| Because charged colloidal particles are much larger than atoms and molecules,and their crystallization time is longer,their shape,size and interaction are easier to control accurately,and there are many observation and measurement methods available,so they can be used as a universal model with enlarged time and space to study crystallization phenomenon.At the same time,the ordered colloidal crystal formed by the crystallization of colloidal suspension is also an important micro nano material,which has a wide range of application value.In the actual process of colloidal crystallization,it is difficult to achieve a completely ideal single component state,which is generally a mixture state of different degrees.In addition,it has been found that the single component colloidal crystal has some defects in structure control and performance control,while the binary colloid can achieve the structure and performance that the single component colloidal crystal does not have.In this paper,we consider a binary charged colloid,which is a mixture of two charged particles,as the model system and research object.The effective interaction parameters between charged particles and colloids can be adjusted freely by changing some conditions,thus corresponding to many kinds of substances or systems,and the results have strong universality.We mainly used molecular dynamics simulation method.The interaction potential between the two charged colloidal particles was represented by the hard core Yukawa model,and the crystallization process of the system was observed from the microscopic point of view.The main research contents are as follows:(1)The effect of volume fraction on the crystallization of binary charged colloid system with different particle size ratio was studied.By simulating the binary colloidal system with the diameter ratio of 1:1.25,1:1.5 and 1:2 respectively,we found that the addition of the second component particles obviously inhibited the crystallization,reduced the crystallization rate and crystallization ratio of the system,and even led to the appearance of glassy structure,compared with the single component colloidal particle crystallization.(2)When the particle size ratio of binary charged colloid is small,the system is easy to crystallize.By observing the crystallization process of the binary charged colloidal particles,we also found that the alloy structure similar to AB type appeared in the crystallization process of the binary colloidal particles,that is,the large-size colloidal particles dispersed in the binary system,evenly embedded in the lattice structure of the small-size particles.(3)The preliminary law and physical mechanism of phase separation and crystallizationof binary charged colloid system were studied.We set the particle size ratio as 1:2.Based on the simple hard core Yukawa model,through many simulations and attempts,we found that phase separation is easy to occur when the Debye constant k is 2.0 and the action potential intensity εis 60.0.When the volume fraction is small,the system will have phase separation but will not crystallize;with the increase of volume fraction,the system will crystallize after phase separation.This is because the volume fraction of each particle gradually reaches the volume fraction of single component crystal in the process of phase separation under the action of volume repulsion potential,which promotes the occurrence of crystallization.Referring to the simulation results and substituting the actual parameters of colloidal particles,we found that phase separation and crystallization can be observed only in the appropriate range of charge number,ion concentration and volume fraction. |
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