mechanical actions and applied time.It has been noted that the viscoelastic spectra of the liquid-to-solid transition(LST)of many complex fluids can be divided into two types,which were called type-Ⅰand type-Ⅱrespectively in the present work.LAPONITE~?suspension and gelatin were selected to study the viscoelastic spectra of the LST of complex fluids as the experimental model of colloid gel and polymer gel.We investigated the initial-state-and probe-scale-dependence of the types of LST,which were understood by its microstructure mechanism.The present work was divided as following parts:1.The oscillation multi-wave test was applied to characterize the LST of pre-sheared LAPONITE~?suspension samples with different concentration of particles and added salt.Samples showed two types of viscoelastic spectra of the LST.A c_S-c_L phase diagram has been established based on the result,which revealed that the types of LST were mainly decided by the particle concentration and not sensitive to the concentration of the added salt.The potential interactions of equivalent model of sample with different components were obtained through simulative calculation.By analyzing the interrelation among the phase diagram,the potential energy curve and the pre-sheared effect,it was concluded that the pre-shear process provided energy to the samples,affecting the formation mode of clusters in the system,and thus influencing the final type of viscoelastic spectra of the LST.2.The LST of 6 wt%gelatin samples were investigated by the oscillation multi-wave test in bulk rheology and multi-particles tracking in micro-rheology,which found,for the first time,that types of viscoelastic spectra of LST of the same system at different measurement scale differed.In bulk rheology,the LST of gelatin samples belonged to TypeⅡwhile that in the micro-rheology belonged to TypeⅠ.According to the fact that multi-particles tracking features a scale-effect,we analyzed that types of viscoelastic spectra of LST in gelatin system were depended on the measurement scale.3.We designed and manufactured an active micro-rheometer that overcame the limitation of magnetic tweezers controlling only single particle,which could detect local information in microscale as well.The active micro-rheometer provided a reliable scheme and experimental basis for establishing a characterization method for the measurement scale between bulk and micro-rheology.Selecting probe particles of the desired measurement scale based on the methods and principles provided by the design,a continuous measurement scale space can be established to help understand the probe-scale dependence of the LST.