title: Use of isothermal titration calorimetry to study surfactant aggregation in colloidal systems.
abstract: BACKGROUND
  Isothermal titration calorimetry (ITC) is a general technique that allows for precise and highly sensitive measurements. These measurements may provide a complete and accurate thermodynamic description of association processes in complex systems such as colloidal mixtures.
  
  
  OBJECTIVE
  This review will address uses of ITC for studies of surfactant aggregation to form micelles, with emphasis on the thermodynamic studies of homologous surfactant series. We will also review studies on surfactant association with polymers of different molecular characteristics and with colloidal particles.
  
  
  CONCLUSIONS
  ITC studies on the association of different homologous series of surfactants provide quantitative information on independent contribution from their apolar hydrocarbon chains and polar headgroups to the different thermodynamic functions associated with micellization (Gibbs energy, enthalpy and entropy). Studies on surfactant association to polymers by ITC provide a comprehensive description of the association process, including examples in which particular features revealed by ITC were elucidated by using ancillary techniques such as light or X-ray scattering measurements. Examples of uses of ITC to follow surfactant association to biomolecules such as proteins or DNA, or nanoparticles are also highlighted. Finally, recent theoretical models that were proposed to analyze ITC data in terms of binding/association processes are discussed.
  
  
  CONCLUSIONS
  This review stresses the importance of using direct calorimetric measurements to obtain and report accurate thermodynamic data, even in complex systems. These data, whenever possible, should be confirmed and associated with other ancillary techniques that allow elucidation of the nature of the transformations detected by calorimetric results, providing a complete description of the process under scrutiny.
authors.affiliation: Institute of Chemistry, University of Campinas (UNICAMP), CP 6154, CEP 13083-970, Campinas, SP, Brazil. Electronic address: wloh@iqm.unicamp.br.
authors.forename: Watson
authors.initials: W
authors.lastname: Loh
authors.affiliation: Institute of Chemistry, University of Campinas (UNICAMP), CP 6154, CEP 13083-970, Campinas, SP, Brazil.
authors.forename: César
authors.initials: C
authors.lastname: Brinatti
authors.affiliation: Department of Chemical Engineering and Waterloo Institute for Nanotechnology, University of Waterloo, 200 University Avenue West, Waterloo, ON N2L 3G1, Canada.
authors.forename: Kam Chiu
authors.initials: KC
authors.lastname: Tam
mesh_terms: D002151:Calorimetry / Q000379:methods; D003102:Colloids; D004247:DNA / Q000737:chemistry*; D057927:Hydrophobic and Hydrophilic Interactions; D008823:Micelles; D053758:Nanoparticles / Q000737:chemistry*; D011506:Proteins / Q000737:chemistry*; D055672:Static Electricity; D013501:Surface-Active Agents / Q000737:chemistry*; D013696:Temperature; D013816:Thermodynamics
chemical_list: D003102:Colloids; D008823:Micelles; D011506:Proteins; D013501:Surface-Active Agents; D004247:DNA
keywords: Calorimetry; Micellization; Polymers; Surfactants; Thermodynamics