Comparative Dynamical Study Of Colloidal Gels And Glasses

Colloid glasses and colloidal gels have become important research topics in the field of soft condensed matter physics.For the classic hard sphere colloid system,the interaction between particles is purely repulsive,and with increasing particle volume fraction the system undergoes a transition from liquid to glass phase.When interaction changes from repulsive to attractive,the system could transform from liquid to gel phase.By computer simulations,people have recognized the differences between the two kinds of condensed states of colloidal system.However,there is little experiment research to investigate the difference in the dynamic behaviors between colloidal glass and gel.In this work,the dynamic behaviors of the colloidal glass and gel are studied by video microscopy.We have discussed the different dynamic behaviors and the corresponding physical mechanisms.Firstly,we form colloidal glass and gel by changing the packing fraction of the particles and their interactions,respectively.Then,the dynamical behavior of colloidal glass and gel are observed and recorded by video microscopy.Finally,the obtained image data are analyzed by means of particle tracking technology.Power-law decay in the correlation function is observed in both colloidal glasses and colloidal gels,indicating that the dynamic behaviors are slow,but their physical mechanisms are different greatly.The slow dynamics in the colloidal glass are driven by excluded volume effects(cage effects),while the slow dynamics in the colloidal gel are dominated by the attractions between the colloidal particles.And we find that,compared with those of the colloidal glass,the particle motions in the colloidal gel are slower.We attribute this behavior to the attractive interaction between the particles in colloidal gel:attractions bind the particle to its neighbors and form 'bond',and thus localize it much more tightly;while repulsions localize the particles less tightly within a cage formed by its neighbors in the colloidal glass.Moreover,colloidal gels exhibit stronger dynamical heterogeneities compared with that of colloidal glasses.Last but not the least,the dynamics of the colloidal system with both "cage" effect and attractive interaction are investigated.A logarithmic decay in the correlation function is observed,which is consistent with the mode coupling theory(MCT).