Silica nanoparticles polymer-coated

FIG. 10 SEM micrographs of (a) sUica nanoparticle/polymer [Si02/PDADMAC)3]-coated PS lat-ices and (b) hollow silica capsules. The hollow sUica capsules were obtained by calcining coated particles as shown in (a). The calcination process removes the PS core and the polymer bridging the silica nanoparticles, while at the same time fusing the silica nanoparticles together. Some of the silica capsules were deliberately broken to demonstrate that they were hollow (b). (From Ref. 106.)... 

Experimentally, Thomas and coworkers found that hydrocarbon-coated gold nanoparticles, with a diameter of 3.5 nm, segregated to the interface between the microdomains of poly(styrene-btock-ethylene propylene) (PS-fe-PEP) copolymer, whereas larger hydrocarbon-coated silica nanoparticles (21.5nm in diameter) were located at the center of the PEP domains [79], In the absence of specific enthalpic interactions between the two types of nanoparticles and the polymer matrix, the result suggests a profound influence of entropic contributions to the self-organization process. For large particles, the decrease in conformational entropy of the respective polymer subchains after particle sequestration is dominant, whereas for smaller particles, the decrease in entropy is outweighed by the particle translational entropy. 

According to SEM (Figure 13.2), details on the skeletal framework remain visible, even after a bulk density increase by up to a factor of 3. The conclusion is that the skeletal silica nanoparticles have been coated conformally with polymer. This process is obviously limited by the amount of the gelation water remaining adsorbed on the skeletal framework, which in turn can be controlled to a certain extent by the number of precrosslinking washes... 

Silica nanoparticles have been widely used as fillers in the manufacture of coatings [103], rubber [104], plastics [105], binders [106], functional fibers [107], etc. In recent years, the preparation of organic-inorganic hybrid materials composed of polymers and functionalized silica nanoparticles has been widely investigated. The combination of organic polymer components with nanometer-sized silica fillers in a single material has extraordinary significance for the development of hybrid materials with unique properties. 

Apart from Au NPs, mesoporous silica nanoparticles (MSNs) have been modified with pH-responsive polymers to control the release of drugs [146-148]. MSNs have been coated with CS to prevent the release of the ibuprofen drug at neutral conditions (pH = 7.4) while promoting its release in acidic conditions (pH = 5) [148]. At pH = 7.4 CS forms a gel-like structure that is insoluble and hence is able to store the ibuprofen. On the other hand, when the pH drops below 6.3, the drug is released due to the protonation of the amino groups present on the polymer backbone, rendering the CS soluble. 

Xing, L. Zheng, H. Cao, Y Che, S. Coordination polymer coated mesoporous silica nanoparticles for pH-responsive drug release. Adv. Mater. 2012, 24, 6433— 6437. 

T. Nahum, H. Dodiuk, A. Dotan, S. Kenig and J. P. Lellouche. Superhydrophobic durable coating based on UV-photoreactive silica nanoparticles. J. Appl. Polym. ScL, 131,41122 (2014). 

---