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Report

Teaser, summary, work performed and final results

Periodic Reporting for period 1 - DiStruc (Directed Colloidal Structure at the Meso-Scale)

Teaser

Summary

DiStruc (Directed Structure at the meso-scale) is a Marie SkÅ‚odowska-Curie Innovative Training Network studying fluid dispersions containing rod-like colloidal particles. These form a plethora of ordered, liquid-crystalline states as well as glassy and gel-like disordered states already at very low concentrations. Despite their remarkable properties, industrial applications have entered the market only relatively recently. To accelerate their exploitation applications, DiStruc pushes the field in a new, innovative direction where rod-like colloidal particles of a very diverse nature are used to form structures with a well-defined direction: Directed Structure (DiStruc) at the mesoscopic level.
The objective of DiStruc is three-fold:
1. The scientific goal is to understand and direct structure formation in dispersions of elongated colloidal particles by internal (particle characteristics, interactions and concentration) and external means (confinement and flow).
2. The practical goal is to actively further the exploitation of this knowledge in the EU for rational product development in industrial sectors involved in the production of novel superior textures for fast moving consumer goods (foods, home and personal care), and high-performance fibres.
3. The educational goal is to train the next generation of European researchers at the highest (PhD) level with a multidisciplinary academic and industrial skill set from physics to biology, experiments to theory/simulations, and product development to marketing.

Work performed

The project has been divided into 4 scientific workpackages. In the first one, we study structure and dynamics in quiescent meso-phases. To this end, we firstly showed that by combining soft-lithography and microscopy, and utilising gravity, the phase behavior in confinement can be explored; isotropic, nematic and smectic phases coexist in single cavities of variable shape. We furthermore studied the behavior of nematic droplets, where the size of the droplet, elasticities, anchoring and surface tension collectively determine the droplet shape; Secondly, we showed how liquid crystalline interfaces can be studied by quantitative light microscopy. This is supported by MD simulations of â€˜simpleâ€™ rods and of rods with patchy interactions. Furthermore, experiments on tactoids, which respond strongly to external electric fields, are compared to and interpreted by lattice Boltzmann simulations; Thirdly, we have been able to quantify and control the self-organization and dynamics of suspensions of rod-like particles through rod flexibility, directional interactions, and thermo-responsive behavior; Fourthly, novel theoretical models were applied to study (i) single rod dynamics in highly ordered phases and (ii) the collective dynamics nearby phase transitions; Fifthly, we report on the study of the competition between chirality-induced twist and long-range positional order in the cholesteric phase.

In the second scientific workpackage, we study dynamic arrest and fluidization of rod dispersions. We developed a theoretical model to study percolation in 2 and 3 dimensions with and without a field. We also investigated the state diagram as a function of rod characteristics (size, aspect ratio, flexibility, polydispersity) and interparticle interactions and the slow dynamics and ageing of concentrated suspensions and non-ergodic states of rod-like colloids as well as their response under shear.

In the third scientific workpackage, we examine structure formation and distortion under the influence of flow. Here, we focus on bulk systems and the role of particle characteristics and flow geometry, as well as the application in fibre spinning processes and especially during the coagulation step. So far, we have experimentally shown that the interaction of rods depends strongly on shear rate, and that Brownian motion always plays an important role, contrary to certain theoretical assumptions. This work has recently been published.

In the last scientific workpackage we describe the production of model and industrially relevant colloidal rods. Here, we discuss state-of-the-art synthesis to fabricate colloidal rods with control over the shape, size, aspect ratio, interactions and materials. We have grafted a temperature- and pH-responsive polymer on the surface of fd-virus particles; modified silica rods in a similar fashion; prepared and characterized complex systems containing cellulose microfibrils; and worked on the production of nanocellulose particles.

We are following the ideas set out in workpackage 5 to ensure that the industrial partners meet their specifications and that the scientific outcomes are implemented industrially.

The last 3 workpackages guarantee a successful outcome of the training, the outreach and the management of the project.
The training program is built on three educational lines, namely (i) On-site (local) training; (ii) Main networkâ€“wide training events; and (iii) Training through intersectorial secondments. The ESRs are profiting from local training opportunities such as seminars, language courses, soft skills training and group meetings and are embarking on secondments. During the first reporting period we have organized 3 scientific training sessions (Heraklion, Eindhoven, Oxford), 2 industrial training sessions (Teijin Aramid, CANOE) and one transferable skills session in Oxford. We have organized 2 workshops with acclaimed invited speakers and very good turnouts.

Regarding exploitation, disseminatio

Final results

As explained in the summary important potential applications of colloidal liquid crystals can be found in the manufacturing of high-performance fibres and in fast moving consumer goods, such as foods and home and personal care. An important example in the EU is given by high-performance fibres such as TwaronÂ®, which are produced by spinning liquid-crystalline solutions of rigid, rod-like aramid polymer molecules. Rodlike colloidal particles/structures are also extensively used in the food industry to structure foods and control texture and stability. A new generation of high-performance yarns based on carbon nanotubes is just behind the horizon, producing not only strength but also electrical conductivity.