Theoretical And Experimental Study Of Bridging Attraction Dominated Colloidal Systems With Small Angle Neutron Scattering

Colloidal systems are very popular in both daily life and industrial field,the key to optimize its performance is to modulate the interaction between colloidal particles.A general way is to add in small components of different properties.When the additive small particles can be reversibly adsorbed onto the surface of big colloidal particles,one small particle can connect two big particles together,acting as a bridge and resulting in an effective attraction between big colloidal particles,called bridging attraction.In bridging attraction dominated systems,with addition of small particles,the systems will show a liquid-gel-liquid phase transition.Currently,the scientists have made a hypothesis of bridging attraction,but it hasn't been verified,nor been applied to the experimental data analysis.Small angle neutron scattering(SANS)has been widely used in colloidal systems,it can study the structure of materials with a size range from nanometer to several micrometers very well.Within the theories of small angle scattering(SAS),this thesis has built up the bridging attraction model and veryfied it by experimental observations,and then studied the phase diagram of two components colloidal systems with bridging attraction both theoretically and experimentally.The main contents are as list below.(1)Within the framework of SAS,building up the bridging attraction model with the theories for multi-component sticky hard sphere(MCSHS)systems,and analytically calculating some key parameters,including the structure factor,scattering intensity,spinodal decomposition line(SDL),maximum bridging attraction(MBA)and equivalent hard sphere(EHS)point;(2)Proposing a method to map the bridging attraction dominated systems into one component sticky hard sphere(SHS)systems,the mapping method makes it possible to apply the research results of one component SHS systems,such as percolation and binodal line,into bridging attraction case;(3)Studying the theoretical phase diagram of mixture of Polystyrene(PS)and Poly N-isopropylacrylamide(PNIPAM),comparing it with the experimental observations,verifying the effectiveness of the bridging attraction model;(4)Within the bridging attraction model,studying the effects of the size ratio of small to big particles and the stickiness parameter between them on the systems' phase diagram,also studying the features of the effective potential between big colloidal particles.The numerical results of several key parameters can help guide experimental operations;(5)Using SANS experiments to study the systems of bovine serum albumin(BSA)with addition of yttrium chloride(YCl3),applying the bridging attraction model for the data analysis to check how the system changes with Y3+concentration.This thesis theoretically verifies the existence of bridging attraction in two components colloidal systems,provides a deep physical insight to the liquid-gel-liquid phase transition.The mapping method from bridging attraction dominated systems to one component SHS systems helps apply the theories in one component SHS systems to bridging attraction case,making the study of colloidal systems with bridging attraction much easier.Meanwhile,this work is the first ever in the world using the SANS and bridging attraction model to understand complex colloidal systems,the methods along with the codes that are available to the scattering community will benefit a lot of users and also they have provided the theoretical and experimental basis for the research of similar systems.