Electrochemical Measurements for Studying the Polymerization Process and Critical Point Behaviors of Hydrogels


Yildiz G. , YILMAZ Y.

JOURNAL OF APPLIED POLYMER SCIENCE, cilt.112, ss.754-760, 2009 (SCI İndekslerine Giren Dergi) identifier identifier

  • Cilt numarası: 112 Konu: 2
  • Basım Tarihi: 2009
  • Doi Numarası: 10.1002/app.29466
  • Dergi Adı: JOURNAL OF APPLIED POLYMER SCIENCE
  • Sayfa Sayıları: ss.754-760

Özet

We propose a new technique based on electrochemical measurements for studying the critical point behaviors of the sol-gel transition of acrylamide-N,N'-methylene bisacrylamide hydrogels. In this technique, no chemical activator is used for accelerating the polymerization reaction. However, a potential difference is applied by means of silver and calomel electrodes placed in the reaction mixture. The silver electrode begins to be ionized and loses its electrons. The free radicals, -O3S-O-center dot, H-center dot, and (OH)-O-center dot, form on the silver electrode via persulfate dissociation. The polymerization is initiated by means of these free radicals. The current measured during the gelation processes passes through a maximum (a Gaussian-like behavior) and varies linearly with the reaction time during linear polymerization. All the parameters (the monomer, initiator, and crosslinker concentrations, the applied voltage, and the stirring rate of the reacting mixture) affecting the current have been studied in detail. We show that the maxima appearing in the current-time plots correspond to the gelation thresholds, the so-called sol-gel transition points. We also analytically prove that the current monitors the weight-average degree of polymerization (DP omega) and the gel fraction (G) below and above the threshold, respectively. The scaling behaviors of DP omega and G have been tested near the gelation thresholds, and we have observed that the critical exponents gamma and beta, defined for DP omega and G, agree with the predictions by mean-field theory. (C) 2009 Wiley Periodicals, Inc. J Appl Polym Sci 112: 754760, 2009