Self-assembly Preparation and Properties of Microgel Materials
Author:Chang Ai Ping
Supervisor:wu wei tai
The structure of polymer materials determines their properties.That is to say,the properties of macroscopic materials are determined by the structure at the multiple length scales including molecular scale(-100 nm),nanoscle(-101 nm),mesoscale(～102 nm up to millimeter level)and so on.Self-assembly is the process by which individual components arrange themselves into a specific structure,which is a powerful technique for creating new materials and features.A good understanding of the principles of self-assembly will be helpful to get the organization of polymers from the molecular scale,to the nanoscale,to the mesoscale,which will control the structure of polymer materials at all levels of hierarchy,and then achieve the goal of optimizing the material properties.But that’s going to be a big problem for a system.So in this work,we developed several polymer systems for providing new insights into exploring self-assembly principles:we design and synthesize conjugated polymers with specific branched chains,which used as models to carry out the relevant research on self-assembly at the molecular scale;Next,we use microgels as models to carry out the relevant research on self-assembly at the mesoscale.Moreover,attempts are also made to use some systems for optical/electrical detection and lithium-sultur battery,which suppling foundation for practical applications.The main contents of this dissertation are showed as following:(1)We design and synthesize poly(3-oligo(ethylene oxide)x-thiophene)(P30ET or P30EXT,x = 2,3 or 4),and ascertain their temperature responsive behavior in aqueous.P3OE3T with a moderate lower critical solution temperature(LCST)was used to carry out the relevant research on self-assembly and regulatory assembly fluorescence(Chapter 2);By the self-assembly of P3OE2T with a lower LCST on ammonia-responsive polymer microgels,we prepare core-shell assembly microgels.This composite materials can combine the properties of both the electrical conductivity from the conjugated polymers and ammonia recognizability from the ammonia-responsive polymer microgels,the cooperation of these properties allows the reversible control of electrical conductivity by the ammonia gas.These features enable their use for electrical detection of ammonia in breath(Chapter 3);For P3OE4T with a higher LCST,we combine the related demand of energy materials such as lithium-ion battery.Immobilization of sulfur in microgels is achieved via free radical polymerization of commercial poly(ethylene glycol)dimethacrylate in the solution of sulfur-terminated P30E4T(S-P30E4T),a copolymer prepared by the inverse vulcanization of Ss with allyl-terminated P3OE4T(Allyl-P3OE4T).This microgelation leads to enhanced Li-S battery performance over the sulfur-terminated polymer(Chapter 4).All of these studies reflect that we can apply controllable self-assembly and functionalization to the applications for design and preparation of optical/electrical materials,and may open up new possibilities for the key issue of hierarchical assemblies from the molecular scale to the macroscopic scale.(2)Next,we use microgels as models to carry out the relevant research on self-assembly at the mesoscale.By using UV-vis absorption spectroscopy and diffusing wave spectroscopy,we analyze intensity correlation function,mean square displacement,storage modulus and loss modulus to study the crystallization of colloidal crystals:Firstly,we use thermoresponsive poly(oligo(ethylene glycol))microgels as a simple model to study microgei self-assembly during the annealing process,thereby investigating the microrheology properties of colloidal systems in different state(Chapter 5);Secondly,we use thermoresponsive poly(N-isopropyl acrylamide-co-acrylic acid)microgels surface modified with carboxylic acid as a model to study the impact of pH on microgel self-assembly,and exploring the principles of self-assembly(Chapter 6).