Coatings uniformity

Slides specifically selected for microarray applications should be used. They are available as ultracleaned (an important consideration) and untreated for those who wish to prepare their own surfaces or they can be purchased with a variety of precoated surface chemistries (e.g., lysine, aldehyde, or epoxide). The densities of reactive groups and surface coating uniformity are difficult to control. Thus, if lot-to-lot slide consistency is most important factor, consider using commercially available slides that are quality controlled. 

Kraemer, S.M. Hering, J.G. (1997) Influence of solution saturation state on the kinetics of ligand-controlled dissolution of oxide phases. Geochim. Cosmochim. Acta 61 2855-2866 Kraemer, S.M., Xu, J., Raymond, K.N. Spo-sito, G. (2002) Adsorption of Pb(II) and Eu(III) by oxide minerals in the presence of natural and synthetic hydroxamate sidero-phores. Environ. Sd. Technol. 36 1287-1291 Kraemer, S.M. Cheah, S.-F. Zapf, R. Xu, J. Raymond, KN. Sposito, G. (1999) Effect of hydroxamate siderophores on Fe release and Pb(II) adsorption by goefhite. Geochim. Cosmochim. Acta 63 3003—3008 Kratohvil, S. Matijevic, E. (1987) Preparation and properties of coated uniform colloidal partides. I. Aluminum (hydrous) oxide on hematite, diromia, and titania. Adv Ceram. Mater. 2 798-803... 

Roll coating is widely used as an efficient way to coat uniform, generally flat or cylindrical surfaces of rigid or flexible substrates. There are many types of roll coating methods the two most common are direct roll coating and reverse roll coating. 

Deposition of the coating is much more precise than is typically achieved using current spray application processes, leading to substantial improvements in coating uniformity both from tablet to tablet and across the surface of each individual tablet. 

The stationary phase must be coated uniformly over the surface... 

J.S. D Arrigo, R.H. Simon and S.Y. Ho, Lipid-coated uniform microbubbles for earlier sonographic detection of brain tumors, J. Neuroimagimg 1 (1991) 134-139. 

The line-of-sight effect is the biggest disadvantage. It means that the part of the substrate, which is located directly above the source, will achieve a much thicker coating that other parts of the substrate. As a consequence, only very simple geometric forms can be coated uniformly by PVD, provided that either the substrate is rotated, or that multiple sources are present in strategic places in the reactor. 

It is possible to mechanize brush methods by using hollow brushes through which the liquid adhesive is fed. This improves production rates and coating uniformity and cuts waste. Uniform films are generally difficult to achieve, but operators can become proficient with time. 

Engraved roll Provides accurate control over coating uniformity best for extremely low adhesive weights... 

Air blade Similar to the kiss coater in that the adhesive is applied where the web touches it possible to apply coating uniformly at high speeds limited use with solvent-based adhesives... 

Wilson, K., and Crossman, E. (1997), The influence of tablet shape and pan speed on intra-tablet film coating uniformity, Drug Dev. Ind. Pharm., 23,1239-1243. 

KuShaari, K., Pandey, P, Song, Y., and Turton, R. (2006), Monte Carlo simulations to determine coating uniformity in a Wurster fluidized bed coating process, Powder Technol., 166, 81-90. 

Mouget, Y., Gossehn, P.,Tourigny, M, and B echard, S. (2003), Three-dimensional analyses of tablet content and film coating uniformity by laser-induced breakdown spectroscopy (LIBS), Am. Lab., 35, 20-22. 

Using these simplified models, process variables can be varied so that the deposition process is either limited by gas-phase diffusion to the substrate surface or by reaction at the substrate. Such control of the process is valuable because, for example, geometric surface irregularities in the substrate (grooves and corners) are coated uniformly in a kinetically controlled process, but in a process controlled by diffusion a protrusion receives a thicker coating while a depression is thinly coated. 

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