Influence of surface functionalization on the hydrophilic character of mesoporous silica nanoparticles

Abstract

We report the synthesis and surface functionalization of MCM-41-like mesoporous silica nanoparticles (MSNs) with spheroidal shape and particle size of 141 ± 41 nm. The success of surface functionalization with aminopropyl and sodium ethylcarboxylate groups (giving amino-MSN and carboxy-MSN, respectively) was ascertained by infrared spectroscopy and ζ potential measurements. The former showed the decrease of surface silanol groups and the corresponding appearance of signals related to NH2 bending mode (δNH2) at 1595 cm(-1) and COO(-) stretching (νas and νsym) at 1562 and 1418 cm(-1). The latter showed a change in surface charge, in that the isoelectric point (IEP) changed from pH 3-4.5 to 8.5 when the MSN was functionalized with the amino groups, while carboxy-MSN showed a more negative charge in the whole pH range with respect to MSN. The hydrophilic character of the prepared materials was ascertained by quantitative microgravimetric measurements, allowing the calculation of the average isosteric adsorption heat (q[combining macron]st). This was found to be 51 ± 3 kJ mol(-1), 61 ± 4, and 65 ± 3 kJ mol(-1) for MSN, amino-MSN, and carboxy-MSN samples, respectively. The increase in q[combining macron]st after functionalization can be ascribed to the specific interaction of water molecules with the functionalizing agents, in agreement with a higher basicity with respect to silanol groups. Moreover, the possibility of multiple H-bonding interactions of water molecules with the carboxylate anion is put forward to account for the higher water uptake with respect to parent MSN.

Surface PEG Grafting Density Determines Magnetic Relaxation Properties of Gd-Loaded Porous Nanoparticles for MR Imaging Applications

“…The negative charge increasing with pH (−35 mV at pH 11) is related to the deprotonation of Si–OH groups; similar results have been observed for silanol-rich mesoporous silica NPs. 28,29 On the other hand, for PEGylated Gd-LTL, the ζ values turn from positive to negative between pH 3 and 11 with an IEP at pH 5.6 and 8.3 for 6.2 and 9.1 wt % of PEG-loading, respectively. The changeover, becoming more pronounced with increasing PEG-grafting, is in good agreement with the results by He et al, who demonstrated that mesoporous silica NPs become less negatively charged upon increase of PEG-loading.…”

Investigating the Interaction of Water Vapour with Aminopropyl Groups on the Surface of Mesoporous Silica Nanoparticles

“…[19,[28][29][30][31][32][33][34] It can be obtained from organosilanes such as 3-aminopropyltriethoxysilane (APTS, the most commonly employed), 3-aminopropylmethyldiethoxysilane and 3-aminopropyl dimethylethox-ysilane. Moreover,s urfacef unctionalisationc an severelyi nfluencei mportant material properties such as surface charge, [32,34,42] hydrophilicity, [34,43,44] dispersibility, [22] toxicity [45] and stability. [42] This functionalisation is usually aimed at optimising the interaction with the desired target adsorptive: CO 2 in carbon capture and storagea pplications, pollutantsi ne nvironmental applications, reactants in catalysis, drugs in nanomedicine and so forth.…”

Active Particle Accumulation at Boundaries: A Strategy to Measure Contact Angles

“…The most utilized method is the measurement of the contact angle ( , see also Figure ), that is, the optical measurement of the angle formed by substrate and the tangent at the droplet. An alternative method is for example the microgravimetric H 2 O adsorption–desorption isotherms to determine the hydrophobicity of microparticles …”

“…Monolayer absorption of molecules with specific characteristics also influences the surface behavior, as demonstrated by Musso et al. by modifying the hydrophobicity of mesoporous silica particles by grafting differently charged silane molecules on the surface …”

“…An alternative method is for example the microgravimetric H 2 O adsorption-desorption isothermst od eterminet he hydrophobicity of microparticles. [5] It is well-known that the wetting properties of substrates are quite sensitive to the morphology of the substrate. For example, micro-textured surfaces can give rise to superhydrophobicity.…”