Download Calcium Carbonate Mesocrystals: A Story

Theme D:
Aggregation-Based Mechanisms of Crystal Growth
Fiona Meldrum, James Elliott, Mike Allen, Roland Kröger
Helmut Cölfen, Nico Sommerdijk
Goals:
• Aggregation-based crystal growth mechanisms
• From crystalline to amorphous precursor particles
• Mesocrystals
• PILP
Nanoparticle interactions in solution (Elliott)
Studying the molecular interactions between calcite nanoparticles in aqueous solution, in
order to deduce coarse-grained potentials of mean force for incorporation into larger
scale models of aggregation (Warwick, year 4) and to reduce the calculation time
required for more complex solvents using AdResS
PILP Phases of Calcium Carbonate (Meldrum/ Sommerdijk)
Investigated PILP formation in the presence of a series of random copoly(amino acid)s
constructed from 80%-20%, 50%-50% and 20%-80% aspartic acid and serine residues
Infiltration of Collagen with PILP Phases (Meldrum/ Sommerdijk)
Studying the infiltration of collagen with calcium carbonate and iron oxides using SAXS/
WAXS and TEM. The collagen matrix provides remarkable control over the morphology
and orientation of the occluded crystalline mineral phase in both the calcium carbonate
and iron oxide systems, and that ultra-thin platelets are generated within the collagen.
High-Magnesian Calcite Mesocrystals (Sommerdijk/ Meldrum)
High-Mg calcite crystals were formed in non-aqueous environments. Mg-containing
ACC was produced by reacting a mixture of organometallic Ca and Mg complexes with
CO2 and control over the Mg incorporation was obtained according to the ratio of the
starting materials. Subsequent crystallization at reduced water activities in an
organic solvent/ water mixture yields high-magnesian calcite mesocrystals.
Liquid-Cell TEM Studies (Kroger)
A three port fluid cell holder has been purchased by Kroger to perform in-situ
investigation of crystallisation processes under atmospheric conditions in a TEM. The
cell holder has two input, and one output channel, which can be used to control the
fluid composition.
Calcium Carbonate Mesocrystals:
A Story
Fiona Meldrum, Yi-Yeoun Kim, Johannes Ihli, Anna Schenk,
Nicola Hetherington
What is a Mesocrystal?
“... a mesocrystal ideally comprises a 3D array of iso-oriented single crystal particles
of size 1–1,000 nm. The highly oriented subunits therefore distinguish a mesocrystal
from a randomly oriented polycrystal, and the identifiable nano-sized building units
distinguish it from a single crystal containing impurities.”
Seto, Ma, Davis, Meldrum, Kim, Colfen et al PNAS 2012, 109(10), 3699.
Evidence for a Mesocrystal ?
1. Morphology – evidence for nanoscale subunits (SEM analysis)
2. XRD – line broadening used as evidence of sub-structure
3. Ultrastructure - evidence for nanoscale subunits (TEM analysis)
4. Surface Area – large surface areas used as evidence of sub-structure
(porosimetry)
“Classic” Synthetic CaCO3 Mesocrystals
Poly(styrene sulfonate) (PSS)
Poly(styrene-alt-maleic acid) (PS-MA)
Poly(styrene sulfonate – co – maleic acid) (PSS-MA)
Review Evidence for Mesocrystal Structure - SEM
Poly(styrene-alt-maleic acid) (PS-MA)
Cobalt ions
• Observe similar morphologies / surface roughness
• Sample precipitated with Co is a single crystal  well-studied in the literature
Seeded Growth
Characteristic morphologies  can be produced simply by growing a rhombohedral
calcite seed crystal in the presence of the polymer additives
2 -3 m seed
Morphology is not defined at nucleation/ early stages of growth
XRD Analysis – Line Broadening
Commonly seen in literature  line broadening attributed to small particles:
Scherrer equation:
 = crystallite size
 = FWHM
K = shape factor
However...
LATTICE STRAIN ALSO CAUSES BROADENING OF XRD PEAKS!!
• Relationship of broadening with diffraction angle () different
• From analysis of whole spectrum one can derive the separate contributions of
particle size and strain to the line broadening
High Resolution Synchrotron Powder Analysis of Calcite Mesocrystals
2 separate batches
PSS-MA
800 nm domain
2 independent analyses
(by people who don’t care...)
PS-MA
1000 nm domain
• Line broadening due entirely to LATTICE STRAIN !
• No nanoparticulate sub-structure
Ultrastructure – TEM Analysis (FIB)
• Distinct interface along the edge, but continuity of crystal orientation and single
crystal structure
• No evidence for nanoparticulate substructure
Surface Area - Porosimetry
Challenging and Interesting !
• Helmut’s calcite mesocrystals  surface areas > 100 m2/g
• Repeated experiments  values < 10 m2/g
• What is going on ??
Surface area is time-dependent !
• If you analyse crystals freshly removed from the solution (after any ageing
time), surface areas > 100 m2/g
• HOWEVER, if you leave a sample in air for  5-7 days before analysing the
surface area, surface area < 10 m2/g
• It has been suggested that mesocrystals undergo a recrystallization with time
• Do the internal nanoparticles fuse, causing a reduction in surface area ?
Synchrotron XRD analysis :
• See no change in the line broadening between new and old samples
• Further, see no change in line width after heating a sample to 400 oC
Results suggest that the difference in surface areas on aging is a
SURFACE EFFECT  possible blocking of surface pores ??
Evidence for Calcite Mesocrystals Mechanism of Formation?
• ACC particles formed
• ACC particles rapidly aggregate
• Subsequent crystallization
No evidence for crystalline
nanoparticles has been obtained
(to-date)
Wang, Colfen, Antonietti, JACS, 2005, 127, 3246.
Characterisation of the Ammonia Diffusion Method
Common observation – “mesocrystal” morphologies only formed with diffusion-based
syntheses
• Nucleation event consumes only a
minor fraction of the Ca ions
• Superaturation
remains
constant
and well above the solubility level of
ACC for the vast majority of the
reaction

New
material
is
constantly
generated throughout the reaction
using the ADM
A Possible Scenario?
• CaCO3 mesocrystals based on the crystallization of assemblies of ACC nanoparticles
rather than the oriented assembly of precursor crystalline nanoparticles
• New particles nucleate on existing polymer-stabilized ACC aggregates, or on
crystalline particles at later stages of the reaction, giving rise to more complex
morphologies.
• Ostwald ripening can be important in generating key mesocrystal morphologies. Even
the slowest reaction conditions, the ADM is complete and the calcium ions depleted
after 6-8 hours.
• Morphological changes in crystals after  12 hrs (days to weeks have been described),
are due to Ostwald ripening/ recrystallization in the presence of polymer.
• Synthetic CaCO3 mesocrystals may resemble biogenic calcite mesocrystals, where the
ultrastructure derives from a memory of the ACC precursor phase.
Biogenic Mesocrystals – Sea Urchin Spines
NMR, SAXS 
• Residual ACC
• Consistent with nanoparticles coated
with ACC
“.... the term mesocrystal defines the structure of a material rather than its mechanism
of formation.”
“ ... while oriented aggregation of crystalline nanoparticles can give rise to either a single
crystal or mesocrystal product ... a mesocrystal can also form when a dense array of
amorphous nanoparticles crystallizes to give a highly co-oriented end-product material.”
Seto, Ma, Davis, Meldrum, Kim, Colfen et al PNAS 2012, 109(10), 3699.
Summary
• Evidence for calcite “mesocrystals” poor  no evidence for oriented
assembly
• Complicated by dominance of ACC precursor phase
• Residual mesoscale structure may originate as a memory of ACC
precursor phase
Modelling:
• Steer well clear of calcite as a model “mesocrystal”
• Address a well-characterised system (eg iron oxides)
Experiment:
• Development of morphologies, crystal growth mechanisms interesting
• Mechanism of crystallization of ACC phase (link with modelling)
Oriented Attachment
Ferrihydrite Nanoparticles Transform to Goethite Single Crystals
Yuwono, Burrows, Soltis, R. Lee Penn J. Am. Chem. Soc., 2010, 132 (7), 2163.
Ultrastructural Analysis of “Meoscrystals”
[Ca] = 10 mM
[Ca] = 1 mM
[Ca] = 5 mM
[Ca] = 0.5 mM
[Ca] = 2.5 mM
[Ca] = 0.1 mM
Investigating particles between polycrystals and mesocrystals, cutting using FIB, TEM analysis
Kulak AN .... Meldrum FC (2007) J. Am. Chem. Soc. 129, 3729-3736.
Investigation of Mechanism
A
B
Titration-based method:
1µm
• Highly reproducible
1µm
C
D
• Can study the reaction with time using
DLS, TEM
• We will do initial dry TEM studies, Nico will
1µm
1µm
ADM
do cryo-TEM of key samples
Titration method
• Longer term  in situ TEM with fluid cell
• Challenges associated with getting these key morphologies in that experimental set-up
Electron Backscatter Diffraction
Erika Griesshaber, Wolfgang Schmahl, Munich
Brachiopod
Schematic model for shell growth
with a microstructure consisting of
splined and interdigitating grains.
ACC is present in confined capsules
delineated by vesicle membranes
Goetz, Steinmetz, Griesshaber, Schmahl et al Acta Biomaterialia, (2011), 7, 2237.