Transformation and Growth of Polymorphic Nuclei through Evaporative Deposition of Thin Films

Yeager, John D.; Ramos, Kyle; Mack, Nathan H.; Wang, Hsing‐Lin; Hooks, D. E.

doi:10.1021/cg301090t

Cited by 3 publications

(4 citation statements)

References 27 publications

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“…Form III is considered the least thermodynamically stable, with processes such as nanoconfinement being used to isolate it ( Figure ) . A study on thin films of 15 revealed that the metastable form II could be stabilized in dip coated films on a silica substrate, while a further study showed that form III , the least stable form, can be stabilized on a silica surface by rapid heat treatment after deposition . An SIP has also been reported for the pharmaceutical compound phenytoin which was found to have improved dissolution properties when compared with the bulk form; such examples highlight the potential for a substrate to be used to stabilize metastable forms of drug molecules with enhanced properties.…”

Section: Experimentally Observed Sipsmentioning

confidence: 99%

Substrate‐Induced and Thin‐Film Phases: Polymorphism of Organic Materials on Surfaces

Jones

Chattopadhyay

Geerts

et al. 2016

Adv Funct Materials

231

280

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2233wileyonlinelibrary.com to that of the bulk liquid; [ 7 ] order typically exists over a few molecular layers before rapidly decaying to bulk behavior as the distance from the wall increases. [ 8 ] Similar ordering effects can also be observed in the quasiliquids which form on the surface of many solids due to surface melting (also known as premelting): [ 9,10 ] the existence of a liquid-like layer a few molecules thick on the surface of a solid below the melting point of the bulk material. [ 11 ] The structure within this layer is also found to be different to that of the bulk isotropic liquid, [ 12 ] highlighting the ordering occurring at the interface. A converse effect, surface freezing, is also observed in some liquids (primarily n -alkanes with 16 ≤ n ≤ 50), where a solid monolayer may exist at an interface up to ≈30 °C above the bulk melting point while the rest of the compound is molten. [13][14][15] Such phase behavior is strongly dependent on molecular shape and has only been observed for chain molecules, which then form layers similar to self-assembled monolayers (SAMs) at the interface with the liquid bulk. [ 16 ] Further examples of molecular ordering at interfaces can be seen in materials which display liquid crystal (LC) phases, a phase behavior also dependent on molecular shape and generally observed for molecules with a highly anisotropic shape (e.g., rod-like, disc-like or bowl-like molecules). [ 17 ] LCs have properties of both solids and liquids and display long range order which may be orientational and/or positional; various types of LC phases (mesophases) are possible and normally exist only over a certain temperature range (i.e., they are thermotropic); a further property of LCs is that they generally reach thermodynamic equilibrium in the bulk and at interfaces as a result of their short relaxation time. Nematic (N) phases of calamitic LCs (rod-like molecules with cylindrical symmetry) have no positional order but an orientational order which can be described by a unit vector, n , known as the director, which represents the preferred molecular orientation ( Figure 1 , left). A scalar order parameter can also be defi ned which is related to the average angle the long molecular axes make to the director, n .Increased order is seen in smetic phases (Sm) which have both orientational and positional order; for example in a smetic A phase (SmA) molecules form layers (positional ordering of the molecular mass centers) which are oriented normal to the plane of the layers (orientational order), while smetic C phases (SmC) form layers where molecules are oriented with the long molecular axes tilted at an angle to the molecular layer normal However, the factors that drive such a process are not clearly understood or studied in depth. In this feature article, we review the current state of understanding concerning SIPs, giving examples of systems where SIPs have been observed, discussing their origins, and which questions remain to be answered. The role of the substrate in controlling the growth a...

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Section: Experimentally Observed Sipsmentioning

confidence: 99%

Substrate‐Induced and Thin‐Film Phases: Polymorphism of Organic Materials on Surfaces

Jones

Chattopadhyay

Geerts

et al. 2016

Adv Funct Materials

231

280

View full text Add to dashboard Cite

show abstract

“…then measured with ellipsometry after 48 hours. This time delay allowed for observation of crystallization of the AN, if it happened immediately, which in our previous research on similar materials was observed to happen shortly after the residual solvent in the film evaporated [20].…”

Section: Plm and Ellipsometrymentioning

confidence: 91%

“…Polarized light allows for enhanced differentiation of crystalline regions from amorphous regions [19][20][21]. PLM was also performed after two months to assess the stability of the AN within the film.…”

Section: Preliminary Sample Characterizationmentioning

confidence: 99%

“…In a series of studies, Lang and Vyazovkin [8][9][10] investigated AN-PVP mixtures with varying AN content (5, 10, 20 … 50% AN) using thermal analysis (TG-DSC) and vibrational spectroscopy. Remarkably, thick films (0.5 mm) of AN-PVP (20,25% AN) revealed that the three solid-solid transitions (IV→III, III→II, II→I) were fully suppressed and a single exotherm at ~160 o C close to the Tg of PVP was observed by DSC. The mass loss associated with this thermal event is close to the amount of AN indicating that breakdown of the PVP matrix results in decomposition of AN.…”

Section: Introductionmentioning

confidence: 99%

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Thermal behavior of glassy phase stabilized ammonium nitrate (PSAN) thin films

Yeager

Chellappa

Singh

et al. 2015

Materials Today Communications

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Ammonium nitrate (AN) is a high interest material because of its wide usage in propellants and explosives but can be difficult to handle from a formulation standpoint. It is soluble in many common solvents and has complex phase behavior. Here, we formulate phase stabilized AN (PSAN) films in a polymer matrix and characterize thermal and phase behavior using neutron reflectometry and ellipsometry. These techniques are highly sensitive to small changes in composition and density which occur during phase transitions. Our PSAN films are generally stable up to 160°C, though we observe small material loss between 60 and 100°C, which we attribute to solvent interactions with the PSAN. Crystallization of AN from supersaturated polymer is most common at thicker regions of the film, suggesting a critical nucleation thickness for the AN which can be avoided by making very thin films.

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A generalized crystal-cutting method for modeling arbitrarily oriented crystals in 3D periodic simulation cells with applications to crystal–crystal interfaces

Kroonblawd

Mathew

Jiang

et al. 2016

Computer Physics Communications

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Transformation and Growth of Polymorphic Nuclei through Evaporative Deposition of Thin Films

Cited by 3 publications

References 27 publications

Substrate‐Induced and Thin‐Film Phases: Polymorphism of Organic Materials on Surfaces

Substrate‐Induced and Thin‐Film Phases: Polymorphism of Organic Materials on Surfaces

Thermal behavior of glassy phase stabilized ammonium nitrate (PSAN) thin films

A generalized crystal-cutting method for modeling arbitrarily oriented crystals in 3D periodic simulation cells with applications to crystal–crystal interfaces

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