University of Cambridge > > BPI Seminar Series > Oppositely Charged Polyelectrolyte/Surfactant Mixtures at the Air/Water Interface: The Dominance of Non-equilibrium Effects

Oppositely Charged Polyelectrolyte/Surfactant Mixtures at the Air/Water Interface: The Dominance of Non-equilibrium Effects

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Oppositely charged polyelectrolyte/surfactant mixtures control the properties of many of the consumer products that we use in our everyday lives. While work has been carried out to understand the properties of these mixtures under dynamic conditions relevant to processing and applications [1–2], there is a growing awareness that also the static properties of such mixtures are strongly influenced by non-equilibrium effects [3–4]. We have worked over the last years to relate the interfacial properties of these systems to different non-equilibrium processes in the bulk and at interfaces [5–13]. In this seminar, it is described how non-equilibrium effects not only influence but in fact dominate the interfacial properties of such mixtures. Our work focuses on the strongly interacting systems Pdadmac/SDS and NaPSS/DTAB measured using a range of bulk and surface-sensitive techniques including neutron reflectometry, ellipsometry and Brewster angle microscopy. With an initial focus on the surface tension behaviour, it is shown that these materials inevitably exist out of equilibrium conditions for a prolonged period due to very slow equilibration of the bulk, even if steady state interfacial properties can be measured in the meantime. The situation is further complicated by the formation of liquid crystalline particles in the bulk that can resist dissolution upon chemical change. Their formation depletes the solution yet their penetration into the interfacial layer – shown to be mediated by different parallel processes such as surface affinity, kinetic trapping and transport under gravity – enhances the interfacial properties. These interfacial interactions can result in dissociation of the particles and the spreading of material by Marangoni flow to form a trapped film. We are currently exploiting this mechanism to form films that are more efficient that adsorbed layers form the bulk. The intricacy of the problem, even for relatively simple mixtures, is quite astounding, and the presented framework provides a platform on which to develop understanding of the actual behaviour of more complex mixtures used in industry and present in nature. poly(diallyldimethylammonium chloride)/sodium dodecyl sulfate poly(sodium styrene sulfonate)/dodecyltrimethylammonium bromide

[1] R. A. Campbell et al. Langmuir 2007, 23, 3242. [2] B. A. Noskov et al. Langmuir 2007, 23, 9641. [3] R. Mészáros et al. Langmuir 2003, 19, 609. [4] A. Naderi et al. Colloids Surfaces A 2005 , 253, 83. [5] R. A. Campbell et al. J. Phys. Chem. Letters 2010, 1, 3021. [6] R. A. Campbell et al. J. Phys. Chem. B 2011 , 115, 15202, [7] R. A. Campbell et al. J. Phys. Chem. B 2012 , 116, 7981. [8] Á. Ábraham et al. Langmuir 2013, 29, 11554. [9] Á. Ábraham et al. Langmuir 2014, 30, 4970. [10] R. A. Campbell et al. Langmuir 2014, 30, 8664. [11] R. A. Campbell et al. Soft Matter 2016, 12, 5304. [12] I. Varga et al. Langmuir 2017, 33, 5915. [13] Tummino et al. Langmuir 2018, 34, 2312.

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