Surface dynamics hydrophilic polymers

A current hypothesis, which is receiving considerable attention, is that one can indeed produce a surface which actively repels proteins and other macromolecules123 124, 133). The basic idea is presented in Fig. 25, which shows that a neutral hydrophilic polymer, which exhibits considerable mobility or dynamics in the aqueous phase, can actively repel macromolecules from the interface by steric exclusion and interface entropy methods. This method has been well-known and applied in the field of colloid stability for many years 120). The most effective polymer appears to be polyethylene oxide, probably because of its very high chain mobility and only modest hydrogen bonding tendencies 121 123>. 

Whether a polymer is hydrophilic or hydrophobic can be explained by the X interaction. However, why the air/hydrogel interface of a gelatin hydrogel is hydrophobic cannot be explained by x interaction because it is a strictly interfacial phenomenon that is governed by the interfacial interaction. The strictly interfacial phenomena could be explained by 7 interaction. The first term in Eq. (25.1) is x interaction and the second term is 7 interaction. The overall rate of surface dynamic change is, therefore, dependent on both 7 interaction and x interaction [7]. Thus,... 

There are differences in the surface of the laser-ablated polymer depending on the mode of operation, static and dynamic laser ablation mode. Rossier et al. investigated differences in surface states of polymer PET as a result of these two modes of ablation [18], Their studies revealed that the static ablation mode produced a homogeneous and hydrophobic surface with poor wettability, whereas the dynamic ablation mode produced an inhomogeneous and hydrophilic surface with high wettability. These differences were attributed to the redeposition of fragments. 

They used amphiphilic methacrylate polymer with a ternary amino group, poly(A,A-diisopropylaminoethyl methacrylate (DlPAM)-co-n-decyl methacrylate (DMA)) (PDD), composed of 25 unitmol% of DMA in the polymer as a polymeric additive to SPU. The content of the PDD in the SPU was in the range of 1-5 wt%. The surface characteristics of the SPU/PDD polymer alloy were examined by XPS and dynamic contact angle measurements with water. These evaluations revealed that the PDD was located on the surface of the polymer alloy. This induced a more hydrophilic and movable surface compared with untreated SPU. Protein adsorption from human plasma was also reduced on the surface of the SPU/PDD polymer alloy. During the blending process, the solubility of the polymer added to the SPU is important. The solubility parameter of the polymer is one of the factors used to estimate the blending state of both polymers. 

Another example of the type of information that can be extracted from electrokinetic data is the hydro-dynamic thickness of ion-penetrable surface layers, e.g. surface-bound, neutral, hydrophilic polymers such as polyethers and polysaccharides (11). Surface-bound, neutral, hydrophilic polymers are known to dramatically reduce protein adsorption. The passivity of these surfaces has been attributed to steric repulsion, bound water, high polymer mobility, and excluded volume effects, all of which render adsorption unfavourable. Consequently, these polymer-modified surfaces have proven useful as biomaterials. Specific applications include artificial implants, intraocular and contact lenses, and catheters. Additionally, the inherent non-denaturing properties of these compounds has led to their use as effective tethers for affinity ligands, surface-bound biochemical assays and biosensors. 

The eluent compatibility of a polymeric adsorbent will be dependent upon the chemical structure of the polymer backbone, chemical type of the cross-linking agent, degree of cross-linking, and any subsequent covalent or dynamic modifications carried out. The natural polysaccharide polymers in their native state are hydrophilic and are therefore compatible with aqueous eluents whereas the synthetic polymers can be hydrophobic, as in the case of polystyrene, and hence compatible with organic eluents, or hydrophilic, as in the case of polyacrylamide, and so be compatible with aqueous mobile phases. It is of course possible to modify the eluent compatibility of a polymeric matrix by surface coating or derivatisation. For example, the very hydrophobic maeroporous polystyrene matrices may be coated with a hydrophilic polymer to make ion exchange adsorbents or materials suitable for aqueous size separations [25]. 

Dynamic hysteresis is caused largely by the change of meniscus shape during a transition stage. Therefore, a hydrophobic surface shows the larger separation of the immersion line and the emersion line than a hydrophilic surface as seen in Figure 26.16, which depicts dynamic hysteresis for untreated, TMS-treated, and (TMS + 02)-treated polymer films. However, dynamic hysteresis is probably not maximal with TMS treatment. 

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