title: Subphase exchange experiments with the pendant drop technique.
abstract: BACKGROUND
  The development of the coaxial double capillary 15 years ago opened up the possibility to undertake accurate desorption and penetration studies of interfacial layers in the pendant drop technique. Drop and bubble methods offer several advantages with respect to other interfacial techniques. They allow a more stringent control of the environmental conditions, use smaller amounts of material and provide a much higher interface/volume ratio than in conventional Langmuir Troughs.
  
  
  METHODS
  The coaxial capillary was developed 15 years ago at the University of Granada as an accessory for the pendant drop surface film balance. It allows exchanging the subphase of the drop without disturbing the surface film and preserving the drop volume throughout the subphase exchange. Hence, this methodology enables one to carry out a great variety of interfacial studies well beyond the usual adsorption profiles. Penetration studies, sequential adsorption measurements, desorption kinetics, reversibility of adsorption and testing of enzymatic treatments on interfacial layers are amongst the principal applications. The coaxial capillary has been recently upgraded to a multi-exchange device which has boosted its applicability. It can be now used to address multilayer formation, create soft interfacial nano-composites such as membranes, polyelectrolyte assemblies and simulate in vitro digestion in a single droplet.
  
  
  CONCLUSIONS
  This review aims to compile the experimental work done, using the pendant drop subphase exchange in the last decade, and how its use has provided new insights into the surface/interfacial properties of many different materials. Special emphasis is placed on recent work regarding simulation of in vitro digestion in order to address issues relating to metabolism degradation profiles. The use of this methodology when dealing with interfacial studies allows setting the foundations of interfacial engineering technology. Based on subphase exchange experiments, we aim to develop models for competitive adsorption of different compounds at the interface and build up layer-by-layer interfacial structures. Future challenges comprise the design of finely adjusted nanoengineering systems, based on multilayer assemblies with tailored functionalities, to match the application demand.
authors.affiliation: Department of Applied Physics, University of Granada, Campus de Fuentenueva, sn, 18071 Granada, Spain. Electronic address: julia@ugr.es.
authors.forename: Julia
authors.initials: J
authors.lastname: Maldonado-Valderrama
authors.affiliation: Division of Food Sciences, School of Biosciences, University of Nottingham, Sutton Bonington Campus, Loughborough LE12 5RD, United Kingdom.
authors.forename: Amelia
authors.initials: A
authors.lastname: Torcello-Gómez
authors.affiliation: Department of Applied Physics, University of Granada, Campus de Fuentenueva, sn, 18071 Granada, Spain.
authors.forename: Teresa
authors.initials: T
authors.lastname: del Castillo-Santaella
authors.affiliation: Department of Software Engineering, University of Granada, C/Periodista Daniel Saucedo Aranda, sn, 18071 Granada, Spain.
authors.forename: Juan A
authors.initials: JA
authors.lastname: Holgado-Terriza
authors.affiliation: Department of Applied Physics, University of Granada, Campus de Fuentenueva, sn, 18071 Granada, Spain.
authors.forename: Miguel A
authors.initials: MA
authors.lastname: Cabrerizo-Vílchez
mesh_terms: D000327:Adsorption; D000818:Animals; D001647:Bile Acids and Salts / Q000737:chemistry / Q000378:metabolism; D006801:Humans; D057446:Hydrodynamics; D011506:Proteins / Q000737:chemistry / Q000378:metabolism; D013500:Surface Tension; D013501:Surface-Active Agents / Q000737:chemistry / Q000378:metabolism
chemical_list: D001647:Bile Acids and Salts; D011506:Proteins; D013501:Surface-Active Agents
keywords: Desorption; In-vitro digestion; Pendant drop; Penetration; Subphase exchange; Surface tension