Aggregation State And Phase Structures Of Typical Patchy Colloids

Colloidal particles with chemically or physically patterned surfaces are generally referred to as patchy colloids,the specific functional regions are called“patch”.The method of thermodynamic perturbation theory is used to investigate patchy systems consisting of A_ftype patchy particles with van der Waals,Lennard-Jones and dipolar-dipolar interactions.The equilibrium free energy and the law of mass action concerning the corresponding system can be obtained,and they can be jointly used to study the thermodynamic properties and the phase structure of related systems.The main contents of the dissertation are as follows:Chapter 1.The recent advances of patchy colloid particles are summarized.In detail,some relevant physical and chemical experiments methods for preparing patchy particles are introduced.Theoretically,the models of patchy particle and simulation methods are outlined.The aggregated structures of the systems are of great potential in material applications.Therefore,it is very important to study the phase behaviors of patchy particles and the regulation mechanism of aggregated structures.Chapter 2.Through the principle of statistical mechanics,the explicit expressions of equilibrium free energy and the law of mass action for associations between patchy particles are obtained.The thermodynamic properties of the system are further studied.As a result,the explicit expressions of the number-and weight-average degrees of association,polydispersity index,isothermal compressibility,specific heat and the internal energy are presented.Moreover,phase structure of A_f type of patchy colloids is presented under various conditions by the principle of phase equilibrium,where the phases of fluid(F),sol and gel are investigated to give the corresponding phase diagrams for F-F and sol-gel transitions.Consequently,the association strength and the number of patches show significant effects on the thermodynamic quantities and gelation mechanism of patchy particles.Chapter 3.We present the phase diagrams for A_f patchy colloidal particles with Van der Waals and Lennard-Jones interparticle interactions respectively.A rich phase structure of patchy particles consisting of F-F,F-SC(simple cubic),F-BCC(body-centered cubic)and F-FCC(face-centered cubic)transitions can be observed.An attempt is made to illustrate how the association strength and the number of patches regulate the phase state of patchy particles.As a consequence,a significant effect of the two factors on the crystallization of the patchy colloid.Meanwhile,the critical temperatures,critical densities,triple points,and nucleation mechanism can be significantly regulated by these factors.Chapter 4.The random close packing(RCP)phase is studied by the thermodynamic,perturbation theory together with the cell theory.The relationship between the RCP and gel phases is discussed.In addition,the phase structure of patchy particles consisting of F-RCP and RCP-crystal transitions(RCP-FCC,RCP-BCC)are presented.It is shown that the associating interaction between patchy particles is predominant in studying the phase equilibria of the patchy colloid.Chapter 5.Under the framework of thermodynamic perturbation theory,the effects of associative interaction,dipole-dipole interaction and external electric field on the aggregation behavior of dipole Janus particles were investigated.The phase diagrams under different conditions indicate there is a competition between chain-like and network structure in patchy colloids.To investigate the dielectric behavior of the dipolar Janus particles,the polarization is calculated in terms of free energy,and the dielectric constant is also obtained.The variations of dielectric constant against associated energy under various conditions are presented,which show that dielectric constant can effectively controled by external conditions.