# Phase Behavior and Rheological Properties of AES/CAPB/H\({}_{2}\)O Ternary System
###### Abstract  
Cleaning products are often formulated as mixtures of surfactants because the properties of surfactant mixtures are easier to adjust than those of a single surfactant. Therefore, it is of great significance to study the phase diagram of surfactant mixtures. In this paper, the phase behavior of the alkyl ethoxysulfate (AES)/cocamidopropyl betaine (CAPB)/H\({}_{2}\)O ternary system was investigated at room temperature using polarizing optical microscopy (POM) and small angle X-ray scattering (SAXS), and the identified phases of the samples with various compositions were used to construct the ternary phase diagram of the AES/CAPB/H\({}_{2}\)O system which contains normal micellar phase (L\({}_{1}\)), normal hexagonal phase (H\({}_{1}\)), lamella phase (L\(\alpha\)), and one transition region (L\({}_{1}\)\(\rightarrow\) H\({}_{1}\)). The viscosity distribution of the AES/CAPB/H\({}_{2}\)O system was determined by a Brookfield DV2T touch screen viscometer. In addition, the effects of the weight percentage of CAPB and salts on the viscosity and rheological properties of the AES/CAPB/H\({}_{2}\)O system were also investigated. This work not only enriches the phase diagram of surfactant systems, but also has important guiding significance for the design and development of cleaning products. alkyl ethoxysulfate; cocamidopropyl betaine; liquid crystalline phase; phase diagrams; rheological properties +
Footnote †: journal: Applied  
0000-0002-4200-3820][PERSON]  
0000-0002-3820-3820][PERSON]  
0000-0002-3820-38  
of surfactant mixtures [5; 6; 7; 8]. The phases that have been reported mainly include normal micellar phase (L\({}_{1}\)) [6; 7], normal micellar cubic phase (I\({}_{1}\)) [8; 9], normal hexagonal phase (H\({}_{1}\)) [6; 7], normal bicontinuous cubic phase (V\({}_{1}\)) [8], lamellar phase (L\(\alpha\)) [8; 9; 10], reverse micellar phase (L\({}_{2}\)) [11], reverse micellar cubic phase (I\({}_{2}\)) [8], reverse hexagonal phase (H\({}_{2}\)) [8; 11], and reverse bicontinuous cubic phase (V\({}_{2}\)) [8]. Here, \"normal\" represents oil-in-water, and \"reverse\" represents water-in-oil. For example, the phase behavior of the AES/LAS/H\({}_{2}\)O system was investigated in depth at room temperature by [PERSON]'s group, and the results showed that the AES/LAS/H\({}_{2}\)O system exhibited a variety of self-assembly behaviors depending on the composition of AES/LAS/H\({}_{2}\)O, forming normal micellar phase and liquid crystal phases (e.g., normal hexagonal phase, lamellar phase, and normal cubic phase) [12]. Moreover, the micellar, hexagonal, and solid phases were observed in the AES/poly(vinyl alcohol)/H\({}_{2}\)O system, but the lamellar phase and the cubic phase were not observed [13]. Since phase behavior reflects the way surfactant molecules are aggregated, it is often closely related to physical properties including viscosity and rheological properties [11]. For normal liquid crystal phases (oil-in-water), hexagonal (H\({}_{1}\)) and cubic phases (I\({}_{1}\) and V\({}_{1}\)) usually exhibit very high viscosities, while the viscosity of the lamellar phase is lower than them [14]. For the normal micellar phase, its viscosity is obviously lower than that of normal liquid crystal phases, usually less than 10 Pa-s. Interestingly, even in the same surfactant mixture system, some surfactant mixtures exhibit viscous characteristics, while other surfactant mixtures exhibit both viscous and elastic characteristics depending on their different compositions [15; 16]. Generally, in rheology, the viscosity level of material is represented by the loss modulus (G\({}^{\prime\prime}\)), and the elasticity level of material is represented by the storage modulus (G\({}^{\prime}\)) [17].