Hydrophilic polymers, polymer brushes surface properties

In this chapter, a series of recent results in surface modification of various surfaces employing the macromolecular anchoring layer approach was overviewed. It was demonstrated that the approach could be used as a virtually universal method for grafting of functional polymer brushes. The properties of the bmshes can be controlled by polymer nature, structural and morphological factors, and external stimuli. The polymer grafting technique developed can be readily applied to surface modification of fibers and textiles, leading to generation of hydrophobic, hydrophilic and switchable fibrous materials. 

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... 

Other sensitive PEMs have been described which respond to different stimuli. Photosensitive multilayers were prepared using polyelectrolytes functionalized with photoisomerizable azobenzene chromophores. Barrett et al. have prepared sensors, the mechanical properties of which change under Hght irradiation [22]. Solvent-responsive polymer brushes have been prepared by anchoring two types of polymers (one hydrophobic and one hydrophilic) on a wafer surface. As a function... 

The combination of brushes with soft surfaces is clearly a key aspect of biological lubrication. However, it is less clear whether carbohydrates possess any specific or unique properties that are absent in other, synthetic brush-forming hydrophilic polymer chains. Moreover, natural lubricant additives appear to form hierarchical bottlebrush structures, such as that shown in the figure, more readily than the synthetic water-soluble brushes that have been investigated to date (9, 12, 14). The role of both the composition and struc-... 

We have previously demonstrated that hydrophilic polymer brushes can effectively reduce the interfacial friction in an aqueous environment under low-sliding-speed conditions.In those studies, we employed grafting to approaches to generate polymer brushes on a variety of substrates. By applying the grafting from method described in this work, the formation of high-surface-density polyelectrolyte brushes became feasible. To date, only little experimental work has been dedicated to the macroscopic lubrication properties of polymer brushes prepared with a grafting from method. ... 

We have stndied the macroscopic frictional properties of high-density polymer brushes prepared by surface-initialed ATRP of methyl methacrylate (MM A) [31] and hydrophilic methacrylates [32, 33] from silicon substrates. Friction tests were carried out using a stainless steel or glass ball as the sliding probe under a normal load of 100 MPa from the viewpoint of practical engineering applications. This chapter reviews the macroscopic frictional properties of polymer brushes under a high normal load, the dependence of solvent qnaUty, the effect of humidity on hydrophilic brnsh, and wear resistance, and we compare these with alkylsilane monolayers. 

Markedly, surface-initiated ATRP provides the opportunity to use a variety of functional monomers, to tailor the composition and thickness of the brushes, and to prepare multiple functional surfaces. For example, Zhang et al. prepared poly(methyl methacrylate) (PMMA), poly(acrylamide) (PAAM), and their diblock copolymer (PMMA/PAAM) on the surface of PET film by surface-initiated ATRP [59]. The results indicated that the surface properties of PET film were greatly improved by grafted polymer, the surface of PET film modified by PAAM was hydrophilic, and the surface of PET film modified by diblock copolymer was amphiphilic. This kind of modified PET film may be applied as biocompatible materials, amphiphilic functional film, or conductive film. 

Several types of surface forces determine the interactions across thin liquid films. In addition to the universal van der Waals forces, the adsorbed ionic surfactants enhance the electrostatic (double-layer) repulsion. On the other hand, the adsorbed nonionics give rise to a steric repulsion due to the overlap of hydrophilic polymer brushes. The presence of surfactant micelles in the continuous phase gives rise to oscillatory structural forces, which can stabilize or destabilize the liquid films (and dispersions), depending on whether the micelle volume fraction is higher or lower. These and other surface forces, related to the surfactant properties, were considered in Sec. VI. 

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