Meso- and Macroporous Polymer Gels for Efficient Adsorption of Block Copolymer Surfactants

Abstract

An understanding of surfactant adsorption at solid−liquid interfaces is important for solving many technological problems. This work evaluates surfactant adsorption abilities of high surface area (200−600 m 2 /g), high porosity (>90%), hierarchically structured open pore polymer gels. Specifically, the interactions of a nonionic block copolymer surfactant, poly(ethylene oxide)−poly(propylene oxide)− poly(ethylene oxide) (PEO-PPO-PEO), with three polymer gels, namely, syndiotactic polystyrene (sPS), polyimide (PI), and polyurea (PUA) offering different surface energy values, are evaluated at surfactant concentrations below and well above the critical micelle concentration (CMC). Two distinct surfactant adsorption behaviors are identified from the surface tension and nuclear magnetic resonance data. At concentrations below CMC, the surfactant molecules adsorb as a monolayer on polymer strands, inferred from the Langmuir-type adsorption isotherm, with the adsorbed amount increasing with the specific surface area of the polymer gel. The study reports for the first time that the gels show a strong surfactant adsorption above CMC, with the effective surfactant concentration in the gel reaching several folds of the CMC values. The effective surfactant concentration in the gel is analyzed using surfactant micelle size, polymer surface energy, and pore size of the gel. The findings of this study may have strong implications in liquid−liquid separation problems and in the removal of small dye molecules, heavy metal ions, and living organisms from aqueous streams.

Separation of Perfluorooctanoic Acid from Water Using Meso- and Macroporous Syndiotactic Polystyrene Gels

“…The amount of surfactant adsorbed scaled directly with the interfacial energy. A similar argument can be invoked in this work to explain the driving force for PFOA adsorption on sPS gels in view of the similar molecular structure of the PFOA molecules to that of the surfactant considered by Gotad et al, with a hydrophilic −COOH group at one end and the 8-carbon long chain with fluorine groups at the other.…”

“…An earlier study by Gotad et al underlined the role of high interfacial energy sPS–water interfaces in driving the adsorption of block copolymer surfactants within the water-filled sPS gel. The amount of surfactant adsorbed scaled directly with the interfacial energy.…”

“…Aerogels can be rendered into various shapes and sizes such as monoliths, sheets, , films, and spherical , or pill-shaped microparticles. The pore size and surface energy of the materials can also be tuned for desired applications. ,− The development of this class of materials over 90 years led to several high value innovations in thermal insulation, air filtration, − energy storage, molecular separation, , and filtration …”

“…Such adsorption capacities are unusually high in reference to the data available for other porous materials − and are attributed to high surface energy and high specific surface area of sPS gels. sPS aerogels were first reported in 2005 by Daniel et al The high specific surface area, large porosity, and hydrophobic surface made these materials suitable for applications as adsorbents, absorbents, , in oil–water separation, and as a ultra- low dielectric constant material …”

An Investigation on Morphology of Emulsion-Templated Polyimide Aerogel Foam Sheets

“…Aerogels offer several attributes, such as low density ∼0.1 g/cm 3 , high surface area, 200–600 m 2 /g, and high porosity (>90%) consisting of mesopores and are used as thermally insulating materials in planetary vehicles − and buildings, as host of catalysts, in removal of low molecular weight additives and surfactants, among other applications . A wide variety of other aerogels have been studied, such as silica, syndiotactic polystyrene (sPs), and polyurea − and organic–inorganic composite aerogels such as polymer-cross-linked aerogels , and interpenetrating network aerogels …”