Bicontinuous Materials from Telechelic Macromonomers Using Thiol-ene Chemistry

Bicontinuous structures are beneficial to many applications from health and medicine to energy and the environment. Although these materials can be used for many applications, current strategies yield bicontinuous structures only under highly specific processing conditions. Development of a versatile platform to reliably obtain bicontinuous morphologies will be broadly beneficial. This work presents two platforms that can be used to produce bicontinuous morphologies using a simple Mitsunobu/thiol-ene strategy. This platform allows for the incorporation of a variety of polymer chemistries to yield well-defined polymer networks or multiblock copolymers (MBCs). It also allows for the systematic investigation of factors affecting the morphology such as the molecular weight between cross-links and the volume fraction of the network components. The ease at which these variables can be systematically investigated allows for rigorous fundamental studies of these composite systems. In the first co-network system, the platform’s ability to tailor mechanical properties while maintaining good ion conductivity was demonstrated by comparing PEG-PDMS co-networks to PEG networks using EIS and DMA. Also, the effect of salt loading on thermal properties was explored using DSC. The second system, PEG-PS co-networks, demonstrated that varying the molecular weight of the precursor polymers results in control over d-spacing that fits well to de Gennes’s prediction (d ~ Mn0.5). Despite the variation in d-spacing, 22 - 55 nm, the ion conductivity and mechanical properties remained relatively consistent, demonstrating versatility in this system. Critical percolation thresholds were investigated by using ion conductivity and storage modulus to probe the continuity of the PEG and PS phases, respectively. Percolation theory suggests this system has a wide bicontinuous compositional window from fPEG = 0.225 -0.675. A preliminary phase diagram was generated by combining results from the molecular weight and volume fraction series. Finally, a simple synthesis for (MBCs) is demonstrated using the same Mitsunobu/thiol-ene platform. MBCs with ~4 blocks and two or three types of macromonomers were synthesized. Disordered phase separation was shown by SAXS and AFM. The versatile Mitsunobu/thiol-ene platform is easily able to synthesize different architectures using a range of polymer chemistries for various morphology and property studies

Phase behavior and morphology of multicomponent liquid mixtures

Multicomponent systems are ubiquitous in nature and industry. While the physics of few-component liquid mixtures (i.e., binary and ternary ones) is well-understood and routinely taught in undergraduate courses, the thermodynamic and kinetic properties of $N$-component mixtures with $N>3$ have remained relatively unexplored. An example of such a mixture is provided by the intracellular fluid, in which protein-rich droplets phase separate into distinct membraneless organelles. In this work, we investigate equilibrium phase behavior and morphology of $N$-component liquid mixtures within the Flory-Huggins theory of regular solutions. In order to determine the number of coexisting phases and their compositions, we developed a new algorithm for constructing complete phase diagrams, based on numerical convexification of the discretized free energy landscape. Together with a Cahn-Hilliard approach for kinetics, we employ this method to study mixtures with $N=4$ and $5$ components. We report on both the coarsening behavior of such systems, as well as the resulting morphologies in three spatial dimensions. We discuss how the number of coexisting phases and their compositions can be extracted with Principal Component Analysis (PCA) and K-Means clustering algorithms. Finally, we discuss how one can reverse engineer the interaction parameters and volume fractions of components in order to achieve a range of desired packing structures, such as nested `Russian dolls' and encapsulated Janus droplets.Comment: 16 pages, 11 figures + hyperlinks to 7 video

Modelling of two-phase flow with surface active particles

Kolloidpartikel die von zwei nicht mischbaren Fluiden benetzt werden, tendieren dazu sich an der fluiden Grenzfläche aufzuhalten um die Oberflächenspannung zu minimieren. Bei genügender Anzahl solcher Kolloide werden diese zusammengedrückt und lassen die fluide Grenzfläche erstarren. Das gesamte System aus Fluiden und Kolloiden bildet dann eine spezielle Emulsion mit interessanten Eigenschaften. In dieser Arbeit wird ein kontinuum Model für solche Systeme entwickelt, basierend auf den Prinzipien der Massenerhaltung und der themodynamischen Konsistenz. Dabei wird die makroskopische Zwei-Phasen-Strömung durch eine Navier-Stokes Cahn-Hilliard Gleichung modelliert und die mikroskopischen Partikel an der fluiden Grenzfläche durch einen Phase-Field-Crystal Ansatz beschrieben. Zur Evaluation des verwendeten Strömungsmodells wird ein Test verschiedener Navier-Stokes Cahn-Hilliard Modelle anhand eines bekannten Benchmark Szenarios durchgeführt. Die Ergebnisse werden mit denen von anderen Methoden zur Simulation von Zwei-Phasen-Strömungen verglichen. Desweiteren wird eine neue Methode zur Simulation von Zwei-Phasen-Strömungen in komplexen Gebieten vorgestellt. Dabei wird die komplexe Geometrie implizit durch eine Phasenfeldvariable beschrieben, welche die charakteristische Funktion des Gebietes approximiert. Die Strömungsgleichungen werden dementsprechend so umformuliert, dass sie in einem größeren und einfacheren Gebiet gelten, wobei die Randbedingungen implizit durch zusätzliche Quellterme eingebracht werden. Zur Einarbeitung der Oberflächenkolloide in das Strömungsmodell wird schließlich die Variation der freien Energie des Gesamtsystems betrachtet. Dabei wird die Energie der Partikel durch die Phase-Field-Crystal Energie approximiert und die Energie der Oberfläche durch die Ginzburg-Landau Energie. Eine Variation der Gesamtenergie liefert dann die Phase-Field-Crystal Gleichung und die Navier-Stokes Cahn-Hilliard Gleichungen mit zusätzlichen elastischen Spannunngen. Zur Validierung des Ansatzes wird auch eine sharp interface Version der Gleichungen hergeleitet und mit der zuvor hergeleiteten diffuse interface Version abgeglichen. Die Diskretisierung der erhaltenen Gleichungen erfolgt durch Finiten Elemente in Kombination mit einem semi-impliziten Euler Verfahren. Durch numerische Simulationen wird die Anwendbarkeit des Modells gezeigt und bestätigt, dass die oberflächenaktiven Kolloide die fluide Grenzfläche hinreichend steif machen können um externen Kräften entgegenzuwirken und das gesamte System zu stabilisieren.Colloid particles that are partially wetted by two immiscible fluids can become confined to fluidfluid interfaces. At sufficiently high volume fractions, the colloids may jam and the interface may crystallize. The fluids together with the interfacial colloids compose an emulsion with interesting new properties and offer an important route to new soft materials. Based on the principles of mass conservation and thermodynamic consistency, we develop a continuum model for such systems which combines a Cahn-Hilliard-Navier-Stokes model for the macroscopic two-phase fluid system with a surface Phase-Field-Crystal model for the microscopic colloidal particles along the interface. We begin with validating the used flow model by testing different diffuse interface models on a benchmark configuration for a two-dimensional rising bubble and compare the results with reference solutions obtained by other two-phase flow models. Furthermore, we present a new method for simulating two-phase flows in complex geometries, taking into account contact lines separating immiscible incompressible components. In this approach, the complex geometry is described implicitly by introducing a new phase-field variable, which is a smooth approximation of the characteristic function of the complex domain. The fluid and component concentration equations are reformulated and solved in larger regular domain with the boundary conditions being implicitly modeled using source terms. Finally, we derive the thermodynamically consistent diffuse interface model for two-phase flow with interfacial particles by taking into account the surface energy and the energy associated with surface colloids from the surface PFC model. The resulting governing equations are the phase field crystal equations and Navier-Stokes Cahn-Hilliard equations with an additional elastic stress. To validate our approach, we derive a sharp interface model and show agreement with the diffuse interface model. We demonstrate the feasibility of the model and present numerical simulations that confirm the ability of the colloids to make the interface sufficiently rigid to resist external forces and to stabilize interfaces for long times

Entropically driven self-assembly of pear-shaped nanoparticles

This thesis addresses the entropically driven colloidal self-assembly of pear-shaped particle ensembles, including the formation of nanostructures based on triply periodic minimal surfaces, in particular of the Ia3d gyroid. One of the key results is that the formation of the Ia3d gyroid, re-ported earlier in the so-called pear hard Gaussian overlap (PHGO) approximation and confirmed here, is due to a slight non-additivity of that potential; this phase does not form in pears with true hard-core potential. First, we computationally study the PHGO system and present the phase diagram of pears with an aspect ratio of 3 in terms of global density and particle shape (degree of taper), containing gyroid, isotropic, nematic and smectic phases. We confirm that it is adequate to interpret the gyroid as a warped smectic bilayer phase. The collective behaviour to arrange into interdigitated sheets with negative Gauss curvature, from which the gyroid results, is investigated through correlations of (Set-)Voronoi cells and local curvature. This geometric arrangement within the bilayers suggests a fundamentally different stabilisation mechanism of the pear gyroid phase compared to those found in both lipid-water and di-block copolymer systems forming the Ia3d gyroid. The PHGO model is only an approximation for hard-core interactions, and we additionally investigate, by much slower simulations, pear-assemblies with true hard-core interactions (HPR). We find that HPR phase diagram only contains isotropic and nematic phases, but neither gyroid nor smectic phases. To understand this shape sensitivity more profoundly, the depletion interactions of both models are studied in two pear-shaped colloids dissolved in a hard sphere solvent. The HPR particles act as one would expect from a geometric analysis of the excluded-volume minimisation, whereas the PHGO particles show deviations from this expectation. These differences are attributed to the unusual angle dependency of the (non-additive) contact function and, more so, to small overlaps induced by the approximation. For the PHGO model, we further demonstrate that the addition of a small concentration of hard spheres ("solvent") drives the system towards a Pn3m diamond phase. This result is explained by the greater spatial heterogeneity of the diamond geometry compared to the gyroid where additional material is needed to relieve packing frustration. In contrast to copolymer systems, however, the solvent mostly aggregates near the diamond minimal surface, driven by the non-additivity of the PHGO pears. At high solvent concentrations, the mixture phase separates into “inverse” micelle-like structures with the blunt ends at the micellar centres and thin ends pointing out-wards. The micelles themselves spontaneously cluster, indicative of a hierarchical self-assembly process for bicontinuous structures. Finally, we develop a density functional for hard solids of revolution (including pears) within the framework of fundamental measure theory. It is applied to low-density ensembles of pear-shaped particles, where we analyse their response near a hard substrate. A complex orientational ordering close to the wall is predicted, which is directly linked to the particle shape and gives insight into adsorption processes of asymmetric particles. This predicted behaviour and the differences between the PHGO and HPR model are confirmed by MC simulations

Mesoscale fluid simulation with the Lattice Boltzmann method

PhDThis thesis describes investigations of several complex fluid effects., including hydrodynamic spinodal decomposition, viscous instability. and self-assembly of a cubic surfactant phase, by simulating them with a lattice Boltzmann computational model. The introduction describes what is meant by the term "complex fluid", and why such fluids are both important and difficult to understand. A key feature of complex fluids is that their behaviour spans length and time scales. The lattice Boltzmann method is presented as a modelling technique which sits at a "mesoscale" level intermediate between coarse-grained and fine-grained detail, and which is therefore ideal for modelling certain classes of complex fluids. The following chapters describe simulations which have been performed using this technique, in two and three dimensions. Chapter 2 presents an investigation into the separation of a mixture of two fluids. This process is found to involve several physical mechanisms at different stages. The simulated behaviour is found to be in good agreement with existing theory, and a curious effect, due to multiple competing mechanisms, is observed, in agreement with experiments and other simulations. Chapter 3 describes an improvement to lattice Boltzmann models of Hele-Shaw flow, along with simulations which quantitatively demonstrate improvements in both accuracy and numerical stability. The Saffman-Taylor hydrodynamic instability is demonstrated using this model. Chapter 4 contains the details and results of the TeraGyroid experiment, which involved extremely large-scale simulations to investigate the dynamical behaviour of a self-assembling structure. The first finite- size-effect- free dynamical simulations of such a system are presented. It is found that several different mechanisms are responsible for the assembly; the existence of chiral domains is demonstrated, along with an examination of domain growth during self-assembly. Appendix A describes some aspects of the implementation of the lattice Boltzmann codes used in this thesis; appendix B describes some of the Grid computing techniques which were necessary for the simulations of chapter 4. Chapter 5 summarises the work, and makes suggestions for further research and improvement.Huntsman Corporation Queen Mary University Schlumberger Cambridge Researc

Enzyme activity in bicontinuous microemulsions

The thesis deals with enzymatic catalysis in bicontinuous microemulsions, which consist of a dynamic network of oil and water domains separated by a monolayer of surfactant molecules, i.e. the interfacial layer. Hence, a microemulsion with the composition buffer – n-octane – nonionic surfactant was tested as a reaction medium for enzyme-catalysed reactions with the emphasis on the conversion of hydrophobic substrates, which are difficult to convert in aqueous buffer solutions. The first part of the thesis focuses on the activity of the lipase B from Candida antarctica (CalB) in bicontinuous microemulsions. First, the optimum reaction conditions determined by temperature, pH and ionic strength were evaluated. Second, it was found that CalB concentrations which showed fast adsorption at an oil-water interface also displayed fast reaction rates. Additionally, no saturation was found for substrate concentrations up to 40 mM of p-nitrophenyl laurate, which according to Michaelis-Menten suggests a Km >> 40 mM. Third, the composition of the interfacial layer had a distinct influence on CalB activity, e.g. the presence of sugar surfactants (b-C10G1) or phospholipids (DOPC) enhanced or decreased CalB activity, respectively. The second part of the thesis describes the activity of the squalene-hopene cyclase from Alicyclobacillus acidocaldarius (Aac SHC) converting its natural substrate squalene in bicontinuous microemulsions. The Aac SHC activity studies revealed a linear dependence on enzyme concentration and a hyperbolic curve for the substrate concentration, with a saturation of Aac SHC at substrate concentrations above 20 mM. The composition of the interfacial layer was found to have neither a significant influence on the activity nor on the conformation of Aac SHC. In summary, good turnover rates were achieved for interfacially-active enzymes (CalB) due to enhanced enzyme-substrate contact at the interfacial layer. For water-soluble enzymes (Aac SHC), a distinctly enhanced selectivity was discovered, although no faster reaction rate was found. The main difference in the catalytic turnover was explained by the adsorption of CalB at the interfacial layer, whereas Aac SHC stays in the aqueous phase of the microemulsion. To conclude, bicontinuous microemulsions were suitable for enzymatic catalysis and are thus interesting in terms of reaction medium engineering to optimise biocatalytic processes

The suitability of polymerised microemulsions as stationary phases for capillary electrochromatography

Capillary electrochromatography (CEC) is an analytical separation technique, coupling the electroosmotic flow principles of capillary electrophoresis (CE) with the stationary phase separation principles of high performance liquid chromatography (HPLC). The development of this technique has been slowed due to technical problems with packing capillary columns. Alteration of the stationary phase to a solid monolithic support enables ease of filling and reduces bubble formation. Polymerisation of bicontinuous microemulsions can yield porous structures that are potentially suitable for use as a stationary phase for this technique. Polymerising bicontinuous microemulsions with different compositions produce monoliths of varying pore sizes. The microemulsions consist of a hydrophobic phase and an aqueous phase. The hydrophobic phase is typically methyl or butyl methacrylate, and a cross-linker, ethylene glycol dimethacrylate. The aqueous phase consists of water and a surfactant, typically sodium dodecyl sulfate. A short chain alcohol (C3-C5) is added as a porogen which also acts as a co-surfactant to aid with the stabilisation of the microemulsion. AMPS (2-acrylamido-2-methyl-l-propane sulfonic acid), added to the aqueous phase provides a charge along the polymer backbone essential for electroosmotic flow mechanism in electrochromatography. SEM analysis shows that polymerisation in-situ yields a structure with a porous topography. Materials prepared were assessed for suitability with a variety of microemulsion compositions