Materials World Network: Composite Single Crystals - From Structural Evolution to Mechanical Characterization

Lead Research Organisation: University of Leeds
Department Name: Sch of Chemistry

Abstract

The combination of synthetic materials science with design concepts adapted from Nature is a promising route to the development of new materials. Biominerals such as bones, teeth and seashells provide an ideal inspiration for this approach, as illustrated by Nature's ability to manipulate mechanically weak engineering materials such as calcium carbonate to produce hard skeletal materials that exhibit excellent fracture toughness and unique morphologies. One key feature of these composite materials, which is an essential feature of their superior mechanical properties, is their structures involve strong intercalation of organic molecules within the mineral host. Here organics can not only be located between crystalline units as for materials such as nacre, but also within single crystals, as found for example in sea urchin spines. Indeed, single crystal biominerals often occlude up to several weight per cent of macromolecules, which is perhaps surprising given that crystallization is traditionally considered to be a method for purifying solids.

We will investigate the application of this biogenic strategy - the encapsulation of "inclusion materials" within single crystals - to create novel composite materials. Although the potential for synthesizing composite materials based on this approach is enormous, our lack of fundamental understanding means that progress in this field remains largely based on trial-and-error experiments. In this project, we have assembled an international team of researchers uniquely positioned to fill this gap, and by doing so we will develop a comprehensive understanding of 1) the mechanisms by which "inclusion materials" are occluded within a crystal lattice; 2) the internal micro- and nano-structure of the resulting single crystal composites; and 3) how the resulting structures ultimately dictate the mechanical properties of the resulting composite material. Our research strategy is based on a systematic study of the incorporation of a broad range of "inclusion" materials - ranging from molecules to microscopic polymer particles, and from compliant to stiff frameworks. We will design and synthesise bespoke molecules, particles and gels with appropriate chemical structures to promote intercalation, and in doing so develop the first truly unified understanding of how additives are occluded within crystals. It is also expected that novel syntheses of polymeric particles and gels will also result from this approach.

Understanding the strategies by which biominerals form, and how their design leads to superior properties is clearly a complex, multidisciplinary problem, encompassing fields such as crystal growth, materials characterisation, polymer chemistry, and analysis of mechanical properties. This joint NSF-EPSRC research grant involves an international collaboration between a consortium of world-leading research groups based in the USA and the UK, who by working closely together seek to combine the multidisciplinary expertise of each team to address this complex scientific problem and hence enable the rational design of novel biomaterials. Our ultimate goal is to create for the first time a truly unified understanding of how additives - ranging from molecular, to polymeric, to particulate, to compliant and ultimately stiff frameworks - can be incorporated within single crystals, and to determine how this strategy can be applied to the design of new materials with specific mechanical properties. This integrated approach will provide a general methodology for synthesizing composite crystals, contribute to our understanding of the biological systems from which the inspiration came, and will ultimately provide the basis for synthesizing next-generation materials such as artificial bone and tough synthetic dental enamel.

Planned Impact

Prof. Armes has worked extensively with many industrial companies, ranging from the world's largest chemical company (BASF) to a single employee SME. Current sponsors include: DSM, P & G, BP, Cytec, Biocompatibles, Reckitt Benckiser, Cabot Plastics, Scott Bader and Vivacta. He sold a U. Sheffield patent application to DSM for 125,000 euros in Sept 2007. This technology is now the basis of a successful anti-reflective coatings business for DSM, which captured 30 % of the global market for high-quality picture glass for fine art within six months of the launch of its first product (ClarylTM; see www.dsm.com). DSM now describes its interaction with Prof. Armes as an exemplar of its recently adopted 'open innovation' policy, which aims to acquire externally-owned IP of potential strategic value. Thus Prof. Armes is well aware of the value of IP protection (he is a named inventor on 16 patent applications) and is undoubtedly 'outward-facing' regarding the potential commercial impact of his work. Moreover, he has recently filed two new U. Sheffield patent applications arising from his joint EPSRC research programme with Prof. Meldrum which underpins the design and synthesis of the diblock copolymer 'nano-objects' described in the present grant application. He has already exploited this strong IP position to leverage £46 K from Scott Bader and £235 K from DSM for industrially-relevant follow-on projects. Prof Meldrum has previously worked with a number of industrial partners, including Nexia Solutions, Unilever (Vlaardingen, the Netherlands and Colworth, UK) and Procter and Gamble. Both Unilever sites funded PhD studentships, as did Nexia Solutions, while technical discussions are ongoing with P&G. She has also recently carried out consultancy work with BP on the topic of the nucleation and growth of gas hydrate compounds.

In 2005 the University of Sheffield sold its entire IP rights to Fusion IP in a ten-year pipeline deal worth £10 M. This AIM-listed company has first refusal to commercialise inventions by University employees arising from Research Council contracts. Prof. Armes is currently negotiating with Fusion IP over the possible formation of a spin-out company to exploit his two new patent applications on the synthesis of diblock copolymer 'nano-objects', which also underpin his scientific contribution to this NSF-EPSRC grant proposal. Alternatively, if a spin-out company is not considered the best business option, Fusion IP can provide appropriate business expertise to aid the negotiation of individual patent licences or outright patent sales. Finally, the Sheffield Polymer Centre (directed by Prof. Armes and managed by Dr. L. R. Sutton) is also a useful vehicle for fielding company-led enquiries for IP generated by U. Sheffield polymer scientists. We have a database of more than 1,000 companies and regularly interact with a wide range of corporate clients. This activity has led to both Beiersdorf and Agilent purchasing samples of Prof. Armes's diblock copolymers for evaluation in specific in-house applications. Thus we have the capacity and infra-structure to respond effectively to external enquiries from third parties. The University of Leeds has a similar pipeline deal with IP Group, which is a privately owned company that has the first right of refusal on the IP generated by both Leeds and nine other UK Universities. The Enterprise and Innovation Office at Leeds University has recently undergone restructuring with a view to streamlining their commercial activities, and has already led to the creation of 47 University spin-out companies including Tracsis, a software company which services global transportation industries, and Chamelic, which manufactures advanced surface coatings based on stimulus-responsive polymers.

Publications

10 25 50

 
Description The goal of this project is to develop novel, bio-inspired synthetic approaches which will generate single crystals with composite structures and properties that mimic or exceed the exceptional properties of biogenic crystals. Our research strategy is based on a systematic study of the incorporation of a comprehensive range of "inclusion" materials within single crystals - ranging from molecules to polymers, from nano- to colloidal particles, and from compliant to stiff frameworks - and will provide the first truly unified understanding of how additives are occluded within crystals. As a major focus of the project, we also performed the first systematic study of the structure and mechanical properties of these composite materials.

Key outcomes

(1) We have carried out extensive investigations into the incorporation of small molecules - and particularly amino acids - within calcite crystals. The occlusion of aspartic acid and glycine within calcite has been studied in detail using a combination of experimental and modelling approaches. We have shown that extremely high amounts of these additives can be occluded without a change in crystal morphology and that we can precisely tune the compositions of our single crystal composites over a wide range. Lattice distortions in these crystals were analyzed using x-ray diffraction, giving information about the effects of the additives on the crystal lattice, and molecular dynamics simulations were used to interpret these experimental data. Solid state NMR was used to demonstrate that the amino acids are present as individual species within the crystal. Finally, the structure/property relationships of these composite crystals were investigated using nanoindentation to determine hardness as a function of composition. The nanoindentation hardness was shown to increase with amino acid content, reaching values equivalent to their calcite biominerals. Together, these data were used to determine the origin of the increased hardness, where a dislocation pinning model revealed that the enhanced hardness is determined by the force required to cut covalent bonds in the molecules.

(2) We developed an experimentally versatile strategy for producing inorganic/ organic nanocomposites, with control over the microstructure at the nano- and meso-scales. Taking inspiration from biominerals, CaCO3 was co-precipitated with anionic diblock copolymer worms or vesicles to produce single crystals of calcite occluding a high density of the organic component. This approach was also be extended to generate complex structures in which the crystals are internally patterned with nano-objects of differing morphologies. Extensive characterization of the nanocomposite crystals using high resolution synchrotron powder XRD and vibrational spectroscopy demonstrated how the occlusions affect the short and long-range order of the crystal lattice. By comparison with nanocomposite crystals containing latex particles and copolymer micelles, it was shown that the effect of these occlusions on the crystal lattice is dominated by the interface between the inorganic crystal and the organic nano-objects, rather than the occlusion size. This was supported by in situ AFM studies of worm occlusion in calcite, which revealed flattening of the copolymer worms on the crystal surface, followed by burial and void formation. Finally, the mechanical properties of the nanocomposite crystals are determined using nanoindentation techniques, which reveals that they have hardness comparable to geological calcite, and comparable to biogenic calcite.


(3) We have carried out in situ studies to investigate the mechanisms by which nanoparticle additives are occluded within crystals. By studying micelle incorporation in calcite with atomic force microscopy (AFM) and micromechanical simulations, we have gained new insight into the mechanisms of occlusion. By simultaneously visualizing the micelles and propagating step edges, we have demonstrated that the micelles experience significant compression during occlusion, which is accompanied by cavity formation. This generates local lattice strain, leading to enhanced mechanical properties. These results give new insight into the formation of occlusions in natural and synthetic crystals, and will facilitate the synthesis of multifunctional nanocomposite crystals.
Exploitation Route Following our high-profile publications on NP occlusion within CaCO3, Tremel (Mainz), Hanying Li (Zhejiang Uni) and Eychmuller (Dresden) are all now researching NP occlusion in single crystals.
Sectors Agriculture

Food and Drink

Construction

Energy

Environment

Healthcare

Pharmaceuticals and Medical Biotechnology

URL http://www1.chem.leeds.ac.uk/FCM/
 
Description Platform Grant
Amount £1,408,821 (GBP)
Organisation Engineering and Physical Sciences Research Council (EPSRC) 
Sector Public
Country United Kingdom
Start 12/2015 
End 11/2020
 
Description Responsive Mode
Amount £803,945 (GBP)
Funding ID EP/P005233/1 
Organisation Engineering and Physical Sciences Research Council (EPSRC) 
Sector Public
Country United Kingdom
Start 01/2017 
End 01/2020
 
Description Exhibition of images 
Form Of Engagement Activity Participation in an activity, workshop or similar
Part Of Official Scheme? No
Geographic Reach Local
Primary Audience Public/other audiences
Results and Impact 6 week exhibition of images of crystals at North bar leeds
Year(s) Of Engagement Activity 2014
 
Description Presentation at 2021 BCA Meeting 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach National
Primary Audience Professional Practitioners
Results and Impact Talk at British Association of Crystallography 2021 Autumn meeting
Year(s) Of Engagement Activity 2021
 
Description exhibition of scientific images 
Form Of Engagement Activity Participation in an activity, workshop or similar
Part Of Official Scheme? No
Geographic Reach Local
Primary Audience Public/other audiences
Results and Impact 6 week exhibition of images of crystals at North bar leeds
Year(s) Of Engagement Activity 2015