Comparison of Same Carbon Chain Length Cationic and Anionic Surfactant Adsorption on Silica

Pengxiang Li,Munehide Ishiguro,Yang Su,Tiejian Li

doi:10.3390/colloids4030034

Abstract

Adsorption of a cationic surfactant dodecyl pyridinium chloride (DPC) on silica was studied to show a comparison with the adsorption of an anionic surfactant sodium dodecyl sulfate (SDS), whose carbon chain length is the same and on the same silica. Results provided a better understanding of the adsorption mechanism of cationic and anionic surfactant on negatively charged silica. The experiment covered different electrolyte concentrations and pH values. Results indicated that at the same pH, the DPC adsorption amounts are higher when the electrolyte concentration is higher; at a higher DPC equilibrium concentration, the adsorption amount difference is larger than that at low DPC equilibrium concentration, and when DPC equilibrium concentration is lower than 0.1 mmol/L, the adsorption amount difference cannot be observed. At charge compensation point (CCP, 0 zeta potential), the negative surface charge of silica was compensated by DP+, a continuous increasing zeta potential indicated a bilayer adsorption of DPC on silica. The adsorption amount increased with increasing pH. The calculated lines by Gu and Zhu model show a two-step property, including a bilayer and hemi-micelle adsorption. DPC adsorbed more strongly on silica than SDS due to the combination of electrostatic and hydrophobic attraction.

Highlights

Surfactant is a commonly used raw material in our life and industry
At CCP, the negative surface charge of silica was compensated by DP+, a continuously increasing zeta potential indicated a bilayer adsorption of dodecyl pyridinium chloride (DPC)
At the same pH, the DPC adsorption amounts are higher when the electrolyte concentration is higher; at higher DPC equilibrium concentrations, the adsorption amount difference is larger than that at low DPC equilibrium concentrations, and when DPC equilibrium concentration is lower than 0.1 mmol/L, the adsorption amount difference cannot be observed

Summary

Introduction

Surfactant is a commonly used raw material in our life and industry. Based on its amphipathy, it can be adsorbed on the surface of clay minerals, polymers, sediments, humic acid and soil [1]. Nevskaia et al [10] showed that only little amounts of anionic surfactants were adsorbed on a silica quartz and the amount increased with the increase in salt concentration. Ahmed and Ishiguro [13] indicated the impact of electric repulsive potential on adsorption of anionic surfactant on negatively charged humic soil. The adsorption of cationic surfactant, especially DPC, on negatively charged minerals such as silica and rutile, was reported in qquuantity. Te.heTnh,eint ,wiat swsahsakshenakwenellwaenldl asntodosdtotoodprteocpiprietcaitpeitthateestihliecasipliacratipclaerst.icFloerst.yF-foivrteym-fiivneutmesinlautteers, l3amterL, 3ofmthLeomf itxhteumreiuxtnudreeruthnedelirqtuhied llieqvueildolef v2elcomf 2wcams wmaosvmedovinetdointhtoe tUheVU-aVbs-aobrbsoarnbcaencceellcebllybpyippeiptteettteototetsetstththeessttaabbiliiltityyooff tthhee ssiilliiccaa ssuussppeennssiioonn wwiitthh aaddssoorrppttiioonn ooff DDPPCC;;. As an approximation for dilute solutions, one can use a = C (C is surfactant monomer concentration), the amount of adsorbed monomer Γ1, the amount of hemi-micelle Γhm, and the number of sites Γs instead of a1, ahm, and as, respectively.

Result

Silica Particle Stability with Adsorption of DPC

Zeta Potential with Adsorption of DPC

Comparison of SDS and DPC Adsorption

Discussion

Conclusions