| The glass-forming materials possess both liquid-like disordered structure and crystal-like rigidity,exhibiting a unique slow dynamical relaxation behavior.The study of glass transition phenomena has important values both in fundamental science and practical applications.In the past few decades,great progress has been made in understanding and predicting the dynamical properties of glass-forming liquids(including molecular,polymer,colloidal and other soft matter systems),while also raising various interesting and profound new questions.Compared with the traditional one-component systems,the glassy dynamics in binary mixtures show a series of rich new complexities that deserve further exploration in many aspects.In this thesis,we systematically improve and establish a set of microscopic statistical dynamical methods suitable for binary glass-forming systems,based on the elastically collective nonlinear Langevin equation(ECNLE)theory framework that has been developed for nearly twenty years.We call this method the self-consistent cooperative hopping theory(SCCHT).We apply SCCHT to study polymer-small molecule mixtures,binary cross-attractive colloidal systems and sticky/non-sticky colloidal blends in detail,revealing a series of novel glassy dynamical phenomena.The specific research contents of this thesis are divided into the following four parts according to the development and application of SCCHT:(1)We presented the core physical picture of the SCCHT framework and derived a complete set of theoretical formulas that can be used to describe the cooperative activated hopping dynamics in glassy binary sphere mixtures through three logically connected steps.Our derivation followed various dynamic self-consistency relationships between the penetrant particles and the matrix particles,and introduced new concepts such as the “two-step coupled dynamic free energy” of the matrix particles,which enabled a comprehensive generalization of the existing ECNLE theory system in binary systems.In the SCCHT framework,the dynamic relationship between penetrant particles and matrix particles hopping displays two general types of behavior: matrix-penetrant co-hopping(regime 1)or penetrant particles with an average hopping time shorter than the average hopping time of matrix particles(regime 2).After establishing the theory,we used SCCHT to conduct two aspects of research on the classical binary hard sphere model system.First,we directly compared the(without any adjustable parameters)SCCHT theoretical calculation results under moderately dense conditions with those from molecular simulation data in the literature and found good consistency.Further,we used SCCHT to make new predictions for the ultra dense conditions(corresponding to the regime where hopping dynamics are beyond the reach of current molecular simulations)of a binary hard sphere system,and systematically studied how particle size ratio and composition affect the cooperative activated hopping dynamics of matrix particles and penetrant particles.The analysis shows that in the case of these high active hopping energy barriers,the long-range elastic distortion associated with a matrix particle hopping over its cage confinement always generates elastic barrier of a nonnegligible magnitude.In summary,the SCCHT provides a unified basis for accurately dealing with the cooperative activation hopping dynamics of penetrant particles and matrix particles with different size ratios,particle-particle interactions,and compositions in dense binary mixtures.SCCHT is applicable to different degrees of dense conditions,as well as various types of soft matter systems,such as polymer-small molecule mixtures and binary colloidal systems.(2)We first applied the SCCHT method to study two types of polymer-small molecule mixtures.The first is a polymer-small molecule mixture based on hard sphere interactions,in which we use a previously established method to map chemically matching polymer-molecule mixtures to effective binary hard sphere systems.We study the effect of different mass weight fraction of toluene on the glass transition temperature of polystyrene(PS)and the diffusion coefficient of toluene in polyvinyl chloride(PVAC),and compare the theoretical predictions with experimental data.The results show that the theoretical predictions are in good agreement with the experimental results,indicating that the SCCHT method can handle this system and further demonstrate the reliability of the SCCHT method.The second type is a polymer-small molecule mixture based on cross-attractive interaction.SCCHT makes a series of predictions for the various cooperative dynamic behaviors that can be achieved in this model system.It is found that increasing the size ratio of penetrant to matrix or the cross-attractive interaction generally increases the composition window of regime 1.For the wide-ranging changes in three system factors,we also quantitatively studied the dynamic characteristics of various aspects of the cooperative activation transition process,including the transient localization length of penetrant and matrix,the jump displacement of penetrant and matrix,the local and elastic energy barriers of different types of particles,as well as the long-term diffusion coefficient,relaxation time,and dynamic fragility of matrix particles.Of particular interest is the predicted“anti-plasticization” phenomenon when the cross-attractive interaction is strong enough.These two examples also demonstrate the ability of SCCHT to handle a richer range of particle interactions.(3)Next,we used the SCCHT method to study the glassy dynamics of binary crossattractive colloidal systems.The ECNLE theory predicts that the elastic effect plays an important role in the glass transition of thermal liquids,while the colloidal glass transition can be ignored because the colloidal particle size is much larger than the molecular liquid.After the introduction of relatively short-range cross-attraction in the two-component hard sphere colloidal system,the system exhibits very rich dynamic behavior and dynamic phase.We comprehensively elucidated for the first time that by adjusting the parameters such as the size ratio of colloidal particles,the packing fraction of penetrate particles,and the attraction strength between the matrix and penetrate particles,the dynamic phases(colloidal gel,attractive glass and repulsive glass)appearing in the one-component colloidal system will appear again in the two-component system after introducing ultra-short-range cross-attraction.In addition,by tuning the unique parameters of the binary colloidal system,new hopping dynamic behaviors that are not present in the single-component colloidal system also appear.For example,under certain conditions,the hopping of the matrix particles will undergo a two-step hopping process,which is the unique case 2 hopping process of the two-component system.(4)We also used the SCCHT method to study the glassy dynamics in sticky/non-sticky colloid blends.When there are only sticky particles in the system,a network containing physical bonds will be formed between the sticky particles.We added non-viscous particles to the networked colloidal system(divided into three cases where the size of the non-viscous particles is smaller than,equal to or larger than the size of the viscous particles),and produced various complex and interesting dynamic behaviors and dynamic phases: no matter how the particle size ratio in the system changes,adding an appropriate amount of non-sticky particles,with the increase of the attraction strength between the sticky particles,the system will appear glass-gel coexistence phase.This is the unique feature of this system.In addition,by adjusting the packing fraction of non-sticky particles,the shear elastic modulus of the system will also show a non-monotonic trend.These studies have provided us with a further understanding of the complex dynamics in two-component soft matter systems and provided meaningful insights into the development of new materials. |
PDF Full Text Request