Control of Crystal Nucleation on Surfaces

Lead Research Organisation: University of Leeds
Department Name: Physics and Astronomy

Abstract

Crystallisation is a widespread phenomenon in nature and technology. Indeed, snowflakes, gemstones, table salt, boiler scale, metals and many advanced materials used for example in nanotechnology or advanced batteries are all crystalline. The ability to control when, where and how crystals form is therefore essential to areas as diverse as climate modelling, pharmaceutical formulation, the semiconductor industry and the design of dental and medical prostheses. At present, our ability to direct and control crystallisation is often very poor, so any improvement would be of far-reaching significance.

The majority of strategies used to control crystallization from solution relies on the use of soluble additives or on changing the reaction conditions. Here, we propose to develop a different and potentially quite general technique. Rather than varying the solution chemistry - which is specific to each different crystal - we will use the topography of the surfaces on which crystals grow to control their formation.

The formation of crystals requires that a substantial energy barrier be surmounted and is hence usually a rare event - liquids such as water may undergo sizeable supercooling before they freeze. The energy barrier is reduced, and crystallization rendered easier if it occurs on a surface rather than in bulk - during a frosty night ice crystals form on surfaces but not in the air away from any objects. Theoretical considerations show that crystallization will become even more favourable if there are pits or grooves in a surface, and there are many observations that attest to the validity of these ideas. There have, however, been very few systematic studies of the effect of topography on crystallization. Consequently, we have almost no understanding of the type of defects that best favour crystallisation, and to what extent they may depend on the nature of the surface and the nature of the crystallising substance. Part of the problem is that the surface defects which are likely to have a large effect are small - of the order of 5 nanometres or less, which is the typical size of a crystal nucleus. Clearly, features on such a length scale cannot be reproducibly created by methods such as scratching or abrading a surface.

Thanks to recent advances in surface engineering techniques we are now in a position to design and manufacture surfaces that contain defects with well-defined geometries and also with dimensions small enough to enable a detailed assessment of their effect on crystallisation. Indeed, our proposal is supported by preliminary data showing that this strategy works! We have succeeded in showing that surfaces in which nanoscale grooves have been deliberately cut nucleate crystals almost exclusively in the grooves, with negligible growth on the flat areas in between.

We now propose to study nucleation of crystals from vapour and from solution using surfaces with a range of different nanoscale surface features such as pits, grooves and trenches with undercuts. We will relate the density and rate of crystallisation of different substances to the type of feature and try to use these findings to establish criteria for the design of good nucleants, or crystallisation promoters. The breadth of the experiments will allow us to establish the extent to which optimisation of nucleation by surface features differs between vapour, liquid and solution and the differences between systems of simple organic molecules, water, and inorganic salts (electrolytes).

This project will therefore ultimately provide us with a novel and potentially quite general approach to control crystallization in a huge number of applications, ranging from the engineering of thin films for solar cell devices to the promotion of natural bone growth on implant surfaces, or to the prevention of crystallization in kettles, oil wells or in building materials (prevention of weathering).

Planned Impact

This project centres on the topic of crystal nucleation control, which is of great significance to UK industry and society. Crystallization is fundamental to a vast array of technological processes and natural phenomena as diverse and significant as the production of pharmaceuticals, foodstuffs and personal care products, the synthesis of nanomaterials, the formation of biomaterials and biominerals such as bones and teeth, the precipitation of ice in the atmosphere and the prevention of scale. Within these areas it is essential to be able to (1) produce crystals of defined sizes, shapes and polymorphs, (2) to control the location of crystals on surfaces and (3) to prevent crystallization on surfaces. Our project will address these requirements by developing a novel, and potentially quite general approach to controlling nucleation, which is based on the use of surface topographical features rather than solution chemistry and additives.

This work offers the possibility of controlling polymorph, which is defined at the moment of nucleation, and other properties such as crystal size, which is related to nucleation density. Better control of crystallisation can be important for the yield of a product, for obtaining it in a form more suitable for packaging and transport, and for obtaining a product of higher activity, as in, for example, pharmaceuticals. Crystallization on the surface of a bone or dental implant often determines whether it will be accepted or rejected. Better control of protein crystallisation is crucial for structure determination of these by X-ray diffraction.

It may also be desirable to avoid or minimise nucleation, as in the prevention of scale formation in water pipes and boilers and the inhibition of crystallisation and freezing damage in building materials, historical and archaeological artefacts. In other cases, nucleation must occur at higher temperatures to avoid freezing damage, e.g. in biological tissues during cryopreservation, or during of freezing of foodstuffs. This is the essence of the link with our project partner Asymptote Ltd., described further in the "Pathways to Impact". Clearly, knowledge of the topographical features that can enhance nucleation can provide the basis for the development of surface treatments that best retard nucleation. There is therefore potential for significant impact on the UK economy in areas ranging from healthcare to everyday technologies to protection of the national heritage.

This project will provide excellent training for the two PDRAs, who will gain an excellent training in the valuable research skills of surface lithographic methods, crystallization techniques and analytical skills. Activities such as writing publications, presenting conference talks, establishing contact with other research groups, investigating commercialisation potential, participating in staff education and outreach work will provide outstanding opportunities for professional development.

Finally, the wider community will benefit through a programme of outreach work, in which all of the researchers will participate. The aesthetic appeal of crystals will ensure the success of such activities. Crystallisation is a phenomenon which can readily be displayed in real time to an audience with the help of microscopes and computer projection, and the investigators have experience in such demonstrations. Leeds hosts the annual "Leeds Festival of Science" where local schools take part in educational workshops related to science and engineering, and we will design a workshop relating to crystal growth, and its relevance to everyday life. We will also prepare a "Schools Talk" based on this material. In addition, the investigators will use the Leeds Centre for Crystallization to offer summer placements in our university laboratories to undergraduate and sixth-form students. This will lead to better contacts with schools, and the possibility of widening the participation of pupils.

Publications

10 25 50
 
Description The formation of ice from vapour on layered aluminosilicate minerals like mica occurs preferentially in very acute surface features that arise from partial delamination. Ice formation in these sites proceeds via condensation of supercooled water, which then freezes. A mechanism operates during crystallisation of many organic compounds from vapour, and there is all reason to conclude that this is a general phenomenon in crystallisation from vapour. The results are particularly relevant to atmospheric ice nucleation on aerosol particles, as many of these are layered aluminosilicates, e.g. mica, kaolinite, illite.

Understanding how surfaces direct nucleation is a complex problem that limits our ability to predict and control crystal formation. We here address this challenge using high-speed imaging to identify and quantify the sites at which ice nucleates in water droplets on the two natural cleavage faces of macroscopic feldspar substrates. Our data show that ice nucleation only occurs at a few locations, all of which are associated with micron-size surface pits. Similar behaviour is observed on a-quartz substrates that lack cleavage planes. These results demonstrate that substrate heterogeneities are the salient factor in promoting nucleation, and therefore finally prove the existence of active sites. We also provide strong evidence that the activity of these sites derives from a combination of surface chemistry and nanoscale topography. Our results have implications for the nucleation of many materials and suggest new strategies for promoting or inhibiting nucleation across a wide range of applications.
Exploitation Route Better prediction of ice formation in the atmosphere.
Sectors Aerospace

Defence and Marine

Agriculture

Food and Drink

Chemicals

Energy

Environment

Manufacturing

including Industrial Biotechology

Culture

Heritage

Museums and Collections

Pharmaceuticals and Medical Biotechnology

Transport

 
Description EPSRC platform grant
Amount £1,408,982 (GBP)
Funding ID EP/N002423/1 
Organisation Engineering and Physical Sciences Research Council (EPSRC) 
Sector Public
Country United Kingdom
Start 12/2015 
End 11/2020
 
Description Effect of Topography on Ice Deposition from Vapour
Amount £162,138 (GBP)
Funding ID RPG-2014-306 
Organisation The Leverhulme Trust 
Sector Charity/Non Profit
Country United Kingdom
Start 08/2015 
End 08/2018
 
Description Programme Grant
Amount £5,436,236 (GBP)
Funding ID EP/R018820/1 
Organisation Engineering and Physical Sciences Research Council (EPSRC) 
Sector Public
Country United Kingdom
Start 03/2018 
End 02/2023
 
Title Data for "The adsorption of fungal ice-nucleating proteins on mineral dusts: a terrestrial reservoir of atmospheric ice-nucleating particles"; 
Description The occurrence of ice-nucleating particles (INPs) in our atmosphere has a profound impact on the properties and lifetime of supercooled clouds. To date, the identities, sources and abundances of particles capable of nucleating ice at relatively low supercoolings (T > -15° C) remain enigmatic. While biomolecules such as proteins and carbohydrates have been implicated as important high-temperature INPs, the lack of knowledge on the environmental fates of these species makes it difficult to assess their potential atmospheric impacts. Here we show that such nanoscale ice nucleating proteins from a common soil borne fungus (Fusarium avenaceum) preferentially bind to and confer their ice-nucleating properties to kaolinite. The ice-nucleating activity of the proteinaceous INPs is unaffected by adsorption to the clay, and once bound the proteins do not readily desorb, retaining much of the activity even after multiple washings with pure water. The atmospheric implications of the finding that biological residues can confer their ice-nucleating ability to dust particles are discussed. 
Type Of Material Database/Collection of data 
Year Produced 2016 
Provided To Others? Yes  
URL http://archive.researchdata.leeds.ac.uk/70/
 
Title High-speed Imaging of Ice Nucleation in Water Proves the Existence of Active Sites - dataset 
Description This is the data for High-speed Imaging of Ice Nucleation in Water Proves the Existence of Active Sites, where we demonstrate that specific locations on the surface of feldspar and quartz are repeatedly the area in which ice growth originates in freezing experiments, i.e. the nucleation active sites. This means that heterogeneities on the surfaces are of first order importance in determining the temperature at which liquid water freezes. The data contained in this repository consists of the ice nucleation experimental data, used to construct the figures in the main text and supplementary materials. These show that nucleation is site specific for both quartz and feldspar. We also present WDS mapping results, where no chemical differences were found at the active sites within the resolution of the technique, leading to our hypothesis that topography is an important factor in determining ice nucleation effectiveness of a site. 
Type Of Material Database/Collection of data 
Year Produced 2019 
Provided To Others? Yes  
 
Title Is black carbon an unimportant ice-nucleating particle in mixed-phase clouds? Dataset 
Description This dataset provides experimental and modelling data used to investigate black carbon as potentially important atmospheric ice nucleating particles. The experimetnal data show no significant ice nucleation activity above the handling blank baseline. The modelling data show that previous parameterizations overerstimate the importance of black carbon, and give an indication of the ice nucleation activity required in order for black carbon to be a significant atmospheric INP. 
Type Of Material Database/Collection of data 
Year Produced 2018 
Provided To Others? Yes  
URL http://archive.researchdata.leeds.ac.uk/355/
 
Description Bristol Festival of Nature 
Form Of Engagement Activity Participation in an activity, workshop or similar
Part Of Official Scheme? No
Geographic Reach Regional
Primary Audience Public/other audiences
Results and Impact 6 members of the research group participated in the 2-day "Bristol festival of nature" where they manned a stand that showcased demonstrations about crystallisation processes.
Year(s) Of Engagement Activity 2015
 
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 the North Bar Leeds
Year(s) Of Engagement Activity 2017
 
Description Lancaster Science Festival 2016 
Form Of Engagement Activity Participation in an activity, workshop or similar
Part Of Official Scheme? No
Geographic Reach Regional
Primary Audience Public/other audiences
Results and Impact 7 members of the research group participated in the 2-day "Lancaster Science festival" where they manned a stand that showcased demonstrations about crystallisation processes.
Year(s) Of Engagement Activity 2015
 
Description Solvay Workshop on Nucleation: multiple pathways multiple outcomes 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Professional Practitioners
Results and Impact Talk on "Controlling Crystallisation using Confinement and Surface Topography"
Year(s) Of Engagement Activity 2022
 
Description Talk at Gordon Conference on Crystal Growth and Assembly 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Professional Practitioners
Results and Impact Invited talk on "Controlling Crystallisation using Confinement and Surface Topography"
Year(s) Of Engagement Activity 2023
 
Description Timms Symposium Bristol 
Form Of Engagement Activity Participation in an activity, workshop or similar
Part Of Official Scheme? No
Geographic Reach National
Primary Audience Professional Practitioners
Results and Impact Timms lecturer
Year(s) Of Engagement Activity 2023
URL https://www.bristol.ac.uk/chemistry/news/2023/timms-symposium-2023.html