Low concentrations of cationic silica nanoparticles impact lung surfactant membrane structure while anionic nanoparticles have minimal effect.

Polymer-bearing surfaces are of particular interest because of their thermal and solvent response, 1,2 their prospective use as protein and cell adhesive platforms, 3À5 or as self-biolubricating substrates, among others. 6 Surface-tethered polymer chains provide the means to tailor the surface properties by undergoing externally stimulated conformational changes. This is particularly true for polyelectrolyte polymers such as poly(acrylic acid) (PAA) whose degree of ionization is highly influenced by pH, ionic strength, and the presence of multivalent species. 7,8 Various polymer conformations including pancake and brushes are possible with end-tethered polyelectrolytes by varying surface density and the media. 9 The control of conformational properties have allowed for advances in areas such as surface friction modulation, switchable wettability, autophobicity, 10À12 antifouling 13À16 and lubricity, 6,17À21 to name but a few.Surface-bound polymers of well-defined discrete degrees of polymerization and high surface homogeneity are desired for ensuring control of surface properties and reversible surface response with external stimuli such as temperature, pH and ionic strength. These polymers can be obtained by controlled polymerization with an ATRP initiator chemically linked to the substrate. For silica substrates, the substrateÀinitiator linkage (Si substrate ÀOÀSi initiator bond) is generally robust enough for both sustaining the reaction conditions required for ATRP and subsequent polymer brush formation and characterization. We recently showed that PAA brushes built on mica by anchoring polystyrene-poly(acrylic acid)(PS-b-PAA) diblock copolymers in a polystyrene monolayer covalently attached to OH-activated mica surfaces resist to cleavage at pH 5.5 with added salt for several days. 22 However, there is still uncertainty regarding the robustness of the substrateÀpolymer bond and whether it is resistant to the extreme pH and ionic strengths that are required for conformational analyses of polyelectrolyte brushes. It is unknown whether these extreme conditions hydrolyze the SiÀOÀSi bond and cleave the polymer from the substrate leading to undesired decrease in polymer grafting density, similar to what was reported for poly(methacrylic acid) brushes and PAA brushes grafted from silica-based substrates. 23À25 Knowing the conditions under which undesired polymer cleavage occurs is pivotal for accurate surface-property studies. They are also important for controlling reversible polymer conformational changes, while preventing polymer degrafting. Although we previously provided indirect evidence for polymer cleavage from mica at high pH and salt concentrations, 23 determining the exact conditions under which PAA cleavage occurred was not possible. Also, unequivocal evidence for polymer degrafting from silica substrates has not yet been demonstrated.ABSTRACT: Poly(acrylic acid) (PAA) covalently immobilized on glass substrates was made fluorescent by grafting a BODIPY derivative (PMOH) via an ester linkage. Although...

No abstract

The interaction of nanoparticles (NPs) with pulmonary surfactant is important for understanding the potential adverse effects of inhaled engineered and incidental nanomaterials. The effects of a low concentration (0.001 wt %) of charged, hydrophilic silica NPs of hydrodynamic diameter of ∼20 nm on the phase behavior and lateral structure of lipid-only and naturally derived surfactant monolayers were investigated at the air/water interface using surface pressure–area isotherms and Brewster angle microscopy, respectively. Atomic force microscopy was used to image the morphology of films transferred onto mica substrate with nanometer resolution. We show that the silica NPs can significantly alter the condensed domain size and shape even in the absence of apparent differences in the monolayer compression isotherms. The cationic particles notably induce structural and morphological progressions in a binary model containing anionic phosphoglycerol that are similar to those observed for the natural surfactant film that contains cationic proteins. These findings specifically highlight the impact of the NP charge on the phase transformations in pulmonary surfactant, with implications for the engineering of nanomaterials for commercial use and bioapplications.

We report the first successful preparation of polyelectrolyte brushes using an ATRP initiator that was covalently grafted to silica and mica substrates via an organophosphonic acid.