Interaction between adsorbed polyelectrolytes

In this paper we briefly describe the apparatus and experimental method, then consider the interactions between i) layers of polystyrene in cyclohexane under poor-solvent and ii) 0 - solvent conditions,iii) the interactions between adsorbed PEO layers in a good (aqueous) solvent and iv) the surface forces between layers of adsorbed poly-L-lysine, a cationic polyelectrolyte, in aqueous salt solutions. We consider briefly the implications of our results for the current theoretical understanding. 

According to the polyelectrolyte character of ODNs, the effect of salt concentration on adsorption should be considered. Indeed, the ionic strength affects (i) the electrostatic interactions between the ODN and the adsorbent and (ii) the lateral repulsive electrostatic interactions between adsorbed ODNs. 

The SBH microparticles were encapsulated within polymer films by the LBL self-assembly of oppositively charged polyelectrolytes (PEI and PABA). The polymer nanofilms fabrication was performed using dichloromethane as a working media. IR-spectroscopy was applied to investigate the chemical interaction between the polyelectrolytes. For preparation of the microcontainers, SBH powder was dispersed in DCM. PABA and PEI were adsorbed sequentially onto the surface of SBH particles. Finally, SBH particles were coated with three double layers of PABA and PEI. 

The coefficients a(p, c) and tj(p, c) describe chemical and physical effects on the kinetics of deposition. The transport of particles from the bulk of the flowing fluid to the surface of a collector or media grain by physical processes such as Brownian diffusion, fluid flow (direct interception), and gravity are incorporated into theoretical formulations for fj(p, c), together with corrections to account for hydrodynamic retardation or the lubrication effect as the two solids come into close proximity. Chemical effects are usually considered in evaluating a(p, c). These include interparticle forces arising from electrostatic interactions and steric effects originating from interactions between adsorbed layers of polymers and polyelectrolytes on the solid surfaces. 

Dahlgren, M. A. G., Waltermo, A., Blomberg, E., Claesson, P. M., Sjdstrdm, L., Akesson, T. and Jdnsson, B., Salt effects on the interaction between adsorbed cationic polyelectrolyte layers - theory and experiment, J. Phys. Chem., 97, 11769-11775 (1993). 

Kjellin, U. R. M., Claesson, P. M. and Audebert, R., Interactions between adsorbed layers of a low charge density cationic polyelectrolyte on mica in the absence and presence of anionic surfactant, J. Colloid Interface Sci., 190, 476-484 (1997). 

The adsorption of polyelectrolytes onto surfaces can be considered quasi-irre-versible and it is possible to assume that once the polyelectrolyte chains are attached to the siuface they remain adsorbed [83]. The chemical nature of the polyelectrolytes, and the assembling conditions play a key role in the assembling of polyelectrolyte multilayers, and on their thickness, structure and properties [84, 85]. More specifically, the hydropholic/hydrophobic balance of the chains is probably the most important factor that affects to the PEMs formation because it determines both the interaction between the polyelectrolytes and the swelling degree of the chains [95]. The effect of the increase of the polymer hydrophobicity on the adsorption of polyelectrolytes is mediated by the existence of a unfavourable contribution to the solvation energy of the chains [86]. Another key variable is the flexibility of the polymer chains. This parameter plays a key role in the interaction between the chains and the adsorbed layers [87]. 

Adsorption of block copolymers onto a surface is another pathway for surface functionalization. Block copolymers in solution of selective solvent afford the possibility to both self-assemble and adsorb onto a surface. The adsorption behavior is governed mostly by the interaction between the polymers and the solvent, but also by the size and the conformation of the polymer chains and by the interfacial contact energy of the polymer chains with the substrate [115-119], Indeed, in a selective solvent, one of the blocks is in a good solvent it swells and does not adsorb to the surface while the other block, which is in a poor solvent, will adsorb strongly to the surface to minimize its contact with the solvent. There have been a considerable number of studies dedicated to the adsorption of block copolymers to flat or curved surfaces, including adsorption of poly(/cr/-butylstyrcnc)-ft/od -sodium poly(styrenesulfonate) onto silica surfaces [120], polystyrene-Woc -poly(acrylic acid) onto weak polyelectrolyte multilayer surfaces [121], polyethylene-Wocfc-poly(ethylene oxide) on alkanethiol-patterned gold surfaces [122], or poly(ethylene oxide)-Woc -poly(lactide) onto colloidal polystyrene particles [123],... 

Using a self-consistent field theory, Varoqui et al. [46] calculated the segment density profile of polyelectrolyte molecules adsorbed on one plate and Podgomik [9] extended the procedure to the interaction between two plates. 

The decrease in the amount of polyelectrolyte adsorbed on the silica surface whilst increasing the salt concentration is in contrast to results obtained for adsorption of poly(diallyldimethylammonium chloride) on different silica samples [75, 76]. Probably the chloride ions shield the segment-segment interactions between charged groups inside the coil of an individual polyelectrolyte chain and the silica surface [77-80]. This explanation is also consistent with the assumption that electrostatic forces determine the adsorption mechanism of PVFA-co-PVAm chains on silica. 

Meagher. L., Maurdev, G., and Gee, M.L., Interaction forces between a bare silica surface and an a-alumina surface bearing adsorbed polyelectrolyte and surfactant, Langmuir, 18, 2649, 2002. 

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