Polysaccharide−Surfactant Interaction. 1. Adsorption of Cationic Surfactants at the Cellulose−Water Interface

Abstract

The extent of adsorption (Γ2 1) of cetyltrimethylammonium bromide (CTAB), myristyltrimethylammonium bromide (MTAB), and dodecyltrimethylammonium bromide (DTAB) from aqueous solution onto a cellulose−water interface has been measured analytically in a wide range of surfactant concentrations below and above the critical micelle concentration (cmc) at different physicochemical conditions and in the presence of different electrolytes and urea. Γ2 1 is found to increase with increase of bulk surfactant concentration C 2 until it reaches a maximum value Γ2 m when C 2 reaches a critical value, C 2 m. With further increase of C 2 beyond C 2 m, Γ2 1 decreases from Γ2 m and becomes zero with attainment of surface azeotropic state at a surfactant concentration C 2 azeo. For C 2 > C 2 azeo, values of Γ2 1 are negative due to the excess hydration of cellulose fibril and desorption of surfactant micelles from the surface to the bulk phase. The value of Γ2 m depends upon the different physicochemical conditions and presence of different electrolytes and urea. Values of C 2 m lie considerably below the cmc in most cases. Γ2 m decreases with decrease of hydrocarbon chain length of surfactant molecules, and in the case of DTAB all values of Γ2 1 are negative. The results also predict involvement of hydrophobic interaction in the adsorption process. The standard free energy change ΔG° for the transfer of surfactant molecules to 1 kg of cellulose at the state of surface saturation has been calculated using an integrated form of the Gibbs adsorption equation. The values of ΔG° follow the same order as those of Γ2 m. The average slope of the linear plot of ΔG° vs Γ2 m is equal to −34.3 ± 0.1 kJ/mol. This corresponds to the standard free energy change (ΔG B°) for the transfer of 1 mol of surfactant from the bulk solution to the cellulose surface when bulk mole fraction of surfactant is altered from zero to unity. The values of ΔG hi° for different systems at high surfactant concentration (>C 2 azeo) have been also calculated using a linear extrapolation method, and they are found to be positive in all cases due to excess positive hydration of cellulose.

Kinetics of Adsorption of Cationic Surfactants at Silica-Water Interface

“…[1] replacing C 2 by C e 2 . The standard devia- (43). All other common electrolytes, acids, and urea used tion in the measurement of G 1 2 was 4-6% based on four sets were of analytical grade.…”

Aqueous Solutions of Sodium Deoxycholate and Hydroxypropylmethylcellulose: Dynamic Surface Tension Measurements

“…The synergistic lowering of the surface tension observed in these mixed systems was the evidence for that interaction (10,11). The interaction of ionic surfactants with polymers at the interface has been recently studied by a few workers (12)(13)(14)(15).…”

Adsorption of biopolymers at hydrophilic cellulose–water interface

“…Using the Langmuir-Boldgett method, several layers of cellular derivatives have been prepared on a mica plate, and uptake of water by these layers and their gelation properties have been critically examined. [7][8][9] Physicochemical studies for adsorption interaction of cationic, anionic, and nonionic surfactants 10,11 with powdered cellulose particles have been carried out at different values of pH and temperature, and certain interesting features of the hydrophobic and electrostatic interactions involved in this adsorption process have been revealed. Both surfactant and water are found to compete for occupation of the adsorption spots of the surface; further, even in the saturated state of surfactant adsorption, significant amounts of solvent are found to exist at the interface of cellulose powder.…”