Surface Microstructure of Various Calcium Alginate Xero-gels and Its Fractal Analysis

Abstract

Air-dried, freeze-dried and alcohol-replaced calcium alginate xero-gels were compared with by the specific surface area, pore-size distribution and fractal dimension. The specific surface areas of air-dried and -20°C freeze-dried xero-gels were less than 0.5m²/g, while those of ethanol-or 1-propanol-replaced xero-gels were about 400mm²/g. The macro-pore size distribution of -196°C freeze-dried xero-gel had a maximum at about 1 μm of pore radius, while that ethanol-replaced xero-gel had broad distribution in the range less than 100nm in pore radius. The micro-pore size distribution was very much affected by the contents of mannuronic acid and gluronic acid of alginate. The micro-pore was most effectively developed by use of 1-propanol. Air-dried, -20°C freeze-dried and ethanol-replaced xerogels had fractal structures with the fractal dimension of 2.4-3.0. The specific surface area of ethanol-replaced xero-gel was independent of the particle diameter, showing that the surface was the fractal with the fractal dimension of 3.0.