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

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 (C 6E 3) 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 C 6E 3 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 coronamore » of the surface micelles.« less
Authors:
 [1] ; ORCiD logo [2] ;  [3] ;  [4] ; ORCiD logo [4]
  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)
Publication Date:
Grant/Contract Number:
AC05-00OR22725
Type:
Accepted Manuscript
Journal Name:
Langmuir
Additional Journal Information:
Journal Volume: 33; Journal Issue: 42; Journal ID: ISSN 0743-7463
Publisher:
American Chemical Society
Research Org:
Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
Sponsoring Org:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22); German Research Foundation (DFG)
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
OSTI Identifier:
1394384