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Stimuli responsive surfactants and materials

Stimuli responsive surfactants and materials



 


 

  1. Soft Matter 2013, 9, 2760-2768.
  2. Soft Matter, 2013, 9, 10832-10840.
  3. J. Mater. Chem. C, 2013, 1 (42), 6930-6933.


 


Electrostatics,
what else ?


 


Responsiveness to external stimuli (temperature, pH, light, magnetic field…) is suited for many applications, including advanced colloids and material science design.
We recently report a very simple way to form dynamic, out-of equilibrium, micelles by combining various fatty acids with a homoditopic polyetheramine (Jeffamine ED900).1 These novel “cataniomeric“ surfactants combining features of ionic liquids and catanionic pairs show an original self-assembling behaviour in water, with a rich polymorphism : dynamic and stimuli responsive micelles (to pH and temperature) and true liquid crystals (cubic Im3m and Fm3m and hexagonal H1 phases). The mesophase formation was triggered by both hydrophobic effect and ionigenic interactions. Despite the fragility of the electrostatic pair in aqueous solution, these "cataniomeric" surfactants could be used as structure directing agent for mesoporous materials, with relatively large pore size (14 nm) compared to their corresponding non-ionic surfactants (4 nm) bearing covalent bonds. 2



On another hand, hexagonally ordered mesoporous materials with magnetic properties could be reached by using magnetic surfactants as structure directing agents of silica.3



Both hybrid (CTAF@SiO2) and ferrisilicate (Fe@SiO2) materials are free of nanoparticles and their magnetic responsiveness is arising from electronic and molecular spin, associated with the ordering in the resulting architectures. The materials exhibit a low to high spin transition due to the geometrical constrains of the isolated iron ions grafted on the silica walls. The transition temperature increases with the decreasing of the iron content.