Amorphous stability

Graeser KA, Patterson JE, Zeitler JA, Gordon KC, Rades T (2009b) Correlating thermodynamic and kinetic parameters with amorphous stability. Eur J Pharm Sci 37(3-4) 492-498 Graeser KA, Patterson JE, Zeitler JA, Rades T (2010) The role of configurational entropy in amorphous systems. Pharmaceutics 2 224-244... 

Selection of stabilizing polymer and other processing aids Formulation complexity and ability to achieve highest drug loading Availability of equipment train from laboratory scale to commercial scale Product robustness (processability, amorphous stability, and dissolution performance)... 

Chauhan H, Hui-Gu C, Atef E (2013) Correlating the behavior of polymers in solution as precipitation inhibitor to its amorphous stabilization ability in solid dispersions. J Pharm Sci 102(6) 1924-1935... 

Polymer as a antinucleation agent A polymer can inhibit nucleation and crystal growth of a drug by specific interaction with functional groups of the drug (Curatolo et al. 2009 Alonzo et al. 2010). Polymers such as PVP, HPMC and HPMC-AS have been extensively studied for the amorphous stabilization effect in aqueous solution (Lindfors et al. 2008 Miller et al. 2008 Alonzo et al. 2010). 

MiCoS shares similar pros and cons to solvent-casting methods. With parallel preparation, it is highly efficient and effective in evaluating polymer types, drug loadings and antisolvent/solvent ratio comprehensively. However, the residue solvent and antisolvent content, which are critical for amorphous stability, cannot be determined due to low amount of solid products. The kinetic solubility results can only be interpreted qualitatively rather than quantitatively, as the particle size of the miniaturized products are not tightly controlled. 

Overall, it was concluded that the micro-structure found in co-amorphous drug-drug formulations, e.g., formation of a heterodimer, can significantly influence the behavior of these systems with respect to dissolution (improved and synchronized), amorphous stabilization, and physicochemical properties (e.g., free volume, glassforming ability). 

An example of the effect of C doping on the thermal-crystallization and electrical properties of PCRAM materials is in work carried out on the binary material, GeTe. Doped GeTei-xCx materials, with x = 0.04, 0.1, show an improved amorphous stability (e.g. 10-year data retention at 127 °C for x = 0.1) [2], as well as a reduction by 50 % in RESET power for the same composition [16]. 

Research has led to alloys which undergo laser-induced crystallization within about 50 ns. This is possible, for example, with TeGe alloys, which also possess the necessary temperature stability up to 180°C and exhibit sufficient reflection (crystalline phase) and transmission characteristics (amorphous phase), respectively. TeGe alloys have not found a practical use because of the formation of depressions in the memory layer typical for them after repeated... 

The following mechanisms in corrosion behavior have been affected by implantation and have been reviewed (119) (/) expansion of the passive range of potential, (2) enhancement of resistance to localized breakdown of passive film, (J) formation of amorphous surface alloy to eliminate grain boundaries and stabilize an amorphous passive film, (4) shift open circuit (corrosion) potential into passive range of potential, (5) reduce/eliminate attack at second-phase particles, and (6) inhibit cathodic kinetics. 

Amorphous Silicon. Amorphous alloys made of thin films of hydrogenated siUcon (a-Si H) are an alternative to crystalline siUcon devices. Amorphous siUcon ahoy devices have demonstrated smah-area laboratory device efficiencies above 13%, but a-Si H materials exhibit an inherent dynamic effect cahed the Staebler-Wronski effect in which electron—hole recombination, via photogeneration or junction currents, creates electricahy active defects that reduce the light-to-electricity efficiency of a-Si H devices. Quasi-steady-state efficiencies are typicahy reached outdoors after a few weeks of exposure as photoinduced defect generation is balanced by thermally activated defect annihilation. Commercial single-junction devices have initial efficiencies of ca 7.5%, photoinduced losses of ca 20 rel %, and stabilized efficiencies of ca 6%. These stabilized efficiencies are approximately half those of commercial crystalline shicon PV modules. In the future, initial module efficiencies up to 12.5% and photoinduced losses of ca 10 rel % are projected, suggesting stabilized module aperture-area efficiencies above 11%. 

The key determinants of future cost competitiveness of a-Si H PV technology are a-Si H deposition rates, module production yields, stabilized module efficiencies, production volume, and module design. Reported a-Si H deposition rates vary by more than a factor of 10, but most researchers report that the high quaUty films necessary for high stabilized efficiencies require low deposition rates often due to high hydrogen dhution of the Si (and Ge) source gases (see Semiconductors, amorphous). 

Silica sols are often called colloidal silicas, although other amorphous forms also exhibit colloidal properties owing to high surface areas. Sols are stable dispersions of amorphous siUca particles in a Hquid, almost always water. Commercial products contain siUca particles having diameters of about 3—100 nm, specific surface areas of 50—270 m /g, and siUca contents of 15—50 wt %. These contain small (<1 wt%) amounts of stabilizers, most commonly sodium ions. The discrete particles are prevented from aggregating by mutually repulsive negative charges. 

In the absence of a suitable soHd phase for deposition and in supersaturated solutions of pH values from 7 to 10, monosilicic acid polymerizes to form discrete particles. Electrostatic repulsion of the particles prevents aggregation if the concentration of electrolyte is below ca 0.2 N. The particle size that can be attained is dependent on the temperature. Particle size increases significantly with increasing temperature. For example, particles of 4—8 nm in diameter are obtained at 50—100°C, whereas particles of up to 150 nm in diameter are formed at 350°C in an autoclave. However, the size of the particles obtained in an autoclave is limited by the conversion of amorphous siUca to quartz at high temperatures. Particle size influences the stabiUty of the sol because particles <7 nm in diameter tend to grow spontaneously in storage, which may affect the sol properties. However, sols can be stabilized by the addition of sufficient alkaU (1,33). 

Treatment of ceUulose with acids results in preferential hydrolysis in the more accessible amorphous regions and produces a product known as microcrystalline ceUulose (MCC). MCC is used to prepare fat-free or reduced-fat food products, to strengthen and stabilize food foams, as a tableting aid, and as a noncalotic bulking agent for dietetic foods. It has GRAS status. 

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