Self-Assembly of Multiple Soft Matter Systems

Abstract

Self-assembly is an exciting process to be exploited for the fabrication of hierarchical sophisticated functional materials with countless technological and medical applications. However, the lack of full understanding of the mechanisms and conditions that yield these structures, has limited its broad use. In this work, we focus on the study of a variety of self- assembling systems with different interactions between the components, along with their final architectures, as an effort to further comprehend the actual self-building process. The first system consists of a binary mixture of hard spheres with a size ratio of 0.39. This mixture was investigated experimentally through particle-resolved studies. Complementary computational work provided insights into the dynamics of the system. Non-equilibrium interstitial solid solutions in coexistence with a fluid phase were found for both experiments and simulations. Here, the large particles form a close-packed mixture of fcc and hcp lattices, whereas the small ones occupy randomly some of the available octahedral sites of the crystalline phase. Although, these are the predicted stable configurations, the composition analysis showed a mismatch between these results and the predictions at equilibrium. This is likely a consequence to poor solubility of the small components in the close-packed ordered structure. Thus, our interstitial solid solutions remain long-lived and out-of-equilibrium. The second system is composed by one-component particles with long Debye screening lengths, that form crystals at packing fractions as low as φ = 0.015. The Yukawa theory was used to study the phase behaviour of the system. Good agreement was found for the prediction of fluid and solid phases for concentrations φ < 0.015: the freezing point and bcc configuration of the solid phases match the model predictions. However, for higher packing fractions, the expected fcc lattice was not present, but a persistent bcc crystal was found. This could be due to lack of system equilibration and the influence of the sample square confinement. A mixture of fluorescent proteins with short-range attractions constitutes the third system. This was used to produce bicontinuous gels with distinctive protein domains through salt addition. Several strategies along with protein surface modification were followed. Due to com- plex protein interactions, the target structures were successfully produced only when one gel was formed before the other. Additionally, control over the coverage of the original gel was also achieved. To our knowledge, this is the first realisation of these bicontinuous gel structures where the proteins retain their functional configuration. Finally, core shell fluorescent silica magnetic nanoparticles were developed to constitute a magnetic responsive component of a binary system, where the other species are bare silica particles. The aim was to deposit iron oxide nanoparticles on the surface of fluorescent silica spheres and coat them with a silica shell. Although the decoration of the core with magnetic nanoparticles was successful, further attempts to coat them with a silica shell to provide stabilisation only produced aggregates. However, the dynamics of the clusters were effectively altered using an external magnetic field, showing the potential of these particles for further studies

Date of Award	23 Jan 2019
Original language	English
Awarding Institution	University of Bristol
Supervisor	C. Patrick Royall (Supervisor)