Isoelectric point adhesion

The isoelectric points of B cells and T cells are reported to be 3.8 and 4.6, respectively. This may explain the higher adhesivity of the former to the HA surface. For this reason, adhesivity of T cells are assumed to be more susceptible than B cells to the decrease in ionic character of the HA surface. 

Electrostatic charges due to ionized acidic or basic amino acids influence protein solubility. At extremes of pH, many poorly soluble proteins are dissolved and their molecular structures unfolded due to surplus of similar repelling charges. Gluten proteins have few charged groups and so are poorly soluble in neutral solution (15). Dispersions of other proteins must be adjusted to their isoelectric point or have salt added to optimize cohesion and adhesion. 

Figure 3. Determination of the isoelectric point of tin by adhesion method. Results are obtained by suspension of negative ( ) and positive ( ) latex particles [46].

Lin, X.Y. Farhi, E., and Arribart, H., Determination of the isoelectric point of planar oxide surfaces by a particle adhesion method, J. Adhesion, 51, 181, 1995. McCafferty, E. and Wightman, J.P., Determination of the surface isoelectric point of oxide films on metals by contact angle titration, J. Colloid Interf. Sci., 194, 344, 1997. 

In an investigation of epoxide joints on iron and titanium using y-APS as a primer, Boerio [39] concluded that although the film structures formed by y-APS adsorbed onto the two metals were very similar, the performance of the films as adhesion promoters was very different. He concluded that the performance was determined by the orientation of the APS molecules at the oxide surface rather than by the overall structure of the film. The orientation was determined by the isoelectric point of the oxide and the pH at which the films were adsorbed onto the oxide [39,40]. A comprehensive account of the structure of APS silane films is provided by Ishida and co-workers [41]. 

Zeta potential also serves for determination of isoelectric point (lEP), which is defined as the point at which the electrokinetic potential equals zero. It is also important characteristic for wrappers, for material for study of living cell adhesion, etc. Fig. 3 present zeta potential of several polymer foils as pH dependent. As it is clear, lEP of all polymer samples are obtained at pH ca 4. For this determination we have titrated samples by 0.1 mol/dm HCl in pH range from 7.0 to 2.5 [52]. 

If Eq. (in.l) is satisfied, the charge observed on the particles after detachment should be zero (isoelectric point), and the electrical component will not affect the value of the adhesive force. Experimental results show that in individual cases this condition is in fact satisfied. For example, the charge determined on removing dust from a metal substrate (copper) equals zero [70],... 

Figure 6.11 Measured peel energy for a pressure-sensitive adhesive (PSA) and pull-off force for poly (methyl methacrylate) (PMMA) versus the isoelectric point of the oxide film. Reprinted from McCafferty (2002), with permission...

The calculation of the separation force in water has assumed that only van der Waals and polar forces contribute to the adhesion. In water there is a possibility of electrical double layer forces reducing the adhesion. No attempt was made to determine the isoelectric point. It would appear from the close agreement between the measured and calculated values that in fact these forces are small for the PET in water. 

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