Stress Relaxation of Hydrogels of Agarose Containing Formamide and Ultrasonic Attenuation in the Process of Sol-Gel Transformation

Abstract

Ultrasonic attenuation of hydrogels of agarose containing formamide was measured by means of the pulse method. The measurement was carried out in order to investigate the change in ultrasonic attenuation accompanying the sol-gel transformation of those gels. Procedures of the preparation of sample gels are the same as those used in our previous studies. The temperature of gelation of aqueous agarose solutions, which was determined from the measurement of ultrasonic attenuation, decreased with an increase in the concentration of added formamide. Stress relaxation of hydrogels of agarose containing formamide was7also measured. Relaxation curves up to 4 hrs for the gels containing 1.5-8 wt% of agarose were obtained in the temperature range from 25°C to 65°C. These curves were represented by a six-element mechanical consisting of three Maiwell elements in parallel. The elastic modulus E, decreased with increasing concentration of the added formamide and decreased rapidly with increasing temperatrure. Unusual behavior in the E, vs. formamide concentration relations was observed at 45°C for 0.51 mf of formamide.