Surface porosity and roughness of micrographite film for nucleation of hydroxyapatite

Asanithi, Piyapong

doi:10.1002/jbm.a.34930

Cited by 22 publications

(16 citation statements)

References 54 publications

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“…Crystallization from solution provides an intermediate case and has perhaps received the most attention. Roughened surfaces have been shown to enhance the nucleation of a range of crystals (7)(8)(9)(10), whereas the nucleation of proteins and organic crystals is promoted within narrow pores of specific diameters (11)(12)(13). The geometries of these pores can even determine the orientation and polymorphs of the product crystals (14)(15)(16).…”

mentioning

confidence: 99%

Observing the formation of ice and organic crystals in active sites

Campbell

Meldrum

Christenson

2016

Proc. Natl. Acad. Sci. U.S.A.

112

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Heterogeneous nucleation is vital to a wide range of areas as diverse as ice nucleation on atmospheric aerosols and the fabrication of high-performance thin films. There is excellent evidence that surface topography is a key factor in directing crystallization in real systems; however, the mechanisms by which nanoscale pits and pores promote nucleation remain unclear. Here, we use natural cleavage defects on Muscovite mica to investigate the activity of topographical features in the nucleation from vapor of ice and various organic crystals. Direct observation of crystallization within surface pockets using optical microscopy and also interferometry demonstrates that these sharply acute features provide extremely effective nucleation sites and allows us to determine the mechanism by which this occurs. A confined phase is first seen to form along the apex of the wedge and then grows out of the pocket opening to generate a bulk crystal after a threshold saturation has been achieved. Ice nucleation proceeds in a comparable manner, although our resolution is insufficient to directly observe a condensate before the growth of a bulk crystal. These results provide insight into the mechanism of crystal deposition from vapor on real surfaces, where this will ultimately enable us to use topography to control crystal deposition on surfaces. They are also particularly relevant to our understanding of processes such as cirrus cloud formation, where such topographical features are likely candidates for the "active sites" that make clay particles effective nucleants for ice in the atmosphere.nucleation | confinement | topography | pores | active sites T he growth of a new phase is almost always dependent on a nucleation event. Nucleation is therefore fundamental to a number of processes including crystallization, freezing, condensation, and bubble formation and is typically described in terms of classical nucleation theory. However, because this theory was developed to describe the nucleation of liquid droplets in vapor it cannot give a complete understanding of all nucleation processes, and in particular the formation of crystalline materials. Nucleation in the real world is also usually heterogeneous, occurring on seeds, impurities, or container surfaces. Although simple models consider nucleation to occur on perfectly flat, uniform surfaces, it is clear that real surfaces inevitably vary in chemistry and topography. We focus here on the effects of surface topography. Classical nucleation theory predicts a lower free energy barrier to nucleation in surface cracks or pores on the length scale of a critical nucleus (1). The extent of the reduction is contact-angle-dependent, such that nuclei with a low contact angle experience a more significant reduction from topography.Topography is known to promote crystallization directly from a vapor (2-5), because these systems typically exhibit low contact angles. Crystallization from the melt, in contrast, is associated with very high contact angles such that topography is usually ineff...

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confidence: 99%

Observing the formation of ice and organic crystals in active sites

Campbell

Meldrum

Christenson

2016

Proc. Natl. Acad. Sci. U.S.A.

112

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“…[7][8][9][10] Polymer films with surface nanopores are better nucleants than smoother polymeric films. [11][12][13][14] Highly porous materials can also be extremely efficient nucleators, but this requires pores of optimal diameters.…”

Section: Introductionmentioning

confidence: 99%

Is Ice Nucleation from Supercooled Water Insensitive to Surface Roughness?

2015

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There is much evidence that nucleation of liquid droplets from vapour as well as nucleation of crystals from both solution and vapour occurs preferentially in surface defects such as pits and grooves. In the case of nucleation of solid from liquid (freezing) the situation is much less clear-cut. We have therefore carried out a study of the freezing of 50 µm diameter water drops on silicon, glass and mica substrates, and made quantitative comparisons for smooth substrates and those roughened by scratching with three diamond powders of different size distributions. In all cases, freezing occurred close to the expected homogeneous freezing temperature, and the nucleation rates were within the range of literature data. Surface roughening had no experimentally significant effect on any of the substrates studied. In particular, surface roughening of mica -which has been shown to cause dramatic differences in crystal nucleation from organic vapours -has an insignificant effect on ice nucleation from supercooled water. The results also show that glass, silicon and mica have at best only a marginal ice-nucleating capability which does not differ appreciably between the substrates.The lack of effect of roughness on freezing can be rationalised in terms of the relative magnitudes of interfacial free energies and the lack of a viable two-step mechanism, which allows vapour nucleation to proceed via a liquid intermediate.

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“…Some of the common methods to generate supersaturation involve cooling, evaporation, and antisolvent addition. 8 On the other hand, template-induced nucleation can provide a favourable heterogeneous nucleation pathway for crystallisation. 4 The process of seeding is frequently used in pharmaceutical crystallisation to achieve polymorph selectivity.…”

Section: Introductionmentioning

confidence: 99%

Establishing template-induced polymorphic domains for API crystallisation: the case of carbamazepine

et al. 2015

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Template-induced nucleation of the model compound, Carbamazepine (CBZ), on substrates with different surface chemistries was studied. Supersolubility regions in which CBZ metastable form II or stable form III preferentially nucleated under the influence of cyano-, mercapto-and fluoro-functionalised templates were determined. Analysis of the resulting Template-induced Polymorphic Domain (TiPoD) plots indicated that cyano-functionalised templates promoted nucleation of form II and, in contrast, mercapto and fluoro surfaces favoured nucleation of form III. By comparing the interaction energies between CBZ crystal polymorphs and each template surface using molecular simulations, we propose that intermolecular interactions during the early stages of crystal nucleation selectively favours heterogeneous nucleation and growth of specific polymorphs on the functionalised surfaces. In the light of recent studies relating solvent effects to preferential nucleation of CBZ polymorphs, we further discuss the role of surface chemistry in directing the molecularassembling process en route template-induced crystal nucleation.

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Surface porosity and roughness of micrographite film for nucleation of hydroxyapatite

Cited by 22 publications

References 54 publications

Observing the formation of ice and organic crystals in active sites

Observing the formation of ice and organic crystals in active sites

Is Ice Nucleation from Supercooled Water Insensitive to Surface Roughness?

Establishing template-induced polymorphic domains for API crystallisation: the case of carbamazepine

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