Structural change of sodium n-alkanecarboxylate hydrous melts with hydrophobicity of the alkyl group

摘要

For several sodium n-alkanecarboxylate hydrous melts (C_nH_(2n+1)COONa centre dot RH_2O, n=0,1,2,3,4,5,7,9), the structural change with carbon number in the alkyl group was investigated by X-ray diffraction measurements. A peak was found over 10 A of d-value (d= lambda /2 sin theta ) for the hydrous melts (n=1,2,3,4,5,7,9) except sodium formate (n=0), which suggested the evidence of the middle-range structure. The peak position was not varied with the water content, while the peak intensity increased with decreasing of the water content. The peak position shifted to lower angle region with increasing carbon number in the alkyl group. It was found that the dimension of the middle-range structure was affected by the carbon number, the hydrophobicity of the carboxylate anion. The d-value of the peak position was proportional to the carbon number with slope of 2.7 A/carbon. It was assumed that the middle range structure is similar to micelle-like structure in the anhydrous sodium carboxylate melts.