A reverse micro-emulsion method has been investigated to control crystal
morphology in a nanometer region and to increase specific surface area for
calcium phosphate. The nanocrystals with the control of its morphology is a
candidate of drug delivery carriers. This study investigated the effects of
mixing volume ratios of two surfactants, tween80 (T) and aliquate 336 (A) in
kerosene as an oil phase, and pH values in the nano-region on crystalline phases
and specific surface area of calcium phosphate synthesized by the reverse
micro-emulsion method. A di-ammonium hydrogen phosphate solution including
phosphoric acid at pH of 6.3 and a calcium nitrate solution at pH of 5.7 were
adjusted, and both the solutions were separately added into the kerosene with
the surfactants. Both the emulsions were then mixed at the same volume and the
Ca/P ratio of 1.0, and stirred at room temperature for 24 hours. The crystalline
phases were dependent on the T amounts; pure DCPD with the specific surface area
of 6.7 to 12 m2/g was obtained at the T/A ratio of 4, the mixture of
DCPD and DCPA with that of 48 to 162 m2/g was at the ratios of 5 to
8, and a low crystalline HAp with 163 m2/g was at the ratio of 9.
These specific surface areas of DCPD (T/A=4) and HAp (T/A=9)
were apparently higher than those prepared with a wet method, 7.8 times and 1.8
times respectively. DCPA with 43 m2/g was successfully produced to
decrease the pH of phosphate solution at T/A of 9. The change of crystalline
phases would be explained as follows; the increase of T amount decreased the
micro-emulsion sizes to reduce bulk water to be DCPA, and increased the pH to
precipitate HAp nanocrystals.