Capillary nanosuspensions for fabrication of smart porous materials

This PhD position is with Prof. Erin Koos, within the Soft Matter, Rheology and Technology section of the Department of Chemical Engineering (https://cit.kuleuven.be/smart/). The PhD research will be conducted in the framework of the Marie Skłodowska-Curie Innovative Training Network nanoPaInt (http://nanopaint-itn.eu/).

Creating strong physical gels in a controlled way with network structure having varying degree of strength from the same components and concentration is useful in many applications such as in the structuring of foods or cosmetic formulations, or as a precursor for porous materials, membranes, and printed electronics. The nature of gel in terms of its structure and strength is a strong function of processing conditions. The gel state when manufactured might differ from its final state during application due to transport and storage. The final application can be at large scale such as in an industrial setting where the material has to flow from point A (where it is manufactured) to point B (where it is stored/shipped) or in a small scale like3D printing where the material has to flow from storage tank via a dispensing nozzle to form complex structures. One of the biggest challenges is to have the same network structure before and after flow so that the final product will have desired properties.

Recently, we have shown that adding a small amount of immiscible secondary fluid to a suspension can lead to dramatic changes in its structure forming space spanning networks that are called capillary suspensions. These suspensions are ternary particle-liquid-liquid systems composed of particles dispersed in a primary liquid having a small amount of secondary immiscible liquid. Depending on the ratio of secondary liquid to that of the primary and the wettability of the particles one can obtain two distinct state: the pendular state where the secondary liquid wets the particles more than the primary; and the capillary state where the wetting is reversed. The addition of secondary fluid leads to dramatic transition from a free-flowing liquid state to a strong gel state. Depending on the composition of particle-liquid-liquid systems, one can transition from a pendular state to spherical agglomeration, or form bicontinuous structures (bijels).

Capillary nanosuspensions can be designed and fabricated with the forces between the nanoparticles responding to external stimuli or chemical reactions, which allows programming the response of the suspensions to changes in environmental pH, temperature or salinity. Capillary suspensions can also be used as precursors for fabrication of porous ceramic materials. The combination of microparticles and nanoparticles leads to a significant increase in the compressive strength of the resulting material. The combination of nanoparticles with different wettabilities enables the fabrication of smart porous materials that can be applied, for example, for the separation of liquids. To understand the influence of combination of particles of different sizes and wettabilities as well as the properties of the liquid phases on the network structure and rheology of capillary nanosuspensions. To fabricate and characterize porous bodies from capillary suspensions containing particles of at least two different wettabilities and nanoparticles.

• Task 1: Development and high resolution characterization ofthe network structure of capillary nanosuspensions with combination of particles with different sizes and wettability. ESR9 will characterize the network structure will be using confocal microscopy. This task will be focused on capillary nanosuspensions which can be used as precursors for new porous materials.

• Task 2: Experimental investigation of rheology of capillary nanosuspensions. Rheology will be measured and benchmarked using different methods and conventional devices present at KU Leuven and Unilever and compared with the results of experiment on fast stretching of liquid bridge. The data will be used for validation of theoretical model.

• Task 3: Development of novel functional materials based on nanosuspensions. ESR9 will develop and optimize methods for fabrication of smart nanomaterials of high porosity and high strength from capillary nanosuspensions. The capillary bridges will be solidified, and the primary liquid phase will be removed by bulk de-binding. The properties of porous nanomaterials produced by both methods (porosity, mechanical strength, structure, pore size distribution, permeability) will be characterized at both nodes.

Based on the proposal, two secondments at Wageningen University (NL) and Sofia University St Kliment Ohridski (BG) are planned during the PhD program. These may be modified if more relevant/productive secondments become available as the work of the ESR and the nanoPaInt network evolves.

This position offers a PhD of KU Leuven, and international environment, guidance by leading scientists and competitive fellowship, social security, and other benefits. The successful candidate will receive an attractive salary in accordance with the MSCA regulations for Early Stage Researchers, includes living allowances, mobility allowance and family allowance if eligible under the MSCA ITN rules. During this time, the candidate also takes up a limited amount (approx. 10% of the time) of teaching activities.

Ideal start time is September 1st, but earlier and later starting dates can be negotiated.

For more information please contact Prof. dr. Erin Koos, tel.: +32 16 37 63 47, mail: erin.koos@kuleuven.be.

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