Factors Controlling the Growth of Polyelectrolyte Multilayers

Abstract

The dependence of polyelectrolyte multilayer thickness on salt concentration, salt type, solvent quality, deposition time, and polymer concentration is evaluated. Polymers are deposited on spinning silicon wafers. For the strong polycation/polyanion pair studied, film thickness is approximately proportional to the number of layers and the salt concentration. The irreversibility of overall molecule adsorption is indicated by the lack of exchange of surface (radiolabeled) for solution polymer. The hydrophobic nature of the driving force for polymer sorption is illustrated by the choice of salt counterion or solvent. Analyzed within the framework of ion exchange, the net energy of ion pair formation is not high, at most a few kT. Salt, competing with polymer segments for the surface, permits localized rearrangements. In the mechanism proposed, excess polymer is accommodated within several layers, rather than in one layer of loops and tails. Steric barriers coupled with slow conformational changes are responsible for long-term polymer adsorption. Considering the disorder and interpenetration, multilayer buildup has much in common with solution phase or coprecipitated polyelectrolyte complexes. Surface hydrophobicity can be enhanced using fluorinated surfactants as counterions.

Differentiation of MC3T3-E1 on poly(4-styrenesulfonic acid-co-maleic acid)sodium salt-coated films

“…In contrast, PSS, a strong anionic polyelectrolyte, possesses a number of negative charges along its backbone chain. Due to their strong ionic charges, both PDADMAC and PSS have been used as the polyelectrolytes for PEM preparation [22][23][24][25] . Since the hydrophobic ring structure of PDADMAC polycations is stiff and consequently difficult to rotate both in water and in air, the outer layer containing the quaternary ammonium end groups will stay hydrophilic both in water and in air.…”

NMR Studies of the Effect of Adsorbed Water on Polyelectrolyte Multilayer Films in the Solid State

“…5 Using techniques such as X-ray and neutron reflectivity, it has been found that binary films of polyelectrolytes resemble polyelectrolyte complexes (PEC), particularly for thick films, as a result of the high amount of interpenetration of the layers. [6][7][8][9] While it is widely accepted that adsorbed water could have a large influence on the behavior of the film, neutron reflectivity is unable to observe it directly, although it has been incorporated into models for the data. 6 Thus, only a few studies so far have been able to probe the behavior of water in the films, [10][11][12] and none have probed it directly in the solid state.…”

Photoresponsive Block Copolymer Photonic Gels with Widely Tunable Photosensitivity by Counter‐Ions

“…[8][9][10][11][12][13] Because the degree of charge dissociation in polyelectrolytes is dependent on the types of ion-pairs, the physical properties of polyelectrolyte hydrogels such as conductivity, elasticity and swelling ratio are affected by counterions as well as external stimuli. [14][15][16][17] Recently, there have been increasing research efforts of combining hydrogels with other functional materials to extend their potential applications. For example, the photonic crystals comprising hydrogels exhibit unique tunable photonic band gaps in response to the various stimuli including temperature, pH, ionic strength, solvent compositions and electric fi eld.…”