Thermo-responsive Wormlike Micelles

Abstract

This chapter summarizes findings on the simplest trigger applied to wormlike micellar: temperature. Thermo-thinning systems are not discussed since a viscosity decrease with temperature is a rather general characteristic of most systems. Instead, the unique thermo-viscosifying behaviour displayed by some WLMs and the possibility of imparting a pseudo "sol/gel" transition in specific systems are extensively addressed. These two types of systems show a transition from either a low-viscosity fluid or a viscoelastic solution to a gel-like state by tuning the temperature. The thermo-thickening behaviour and the underlying mechanisms of various types of thermo-thickening wormlike micellar systems (non-ionic, cationic, anionic, and zwitterionic) are discussed in terms of molecular structure-property relationships.Keywords Thermo-responsive · Thermo-thickening · Thermo-viscosifying · Wormlike micelles · Sol/gel transition · Surfactant gel This chapter deals with the simplest possible trigger, which is temperature. Stimuli responsiveness can be defined as a physicochemical change resulting from a small external variation in environmental conditions. From this point of view, one may regard both thermo-thinning (i.e. a viscosity decrease with temperature) and thermo-thickening (i.e. a viscosity increase with temperature) fluids as examples of temperature responsiveness. Generally, however, the micellar contour length decays exponentially with increasing temperature, which in turn leads to an exponential decrease in zero-shear viscosity η 0 , following an Arrhenius law [1]:where A is a pre-exponential factor, T is the absolute temperature, E a is the flow activation energy, and R is the gas constant. Thermo-thinning is therefore a general characteristic of WLMs and for this reason will not be discussed here. Instead, we will focus in this chapter on the unique thermo-viscosifying behaviour displayed by some WLMs [2-10] (Sect. 2.1) and the possibility of imparting a pseudo (2.1)

Parabolic Viscosity Behavior of NaCl-Thickened Surfactant Systems upon Temperature Change

“…It has been reported that surfactant systems, especially the anionic ones, generally manifest a parabolic viscosity–temperature behavior . This behavior can be utilized to modulate the viscosity profiles of home care products by a careful formulation design to achieve an ideal viscosity in which case the system goes through a stretched parabolic curve, resulting in an accepting viscosity profile in the low-temperature range, and the system would not go through a monotonic increase when the temperature decreases.…”

“…Although parabola-type formulas have been reported in some cases, gemini or cationic surfactants have to be used in these formulas, and the vertex of the parabola is located in the high-temperature region, higher than room temperature. ,– In the meantime, most of the rheological studies have focused on dilute system solution, and only a few reports have studied the concentrated surfactant solution, which is close to the real applications. – It has been reported that, in a concentrated solution, a giant micelle including wormlike micelle will be formed, which is an important hotspot in surfactant studies due to its unique polymer-like behavior. ,– In dilute surfactant systems, the shape transition of micelles can be studied by static and dynamic light scattering, while it is not feasible in a concentrated solution. Thus, the giant micelle for the latter has been studied by rheology, NMR, SANS, and visually FF-TEM or cryo-TEM. – …”

“…It has been reported that surfactant systems, especially the anionic ones, generally manifest a parabolic viscosity–temperature behavior. 5 This behavior can be utilized to modulate the viscosity profiles of home care products by a careful formulation design to achieve an ideal viscosity in which case the system goes through a stretched parabolic curve, resulting in an accepting viscosity profile in the low-temperature range, and the system would not go through a monotonic increase when the temperature decreases. For that purpose, existing colloidal theories such as negative interfacial tension in mixed films proposed by Schulman and Prince; 6 double-layer theory proposed by Schulman and Bowcott; 7 geometry arrangement theory proposed by Israelachvili, Mitchell, and Ninham; 8 and Winsor’s R ratio of interaction between the interfacial layer and both phases 9 could all provide important directions.…”