Efficiency of Solute Release from Thermoresponsive Poly(N-isopropylacrylamide) Gels:  Electrochemical Studies

Abstract

An electrochemical method for the simultaneous determination of the diffusion coefficient and efficiency of release of probe species from thermoresponsive gels due to their volume phase transition is presented. The method combines steady-state voltammetry at microelectrodes and conductometry, and it is designed for charged redox species. This method might be modified for uncharged systems; in this case instead of the conductometric measurement an additional independent voltammetric experiment in the solution is required. The approach presented here has been examined for positively and negatively charged and uncharged ferrocene derivatives as probes in the poly(N-isopropylacrylamide) hydrogel. The release coefficient, θ, defined as the ratio of the concentrations of the probe in the expelled solution and the swollen gel, and determined for the charged ferrocene-based probes, is greater by approximately 25% than that found for the uncharged ferrocene derivative. The larger release efficiency for the charged probes is explained in terms of substantial dehydration of polymeric chains during the gel phase transition. The experiments were performed under the conditions of excess supporting electrolyte. No influence of the identity and concentration (up to 0.05 mol/L) of supporting electrolytes (i.e., either LiClO 4 or KCl) on the release coefficient was observed. The average values of release coefficients were determined to be 0.80 ( 0.02, 1.03 ( 0.16, and 1.07 ( 0.14 for 1,1′-ferrocenedimethanol, sodium ferroceneacetate, and ferrocenylmethyltrimethylammonium hexafluorophosphate, respectively.

Diffusion-controlled currents of redox latex particles with polystyrene-core and polyallylamine-ferrocenyl shell

“…The one-third of or the experimental current value cannot be explained in terms of D. It is necessarily to ascribe to n < n UV or the partial charge transfer, as has been suggested in the dendrimers [38,39] and the vinylferrocene adsorbed polystyrene particle [13]. This type of the partial charge transfer is specific to hard big core redox particles, rather than soluble redox polyelectrolytes [40][41][42]. We define the number of electrons calculated from Eq.…”

Oxidation of ferrocenemethanol grafted to a hydrogel network through cysteine for triggering volume phase transition

“…[1][2][3][4][5][6][7] Environmentally sensitive gels have great potential in several technologically important areas such as drug delivery, articial muscles, separation techniques, sensor construction, swing absorbers, and molecular recognition. [8][9][10][11][12][13][14][15][16][17][18][19][20] Additionally, their attachment to the surface of an object widens their usefulness, for instance in the construction of switchable sensors/biosensors, switchable electrochemical systems, signal-responsive interfaces, and surface patterning. [21][22][23][24][25][26][27][28] The environmentally sensitive gels that are most oen investigated are thermo sensitive gels based on N-isopropylacrylamide.…”

Swelling behavior of polyacrylamide/laponite clay nanocomposite hydrogels: pH-sensitive property

“…Because of their environmental sensitivity and unique structure, these polymeric hydrogels have been investigated for many biomedical and pharmaceutical applications including drug delivery systems, separation techniques, musclelike actuators, and construction of sensors [4][5][6][7][8]. Among these intelligent polymers, pH-and temperature-sensitive hydrogels are the most widely investigated.…”