Journal of Surface Science and Technology

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Study on the Effect of an Electrolyte on the Self-Aggregation and the Geometry of the Dye Aggregates of Methylene Blue in Aqueous Media


Affiliations
1 Department of Chemistry, Manipur University, Canchipur, Imphal - 795003, Manipur, India
     

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The self-aggregation of Methylene Blue (MB) dye in aqueous media has been investigated spectrophotometrically in presence of sodium chloride (NaCl) at 293.15, 303.15 and 313.15K. The dimerization constant (KD) of the MB dye in aqueous solution with or without the electrolyte has been computed using a non-linear least square regression technique. It is observed that presence of the electrolyte resulted into sharp increase in KD of MB indicating that presence of the electrolyte favours formation of dye aggregates. There is, however, a decrease in KD with increase in temperature. From the observed spectra of the dye, the twist (θ1) and the tilt (θ2) angles between the dipoles of MB molecules in the aggregates have been computed based on exciton model. Change in the monomeric fractions of the dye (α) in presence of the added electrolyte as a function of the dye concentration has also been computed. The results indicated that the dye aggregates formed is essentially of the sandwich type geometry (H-aggregates) with a slight deviation from an exact parallel stacking arrangement and reduced twist angle. The thermodynamic parameters of the aggregation process in presence of the electrolyte have been evaluated from the temperature dependence of KD. It is observed that the aggregation process is an enthalpy rather than entropy controlled one.

Keywords

Aggregate Geometry, Dimerization Constant, Effect of Electrolyte, Exciton Model, Methylene Blue.
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  • Study on the Effect of an Electrolyte on the Self-Aggregation and the Geometry of the Dye Aggregates of Methylene Blue in Aqueous Media

Abstract Views: 331  |  PDF Views: 2

Authors

Ng. Florence
Department of Chemistry, Manipur University, Canchipur, Imphal - 795003, Manipur, India
H. Naorem
Department of Chemistry, Manipur University, Canchipur, Imphal - 795003, Manipur, India

Abstract


The self-aggregation of Methylene Blue (MB) dye in aqueous media has been investigated spectrophotometrically in presence of sodium chloride (NaCl) at 293.15, 303.15 and 313.15K. The dimerization constant (KD) of the MB dye in aqueous solution with or without the electrolyte has been computed using a non-linear least square regression technique. It is observed that presence of the electrolyte resulted into sharp increase in KD of MB indicating that presence of the electrolyte favours formation of dye aggregates. There is, however, a decrease in KD with increase in temperature. From the observed spectra of the dye, the twist (θ1) and the tilt (θ2) angles between the dipoles of MB molecules in the aggregates have been computed based on exciton model. Change in the monomeric fractions of the dye (α) in presence of the added electrolyte as a function of the dye concentration has also been computed. The results indicated that the dye aggregates formed is essentially of the sandwich type geometry (H-aggregates) with a slight deviation from an exact parallel stacking arrangement and reduced twist angle. The thermodynamic parameters of the aggregation process in presence of the electrolyte have been evaluated from the temperature dependence of KD. It is observed that the aggregation process is an enthalpy rather than entropy controlled one.

Keywords


Aggregate Geometry, Dimerization Constant, Effect of Electrolyte, Exciton Model, Methylene Blue.

References





DOI: https://doi.org/10.18311/jsst%2F2016%2F6599