Electrokinetics of soft polymeric interphases with layered distribution of anionic and cationic charges

International audienceSoft surface coatings attract increasing attention due to the versatile options they provide in numerous applications e.g. in the flourishing nanomedicine and nanobiotechnology areas. Optimisation of the performance of such ion- and solvent-permeable polyelectrolytic materials requires a detailed understanding of their electrostatic properties. This task is rendered difficult by the inherent non-uniform distribution of their structural charges. In this article, we review recent advances made in the measurement and theory of the electrokinetics (electrophoresis/streaming current) of soft surface coatings that carry spatially-separated cationic and anionic charges. Examples of such charge-stratified systems are polyelectrolyte-coated particles, polyelectrolyte multilayers, particles with zwitterionic interfacial functionality, microbial cells or hard–soft composite interfaces. It is shown here that the electrokinetic features of such colloidal systems are remarkably different from those of their counterparts with homogeneously distributed cationic and anionic charges. In particular, the interplay between electrostatic and hydrodynamic flow fields developed under electrokinetic conditions in the bulk and interfacial compartments of charge-stratified colloids/films are shown to induce a reversal of their electrokinetic response (electrophoretic mobility/streaming current) that depends on the concentration of monovalent electrolyte in solution. The prerequisites for occurrence of such spectacular behaviour are theoretically identified in terms of the Debye length, the spatial length scales defining charge layering, and the typical length for flow penetration within the colloids/films. Electrophoresis and streaming current results recently reported for poly(amidoamine) carboxylated nanodendrimers, natural rubber colloids and poly(ethyleneimine)-supported lipid bilayers are further discussed to illustrate the generic electrokinetic properties of soft interfaces defined by a given stratification of their anionic and cationic structural charges

On the analysis of ionic surface conduction to unravel charging processes at macroscopic soft and hard solid-liquid interfaces

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On the applicability of the Brinkman equation in soft surface electrokinetics

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On the use of electrokinetics for unraveling charging and structure of soft planar polymer films

International audienceDuring the past decade, much attention has been devoted to the use of electrokinetic phenomena for addressing both charging mechanism and structure of multi-responsive soft polymeric layers whose thickness may range from few tens of nanometers to several microns. In particular, major progress was achieved in the quantitative reconstruction of streaming current data collected over a wide range of physico-chemical conditions using recent theories for electrohydrodynamics of soft diffuse planar interphases. In this article, we review the basics of the methodology adopted for deciphering the mechanisms governing the charging of electric double layers at soft planar films in connection with their structure that may vary according to pH, salt concentration or temperature depending on the responsive character of the system. It is demonstrated how the combination of streaming current, surface conductivity and swelling measurements allows for a comprehensive understanding of the interrelated protolytic, hydrodynamic, electrostatic and structural properties of polymer layers. We discuss the benefits and limits of the approach on the basis of studies carried out on uncharged, moderately charged and highly charged soft polymeric films supported by hard charged carriers. In a final part, the basic processes governing the peculiar electrokinetic properties of soft planar polyelectrolyte multilayers under lateral flow conditions are described

Interrelations between charging, structure and electrokinetics of nanometric polyelectrolyte films

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