Surface Functionalization of Nanoparticles

In general, the chemical modification of the nanoparticle surface can be carried out either in situ after the nanoparticle formation or via a postmodification route. 

Although alkoxysilanes are the compounds of choice for silica surfaces, they do not always form stable bonds with transition metal oxide nanoparticles. It 

highly hydrophilic silica particles can be obtained when ethylene glycol chains are attached to the surface [41]. These groups are important if the matrix consists of hydrophilic polymers, such as epoxy resins. The ethylene glycol 

Silica nanoparticles found a wide application as fillers in the preparation of polymer nanocomposites [49]. This was driven by the increased demand for new polymeric materials with improved thermal, mechanical, physical, and chemical properties. Due to the broad application of the sol-gel process in the production 

The major challenge in the production of nanoparticle-polymer nanocomposite is the ability to achieve a homogeneous filler dispersion, which determines the overall performance of the nanocomposites. Chemical surface functionaliTa-tion and effective mixing methods are the two main routes that can lead to a homogeneous filler distribution. Three main methods can be identified for the production of sol-gel particle-polymer nanocomposite (i) solution mbdng, 

---

Saha K, Kim ST, Yan B, Miranda OR, Alfonso FS, Shlosman D, Rotello VM (2013) Surface functionality of nanoparticles determines cellular uptake mechanisms in mammalian cells. Small 9(2) 300-305... 

The surface functionalization of nanoparticles is an important requirement to control the compatibility between fillers and polymer matrix and as a result the dispersion state of nanofillers. For example, to tune the organophilic character of nanoparticles and promote dispersion within polymers, chemical surface treatments such as cationic exchange, grafting of organosilanes, or the use of copolymers have been extensively practiced (Avalos et al., 2009 Giannelis, 1996 Patel et al., 2007). For example, Ngo et al. (2010) have shown the influence of the chemical nature of the surfactant used for the modification of the layered silicates on polystyrene foam morphologies. Smaller... 

In this chapter, only a few of the current applications of silver nanoparticles of well-defined size and shape have been described. Clearly, future studies must include the surface functionalization of nanoparticles that wiU, in turn, allow for their easier incorporation into useful assemblies, and ultimately into nanoscale devices. 

Li et al. reported first on the decoration of hydrothermal carbon spheres obtained from glucose with noble metal nanoparticles [19]. They used the reactivity of as-prepared carbon microspheres to load silver and palladium nanoparticles onto then-surfaces, both via surface binding and room-temperature surface reduction. Furthermore, it was also demonstrated that these carbon spheres can encapsulate nanoparticles in their cores with retention of the surface functional groups. Nanoparticles of gold and silver could be encapsulated deep in the carbon by in situ hydrothermal reduction of noble-metal ions with glucose (the Tollens reaction), or by using silver nanoparticles as nuclei for subsequent formation of carbon spheres. Some TEM images of such hybrid materials are shown in Fig. 7.4. 

Ethirajan A, Ziener U, Landfester K (2009) Surface-functionalized polymeric nanoparticles as templates for biomimetic mineralization of hydroxyapatite. Chem Mater 21(11) 2218-2225... 

Figure 13.15 Schematic representation of synthesis and surface modification of nanoparticles [54]. (Reproduced with permission from W.J. Rieter et al., Surface modification and functionalization of nanoscale metal-organic frameworks for controlled release and luminescence sensing, Journal of the American Chemical Society, 129, 9852-9853, 2007. 2007 American Chemical Society.)...

Surface functionalization of dendrimer nanoparticles with suitable ligands, size, surface groups, and surface charge plays a key role on the cellular internalization by endocytosis, phagocytosis, miCTopinocytosis, or fluid-phase endocytosis. 

Besides the above-mentioned experiments using PS-based nanoparticles, PMI could be successfully incorporated into phosphate-functionalized PMMA and PS [42], polyisoprene (PI), PS-co-PI [43], polyester [44], and poly(butylcyanoacrylate) (PBCA) [45,46] matrices (Fig. 4) for the investigation of cellular response to these polymeric nanoparticles. It could be shown that the internalization in different cell lines depends on the cell line, the polymer, and the surface functionalization of the nanoparticles. 

Ghosh, S., Hui, T., Uddin, M. S., Hidajat, K. (2013). Enantioselective separation of chiral aromatic amino acids with surface functionalized magnetic nanoparticles, 105, 267-277. 

In this system, the adsorption of the stabilizer was characterized throroughly employing various spectroscopic techniques. Especially, H and C liquid state NMR spectroscopy proved as a useful probe for the surface chemistry of nanoparticles in concentrated dispersions, as species adsorbed to the surface can be identified, however the functional groups directly adjacent to the surface are motionally hindered, which results in spectral broadening [85], It is hence possible to assess the amount of surface-bound species, determine the functional groups binding to the particle surface, and qualitatively investigate the chemistry of both particle surface and bulk solution. In the zirconia case, it was detected that indeed only partially the initially bound benzyl alcohol solvent is replaced by the stabilizer... 

Plasma treatment of diamond nanoparticles can functionalize the nanoparticles surfaces with polar groups that have improved interactions with water molecules and thus strong affinity to water medium. Lifshitz-van der Waals/ acid-base (LW-AB) approach can be used to quantify the contributions of these plasma-induced polar groups to surface energy increase of the plasma-treated nanoparticles. As described by Van Oss et al. [9], the total surface energy of nanoparticle, which combined both Lifshitz-van der Waals and Lewis acid-base (LW-AB) interactions, can be expressed by following expression ... 

Changing the surface functionality of the cellulose nanoparticle can also affect the permeability of nanocellulose films. Films constituted of negatively charged cellulose nanowhiskers could effectively reduce permeation of negatively charged ions, while leaving neutral ions virtually unaffected. Positively charged ions were found to accumulate in the membrane [70]. 

By using AFM, the image of a surface can be obtained in atomic resolution with force of interaction at nano-Newton scale. Specific surface area is one of the characteristic features for nanopowder. However, the functionalization of nanoparticle is one of the main challenges to provide top-end functional applications [47]. 

Baraton M-I. Synthesis, functionalization and surface treatment of nanoparticles. American Scientific Publisher 2002. 

---