Title of article :
Molecular attributes of an effective steric agent: Yield stress of dispersions in the presence of pure enantiomeric and racemate malic acids
Author/Authors :
Hazlina Husin، نويسنده , , Yee-Kwong Leong، نويسنده , , Jishan Liu، نويسنده ,
Issue Information :
روزنامه با شماره پیاپی سال 2012
Pages :
6
From page :
459
To page :
464
Abstract :
The effects of pH on the yield stress and zeta potential behaviour of α-Al2O3 dispersions with addition of d-, l- and racemate (DL) malic acids were evaluated. Conformational structures and intramolecular hydrogen bonding of the adsorbed malic acids obtained via MM2 modeling were used to explain the surface forces operating in the dispersions. We found that the yield stress-pH behaviour is almost identical for d-, l- and racemate malic acids. At low surface coverage of adsorbed malic acid, the maximum yield stress was reduced by as much as 55%. At complete surface coverage the reduction decreased to ∼40%. MM2 modeling showed the presence of intramolecular hydrogen bonding between the hydroxyl and the (free) charged carboxylate group within the malic acid molecule. Intra-molecular hydrogen bonding and the high number of strongly bound water molecules (hydration number of malic di-ionic species) were likely responsible for the di-ionic malic acid species acting as a very effective steric agent. At complete surface coverage, the inter-molecular hydrogen bond formed between the layers of adsorbed malic acid, is responsible for the small rise in the maximum yield stress. Racemate malic acid produced a smaller maximum yield stress at complete surface coverage compared to the pure enantiomers. This may be related to the two different types of hydrogen bonds found in the racemate. Only one type is found in the pure enantiomers.
Keywords :
Citric acid , Intra-molecular hydrogen bond , zeta potential , Malic acid enantiomers , Racemate , Hydrogen bond , Conformational structure
Journal title :
Advanced Powder Technology
Serial Year :
2012
Journal title :
Advanced Powder Technology
Record number :
1248120
Link To Document :
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