Counteranion-Controlled Properties of Polyelectrolyte Multilayers

Abstract

Polyelectrolyte multilayers consisting of poly(diallyldimethylammonium chloride) (PDADMA) and poly(sodium 4-styrenesulfonate) (PSS) were studied on a quartz crystal microbalance (QCM) utilizing a novel method to determine the elastic properties of the films. Since the multilayer was found to consist of a hard core and soft outer layer, as can be realized on the basis of the multilayer zone model, the multilayer films were made thick enough to reveal the elastic properties of the bulk material of the film. Several hundreds of layers were deposited using a fully automated multilayer deposition machine. We found out that, in addition to the increase in the bilayer mass, a remarkable increase of stiffness of the polyelectrolyte multilayer was observed while changing the counteranion used in the deposition process. The increase of stiffness was found to be comparable to the glass transition of common polymers. The increase is attributed to the counteranions that take part in polyelectrolyte charge compensation. The correlation of storage shear modulus and mass density to the hydration entropy of the anion could be clearly observed.

Multiple Functionalities of Polyelectrolyte Multilayer Films: New Biomedical Applications

“…Ions from the Hofmeister series, a classification of ions going from cosmotropic (water structure making, highly hydrated ions) to chaotropic (water structure disrupting, weakly hydrated ions), were used in several studies to assess the importance of the ion type. It was found that thickness, [49] stiffness, [50] and swelling behavior [51] could all be modified by changing ion type.…”

“…[98,99] Several other methods, relying on different physical principles, are well suited to characterizing thin films, some of them in a liquid state. These include quartz crystal microbalance, [50,100] piezo-rheometry, [101] resonance frequency, [102] bulging tests, [103] the pendant drop technique, [104] osmotic pressure, [105] or the capillary wave technique [106] in the case of free-standing films. The stiffness of PEM can be modulated from a few kPa to several GPa depending on the structural properties of the polyelectrolytes, but also on the degree of cross-linking inside the film.…”

Recent developments in the properties and applications of polyelectrolyte multilayers

“…This picture has changed over the past few years as several innovative mechanical testing methods, such as the quartz crystal microbalance [23], capillary wave techniques [24] ], PEMUs showed aspects reminiscent of both rubber-like and glass-like materials, with a broad elastic modulus ranging from 0.00001 to 12 Gpa [29,30].…”

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.…”