Effects of Operating Variables on the morphology of CaCO3/Organic Hybrid Thin-Film
Date Issued
2011
Date
2011
Author(s)
Chou, Che-Yu
Abstract
Biominerals, such as the nacre of shells, spicules of sea urchins, teeth, and bones are inorganic-organic hybrids that have highly controlled hierarchical and complex structures. These structures are formed in mild conditions, and the processes are controlled by macromolecular templates of proteins, peptides, and polysaccharides. Materials scientists can obtain ideas from the structures, properties, and formation processes of biominerals for use in creating synthetic, biomimetic materials. Kato et al. conducted a series of experiment in vitro. Thin-film crystals of CaCO3 had been developed on the surface of solid matrices from supersaturated calcium bicarbonate solution using Kitano’s method in the presence of the soluble polymer. Although the Kitano’s method, i.e. by bubbling CO2 gas, was simple to operate and able to discuss the effect of the soluble polymer/solid matrices, the composition of supersaturated solution can’t be controlled; moreover, it took too long to finish an experiment, about 5 hours spent on solution preparation and five days on crystal growth. If we intend to study the operating variables on the growth behavior of CaCO3 film, the experimental method should be improved.
Beginning of our research, the suitable soluble polymer and the insoluble matrix were found by repeating the Kato’s experiments. Kato et al. (1998; 2000) selected poly(acrylic acid)/chitosan and poly(aspartic acid)/chitosan as the soluble polymer/the solid matrix respectively. Nevertheless, the surface structure of the CaCO3 thin-film is different from that reported by Kato et al. (1998; 2000).
The technique developed in our laboratory can be used to prepare and control supersaturated solution falling on the metastable region. Through the computer programs the required amount of NaCO3 and CaCl2 were calculated and then they were slowly mixed to form the supersaturated solution. It took about 1 hour for the solution preparation. As far as the matrix is concerned, poly(acrylic acid), which is cheap, and chitosan, which is easy to prepare, were used as the soluble polymer and solid matrix. In the second stage of our research the liquid-phase batch system was adopted to search for the operating conditions suitable for film growth, with emphasis on supersaturation and activity ratio. Thin-film of CaCO3 formed on the chitosan matrix, when the supersaturation was higher than 6. The surface of thin-film of CaCO3 were more rough, when the activity ratio was higher.
The experiment was further carried on using the liquid-phase circulating system. We discussed that effect of the solution of pH and the concentration of PAA on the morphology of the CaCO3 thin-films. The results indicated the solution of pH and the concentration of PAA both had a great effect on the morphology of the CaCO3 film. When the solution pH was 10.0, the mole fraction of aragonite reached a maximum value. On the other hand, the mole fraction of aragonite decreased with an increase in the PAA concentration. When the concentration of PAA was too low to inhibit nucleation, the particles fell on the film from the bulk solution.
Finally, a magnetic field was incorporated into the liquid-phase circulating system, because the magnetic effect was in favor of aragonite formation and growth formed in our laboratory. Thin-films of CaCO3 had a tendency to form aragonite film, when the system was in the presence of a magnetic field.
Subjects
biomimetic material
CaCO3/organic hybrid thin-film
effect of operation variables
effect of magnetic field
Type
thesis
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