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InstitutionProject TitleWPResearcher in Charge
University of ViennaMagnetic dipolar colloids: anisotropy and anisometryWP2S. Kantorovich
Self-associating hybrid polymers under shearWP2C. Likos
Complex solutes at liquid-liquid interfacesWP1M. Sega
Cambridge UniversityLiquid and gel-droplets moved by light on a surfaceWP2E. Eiser
Design of functional colloids via computer simulationsWP3J. Dobnikar
University of EdinburghSystems of growing dropletsWP1P. Clegg
Lattice Boltzmann simulations of liquid crystalline emulsionsWP1D. Marenduzzo
Jozef Stefan InstituteLiquid drop modelWP1P. Ziherl
Ecole Superieure de Physique et de Chimie IndustriellesStructure and dynamic of dense suspensions of soft colloids with tunable short-range attractionWP2M. Cloitre
Foundation for Research and Technology – HellasConcentrated suspensions of repulsive soft particles undergoing solid- liquid transitions: Structure and rheologyWP1D. Vlassopoulos
The effects of particle microstructure on the dynamic arrest in colloidal-polymer mixturesWP3B. Loppinet
University of Rome “La Sapienza”Grasping the origin of compressed exponential relaxation in colloidal gelsWP2E. Zaccarelli
Melting on heating DNA hydrogelsWP3F. Sciortino
UnileverParticle stabilised emulsions and foams in particle gelsWP3W. Frith
SolvayFiltration and dilution of soft colloidsWP3P. Guillot

WPs

WP1: Deformable Colloids

WP2: Hybrid Colloids

WP3: Mixtures

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Project Descriptions

Deformable Colloids

Complex solutes at liquid-liquid interfaces
The main target of the project is the study of single and multi-droplet dynamics out of equilibrium in presence of different surfactants, aimed at the identification of the combinations of those physical (concentration), topological (linear vs branched, open vs closed structure), and electrical (charge state, ionic strength) parameters, that lead to desirable rheological properties. We will be using a novel multiphysics approach to understand the role of surfactant topology and electrostatic features in determining the dynamical properties of single droplets and emulsions, combining efforts with projects ‘Systems of growing droplets’ and ‘Lattice Boltzmann simulations of liquid crystalline emulsions’, to fill the gap in the studies of complex emulsion.

Systems of growing droplets
The experimental system project is comprised of water droplets, which gain elasticity due to an interfacial layer of silica particles, in an oil phase (toluene). The droplets grow and change shape when a solute (e.g. ethanol) is present in the toluene in modest concentrations because the solute partitions into the droplets. We will use changes to the particles and changes of solute to map out and explore the behaviour of growing droplets. In general, interfacial elasticity is a key feature of blood cells, drug delivery capsules and residual water droplets in crude oil. While the impact of the interface on a change of shape has previously been probed, this project is aimed at exploration of the interplay between interfacial properties and changes in volume. This project will give ESRs the opportunity to gain hands-on experience preparing and studying emulsions. Hence it will beautifully complement other COLLDENSE projects.

Lattice Boltzmann simulations of liquid crystalline emulsions
Changing from experiment in the previous project,in this project computer simulations will be used to investigate the phase behaviour, and dynamics under external fields, of liquid crystalline emulsions, i.e. of droplet suspensions where one of the components (the droplets or the ambient fluid) is liquid crystal. The current project falls squarely in the remit of COLLDENSE. This project will be executed in close collaboration with collaborations experts in the simulation of more conventional colloidal suspensions under shear (projects ‘Grasping the origin of compressed exponential relaxation in colloidal gels’ and ‘Self-associating hybrid polymers under shear’), so there will be plenty of opportunity for the ESR to travel between the nodes of COLLDENSE for scientific collaboration.

Liquid drop model
During the past two decades, mounting experimental evidence of a range of non-close- packed lattices and quasicrystals in soft colloidal and nanocolloidal systems raised the question of underlying effective interparticle interactions. Here we will systematically explore a new effective model of deformable nanocolloidal particles represented by gas bubbles characterized by a single parameter, which measures their compressibility. We will statistical-mechanically elaborate the microscopic origin of the model. Finally, signatures of the gas-bubble model will be searched for in other features in condensed phases of soft colloids, e.g., in glassy dynamics, normal modes, etc. This project will advance the existing spectrum of effective theories of interactions in soft colloids, providing testable predictions that will be verified using simulations (project ‘Self-associating hybrid polymers under shear’) and experiments (project ‘Concentrated suspensions of repulsive soft particles undergoing solid-liquid transitions: Structure and rheology’).

Concentrated suspensions of repulsive soft particles undergoing solid- liquid transitions: Structure and rheology
It is well known that concentrated suspensions of stable, repulsive colloidal particles in molecular solvents can undergo two types of liquid-to-solid transitions: crystallization and glass transition. Turning to soft particles, it is clear that deformability marks their departure from their hard analogues. This already suggests that the volume fraction cannot be determined unambiguously, and it is customary to use an effective volume fraction based on the unperturbed size of the single particle. The only systematic study on this topic was performed by Cloitre and co-workers with slightly polydisperse microgel suspensions, thus this project, aimed at investigation of possible transitions in soft colloids, will be executed in active collaboration with the previous project.

Hybrid Colloids

Magnetic dipolar colloids: anisotropy and anisometry
We focus on colloids with a magnetic core and nonmagnetic soft shell. The behaviour of these particles can be effectively controlled by an applied magnetic field, and we will harness this to investigate the dynamic magnetic response of the hematite ellipsoids, maghemite ellipsoids, magnetically capped colloids and magnetic Janus particles. After understanding the dynamic magnetic response, the rheology of these systems will be addressed. The project will be executed in close collaboration with University of Rome, University of Edinburgh and with the ‘Self-associating hybrid polymers under shear’ project.

Self-associating hybrid polymers under shear
Telechelic star polymers (TSP’s) are hybrid materials at the microscopic scale, since they feature competing interactions between their blocks: the inner monomers are repulsive and the end- monomers attractive. As such, they also feature a different kind of hybridity, in the sense that the inner blocks are chemically associated at their centre, whereas the terminal blocks associate physically (i.e., reversibly) with one another. In the recent past, linear telechelic polymers have been used as reversible linkers between colloidal entities of a different chemistry, and the rheology of the mixture has been investigated experimentally. However, very little is known about the rheological properties of pure telechelic star-polymer solutions. The system is new and highly promising, since TSP’s have been shown to self-organize into a large variety of structures, including networks and living wormlike micelles.

Liquid and gel-droplets moved by light on a surface
More information on this project can be found here.
The successful student will develop a new type of microfluidic devise, based on functional droplets that can be directed on ‘soft surfaces’ with light as an external field. The project will form part of COLLDENSE, focusing on the design of colloidal systems using experiments and if time allows computer simulation, and will build on the recent work by the Eiser group. Various specialized microscopy methods and custom-made image analysis packages will be used to create DNA-functionalized colloids that could be used in self-assembly and driving these on surfaces using external fields.

Structure and dynamic of dense suspensions of soft colloids with tunable short-range attraction
Microgels particles, micelles and star of hyperbranched polymers, which are ubiquitous in chemical in real life applications are able to adjust their shape, volume or locally interpenetrate. The importance of these phenomena begins to be recognised in the case of repulsive interactions but their interplay with attractive interactions has been far less studied. Questions of outstanding importance concern the phase diagram, the exact scenarios for the glass and jamming transitions, the nature and the dynamic response of the arrested phases, the possible occurrence of gelation, as well as the importance of the nature and strength of the interactions at work. This project is closely connected to the previously described project ‘Self-associating hybrid polymers under shear’ and will be of great help when dealing with mixtures in WP3.

Grasping the origin of compressed exponential relaxation in colloidal gels
This project is devoted to the simulation study of clays. In recent years, clays have emerged as building blocks of unusual self-assembled states due to the anisotropy of both their shape and of their interparticle interactions, i.e. they are discotic heterogeneous charge distribution. Among clays, ones of the most studied is Laponite, a synthetic clay with many technological applications. A recent review has revealed the complex phase diagram of Laponite. This ESR project will tackle the behaviour of clays by studying simple models for gel-forming systems, both spherical and disk-like. The use of different models for gel formation will allow us to elucidate the role of the anisotropicity.

Mixtures

Design of functional colloids via computer simulations
The aim of this project is to explore novel designs of functional colloids that make it possible to have truly multicomponent colloidal structures form by self assembly. The project will build on the recent theoretical work of Reinhard and Frenkel (2014). During the project, model simulations will be used to design the building blocks that could be used in self-assembly experiments. The candidate is expected to have knowledge of statistical mechanics, preferably in the context of liquids and soft materials. Demonstrated knowledge of computer simulation techniques is considered to be an advantage.

The effects of particle microstructure on the dynamic arrest in colloidal-polymer mixtures
This project is devoted to the investigation of systematically colloid-polymer mixtures usingspherical particles of different softness. The main goal is to identify the role of softness in the morphology of colloid- polymer mixtures at different size ratios and volume fractions with linear polymers and in the repulsive- glass to liquid to re-entrant solid transition. We will address the question of the soft attractive glass existence. Here, the connection to project ‘Gas-bubble model’ is of strong assistance. Additionally, we address the possibility of gel formation in high-volume fraction soft colloidal mixtures (in collaboration with project ‘Self-associating hybrid polymers under shear’) and exploring the effects of temperature. As such, this project is closely related to ‘Melting on heating DNA hydrogels’. In connection to the simulation project, ‘Self-assembly and colloidal dynamics in polymer layers’, we will study experimentally mixtures of soft colloids and large linear polymers at different volume fractions of particles and polymers to elucidate the dynamic arrest.

Melting on heating DNA hydrogels
This project addresses a material recently predicted theoretically that without the interference of a first order transition and reversibly gels upon heating. In this work it was shown how a binary mixture of limited valence particles can provide a model in which the competition between entropy and potential energy causes the system to show a re-entrant behaviour, passing reversibly from a fluid to a gel and again to a fluid if temperature is varied. The time is ripe for an experimental realisation of this theoretical design. In this project we will experimentally realise such a system, building on the recent development in DNA nanotechnology. In this project we will investigate the possibility of designing a binary-mixture of DNA constructs that gels on heating, exploiting the DNA-DNA selective recognition and then characterise the self-assembly process of the DNA sequences and the formation of the expected constructs, actively collaborating with projects, ‘Structure and dynamic of dense suspensions of soft colloids with tunable short-range attraction and ‘The effects of particle microstructure on the dynamic arrest in colloidal-polymer mixtures’.

Particle stabilised emulsions and foams in particle gels
There is a growing need in the 21st century for developing new ways to control the stability and break-down of emulsions such as those employed in the foods and personal care industries. Technologies in this field would lead to new applications in controlled delivery of active ingredients, and improved ability to reformulate with new ingredients in an increasingly resource limited environment. Particles trapped at liquid interfaces are an important example of a system arrested far from thermodynamic equilibrium. The presence of interfacial particles can modify a liquid droplet’s flow properties and interactions with its environment. The aim of this project is to tune the behaviour of liquid droplets using two populations of colloidal particles, at least one of which is trapped at the interface. We are also interested in the stability of individual droplets and the bulk flow properties of a complete sample in close connection to other COLLDENSE projects. Our heterogeneous samples will provide a contrasting test case for comparison with other mixture projects. The difference between the two particular components in these samples is defined via their interactions with the liquid interfaces.

Filtration and dilution of soft colloids
The aim of the project is to study the flows of suspensions of complex and deformable colloidal particle in the context of filtration processes encountered in the chemical industry. Filtration is a key aspect of the global process of the synthesis of many particle-based materials. The industrial synthesis of silica particles leads to a complex and polydisperse mixture of aggregated colloidal particles (from several nanometers to several micrometers) and ionic species. Filtration of this mixture is necessary to remove ionic species and lead to a dense silica cake and leads to high ecological and economical cost notably because of membrane fouling that requires the periodic flushing of membranes. In-situ investigations of this filtration process is closely related to projects ‘Grasping the origin of compressed exponential relaxation in colloidal gels’ and ‘Complex solutes at liquid-liquid interfaces’.