Orientation and morphology of calcite nucleated under floating monolayers: A magnesium-ion-enhanced nucleation study

Charge, Stereochemistry, or Epitaxy? Toward Controlled Biomimetic Nucleation at Mixed Monolayer Templates

“…With both the acid–DODAB and sulfate–DODAB mixtures, we find that {104} rhombohedral crystals grow for DODAB concentrations of 50% and above. This result is not unexpected: {104} rhombohedral growth has been observed on neutral surfaces before. , While the entire tilted phase of the acid–DODAB mixtures grows {104} rhombohedral crystals, this is most likely due to the low charge of the monolayer. Note that while the DODAB is positively charged, the 100% DODAB sample has nearly 3 times the area per headgroup compared to the acid monolayer, or at most 1/3 the net charge density compared to the acid monolayer. ,, It appears that with neutral or lower charged monolayers we see {104} growth, and to this extent monolayer charge plays a definite role.…”

“…Figure shows SEM images of samples collected by surface tension transfer onto silicon substrates. Image a shows CaCO 3 grown under pure acid oriented with the [1̅10] direction normal to the surface as reported previously. ,, Image b shows crystals grown under a 90:10 acid–DODAB mixture. The crystals no longer grow as large or irregularly as under pure acid; instead the crystals have adopted a nearly triangular wedge morphology, but still display irregular edges similar to those of the previous crystals.…”

“…Crystal growth GID data were collected at Beamline X14A of the National Synchrotron Light Source, Brookhaven National Laboratory. This beamline was used due to its larger available beam footprint and larger beam divergence, which gave us better statistical averaging of the growing crystals (see refs and for more details). All data were taken after 12 h of in situ crystal growth time.…”

“…Simple carboxylic acid monolayers are seen to form an untilted centered rectangular phase ( a = 5 Å, b = 7.5 Å) which corresponds to 18.7 Å 2 per molecule compared to 19.7 Å 2 per molecule on silver substrates and 21.6 Å 2 per molecule on gold substrates . The crystals grown under floating carboxylic acid monolayers are thought to begin as [1̅10]-oriented but quickly grow into large irregular crystals. ,, Both Langmuir monolayers and self-assembled films contain carboxylic acid terminated alkane chains; in one system the tails are firmly tethered, and in the other system the chains are compressed latterly. Ideally the carboxylic ends of the chains in either system should appear very similar as seen from the aqueous solution, but the same control of oriented growth has not been demonstrated in both systems.…”

“…Recent studies have reported that disordered Langmuir monolayers maximize the uniformity of the crystal morphology across the monolayer. , While these disordered templates do an excellent job of nucleating a fairly uniform truncated rhombohedral morphology, the nucleated crystals have multiple orientations. Fixed templates with well-defined order have shown better control of both uniform morphology and uniform orientation, despite the fact that in most cases there is no direct evidence of epitaxy. ,,, …”