Polyethylene Glycol Adsorption on Silica:  From Bulk Phase Behavior to Surface Phase Diagram

Abstract

A characterization of the bulk-phase diagram from literature data and new NMR and DSC measurements provided us with valuable elements that are helpful for gaining, from aqueous solution, better insight into the surface behavior of polyethylene glycol on Aerosil 200. Adsorption isotherms built further to measurements by a depletion method showed a strong and temperature-dependent variation of the isotherm shape in agreement with the variations of interactions already evidenced in the bulk. In temperature-concentration areas, where water is behaving as a helix-promoting solvent, the finding of positive PEG adsorptions and stairlike isotherms agrees with observations reported in the literature. We identified some of the vertical parts as corresponding to the formation of monolayers of helix-shaped PEG molecules. In poor-solvent zones, adsorptions were null or negative, and the isotherms exhibited oscillations suggesting very different surface behavior. Our data analysis evidenced the presence of a much greater amount of water than in the previous surface states; however, the similar analysis of PEG behavior remains relevant. Indeed, the occurrence of first-order transitions in the surface layer implies some water reorganization, permitting the PEG molecules to move closer to the surface and become helix-shaped to rearrange in a monolayer. The surface phase diagram confirmed this analysis in a very satisfying way.

Fluorinated Pickering Emulsions with Nonadsorbing Interfaces for Droplet-based Enzymatic Assays

“…In addition, the adsorption of PEG is known to be driven by the formation of hydrogen bonds in the presence of polar groups such as silanol groups on surfaces. [25][26][27] Formation of hydrogen bond between PEG chains and silanol groups is expected in our case since our silica nanoparticles were only partially fluorinated (see XPS characterization in our previous paper 16 ). Subsequent enzyme adsorption on particle surface is prevented due to steric repulsions between the PEG chains and enzymes.…”

Determination of a setup correction function to obtain adsorption kinetic data at stagnation point flow conditions

“…It is well-known that PEG readily adsorbs to a variety of materials with high affinity and with no significant energy barriers [9, 64, 65]. Therefore, the adsorption of PEG is determined by the mass transfer rate from the bulk solution, making it reasonable to assume β = 1 [1].…”

A mechanistic investigation of Pickering emulsion polymerization

“…A good explanation is the strong attractive interaction between the pendant ethylene oxide units and the silica surface. 46 Whereas hydroxypropyl methacrylate (HPMA) is too hydrophobic, surprisingly the more hydrophilic 2-hydroxyethyl methacrylate (HEMA) was not effective. In the case of acrylamide, the reason why this comonomer led to poor results may originate from unfavourable reactivity ratios.…”