|Title||Supramolecular networks of telechelic polymers|
|Source||University. Promotor(en): Jasper van der Gucht, co-promotor(en): Joris Sprakel. - Wageningen : Wageningen University - ISBN 9789462578678 - 117 p.|
Physical Chemistry and Soft Matter
|Publication type||Dissertation, internally prepared|
|Keyword(s)||supramolecular chemistry - networks - polymerization - gels - mechanical properties - separation technology - rheology - supramoleculaire chemie - netwerken - polymerisatie - mechanische eigenschappen - scheidingstechnologie - reologie|
This thesis focuses on the fundamental understanding of phenomena associated with the gelation of end-functionalized polymers and the dynamic processes occurring inside of the gel network. To address particular questions we use two types of telechelic polymers, in which the assembly occurs due to the solvophobic interactions and due to the metal-ligand coordination, respectively. In this research we employ a number of methods, mostly rheology and light scattering.
In Chapter 2 we revealed new insights into the complex microscopic dynamics of transient networks, assembled by hydrophobic forces. Using light scattering experiments we show how these materials exhibit complex multimodal relaxation spectra. To shed light on the nature of such relaxation processes we systematically changed the network architecture by gradually reducing the network connectivity while keeping the polymer concentration constant. This strategy allows us to disentangle the roles of concentration and connectivity on the dynamic modes of these systems.
In Chapters 3 and Chapter 4 we experimentally explored the pathways of network formation from telechelic polymers association by means of metal-ligand complexation. Interestingly, while some networks exhibit near-ideal Maxwellian behavior, as expected for transient networks, we find certain cases where we observe scale-free critical mechanics. To date this latter behavior was only identified close to a covalent percolation transition. The critical behavior observed for these end-functional self-assembled polymer networks, however, is robust to changes in concentration, temperature and crosslinking degree. Our studies show that such a self-organized and robust critical state is the results of arrested phase separation that kinetically traps the network-forming system at its percolation point. The system thus remains trapped in a critical state resulting in robust power-law scaling of shear and relaxation moduli. We also show how this state depends sensitively on the relaxation kinetics of the nodes by demonstrating an intermediate case where initial critical behavior slowly relaxes over the course of several days to the ideal linear Maxwell case. With our research we highlight the complex pathway where self-assembling systems reach their equilibrium ground state, involving persistent and long-lived kinetically arrested states which give rise to unusual mechanics and highly heterogeneous spinodal structures.
Chapter 5 brought us towards more applicable materials where we develop a highly tunable composite network based on orthogonal supramolecular interactions. For such a design we generate multivalent nanoparticle tectons, which are subsequently linked together into network structures, using metal-coordination interactions. Materials built this way are highly tunable with moduli and viscosities spanning many orders of magnitude.
In the remainder of this chapter, we focus on some unresolved and outstanding questions regarding the physical chemistry and properties of supramolecular networks and we will discuss some preliminary data obtained in our efforts to resolve them.