The effects of octanol addition to DHDAB / C12E12 surfactant mixtures, showing the different nano-structures formed.
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In many commonplace surfactant-based formulations (comprising ionic/nonionic surfactant mixtures) the addition of cosurfactants such as straight-chain alkanols and more complex alcohol structures (such as perfumes) can have an impact upon the structure and stability of the solution.
Recently we have used Small Angle Neutron Scattering (SANS) to study the impact of a range of straight-chain alkanols on the phase behaviour and microstructure of a di-alkyl chain cationic (DHDAB) and non-ionic (C12E12) surfactant mixture.
In the absence of alcohol the DHDAB / C12E12 mixture exhibits a rich structural evolution with composition – from small globular micelles for C12E12-rich compositions to large polydisperse bilamellar or multilamellar vesicles for DHDAB-rich compositions. The addition of the larger alkanols (dodecanol and hexadecanol) results in micelles and vesicles coexisting, and to vesicles occurring at solution compositions progressively less rich in DHDAB.
Most notable, however, is the observation that the smaller alkanols (octanol and decanol) produce a transition from large polydisperse bilamellar or multilamellar vesicles to very small monodisperse unilamellar vesicles, or nano-vesicles.
These results highlight the importance of SANS in elucidating these remarkable nano-structures. These structures offer great potential for the formulation of systems in which it is important to maintain a high degree of fluidity and transport.
J Penfold (ISIS, Oxford University), I Tucker (Unilever), RK Thomas, R Bradbury (Oxford University), I Grillo (ILL)
Research date: September 2009
Contact: Prof J Penfold, Jeff.Penfold@stfc.ac.uk
Further reading: J Penfold et al, Langmuir 24 (2008) 12209; I Tucker et al, Langmuir 25 (2009) 7674
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