Adsorption and Depletion Regimes of a Nonionic Surfactant in Hydrophilic Mesopores: An Experimental and Simulation Study

Journal Article · Tue Aug 15 00:00:00 EDT 2017 · Langmuir

DOI:https://doi.org/10.1021/acs.langmuir.7b02262· OSTI ID:1394384

Müter, Dirk ^[1]; Rother, Gernot ^[2]; Bock, Henry ^[3]; Schoen, Martin ^[4]; Findenegg, Gerhard H. ^[4]

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1. Univ. of Copenhagen (Denmark). Nano-Science Center, Dept. of Chemistry
2. Technical Univ. of Berlin (Germany); Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
3. Heriot-Watt Univ., Edinburgh, Scotland (United Kingdom)
4. Technical Univ. of Berlin (Germany)

Adsorption and aggregation of nonionic surfactants at oxide surfaces has been studied extensively in the past, but only for concentrations below and near the critical micelle concentration. In this paper, we report an adsorption study of a short-chain surfactant (C₆E₃) in porous silica glass of different pore sizes (7.5 to 50 nm), covering a wide composition range up to 50 wt % in a temperature range from 20 °C to the LCST. Aggregative adsorption is observed at low concentrations, but the excess concentration of C₆E₃ in the pores decreases and approaches zero at higher bulk concentrations. Strong depletion of surfactant (corresponding to enrichment of water in the pores) is observed in materials with wide pores at high bulk concentrations. We propose an explanation for the observed pore-size dependence of the azeotropic point. Mesoscale simulations based on dissipative particle dynamics (DPD) were performed to reveal the structural origin of this transition from the adsorption to the depletion regime. The simulated adsorption isotherms reproduce the behavior found in the 7.5 nm pores. Finally, the calculated bead density profiles indicate that the repulsive interaction of surfactant head groups causes a depletion of surfactant in the region around the corona of the surface micelles.

• Research Organization: Oak Ridge National Laboratory (ORNL), Oak Ridge, TN (United States)
• Sponsoring Organization: USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22); German Research Foundation (DFG) (Germany)
• Grant/Contract Number: AC05-00OR22725
• OSTI ID: 1394384
• Journal Information: Langmuir, Journal Name: Langmuir Journal Issue: 42 Vol. 33; ISSN 0743-7463
• Publisher: American Chemical Society
• Country of Publication: United States
• Language: English

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37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY