On determination of gel point

In this paper, the gel-forming compositions exhibiting a low-viscosity Newtonian fluid behavior at the initial stage and a viscoelastic body–gel behavior at the final stage are considered. A gel point is referred to as the time instant when the shear modulus of elasticity of the composition becomes greater than zero. The interaction between sensor and gel-forming composition in the vibration rheometer is numerically studied using the Kelvin–Voigt rheological model. It is revealed that the method that uses the results of two experiments at different frequencies can be applied to determine the gel point within the framework of classical vibration viscosimetry. It is shown that the proposed method is independent of the size of measuring vessel. The algorithm for determining the gel point in the case of the noise presence in the experimental data is described. A test problem is considered using the idealized dependencies of the shear modulus of elasticity and dynamic viscosity on time for gelation process. Based on the test problem solution, the assessment of the impact of the noise factor and length of averaging segment on the results is obtained. The efficiency of proposed method is exposed. Two versions of practical implementation are proposed: two sensors oscillating at their own frequencies or one sensor switching to different harmonics.