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A multiscale approach towards mesostructured porous material design

Periodic Reporting for period 2 - MULTIMAT (A multiscale approach towards mesostructured porous material design)

Reporting period: 2018-03-01 to 2020-02-29

"Our contemporary society is endangered by upcoming challenges such as drinking water shortages, deprivation of oil reserves and climate change. Advanced materials will form a major contribution towards addressing these issues as they can provide e.g. efficient filters for desalination, catalysts for efficient conversion of resources, affordable CO2 capturing devices, optimised insulating materials and more efficient fuel cells. Unfortunately, most current materials at hand for these applications are either elaborate and based on fossil-fuel or energy-intense raw materials and processes, or lack the combination of a highly defined and large porosity together with required (mechanical, chemical, thermal) robustness.

MULTIMAT addressed (1) the industrial and societal need for affordable materials that have a highly defined and large porosity together with the required (mechanical, chemical and/or thermal) robustness for application in thermal insulation, catalysts, fuel cells and oil spill remediation and (2) the scientific need to better understand the mechanisms underlying the assembly of small building blocks into larger structures that are ordered hierarchically across multiple scales (""multiscale assembly""). Together this will contribute to achieving MULTIMAT's future aim: understanding and ultimately steering the bottom-up construction of materials with complex hierarchical structures.

MULTIMAT’s overall objectives were to:
- Generate objects with well-defined shapes from organic and inorganic components and use their colloidal self-organisation to produce hierarchical porous materials (BUILDING-BLOCK DESIGN)
- Control the assembly of building blocks into novel high-performance mesostructured porous materials using directional forces and templates (DIRECTING COLLOIDAL ASSEMBLY), modelling approaches (MULTISCALE MODELLING) and advanced in situ analysis methods (IN-SITU ANALYSIS)
- Provide a good understanding on mesoscopic structure-property relationships, with a focus on applications that require a combination of good mechanical properties and high porosity (PROPERTIES & FUNCTION)."
The program was divided into 5 interconnected work packages (WP): 1) Building Block Design 2) Directing Colloidal Assembly 3) Properties & Function 4) Multiscale Modelling 5) In-situ Analysis.

In WP1, different building blocks have been designed and utilised to template the growth of silica. The ESRs involved have synthesized a range of; inorganic (silica, gold), organic (polymer and nanocellulose), and hybrid building blocks with controlled sizes and surface modifications, which have been used to produce colloidal assemblies with useful properties. Block copolymer assemblies have been synthesised with varying sizes, morphologies, internal structure and tuneable surface charge.

The objective of WP2 was to direct the colloidal assembly of the building blocks obtained in WP1. ESRs in this work package made a variety of superstructures by controlling the assembly of different building blocks using different approaches. Especially, a wide range of silica nanoparticles were assembled either by emulsification followed by solvent evaporation procedures or by employing a centrifugal field.

The ESRs involved in WP3 have amongst others synthesized inorganic (silica) and organic (nanocellulose), and hybrid mesostructured materials with defined porosity characteristics for use in adsorption, separation, insulation and catalysis and analysed the material structure using advanced characterization techniques. Environmentally friendly procedures have been developed to synthesize hybrid nanocellulose foams with enhanced mechanical and thermal conductive properties. Two types of foams were produced, an ultralight foam via the mineralization of nanocellulose with zeolitic imidazolate frameworks and a composite foam with columnar porous structures via the silicification of nanocellulose with silica nanoparticles.

WP4 utilised multiscale modelling to obtain a better fundamental understanding of the building block formation and their subsequent assembly into larger structures. They developed a coarse-grained model to mimic the self-assembly of methacrylate-based block copolymers. This model was applied to map the phase diagram of PEO-b-PBMA and PEO-b-PMMA in mixtures of water and THF. They have also studied the properties of viscous fluids in nanoporous materials to understand the effect of pore saturation on the fluid’s transport properties.

The objective of WP5 was to develop liquid phase electron microscopy for its application to the in-situ dynamic multiscale analysis of building block formation and colloidal assembly. ESRs involved have among others developed various low-dose LP-EM imaging protocols using different microscopy modalities to study both organic and inorganic building block assembly and colloidal self-organisation processes. A general workflow for an LP-EM experiment was proposed and the validation of low dose LP-EM observations has been demonstrated by various control experiments and cryo-TEM.

In total MULTIMAT has already resulted in 25 publications and 1 patent application.
The far-reaching aim of MULTIMAT was to understand and ultimately steer the bottom-up construction of materials with complex hierarchical structures. The industrial partnerships within the consortium has driven the socio-economic impact of the work performed herein.

In this program we have already begun to develop novel materials and building blocks, and the subsequent assemblies are materials that exhibit superior thermal and anti-fouling properties. The exploitable results include the reliable coarse-grained models for polymeric self-assembly in solvent mixtures (already achieved), new electron microscopy hardware for controlling experimental conditions during in-situ analysis; and the development of new porous materials for novel separation technologies is currently underway.

Building block formation and the subsequent assembly has been achieved by combining experiment with modelling and in-situ analysis to inform and direct the materials' design (i.e. surface modification, polymer assembly in solution). This bottom-up approach has enabled the formation of porous silica-based materials with highly defined and large porosity for important societal and industrial needs, such as improved thermal insulation and anti-biofouling and mechanical properties. By the end of the project, this will be extended to applications in fuel cells, anti-reflective coatings and catalysis. We foresee that these design and methodology principles will be directly applicable to other material types with various different physical properties (e.g. magnetic, optical and electrical materials).
Summary of MULTIMAT results
Overview of the MULTIMAT concept