Narrow Results

The temperature and concentration dependences of the transmission spectrum of an aqueous solution of agar are investigated. Measurements taken in the heating and cooling modes show strong thermal hysteresis in the spectral properties. Analysis of the results suggests that the formation of a gel network occurs in a much narrower temperature range than its collapse. The study of the temperature dependence of transmittance indicates that the association bispirals by cooling the solution and responsible for the formation of network occurs at temperature about $40^{\circ }$C. A breakdown of these associates by heating of the gel begins at $60^{\circ }$C and covers a wide temperature range. The gel point $T_g$ and the gel melting point $T_m$ increase with increasing polymer concentration, but for $T_m$ this dependence is stronger. Growth of turbidity (light scattering) of gel by increasing of agar concentration is due to the increasing of number and size of gel associates.

Thermal hysteresis and stability of agarose–water gelling systems were studied by the spectrophotometer for different concentrations at different temperatures. Gelation temperature depends on the concentration of agarose. With the increase in the concentration of agarose gelation temperature, strength of agarose increases too. With the increase in the concentration of polymer solvent–gel phase transition, gel melting happens at higher temperatures. The price of enthalpy was determined (150.0127 KC/mol). In gelation process, the phase separation is completed and in this process, the value of this $\mathrm{\Delta }t=t_{\mathrm{\text{melting}}}-t_{\mathrm{\text{gelation}}}$ equally increases.

Agar gel is a linear viscoelastic material with low deformations ($<0.01\%$). Here, characterization technique used is the rheometer-type Carri-Med “CSL 100”. This rheometer offers us the opportunity to study the gel in static and dynamic shear. The study is done at low frequencies ($0.1$–$40\mathrm{\text{Hz}}$). Mechanical characterization of the agar gel in terms of dynamic modulus is performed for different concentrations. The dynamic rigidity of the gel decreases with increasing concentration. The 8% agar gel simulates very well the dynamic rigidity of brain tissue at low frequency. The range of low frequencies is rarely studied for this material (brain) in the literature. Most tests done on brain tissue are in a frequency range between $50\mathrm{\text{Hz}}$ and $600\mathrm{\text{Hz}}$. Yet, the Maxwell–Kelvin–Voigt model simulates very well the 8% agar gel. The instant elasticity derived from mathematical modeling of agar gel is similar to that measured in the literature for the brain tissue. Hence agar gel can be used in the construction of physical models of the human head used to analyze the dynamic response of the head to shock or to an inertial load.