Poly brushes surface hydrophobicity

The adsorption of block copolymers can be controlled by different stimuli, in particular by the pH since most of the brushes formed by block copolymers adsorption are polyelectrolyte brushes [129, 130], The group of Armes, for instance, studied the pH-controlled adsorption of a series of block copolymers [131, 132], In the case of copolymers bearing hydrophobic 2-(diethylamino)ethyl methacrylate groups (DEA) and a water-soluble zwiterionic poly(2-methacryloyl phosphoryl-choline) (MPC) block, they showed that at low pH the cationic DEA flatted to the anionic silicon surface while the MPC was in contact with the solution [132], At around neutral pH, micelles were formed in solution and adsorbed onto the surface because the DEA core was still weakly cationic. The MPC block formed the micelle coronas. Nevertheless, at higher pH the micelles became less cationic and the adsorption rate decreased. 

Thermally responsive polymers, such as poly( V-isopropyl acrylamide) (NI-PAm), have also been studied extensively for applications related to those previously discussed [112], De las Heras et al. described the synthesis and patterning of NIPAm brushes on SAMs and their subsequent performance during temperature-dependent adhesion assays of BSA and Streptococcus mutans (Fig. 7). The authors employed p.CP to pattern features of hydrophobic hexadecanethiol and backfilled the surface with an initiator-functionalized alkanethiol. Polymer brushes were grown via surface-initiated atom transfer radical polymerization (ATRP). FITC-BSA was then... 

Recently, core-shell type microgels, which contain a hydrophobic core and a hydrophilic thermosensitive shell, have become attractive for scientists because such systems can combine the properties characteristic of both the core and the shell [53], We have prepared core-shell microgel particles consisting of a poly(styrene) core onto which a shell of polyCA-isopropylacrylamide) (PS-PNIPA) has been affixed in a seeded emulsion polymerization [54-56], In this case, the ends of the crosslinked PNIPA chains are fixed to a solid core, which defines a solid boundary of the network. In this respect, these core-shell latex particles present crosslinked polymer brushes on defined spherical surfaces. The solvent quality can be changed from good solvent conditions at room temperature to poor solvent conditions at a temperature... 

Figure 6. Interaction of a water droplet with 200 micron features of a patterned polymer brush prepared by surface-initiated polymerization. The unusual wetting profile is due to preferential interaction of the water droplet with the polymery lie acid) brush domains (light) and complete non-wetting of the hydrophobic poly(tert-butyl acrylate) domains (dark).

In some applications it is useful to have hydrophilicity in the bulk of the polymer instead of just at the surface. One way of doing this is by simultaneously end linking hydrophilic poly(ethylene glycol) (PEG) chains and hydrophobic PDMS chains. Another way is to make a PDMS network with a trifunctional organosilane R Si(OR)3 end linker that contains a hydrophilic R side chain, such as a polyoxide. Treating only the surfaces is another possibility, for example, by adding hydrophilic brushes by vapor deposition/hydrolysis cycles.Such hydrophilic polysiloxanes can also serve as surfactants. It has also been possible to make radially layered copolymeric dendrimers with hydrophilic polyamidoamine interiors and hydrophobic organosilicon exteriors. " ... 

Brzozowska et al. [18] reported on the stability of the polymer brushes formed by adsorption of ionomer complexes on hydrophilic and hydrophobic surfaces. The ionomer complexes or micelles consisted of oppositely charged polyelectrolyte blocks (poly(acrylic acid) and poly(N-methyl-2-vinyl pyri-dinium iodide)), and a neutral block (poly(vinyl alcohol)) or neutral grafts (poly(ethylene oxide)). The results showed that adsorbed micellar layers were relatively weakly attached to hydrophobic surfaces and much stronger... 

A variant on the grafting method is to use a diblock copolymer made out of two distinct blocks, as shown in Fig. 3c. The first block is insoluble and is attracted to the substrate, and thus acts as an anchor fixing the chain to the surface it is drawn as a thick line in Fig. 3c. It should be long enough to cause irreversible fixation on the surface. The other block is a soluble one (the buoy ), forming the bmsh layer. For example, fixation on hydrophobic surfaces from a water solution can be made using a polystyrene-poly(ethylene oxide) (PS-PEO) diblock copolymer. The PS block is insoluble in water and is attracted towards the substrate, whereas the PEO forms the brush layer. The process of diblock copolymer fixation... 

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