Stable Frank-Kasper spherical packing phases have been observed in a wide variety of soft-condensed matter systems, but the universality of these phases is not well understood. Recently, it was shown that the Frank-Kasper $\sigma$ and A15 phases are stable in the well-known Landau-Brazovskii (LB) model. In this work we consider the $\sigma$ and A15 phases, as well as the Laves C14 and C15 phases, and show that none of these is stable in the Ohta-Kawasaki (OK) model, which is another widely studied Ginzburg-Landau theory. The LB and OK models differ only in their quadratic coefficients. We conduct a thorough investigation of the role that this coefficient plays in stabilizing the complex phases. We uncover generic principles linking the functional form of the coefficient in reciprocal space with the stability of the complex phases. A Ginzburg-Landau theory for a for diblock copolymer system with a conformational asymmetry parameter is derived, but the complex phases are not found to be stable in this model. We also consider a Ginzburg-Landau theory for a system of hard spheres interacting via a pairwise short-range attractive, long-range repulsive (SALR) potential, and use our framework to demonstrate how the parameters in the potential influence the stability of the Frank-Kasper phases. Taken together, these results provide insight into the universal mechanisms that underlie the formation of the complex spherical packing phases in soft condensed matter. / Thesis / Doctor of Philosophy (PhD) / Soft condensed matter physics is the study of soft, deformable materials, such as soap bubbles, foams, and plastics. Many different soft matter systems undergo a fascinating phenomenon known as self-assembly, wherein the constituent particles spontaneously arrange themselves to form various ordered structures. In particular, the spherical packing phases appear when the particles first cluster into spherical aggregates, which then pack into larger arrangements. This sort of self-assembly is interesting because many different spherical arrangements are observed, including the complex spherical packing phases (also known as the Frank-Kasper phases). The fact that these complex phases appear in many different types of materials is not well understood. In this thesis we use a model known as the Ginzburg-Landau theory to ask which of these arrangements will form in a given system, and why. We uncover generic features of the Ginzburg-Landau theory that control which spherical packing phases appear, and we connect these features to several specific systems. These results provide insight into the mechanisms behind the formation of the complex spherical packing phases in a diverse range of systems.

Neste trabalho realizamos dois estudos independentes sobre a termodinâmica de modelos de água e o dobramento de proteínas em rede. / On this work we develop two independent studies on lattice models for water thermodynamics and protein folding.

Small devices capable of self-propulsion have potential application in areas of nanoscience where autonomous locomotion and programmability are needed. The specific base-pairing interactions that arise from DNA hybridisation permit the programmed assembly of matter and also the creation of controllable dynamical systems. The aim of this thesis is to use the tools of DNA nanotechnology to design synthetic active matter at the micro and nano scales. In the first section, DNA was used as an active medium capable of transporting information faster than diffusion in the form of chemical waves. DNA waves were generated experimentally using a DNA autocatalytic reaction in a microfluidic channel. The propagation velocity of DNA chemical waves was slowed down by creating concentration gradients that changed the reaction kinetics in space. The second section details the synthesis of chemically-propelled particles and the use of DNA as a 'programmable glue' to mediate their interactions. Janus micromotors were fabricated by physical vapour deposition and a wet-chemical approach was demonstrated to synthesise asymmetrical catalytic Pt-Au nanoparticles that function as nanomotors. Dynamic light scattering measurements showed nanomotor activity that depends on H₂O₂ concentration, consistent with chemical propulsion. Gold nanoparticles/Origami hybrids were assembled in 2D lattices of different symmetries arranged by DNA linkers. The third section details the design process and synthesis of nanomotors using DNA as a structural scaffold. 3D DNA Origami rectangular prisms were functionalised site-specifically with bioconjugated catalysts, i.e. Pt nanoparticles and catalase. Enzymatic nanomotors were also conjugated to various cargoes and their motor activity was demonstrated by Fluorescence Correlation Spectroscopy. In the final section, control mechanisms for autonomous nanomotors are studied, which includes the conformational change of DNA aptamers in response to chemical signals, as well as a design for an adaptive dynamical system based on DNA/enzyme reaction networks.

Neste trabalho realizamos dois estudos independentes sobre a termodinâmica de modelos de água e o dobramento de proteínas em rede. / On this work we develop two independent studies on lattice models for water thermodynamics and protein folding.

De nombreuses études théoriques et expérimentales ont été menées au cours des 30 dernières années afin d'établir le lien entre les propriétés d'interaction des protéines, leurs transitions de phase et leur auto-assemblage. Des avancées significatives ont ainsi été permises grâce à l'application de concepts et méthodes de la physique des polymères et des colloïdes. Ces études ont, pour la majeure partie d'entre elles, été limitées à des protéines d'intérêt médical et à des protéines animales. Ce travail de thèse vise à appliquer ce type d'approche aux protéines végétales afin de mieux comprendre leurs propriétés d'interaction à l'origine de leurs propriétés fonctionnelles au sein des grains et dans les matrices alimentaires. Ce travail a été mené sur un isolat de protéines de réserve du blé composé principalement de la fraction monomérique: les gliadines. Nous avons étudié les transitions de phase des gliadines afin de mieux comprendre leurs propriétés d'interaction d'une part et les structures associées d'autre part. Dans un premier temps, une procédure d'extraction a été développée afin de travailler sur un isolat de composition contrôlée dont les masses moléculaires sont comprises entre 20 kDa et 300 kDa. Le comportement de phase de cet isolat a ensuite été étudié en diminuant la qualité du solvant. Nous avons ainsi déterminé le diagramme de phases (T-Φ), où T est la température et Φv la fraction volumique des gliadines. Cette étude a mis en évidence une séparation de phase de type liquide-liquide dans le système par diminution de la température. Une analyse détaillée de la répartition des protéines au sein des deux phases en fonction de leur masse moléculaire a permis d'identifier une masse moléculaire critique séparant des protéines de comportement de type colloïdal et des protéines de comportement de type polymérique. A partir du diagramme de phase, deux études structurales ont été effectuées. La première a étudié les cinétiques de séparation de phase lors de la diminution de la température pour caractériser la dynamique locale de séparation de phase et identifier les mécanismes qui génèrent les systèmes concentrés. Deux grands types de mécanismes de séparation de phase ont été identifiés : nucléation-croissance et décomposition spinodale. La seconde étude structurale a consisté à établir l'équation d'état pression osmotique vs concentration dans des conditions de bon solvant et à caractériser la structure des dispersions de protéines associée. La relation pression osmotique vs fraction volumique a permis de mettre en évidence l'existence de plusieurs régimes de structuration, associés à des changements de structure secondaire et de propriété rhéologique. La discussion générale permet de mettre en relation les propriétés thermodynamiques déduites de cette approche expérimentale et les changements structuraux observés à différentes échelles. / A substantial body of theoretical and experimental studies has been conducted over the last 30 years to establish the link between protein interaction properties, phase transitions and self-assembly. Both colloidal and polymer physics provide a new framework for understanding the driving force for proteins phase behaviour. Such studies have been limited to health-related proteins and to a few food proteins, mainly animal proteins such as casein, whey proteins. This thesis aims to apply this approach to plant proteins to better understand their interactions properties, at the basis of their functional properties within grains and food matrices. This work was carried out on a wheat storage protein isolate mainly composed of the monomeric fraction: gliadins.The objective of this PhD thesis is to investigate the phase transitions of wheat proteins to develop our knowledge on their interaction properties and the associated structures. We organized our experimental approach in five steps. First, we developed an extraction procedure to work on a protein isolate of controlled composition with molecular weight ranging from 20 to 300 kg mol-1. Then, we investigated the phase behaviour of the protein isolate by decreasing the solvent quality, here the temperature. We determined the T-Φ phase diagram, where T is the temperature and Φv the protein volume fraction, that maps the phase and structural transitions of the proteins. This study showed the existence of a liquid-liquid phase separation in the system upon a temperature decrease. We evidenced two different behaviours among proteins as a function of their MWs and highlighted a critical protein size above which the molecular weight is the key determinant of the protein properties. From the phase diagram, two structural studies were conducted. The first one studied the kinetics of phase separation upon temperature decrease to characterize the local dynamics of phase separation and to identify the mechanisms that generate concentrated systems. Two main mechanisms of phase separation have been identified: nucleation-growth and spinodal decomposition. The second one studied the effect of protein concentration on the multi-scale structure of wheat gliadins in good solvent. The integration of all these results allowed us to build the phase diagram of wheat gliadins, integrating thermodynamic and structural data.