Comparative studies of natural and synthetic surfactants for dyes interactions at their second point of micellisation

ABSTRACT

The presented work describes the interaction behaviour of natural and synthetic ionic surfactants with the oppositely charged dyes at the point of second critical micellar concentration (CMC). These interactions were monitored at different times, with additive at varying temperatures. The surfactant changes its shape at second CMC and therefore the interactional changes occurred owing to its structural changes. The obtained second CMC for the natural surfactant (NS) was 6.6 mM, whereas the counter, synthetic surfactants (SS) like cetyltrimethylammonium bromide (CTAB) and sodium dodecyl sulphate (SDS) possess 20 and 65 mM, respectively. The cationic CTAB showed a red shift, whereas the anionic SDS showed hypochromic shift and comparable results with NS. The interactions were found to be spontaneous at all monitored temperatures. The studied NS provides a suitable replacement to the SS. This interactional study will be helpful in various applications, such as soil washing, oil recovery and in different medicinal uses, and found to be economical.

KEYWORDS:

• Second CMC
• synthetic surfactants
• natural surfactant
• additives
• surfactant dye interactions

Article highlights

• Second CMC of NS is much lower than the CMC of SS.

• The dye solubilisation is efficient and efficient in working at second CMC of both SS and NS.

• This studied dye surfactant interactions are thermodynamically favourable.

• Natural surfactant retains its amphoteric interactional behaviour even at second CMC.

Disclosure statement

No potential conflict of interest was reported by the authors.