Research Article Phase Transitions of Binary Lipid Mixtures: A Combined Study by Adiabatic Scanning Calorimetry and Quartz Crystal Microbalance with Dissipation Monitoring P. Losada-Pérez, 1,2 N. Mertens, 3 B. de Medio-Vasconcelos, 4 E. Slenders, 3 J. Leys, 3 M. Peeters, 1 B. van Grinsven, 5 J. Gruber, 4 C. Glorieux, 3 H. Pfeiffer, 6 P. Wagner, 1,2 and J. Thoen 3 1 Institute for Materials Research IMO, Hasselt University, Wetenschapspark 1, 3590 Diepenbeek, Belgium 2 Division IMOMEC, IMEC vzw, Wetenschapspark 1, 3590 Diepenbeek, Belgium 3 Laboratorium voor Akoestiek en hermische Fysica, Departement Natuurkunde en Sterrenkunde, KU Leuven, Celestijnenlaan 200D Bus 2416, 3001 Leuven, Belgium 4 Instituto de Qu´ ımica, Universidade de S˜ ao Paulo, 748 Av. Prof. Lineu Prestes, 05508-000 S˜ ao Paulo, SP, Brazil 5 Maastricht Science Programme, Maastricht University, 6200 MD Maastricht, Netherlands 6 Structurele Materialen, Departement Materiaalkunde, KU Leuven, Kasteelpark Arenberg 44 Bus 2450, 3001 Leuven, Belgium Correspondence should be addressed to P. Losada-P´ erez; patricia.losadaperez@uhasselt.be Received 19 November 2014; Accepted 17 December 2014 Academic Editor: Charles Rosenblatt Copyright © 2015 P. Losada-P´ erez et al. his is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. he phase transitions of binary lipid mixtures are studied by a combination of Peltier-element-based adiabatic scanning calorimetry (pASC) and quartz crystal microbalance with dissipation monitoring (QCM-D). pASC, a novel type of calorimeter, provides valuable and unambiguous information on the heat capacity and the enthalpy, whereas QCM-D is proposed as a genuine way of determining phase diagrams by analysing the temperature dependence of the viscosity. Two binary mixtures of phospholipids with the same polar head and difering in the alkyl chain length, DMPC + DPPC and DMPC + DSPC, are discussed. Both techniques give consistent phase diagrams, which compare well with literature results, showing their capability to map the phase behaviour of pure lipids as well as lipid mixtures. his work can be considered as a departure point for further investigations on more complex lipid mixtures displaying relevant phases such as the liquid-ordered phase and solid-lipid interfaces with biologically functional importance. 1. Introduction During the last decades, the approach to overcome the complexity of biological membranes is to use simpliied biomimetic models mainly consisting of binary or ternary mixtures of lipids [1, 2]. One of the most debated issues in the biophysics of lipids is lipid miscibility and its relevance to the function and organization of biological membranes. In 1997, Simons and Ikonen renewed the interest in lipid phase studies, suggesting that lateral phase separation in biological membranes could be functionally important [3]. Lipid rats or ordered lipid domains may play a role in the localization, transport, and function of diferent proteins. As a matter of fact, the number of studies on the inluence of domain partitioning on interactions with peptides and nucleic acids has increased signiicantly in recent years [4– 7]. In spite of the relevance of lipid-protein interactions, the phase behaviour of the lipid components of the cell membrane is believed to be of major importance to uncover some underlying principles behind the membrane function. From a fundamental viewpoint, the interest in lipid phase behaviour stems from the nature and the thermodynamics Hindawi Publishing Corporation Advances in Condensed Matter Physics Volume 2015, Article ID 479318, 14 pages http://dx.doi.org/10.1155/2015/479318