Complex Behavior of Aqueous α-Cyclodextrin Solutions. Interfacial Morphologies Resulting from Bulk Aggregation.
The spontaneous aggregation of α-cyclodextrin (α-CD) molecules in the bulk aqueous solution and the interactions of the resulting aggregates at the liquid/air interface have been studied at 283 K using a battery of techniques: transmission electron microscopy, dynamic light scattering, dynamic surface tensiometry, Brewster angle microscopy, neutron reflectometry, and ellipsometry. We show that α-CD molecules spontaneously form aggregates in the bulk that grow in size with time. These aggregates adsorb to the liquid/air interface with their size in the bulk determining the adsorption rate. The material that reaches the interface coalesces laterally to form two-dimensional domains on the micrometer scale with a layer thickness on the nanometer scale. These processes are affected by the ages of both the bulk and the interface. The interfacial layer formed is not in fast dynamic equilibrium with the subphase as the resulting morphology is locked in a kinetically trapped state. These results reveal a surprising complexity of the parallel physical processes taking place in the bulk and at the interface of what might have seemed initially like a simple system.
Laboratorio de Biofisicoquímica, Departamento de Fisicoquímica, Facultad de Química, Universidad Nacional Autónoma de México , México D. F. 04510, Mexico.
Jorge
J
Hernandez-Pascacio
Soft Matter and Molecular Biophysics Group, Department of Applied Physics, University of Santiago de Compostela , Santiago de Compostela 15782, Spain.
Ángel
Á
Piñeiro
Soft Matter and Molecular Biophysics Group, Department of Applied Physics, University of Santiago de Compostela , Santiago de Compostela 15782, Spain.
Juan M
JM
Ruso
Soft Matter and Molecular Biophysics Group, Department of Applied Physics, University of Santiago de Compostela , Santiago de Compostela 15782, Spain.
Natalia
N
Hassan
Institut Laue-Langevin , 71 avenue des Martyrs, CS 20156, 38042 Grenoble, Cedex 9, France.
Richard A
RA
Campbell
Departamento de Procesos y Tecnología, Universidad Autónoma Metropolitana , Unidad Cuajimalpa, Av. Vasco de Quiroga 4871, Col. Santa Fe, Delegación Cuajimalpa de Morelos 05348, Mexico.
José
J
Campos-Terán
Laboratorio de Biofisicoquímica, Departamento de Fisicoquímica, Facultad de Química, Universidad Nacional Autónoma de México , México D. F. 04510, Mexico.
Miguel
M
Costas