1. PHYSICOCHEMICAL STUDIES ON STRUCTURED AGGREGATES WITH SPECIAL REFERENCE TO IONIC LIQUIDS
Raja Ghosh , Amiya Kumar Panda
 Department of Chemistry, University of North Bengal, Darjeeling –
Abstract
Science of Surfactant is useful in almost every aspect of life. These include furtherance of industry to agriculture or for everyday life. [1] [2] [3]. IL’s are neoteric & environmentally friendly solvents for which they find manifold significance & applications in the present day context.[4]
One of the main objective of the work is to mix up systematically unique properties of this two kind of chemicals namely Surfactant and IL’s to find out new kind of chemicals with advanced and enhanced applications which may fulfill multifold demands of modern generation. Here expected new chemicals are IL’s based surfactant. It has been trying to prepare by replacing cationic part of usual inexpensive anionic surfactant by IL’s to manipulate it physicochemical properties towards betterment of it’s applications. In this work, halogen-free[5] BMIMDS and BMPDS derived from inexpensive chemicals, were synthesized using ion exchange, a method easier than that of the literature,[5] and described elsewhere. [6] Precursor for synthesis were BMIMCl and BMPBF4 with Sodium dodecyl sulfate as common precursor . Characterization was completed by FT-IR as well with more sensitive NMR which validate simple and standerdized synthetic methodology as well as purity of the both products.
Physicochemical studies done was included Surface tensiometry, conductivity, DLS, zeta potential, Fluorimetry, polarisation optical microscope, Isothermal titration calorimetry etc. CMC values obtained from surface tensiometry and conductometry were justified further by fluorimetry. CMC values of both synthesized surfactants were multifold lesser compare to our well know anionic surfactant as well as the common precursor Sodium dodecyl sulfate. Aggregation number of both was also determined with static fluorescence quenching technique as CPC as quencher. Aggregation number will further be justified with surface tensiometry in soon.[7]
Objectives
a) To study the micellization behavior of IL’s based surfactants in aqueous media.
b) To study the micellization behavior of conventional surfactants in IL’s + water mixed solvent systems.
c) To compare the micellization behavior of ionic liquid based surfactants in water and conventional surfactants in IL’s + water mixed solvent systems.
d) To study the IL’s-in-oil type microemulsion by using either IL’s based surfactant or IL’s in the polar domain.
Characterization
Experimentation
Fig 1. FT-IR of 3 precursor and 2 IL’s based surfactant.
1H NMR of BMIMDS in CDCl3
1H NMR of BMPDS in CDCl3
Figure 1. Variation in the conductivity of the common precursor SDS & 2 ionic liquid derived surfactant.
Figure 2. Variation in the surface tension of the common precursor SDS & 2 ionic liquid derived surfactant.
Figure 3. Variation of the I1/I3 ratio of the BMIMDS with it’s concentration.
Figure 4. Variation of the I1/I3 ratio of the BMPDS with it’s concentration.
Fig.-1
Fig.-2
Fig.-3
Fig.-4
Fig.-10
Fig.-5
Fig.-6
Fig:7
Fig.-8
Fig.-9
Fig.-5. Fluorescence spectra comparison of (Quenching) BMIMDS and BMPDS. CPC is used as quencher.
Fig.6. Comparison of change of the Zeta potential with concentration of BMIMDS & BMPDS
Fig.7. Comparison of change of the size with concentration of BMIMDS & BMPDS
Fig.-8. Comparison of change of the dispersity with concentration of BMIMDS & BMPDS
Fig.9. Texture of BMPDS under Polarisation optical microscope
Fig.10. Texture of BMIMDS under Polarisation optical microscope
Result and Discussion
Fig.- 1. & 2. Ionic liquid based surfactant are more superior than the precursor i.e. conventional surfactant. This figure clearly indicate that CMC values of both BMIMDS & BMPDS is lower compare to their precursor SDS.
Fig.-3. & 4. Ionic liquid based surfactant are again proved to be more efficient that conventional one and values obtained from the conductometry and surface tensiometry were justified.
Fig.-5. Comparison of quenching of two ionic liquid based surfactant by the same quencher CPC & it show different behavior which was obvious as they have different head group. From this the values of the aggregation number was also obtained. Quenching is more faster in the case of BMIMDS as it charge is delocalized on aromatic head group.
Fig.-6. Zeta potential value increase up to a certain concentration above the CMC & then it’s value decreases.
Fig.-7. With increasing concentration both of them show similar trend of change in size. Initial dissimilarity due to difference of head group and obviously their size.
Fig.-8. BMIMDS reached unit value of dispersity faster than BMPDS as it’s CMC value was lower & it form aggregation quicker compare to BMPDS.
Fig.-9. Show some crystalline nature which may more improved.
Fig Jelly type character are more prominent here which may be due distinguish charge density of lipophilic and partial lipophobic part.
Melting point & characteristic DSC peak of the 3 precursor & 2 synthesized compounds
Table 1.
Serial no.
Sample name
Melting point(oC) & DSC
Prominent peak 1.
SDS
206 & 202 2.
BMPyBF4
158 & _ 3.
BMIMCl
70 & _ 4.
BMIMDS
43 & 41 5.
BMPDS
Viscous liquid & _
Table 2. CMC values from different techniques
Surfactants
CMC values (mM) Conductometrically
CMC values(mM)
Surface tensiometrically
Fluorimetry
SDS
8.1
7.91
7.9
BMIMDS
2.97
1.87 2
BMPDS
2.53
2.29
2.15
From the table 1. it is observable that the DSC characteristic peak was appear before their melting point. So it give idea about phase transition & further recognize the melting point values.
Critical micellization values were obtained by average of 3 values from different experimentation in most cases. They were quite close to each other.
Acknowledgement
Conclusion
Financial support from the University Grants Commission(MRP approval No. and Date: F. No /2014 (SR) Dt
and Research Guidance from Prof . A. K. Panda, Department of Chemistry, University of North Bengal. All faculty of the Department of Chemistry, University of North Bengal. Special thanks to Prof. S K Saha & his scholar.
Ionic liquid based surfactant were synthesized which were made halogen free sincerely. They show more effectiveness as surfactant. They also further reduce the chances of environmental pollution due to the absence of the caustic alkali metal ion. Physicochemical studies was carried out by different technique brought out different interesting result which would further promote such research. POM picture given some prove of partial existence of liquid crystalline properties, which may be much prominent if recrystallization of IL’s and IL’s based surfactant can be carried out before focusing.
Future Plan
Fluorescence anisotropy and Rheology stuty will be carried out very soon. More IL’s based surfactant may be prepared by increasing chain length & with broder counter ion which would expected to be more affective surfactant. In future b) , c) & d) of the objectives part will require sincere and dedicated effort.