Polyelectrolyte shell

Scheme 4. Synthetic routes for a silica particle with hyperbranched polymer shell (a) and branched polyelectrolyte shell (b)...

Germain M, Balaguer P, Jc N et al (2006) Protection of mammalian cell used in biosensors by coating with a polyelectrolyte shell. Biosens Bioelectron 21 1566—1573... 

Sukhorukov GB, Brumen M, Donath E, Mohwald H. Hollow polyelectrolyte shells exclusion of polymers and donnan equilibrium. Journal of Physical Chemistry B 1999, 103, 6434-6440. 

Mesoporous Particles with Polyelectrolyte Shell as Nanocontainers for Inhibitors... 

Mesoporous silica containers can be used as inhibitor hosts with controlled release properties triggered at the beginning of the corrosion process in response to local pH changes. For instance, mesoporous silica nanoparticles covered with polyelectrolyte layers can be loaded with an inhibitor (2-(benzothiazol-2-ylsulfanyl)-succinic acid) prior to introduction into a hybrid zirconia-silica sol-gel film. This hierarchical design avoids spontaneous release of the inhibitor by the formation of a polyelectrolyte shell over the container s outermost surface. 

The pH sensitivity of halloysite can be enhanced by using retardant polymers, a cationic coating for the formation of a pH-sensitive polyelectrolyte shell on the nanotubes after their saturation with corrosion inhibitor. To equip the halloysite nanotubes with controlled release properties, the surface of the nanotubes was first loaded with benzotriazole and subsequently modified by LbL deposition of two polyelectrolyte bilayers, thus blocking the tubes openings with polyelectrolytes. 

To make the containers sensitive to IR laser light, preformed silver nanoparticles were directly incorporated into the polyelectrolyte shell. For this purpose, AgNPs were added into solutions of polyelectrolytes for LbL deposition and hence fixed between the polyelectrolyte layers. The AFM images of the resultant nanocontainer-impregnated him showed a uniform distribution of the containers over the coating, with the concentration of the silica containers equalling 107 containers per meter squared. 

In dilute aqueous solutions, polyelectrolyte block copolymers self-assemble into micelles consisting of a hydrophobic core and a polyelectrolyte shell. The study of their structural properties is expected to provide a basic understanding of the properties of dense polyelectrolyte layers, electro-steric stabilization mechanisms, and actuator functions based on variations in the electrostatic interactions. 

Fig. 2 TEM-image of spherical polyelectrolyte block copolymer micelles (PB-P2VP.MeI). The pronounced contrast of the polyelectrolyte shell is due to the counterions (I-) [19]...

From SANS-experiments it is possible to determine the ionic strength inside the polyelectrolyte shell, cs nt. Its dependence on the added salt concentration is shown in Fig. 7 [49]. 

Fig. 7 Ionic strength of the micellar polyelectrolyte shell as a function of added salt concentration. The solid line is a fit to a simple Donnan equilibrium as described by Eq. (2) [49]...

This is the dependence expected for purely electrostatic stabilization of polyelectrolyte layers. Electro-steric interactions involve steric contributions [Eq. (3)] and electrostatic contributions [Eq. (4)]. For high ionic strength as in the interior of the polyelectrolyte shell the measured shear modulus should exhibit a characteristic G (r) e Kr-dependence which is apparent in a semi-logarithmic presentation of the data as in Fig. 13. The measured shear moduli are plotted as a function of the reduced distance r/2Rm which is... 

Here, dichloromethane (DCM) was used as a solvent for performing LbL nanoassembly onto the surface of sodium borohydride (SBH) particles. The polyelectrolytes chosen for LbL self-assembly are polyethyleneimine (PEI) and poly(acrylonitrile-co-butadiene-co-acrylic acid) (PABA) as polycation and polyanion, respectively. It was observed that microparticles of SBH coated with a polyelectrolyte shell are more stable in the open atmosphere as compared to pure SBH. 

The release characteristics of nanocontainers with the polyelectrolyte shell (Fig. Ic) were studied in aqueous neutral solutions under laser irradiation. It is seen from Fig. Id that under the dark conditions the release of eneapsulated BSA is almost completely suppressed. The release of BSA under IR laser irradiation was observed for Si02- and Ti02-based containers modified with Ag nanoparticles, while only Ti02-based containers (both bare and silver-modified ones) exhibit switching into the open state under UV irradiation. It is seen from Fig. Id that the UV-induced release appears to be especially effective in the case... 

Figure 1. (a) SEM image of porous Ti02 cores (b) SEM image of porous SiOi cotes (c) SEM image of porous TiOi cores with the polyelectrolyte shell (d) kinetic curves for the release of BSA from TiOj. Ag/PEI/PSS/PEl/PSS containers with pdydectrolyte shell at neutral pH (1) widiout irradiation, (2) under IR-laser irradiation, (3) under UV-irradiation, (4) from TiOz containeis with polyelectrolyte shell at neutral pH under UV-irradiation. 

By contrast, opening of polyelectrolyte nanocontainers with silver-modified TiOz cores results from the photothermal transitions in the polyelectrolyte shell. Similar mechanism is responsible for the opening of SiOz-based containers with silver nanoparticles incorporated directly into the polyelectrolyte shell. The possibility of selective light-addressable opening of containers embedded into the SiOxiZrOx matrix was confirmed with the use of... 

Four (PtS/AlA) bilayers were formed on the calcium carbonate cores as described above. The initial cores are monodisperse and have a spherical form with the diameter of approximately 3 pm (Fig. la). A direct evidence for polyelectrolyte (PtS/AlA)4 coating of the matrix is provided in the corresponding fluorescence image (Fig. lb). It shows the distribution of fluorescence due to rhodamin C, which is adsorbed in the polyelectrolyte shell. The appearance of fluorescent rings confirms that the dye molecules interact only with the (PtS/AlA)4 multilayer coating and do not penetrate into the interior of the CaC03 cores. The multilayer coatings on the carbonate cores were stable for several days when stored in the aqueous medium at pH 5.5. 

Energy-transfer measurements have also provided an insight into the structure of amphiphilic block copolymer micelles with hydrophobically modified polyelectrolyte shells [172]. 

Furthermore, porous CPs (e.g., polypyrrole, polyanUine) films have been used as host matrices for polyelectrolyte capsules developed from composite material, which can combine electric conductivity of the polymer with controlled permeability of polyelectrolyte shell to form controllable micro- and nanocontainers. A recent example was reported by D.G. Schchukin and his co-workers [21]. They introduced a novel application of polyelectrolyte microcapsules as microcontainers with a electrochemically reversible flux of redox-active materials into and out of the capsule volume. Incorporation of the capsules inside a polypyrrole (PPy) film resulted in a new composite electrode. This electrode combined the electrocatalytic and conducting properties of the PPy with the storage and release properties of the capsules, and if loaded with electrochemical fuels, this film possessed electrochemically controlled switching between open and closed states of the capsule shell. This approach could also be of practical interest for chemically rechargeable batteries or fuel cells operating on an absolutely new concept. However, in this case, PPy was just utilized as support for the polyelectrolyte microcapsules. 

Studies of Reference Systems of Nonmodified Weak Polyelectrolyte Shells in Solutions with Low Ionic Strength... 

In Figure 3, the curves 1, 2 shows the ratio R dependences on pH value for free fluorescent dye in comparison with SNARF-1 dextran capsules. The calculation of pK values (Figure 4, the curves 1,2) has demonstrated that for encapsulated e it is less, than for the free dye solution. It is reasonable to assume that this effect is the result of the interaction between SNARF-1 dextran and polyelectrolyte shell, notably with PAA, because they have opposite charges. 

Thus, if the pH is less than the isoelectric point (p/ 4.7), a protein is positively charged, while the inner layer of polyelectrolyte microcapsules is presented as a polycation, the protein molecules are distributed throughout its volume. Protein molecules lose their chaige values near the isoelectric point and are concentrated in the wall space of the capsule due to hydrophobic interactions with a polyelectrolyte shell. If the polyanion PSS was nsed as the first layer in the formation of a shell, the protein at all pH valnes in the range stndied was located in the wall space (Figure 3). We attribute this to the electrostatic interaction between protein molecules and the polyelectrolyte at low pH and hydrophobic interactions in the region of the isoelectric point. 

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