Adsorption, polymer surface

Madey and co-workers followed the reduction of titanium with XPS during the deposition of metal overlayers on TiOi [87]. This shows the reduction of surface TiOj molecules on adsorption of reactive metals. Film growth is readily monitored by the disappearance of the XPS signal from the underlying surface [88, 89]. This approach can be applied to polymer surfaces [90] and to determine the thickness of polymer layers on metals [91]. Because it is often used for chemical analysis, the method is sometimes referred to as electron spectroscopy for chemical analysis (ESCA). Since x-rays are very penetrating, a grazing incidence angle is often used to emphasize the contribution from the surface atoms. 

In the following paper, the possibility of equilibration of the primarily adsorbed portions of polymer was analyzed [20]. The surface coupling constant (k0) was introduced to characterize the polymer-surface interaction. The constant k0 includes an electrostatic interaction term, thus being k0 > 1 for polyelectrolytes and k0 1 for neutral polymers. It was found that, theoretically, the adsorption characteristics do not depend on the equilibration processes for k0 > 1. In contrast, for neutral polymers (k0 < 1), the difference between the equilibrium and non-equilibrium modes could be considerable. As more polymer is adsorbed, excluded-volume effects will swell out the loops of the adsorbate, so that the mutual reorientation of the polymer chains occurs. 

Moreover, the interaction of the surface of the fillter with the matrix is usually a procedure much more complicated than a simple mechanical effect. The presence of a filler actually restricts the segmental and molecular mobility of the polymeric matrix, as adsorption-interaction in polymer surface-layers into filler-particles occurs. It is then obvious that, under these conditions, the quality of adhesion can hardly be quantified and a more thorough investigation is necessary. 

Adsorption The first stage, applying when a polymer contacts a fluid, is that the latter adsorbs into the polymer surface, reaching equilibrium solubility here. 

The performance of stabilisers in respect of their physical persistency can also be improved by physical adsorption on surfaces of reinforcing fillers, e.g. of CB or amorphous microground silica [589]. Mineral fillers are well known to adsorb polymer additives, especially stabilisers necessary for processing and... 

The effects of calcium on polymer-solvent and polymer-surface interactions are dependent on polymer ionicity a maximum intrinsic viscosity and a minimum adsorption density as a function of polymer ionicity are obtained. For xanthan, on the other hand, no influence of specific polymer-calcium interaction is detected either on solution or on adsorption properties, and the increase in adsorption due to calcium addition is mainly due to reduction in electrostatic repulsion. The maximum adsorption density of xanthan is also found to be independent of the nature of the adsorbent surface, and the value is close to that calculated for a closely-packed monolayer of aligned molecules. 

Bale, M.D., Danielson, S.J., Daiss, J.L., Goppert, K.E., and Sutton, R.C. (1989) Influence of copolymer composition on protein adsorption and structural rearrangements at the polymer surface. J. Colloid Interface Sci. 132, 176-1874. 

One interesting development in the carbon nanotube-based electrochemical sensor is the ability to self-assemble the CNT to other types of nano materials such as gold and silver nanoparticles or to a polymer surface. The enhancement of Raman signals of carbon nanotubes through the adsorption on gold or silver substrate has been also reported [142-146],... 

Szleifer I (1997) Protein adsorption on surfaces with grafted polymers a theoretical approach. Biophys J 72 595-612 Tanford C (1973) The hydrophobic effect. John Wiley Sons, Inc., Hoboken Van Dulm P, Norde W, Lyklema J (1981) Ion participation in protein adsorption at solid surfaces. J Colloid Interf Sci 82 77-82 Zoungrana T, Findenegg GH, Norde W (1997) Structure, stability and activity of adsorbed ensymes. J Colloid Interf Sci 190 437-448 Zoungrana T, Norde W (1997) Thermal stability and enzymatic activity of a-chymotrypsin adsorbed on polystyrene surfaces. Colloid Surf B 9 157-167... 

Of course, many investigators have realised that changes in solvent may not only affect the x parameter, but also the effective polymer/surface interaction, expressed by the adsorption... 

An adsorption-desorption transition is illustrated schematically in Figure 1, where we plot a displacement isotherm, i.e. the adsorbed amount of a polymer as a function of the composition of a mixture of solvent and displacer. At the left in Figure 1, where the concentration of displacer is low, the polymer surface excess is positive. As we increase the proportion of displacer in the mixture, we observe a decrease in the adsorbed amount. At a certain composition the adsorbed amount of polymer becomes zero. The concentration at which the polymer surface excess just vanishes will be denoted as the critical displacer concentration cr. Beyond 4>cr, the surface excess of the polymer is negative (and very small if the polymer concentration is low). 

Smooth and uniform polymer surface after vacuum plays a key role to ensure good OFRR sensing performance. We have observed in experiments that toluene after vacuum is prone to leave a number of cavities of a few micrometers in diameter on the surface. These cavities will induce additional scattering loss for the WGMs in the OFRR, which greatly degrade the g-factor, and hence the detection limit of the OFRR vapor sensor. Moreover, these small cavities have different adsorption characteristics compared to smooth polymer surface. Vapor molecules may be retained for a longer time at the cavity, which increases the response time and recovery time. Acetone and methanol are found to be better candidates for solvents because they usually leave uniform and smooth surface after vacuum. 

Antrade, J. D., Principles of protein adsorption, In Surface and Interfacial Aspects of Biomed ical Polymers Antrade, J. D., Ed. Plenum Press, New York, 1985, Vol. 2... 

These results were extended by Tilton et a/.(n8) to adsorption of eosin-labeled BSA on polymer surfaces. They also found a component that surface diffuses, with coefficients ranging from 1.2 x 10 9 to 2.6 x 10 9cm2/s, depending on surface type. In this study, intersecting TIR laser beams rather than a focused stripe were used to define the spatial intensity variation. Surface diffusion was even noted for the most irreversibly adsorbed eosin-labeled BSA components this was evident on samples rinsed for long periods with unlabeled BSA after exposure to eosin-labeled BSA. The surface diffusion coefficient of the irreversibly bound BSA was found to be a strong function of adsorbed concentration.(n9)... 

Weber N, Bolikal D, Bourke SL, Kohn J (2004) Small changes in the polymer stmcture influence the adsorption behavior of fibrinogen on polymer surfaces validation of a new rapid screening technique. J Biomed Mater Res Part A 68A 496-503... 

For fused silica the magnitude of the EOF is controlled by the pH value of the electrophoretic buffer used. At high pH where the silanol groups are predominantly deprotonated, the EOF is significantly greater than at low pH (pH < 4) where they become protonated. Depending on the specific conditions, the EOF can vary by more than one order of magnitude between pH 2 and pH 12. In nonionic materials such as Teflon and other polymers, electroosmotic flow is also encountered. The electrical double layer in this case results from adsorption of buffer anions to the polymer surface. 

R. G. Lee, S.W. Kim, Adsorption of protein onto hydrophobic polymer surfaces adsorption isotherms and kinetics, J. Biomed. Mater. Res. 8 (1974) 251-259. 

Surface free radicals are assumed to be produced by the dissociation of bonds at the polymer surface as well as by the adsorption of radicals from the gas phase. New polymer is formed by the recombination of surface and gas phase free radicals. Within the context of this model, the rate of polymerization should depend upon the rates at which surface and gas phase free radicals are produced. The influence of the discharge frequency on the rates of these processes can now be examined. 

Partial results of the calculation are cited in Table 2, which shows that the work of adhesion is expressed as a bell-shape curve. In other words, the maximal adsorption of protein takes place on polymer surface having intermediate hydrophilicity. Ikada et al. confirmed this by the results of BSA adsorption on 8 polymer surfaces [12], and also by those of albumin and fibronectin adsorption on 13 polymer surfaces [14]. L-Cell attachment also showed a bell-shape profile [15],... 

Peppas et al. [16] presented a new method for calculating protein adsorption on polymeric surfaces. In their model, protein adsorption is regarded as an equilibrium reaction, which takes place on the polymer surface in competition with the adsorption of water. 

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