title: Rheological investigation of self-emulsification process.
abstract: OBJECTIVE
  Aim of this study is to investigate the mechanism of self-emulsification through rheological analysis of intermediate liquid crystalline (LC) phase formed during self-emulsification process.
  
  
  METHODS
  Binary system of tween 80 (T80) and imwitor 742 (I742) was used and different SES were prepared with I742 at 10, 30, 50, 70 and 90% w/w concentration levels. Self-emulsification was monitored by visual observations and droplet size measurement. Mesophases obtained by 50% v/v hydration of SES were utilized for polarizing microscopy, differential scanning calorimetry and rheological studies.
  
  
  RESULTS
  Good emulsification with nano sized droplets was observed for SES 30% as compared to micron sized droplets for other SES. In polarizing microscopy, formation of intermediate LC phase was observed in all SES. Lamellar phase was evident in 30% SES while other SES exhibited micellar cubic phase. Presence of high level of structurally bound water in thermal analysis confirmed mesophase formation in all SES. In frequency sweep, decrease in elastic modulus, and an increase in phase degree and loss tangent was observed for 30% SES. Exactly opposite trend was seen in other SES. Thus, rheological studies concluded presence of weak and fragile mesophase structure in 30% SES while LC phase structure with little structural buildup was observed in other SES. This weak mesosphere structure in SES 30% presented no or very little resistance against strain induced deformation. Therefore, during emulsification, weak mesophase in SES 30% ruptured with ease and released jet of nanosize droplets compared to coarse droplets for other SES.
  
  
  CONCLUSIONS
  This study signifies the effect of viscoelastic properties of intermediate LC phase on self-emulsification performance.
authors.affiliation: Department of Pharmaceutics, Bharati Vidyapeeth University, Poona College of Pharmacy, Erandwane, Pune 411 038, India.
authors.forename: Shailesh V
authors.initials: SV
authors.lastname: Biradar
authors.forename: Ravindra S
authors.initials: RS
authors.lastname: Dhumal
authors.forename: Anant
authors.initials: A
authors.lastname: Paradkar
mesh_terms: D004355:Drug Stability; D045703:Emulsifying Agents; D005989:Glycerides / Q000737:chemistry; D011136:Polysorbates; D012212:Rheology; D013499:Surface Properties; D013696:Temperature; D013818:Thermogravimetry; D014867:Water / Q000737:chemistry
chemical_list: D045703:Emulsifying Agents; D005989:Glycerides; D011136:Polysorbates; D014867:Water