Polyelectrolyte gel

In this lecture we will be concerned by exocytosis of neurotransmitters by chromaffin cells. These cells, located above kidneys, produce the adrenaline burst which induces fast body reactions they are used in neurosciences as standard models for the study of exocytosis by catecholaminergic neurons. Prior to exocytosis, adrenaline is contained at highly concentrated solutions into a polyelectrolyte gel matrix packed into small vesicles present in the cell cytoplasm and brought by the cytoskeleton near the cell outer membrane. Stimulation of the cell by divalent ions induces the fusion of the vesicles membrane with that of the cell and hence the release of the intravesicular content into the outer-cytoplasmic region. 

The swelling pressure of polyelectrolyte gels is usually considered as a sum of the network (jtnct) and ionic contributions (nion) [4, 99, 101, 113, 114]. The former describes the uncharged gel while taking into account the interaction between the polymer segments and the solvent as well as the network elasticity [4] ... 

Polyelectrolyte gels that showed bending motion by shrinking in an electric field139-145 were called electrochemomechanical devices, electro-... 

Tanaka, T, Phase Transitions of Gels. In Polyelectrolyte Gels, Properties, Preparation, and Applications, ACS Symposium Series Harland, RS Prud homme, RK, eds. American Chemical Society Washington, DC, 1992 Vol. 480, p 1. 

Branched polyelectrolytes have become of special interest because of their industrial importance and scientifically interesting properties. Poly(ethyl-eneimine), which is important in various industrial applications, can provide an excellent example branched and linear polyelectrolytes have quite different properties due to both their different topographies and structures [89-91]. As another practical point, branched polyelectrolytes can act as precursor or fragments of polyelectrolyte gels. A variety of theoretical approaches have been reported on the investigations of branched polyelectrolytes [92-97]. However,... 

Donnan-Type Equilibria in Polyelectrolyte Gels.—In a somewhat more rigorous fashion we consider the reduction of the chemical potential of the solvent in the swollen gel to be separable into three terms which severally represent the changes due to the mixing of polymer and solvent, to the mixing with the mobile ionic constituents, and to the elastic deformation of the network. Symbolically... 

While the condition of stoichiometric neutrality invariably must hold for a macroscopic system such as a space-network polyelectrolyte gel, its application to the poly electrolyte molecule in an infinitely dilute solution may justifiably be questioned. In a polyelectrolyte gel of macroscopic size the minute excess charge is considered to occur in the surface layer (the gel being conductive), which is consistent with the assumption that the potential changes abruptly at the surface. This change is never truly abrupt, for it must take place throughout a layer extending to a depth which is of the order of magnitude of the... 

Siegel, R, A, Hydrophobic Weak Polyelectrolyte Gels Studies of Swelling, Equilibria and Kinetics. Vol. L 09, pp. 233-268. 

The equation for the equilibrium swelling degree is more complicated for polyelectrolyte gels—those with ionizable groups—because of the need to include the additional ion-related terms in Eq. (5). The nion term can be substantial... 

Figure 3 Equilibrium swelling degree of polyelectrolyte gels as predicted by Eq. (12).

RA Siegel. Hydrophobic weak polyelectrolyte gels—Studies of swelling equilibria and kinetics. Adv Polym Sci 109 233-267, 1993. 

One effect of the electrochemical reactions in an aqueous system is a local pH change around the electrodes. By water electrolysis, hydronium ions (H30+) are generated at the anode, while hydroxyl ions (OH ) are produced at the cathode. These changes have been utilized for controlling the permeability of polyelectrolyte gel membrane or on-off solute release via ion exchange or surface erosion of interpolymer complex gels. 

K Sawahata, M Hara, H Yasunaga, Y Osada. Electrically controlled drug delivery system using polyelectrolyte gels. J Controlled Release 14 253-262, 1990. 

Electric field-induced deformation of polyelectrolyte gels has attracted much attention because of the property of smartness. If the size and shape of gels can be controlled as we hope, this may open a new door for gel technology. In this Section, studies on electric field-induced deformation of gels will first be surveyed. 

The electric field-induced deformation of polyelectrolyte gels was first reported by Hamlen et al. in 1965 [4], They observed that an ionic PVA gel fiber, which was placed touching the anode in a 1% NaCl solution, shrank at the anode side as a result of an applied dc EMF of 5 V. When the polarity of the applied voltage... 

With regard to the response time of the gel, polyelectrolyte gels require seconds to minutes to deform in electric fields. Needless to say, the deformation speed depends on the thickness of the gel and the intensity of the applied field. In 1993, a fast-responsive gel was found by Nanavati and Fernandez. A secretory granule gel particle obtained from beige mice and having a diameter of 3 pm at negative potentials was transparent and swollen within milliseconds of the application of an electric field of 5000 V/cm [19]. 

Understanding the elements which affect the deformation in electric fields is important in designing gel devices. In Sect. 2.2, the aspects of deformation of PAANa gel, which is a typical negatively charged polyelectrolyte gel having ionizable -COO Na+ groups, are reviewed. In particular, the deformation of PAANa gel in a solution of monovalent cations is described. 

Oppermann, W., Swelling Behavior and Elastic Properties of Ionic Hydrogels, in Polyelectrolyte Gels Properties, Preparation, and Applications (R. S. Harland and R. K. Prud homme Eds.), pp. 159-170. American Chemical Society, Washington (1992). 

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