Surface Coverage and Competitive Adsorption on Carbon Nanotubes

The binding strength of dispersants to the surface of carbon nanotubes is of crucial importance for the efficiency of the dispersion process and for potential applications, yet data are scarce on this subject. Here we present the results of diffusion NMR experiments in dispersions of single-walled carbon nanotubes (SWNTs) prepared by either the polymer Pluronics F127 or the protein bovine serum albumin (BSA). The experiments detect the amount of F127 molecules adsorbed onto the SWNT surface. This quantity is recorded (i) in F127-SWNT dispersions to which BSA molecules are added and (ii) in BSA-SWNT dispersions to which F127 molecules are added. The data clearly show that F127 replaces BSA adsorbed at the SWNT surface, while BSA leaves the adsorbed F127 coverage intact. Consequently, F127 binds to the nanotube surface more strongly than BSA. Hence, we provide a way to categorize dispersants by adsorption strength. We also provide evidence showing that the nanotubes dispersed by BSA form loose aggregates where a large part of the surface is not in direct contact with the surrounding liquid. The results are discussed in relation to previous findings in the literature

Recovery capability of NCTC 2544 cells 48 h after removing surfactants from the culture medium.

<p>Cell viability values are presented as mean±SD of a characteristic profile (3 repetitions) selected from 5 independent experiments.</p

Membrane destabilization (%± SD) as obtained by the calcein fluorescent die released from PE:PC:PS:CHO (1∶1∶1∶1) liposomes, for the indicated surfactant concentrations.

<p>Experiments were conducted at room temperature.</p

Pictorial illustration of the positioning and general conformational of gemini molecules embedded in the membrane, as well as the consequent morphological modification of the latter, based on the ³¹P-NMR and MD simulation results.

<p>From the top to the bottom, gemini surfactants represented correspond to short spacer/short tail, short spacer/long tail and long spacer/short tail architectures.</p

Dispersing Carbon Nanotubes with Ionic Surfactants under Controlled Conditions: Comparisons and Insight

A fundamental understanding of the mechanisms involved in the surfactant-assisted exfoliation and dispersion of carbon nanotubes (CNTs) in water calls for well-controlled experimental methodologies and reliable comparative metrics. We have assessed the ability of several ionic surfactants to disperse single and multiwalled carbon nanotubes, resorting to a stringently controlled sonication-centrifugation method for the preparation of the dispersions. The CNT concentration was accurately measured for a wide range of surfactant concentration, using combined thermogravimetric analysis and UV–vis spectroscopy. The obtained dispersibility curves yield several quantitative parameters, which in turn allow for the effects of nanotube morphology and surfactant properties (aromatic rings, chain length, headgroup charge, and <i>cmc</i>) to be assessed and rationalized, both in terms of dispersed nanotube mass and surface area. The data also indicate that the CNT-surfactant association follows patterns that are markedly different from other equilibrium processes governed by hydrophobicity (such as micellization); in particular, the surfactant concentration needed for maximum dispersibility, <i>c</i>_s,max, and the number of surfactant molecules per unit CNT area at <i>c</i>_s,max are shown to depend linearly on chain length. The results further suggest that the presence of micelles in the exfoliation process is not a key factor either for starting CNT dispersibility or attaining its saturation value

DSC thermograms of the DPPC:Chol:12-10-12 system for the lipid:surfactant molar ratios indicated.

<p>A scanning rate of 10°C/min was used.</p

DSC thermograms of the DPPC:Chol:12-2-12 system for the lipid:surfactant molar ratios indicated.

<p>A scanning rate of 10°C/min was used.</p

Radial distribution functions of water relative to the (a) gemini polar heads, and (b) gemini spacer, calculated from the MD.

<p>Simulations were carried out at 325 K.</p

³¹P-NMR spectra of a DPPC:surfactant systems ([DPPC] = 30 mg/mL, (surfactant) = 20 mol%), in the (a) absence of surfactant, and in the presence of (b) DTAB, (c) 12-2-12 and (d) 12-10-12.

<p>The chemical shift is represented in the horizontal axis.</p

Schema of the distances, extracted from the MD, used to characterize the conformation and relative position of gemini molecules in the bilayer.

<p>A summary of the respective values for the 12-2-12, 12-10-12, 14-2-14, and 18-2-18 surfactants are presented in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0026965#pone-0026965-t002" target="_blank">Table 2</a>.</p