Tuning Micellar Structures in Supercritical CO2 Using Surfactant and Amphiphile Mixtures.
Jocelyn Peach1, Adam Czajka1, Gavin Hazell1
1School of Chemistry, University of Bristol , Bristol, BS8 1TS, United Kingdom.
Langmuir : the ACS Journal of Surfaces and Colloids
|February 21, 2017
Summary
Anisotropic micelles in water-in-CO2 microemulsions increase viscosity compared to spherical ones. Novel surfactants create elongated micelles with lower fluorination and higher water dispersion, enabling viscosity prediction.
Area of Science:
- Physical Chemistry
- Materials Science
- Chemical Engineering
Background:
- Anisotropic micelles generally lead to higher viscosity in microemulsions than spherical micelles.
- Water-in-CO2 (w/c) microemulsions often utilize fluorinated surfactants, with existing systems showing high fluorination levels.
- High-pressure conditions (100-400 bar) are relevant for supercritical CO2 applications.
Purpose of the Study:
- To investigate the formation of elongated micelles in w/c microemulsions using novel, partially fluorinated surfactants.
- To explore the influence of water content, surfactant structure, and hydrotrope tail length on micelle formation and properties.
- To develop a predictive model for viscosity increases in CO2-based microemulsions based on micelle characteristics.
Main Methods:
- Formulation of novel w/c microemulsions with custom-synthesized CO2-philic surfactants, hydrotropes, and cosurfactants.
- High-pressure small-angle neutron scattering (HP-SANS) to probe dispersed water domains and micelle structure.
- Estimation of intrinsic and relative viscosities based on micelle aspect ratio and volume fraction.
Main Results:
- Evidence of elongated reversed micelles in supercritical CO2 was obtained using HP-SANS.
- The novel surfactants exhibited significantly lower fluorination (6-29 wt %) compared to existing systems (14-52 wt %).
- These systems supported higher water dispersion levels (w=15) than related systems (w=5).
Conclusions:
- Novel, partially fluorinated surfactants can effectively form elongated reversed micelles in w/c microemulsions at high pressures.
- These elongated micelles offer advantages of lower fluorination and enhanced water dispersion capabilities.
- The study provides a framework for predicting viscosity in CO2 microemulsions based on micelle geometry and surfactant properties.
Related Concept Videos
01:30Micelles
91
Micelle formation is an intricate process that hinges on the properties of amphiphilic or amphipathic molecules and the conditions of the system in which they are found. Amphiphilic molecules, which have both hydrophilic (water-attracting) and hydrophobic (water-repelling) parts, play a critical role in this process.In aqueous environments, these molecules arrange themselves such that their hydrophilic heads are turned towards the water phase, while their hydrophobic tails are oriented away...
91
03:22Colloids
21.8K
Children at play often make suspensions such as mixtures of mud and water, flour and water, or a suspension of solid pigments in water known as tempera paint. These suspensions are heterogeneous mixtures composed of relatively large particles that are visible to the naked eye or can be seen with a magnifying glass. They are cloudy, and the suspended particles settle out after mixing. On the other hand, a solution is a homogeneous mixture in which no settling occurs and in which the dissolved...
21.8K
01:27Surface Active Agents
50
Surfactants, named for their behavior at interfaces, positively adsorb at the interfaces of two phases, reducing interfacial tension. Their versatility as emulsifiers, detergents, and foaming agents stems from this ability. Surfactants, often termed amphiphiles, share the property of amphipathy, with molecules having both hydrophilic and hydrophobic portions. The hydrophilic part is called the head, and the hydrophobic part, including an elongated alkyl substituent, forms the tail.Surfactants...
50
01:18Detergent Purification of Membrane Proteins
6.7K
Detergents are used to purify the integral proteins of the membrane. The hydrophobic portion of the detergent can replace membrane phospholipids while solubilizing the membrane proteins. When detergent monomers reach a specific concentration in a solution called critical micelle concentration (CMC), they form micelles. Above CMC, the concentration of the detergent monomers remains in equilibrium with the micelle. The number of detergent monomers present in the CMC varies for each detergent, and...
6.7K