PVP brush

In the case of dense, surface-grafted polymer brush thin hlms, cross-links are introduced by the simple addition of solutions containing bis(Pd -pincer) compounds 4a or 4b to grafted PVP brushes (Loveless et al. 2006). Because the association constants for pyridine coordination are similar, the uptake of 4a and 4b from equimolar solutions into the PVP brushes (at constant grafting density and molecular weight) is effectively equivalent, producing samples with comparable structure (number and placement of cross-links). 

Fig. 13 (above) Waveguide-spectra (p-polarization) of a 490 nm thick PVP brush on a LaSFN9/Au/SiOx substrate, and the same sample at a constant relative humidity of 70% after quaternization with methyl iodide (MePVP, thickness 870 nm) (below) FTIR detail spectrum of a PVP brush attached to both sides of a silicon wafer, and the same sample after the polymer-analogous quaternization... 

Table 6 Light-scattering and IR characterization of cylindrical polyelectrolyte brushes prepared by quaternization of PVP brushes...

In Situ Infrared Spectroscopy, Fig. 1 Infrared PAA-PVP brush has a thickness of 11 nm. A sketch... 

It should be mentioned that no equilibrium structures (neither in methanol nor in DMF) have been obtained so far with plasmid and various linear DNA-surfactant complexes and cylindrical PVP brushes [154]. 

Fig. 19 Switching of the water contact angle of the gradient PAA-mix-PVP brush ra. composition (upper X-axis) and location of the probing drop on the sample (lower Z-axis) upon exposure to water of different pHs(( )pH = 2,(O)pH = 2.5,(A)pH = 5,(D)pH = 9,(B)pH = 10). ...

The fabrication of a polyvinylpyridine (PVP) brush inside a single PET nanopore by surface-initiated free radical polymerization [8]... 

The above-described (see Section 18.6) polyvinylpyridine (PVP) brush functionalized with the Os(dmo-bpy)2Cl redox centers was used to generate the pH-switchable interface capable of mediating electron transport with enzymes only being in the ON state at pH < 4.5 [30]. Laccase is a well-known enzyme frequently... 

AFM studies on the thin ( 50 nm) brush layers demonstrate that the dynamics of supramolecular cross-links contribute to the friction of the soft brush surfaces (Fig. 3.11). When the faster 4a cross-linker is added, both the absolute friction values and the coefficient of friction (COF) drop to 30% of those of the uncross-linked PVP control. When the slower cross-linker 4b is added, however, the absolute friction value and the COF increase dramatically both the COF and the absolute friction values for PVP 4b are more than twice that of PVP alone. The absolute lateral force measured is proportional to the normal force applied this is consistent with the model that the more the tip is pressed into the brush layer the more force it takes to drag it laterally through the brushes. 

The effect of the interdigitation between the polymer chains of two brushes on the interaction force profile is plotted in Fig. 8 for three polymers PVP-PI 69-39, PVP-PI 38-69, and PS-X (140 K). The solid curves present the results in which the interdigitation was taken into account, while the dashed ones those in which the interdigitation was neglected. For the former, the chain conformational partition function [Eq. (5)] involves a 2mX2m supermatrix G for which the chain free ends can be located in any lattice layer between the two surfaces. For the latter, the conformational partition function involves a m X in supermatrix G with chains con-... 

Three homopolymer (diblock copolymer) phase boundary systems have been studied extensively the system of polystyrene (PS) and poly(2-vinylpyridine) (PVP) reinforced with diblock copolymers ofPS-PVP [22,25,28,31-33], the system of poly(methyl methacrylate) (PMMA) and PS reinforced with diblock copolymers of PMMA-PS [17,24,34,35] and the system of PMMA and poly(phe-nylene oxide) (PPO) reinforced by diblock copolymers of PMMA-PS [ 14,36,37]. Phase boundaries between PS and a crosslinked epoxy (XEp) were reinforced with carboxy-terminated PS chains whose -COOH ends reacted with either excess amines or epoxy to form a grafted brush at the interface [38,39]. In a similar manner, interfaces between rubber-modified PS (HIPS) and XEp reinforced with grafted PS-COOH chains have been investigated [40]. 

Fig. 36. Comparison of the Cjl values at multilayer coverage for the PS-b-PMMA diblock at a PPO/PMMA interface ( ), where failure occurs through the PS lamella, with the C]t maximum observed for the PS-fo-PVP diblock at a PS/PVP interface ( ), where failure occurs in the brush. Data from [37]...

Recently, pH-responsive redox brushes have been described by Katz and Minko [61]. It has been shown that the electrochemical response of PVP-Os grafted to ITO completely disappears when going from pH 4 to pH > 6, which was attributed to film collapse due to deprotonation of pyridine units. The same effect was not observed for randomly adsorbed polyelectrolytes. 

Fig. 41. The segmental interaction parameter %AP between the anchoring block (PVP) of the dPS (N=597)-PVP copolymer and the seven different P-mer PS host matrix molecules, as obtained from fitting the segregation data by Dai and Kramer [253] with mean field models describing dry-wet (O) and dry-dry ( ) double brush layer at the PS//PVP interface...

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