Thesis subject

MSc - Surfactant formulation for modifying the surface forces in apolar media: effect of alcohol

Dry-cleaning is a process for removing soils and stains from fabrics and garments using a non-aqueous solvent with added detergent. Traditional dry-cleaning methods employ organic solvents such as PERC (perchloroethylene), which is toxic and environmentally harmful. PERC has many adverse effects such as damages kidneys and liver, and causes gastrointestinal irritation. It can also cause eye, nose and throat irritation. Repeated dermal exposure may result in dry, scale, and fissured dermatitis.

Carbon dioxide is non-toxic, nonflammable, ecologically sound, cheap, and available on a large scale. An important difference between dry cleaning with PERC or other currently used solvents, and dry-cleaning with CO2 is that carbon dioxide dry cleaning needs a substantially higher pressure (45-60 bar) than atmospheric pressure. Therefore, a new process for dry-cleaning has to be developed. Literature on dry-cleaning using liquid CO2 revealed that removal of oily soil was comparable or in some cases better than PERC, however, detergency of small particulate soil (size less than 20 μm) was inadequate compared to the cleaning performance of PERC. Higher input of mechanical action could not improve the cleaning performance of particulate soil in liquid CO2 and as a result the perspectives of liquid CO2 as a dry cleaning solvent remained limited. Cleaning efficiency can be improved by the use of surfactants in the system. But finding a surfactant for liquid CO2 is another challenge. Liquid CO2 near the critical pressure and temperature is a very poor solvent and hence solubility of surfactants is very low. Our research is focusing on the following three things:
  • Finding a suitable surfactant or a surfactant formulation
  • Understanding of the fundamental science behind the dry-cleaning which involves knowledge of colloid and interfacial science in apolar media and
  • Improvement of the hydrodynamics involved in the dry-cleaning process using liquid CO2

In dry-cleaning formulation, alcohol is one of the additives which has been proved to act as a cleaning aid in liquid CO2. Among the alcohol studied, isopropyl alcohol has shown the best result. The reason for this is still unknown.

We will investigate (a) the molecular interaction (interaction force) between a model hydrophilic surface and a colloidal particle through low dielectric liquids saturated with alcohol using atomic force microscopy. (b) The effect of chain length and branching on the force of interaction will be also measured. (c) In addition to this, we will also measure the effect of alcohol on the force of interaction between a hydrophobic surface and a hydrophobic particle (d) the effect of the alcohol on the phase diagram of the existing surfactant formulation developed in our lab will be studied and an optimum formulation will be designed to improve the cleaning efficiency of the liquid CO2 dry-cleaning.

Experimental techniques:

  • Spin coating to prepare model surface layers
  • Preparation of the colloidal probe and its hydrophobization/modification
  • Measurement of adhesion force: Dynamic force spectroscopy
  • Confocal microscopy to visualize presence /absence of water capillary bridge
  • Equilibrium and advancing/receding contact angle measurement using Goniometer
  • Measurement of the interfacial tension between water and the apolar media-alcohol mixture using interfacial tensiometer
  • Polarized optical microscopy, phase penetration technique, confocal microscopy to determine the phase diagram of the surfactant formulation
  • Dynamic light scattering to characterize the size of the mesophases in the formulation
  • Together with TU Delft, pilot scale trial will be taken to test the efficacy of the surfactant formulation in real system of liquid CO2 in pilot scale dry-cleaning machine
  • Using the high pressure observation cell in the University of Twente, the cloud point behaviour of the surfactant formulation in liquid CO2 will be tested. This may lead to determination of phase diagram in liquid CO2