Rheological properties of candelilla wax and dotriacontane organogels measured with a true-gap system Article uri icon

abstract

  • The rheology of organogels developed by candelilla wax (CW) and a pure n-alkane (dotriacontane, C32) was evaluated with a rheometer equipped with a true-gap system and compared with the rheograms obtained with a fixed-gap system. The two systems used a cone and plate geometry. In contrast to the fixed-gap system, the true-gap system makes the corrections in the gap size associated with the expansion/shrinkage of the sample and/or the rheometer geometry when changing temperature conditions are used during measurements. The CW and C32 organogels were prepared using safflower oil high in triolein (SFO) as the liquid phase, and the treatments studied resulted from the factorial combinations of two levels of gelator concentration (1 and 3%25) and two gel setting temperatures (T set; 5 and 25°C) achieved using a cooling rate of 1 or 10°C/min. The use of the true-gap system provided rheological parameters (i.e., G%27 profiles) that agreed with the micro structure and the calorimetric (i.e., heat of melting, ΔH M) behavior of both the CW and the C32 organogels. The use of a fixed-gap system in the rheological characterization of organogels must be treated with caution, specially with time dependent G%27 determinations involving the use of fast temperature ramps (i.e., 10°C/min). © AOCS 2009.
  • The rheology of organogels developed by candelilla wax (CW) and a pure n-alkane (dotriacontane, C32) was evaluated with a rheometer equipped with a true-gap system and compared with the rheograms obtained with a fixed-gap system. The two systems used a cone and plate geometry. In contrast to the fixed-gap system, the true-gap system makes the corrections in the gap size associated with the expansion/shrinkage of the sample and/or the rheometer geometry when changing temperature conditions are used during measurements. The CW and C32 organogels were prepared using safflower oil high in triolein (SFO) as the liquid phase, and the treatments studied resulted from the factorial combinations of two levels of gelator concentration (1 and 3%25) and two gel setting temperatures (T set; 5 and 25°C) achieved using a cooling rate of 1 or 10°C/min. The use of the true-gap system provided rheological parameters (i.e., G' profiles) that agreed with the micro structure and the calorimetric (i.e., heat of melting, ΔH M) behavior of both the CW and the C32 organogels. The use of a fixed-gap system in the rheological characterization of organogels must be treated with caution, specially with time dependent G' determinations involving the use of fast temperature ramps (i.e., 10°C/min). © AOCS 2009.

publication date

  • 2009-01-01