Surface rheology of block-copolymer stabilized interfaces: a combined computational & experimental study. SNF project 200021_156106 at www.complexfluids.ethz.ch/snf15
We investigate the conformation, position, and dynamics of core-shell nanoparticles (CSNPs) composed of a silica core encapsulated in a cross-linked poly(N-isopropylacrylamide) shell at a water-oil interface for a systematic range of core sizes and shell thicknesses. We first present a free-energy model that we use to predict the CSNP wetting behavior at the interface as a function of its geometrical and compositional properties in the bulk phases, which is in good agreement with our experimental data. Remarkably, based on the knowledge of the polymer shell deformability, the equilibrium particle position relative to the interface plane, an often elusive experimental quantity, can be extracted by Shell thickness measuring its radial dimensions after adsorption. For all the systems studied here, the interfacial dimensions are always larger than in bulk and the particle core resides in a configuration, wherein it just touches the interface or is fully immersed in water. Moreover, the stretched shell induces a larger viscous drag at the interface, which appears to depend solely on the interfacial dimensions, irrespective of the portion of the CSNP surface exposed to the two fluids. Our findings indicate that tailoring the architecture of CSNPs can be used to control their properties at the interface, as of interest for applications including emulsion stabilization and nanopatterning. Vasudevan, Siddarth A./Q-5449-2019; Kroger, Martin/C-1946-2008; Karg, Matthias/C-7555-2012; Isa, Lucio/F-1529-2010 Vasudevan, Siddarth A./0000-0003-2471-2793; Kroger, Martin/0000-0003-1402-6714; Isa, Lucio/0000-0001-6731-9620 Swiss National Science Foundation [PPOOP2 172913/1, 200021_156106]; German Research Foundation (DFG) through the Emmy Noether-Program [KA 3880/1-1]; ETH Research Grant [ETH-13 14-1] We thank J. Vermant and V. Garbin for useful discussions. S.V. and L.I. acknowledge the financial contribution from the Swiss National Science Foundation Grant PPOOP2 172913/1 and the ETH Research Grant ETH-13 14-1. M.K. acknowledges financial support from the German Research Foundation (DFG) through the Emmy Noether-Program (KA 3880/1-1). M.K. acknowledges the support from the Swiss National Science Foundation through grant 200021_156106. [hide]
Principal Investigators
Leonard Sagis (PL)
Polymer Physics, ETH Zurich, Switzerland ►
Wageningen University, Netherlands ►
Patrick Ilg (PL)
Polymer Physics, ETH Zurich, Switzerland ►
University of Reading, United Kingdom ►
Peter Fischer (Co-PI)
Inst. Food, nutrition and health, ETH Zurich, Switzerland ►
Martin Kröger (PI)
Polymer Physics, ETH Zurich, Switzerland ►
Secretary
Patricia Horn
Polymer Physics, ETH Zurich, Switzerland ►
Involved Students
Ahmad Moghimikheirabadi
Polymer Physics, ETH Zurich, Switzerland ►
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Selected conferences (co-)organized by project members
IWNET 2015
05 Jul - 10 Jul 2015, 7th International workshop on nonequilibrium thermodynamics (IWNET 2015), Hilvarenbeek, The Netherlands ►
learn more ► About this project
Complex fluid-fluid interfaces are interfaces in which the adsorbed species self-assemble into complex microstructures. Such interfaces are ubiquitous in nature, industrial processes, and consumer products, and can be found in living cells, nano- and microcapsules, vesicles, food emulsions, or foam. Compared to simple liquid-like interfaces (stabilized by low molecular weight surfactants), complex interfaces display significant viscoelasticity, with high values for their surface shear and dilatational moduli. Their stress-deformation behavior dominates the macroscopic dynamics of multiphase materials that contain such interfaces, and when this occurs those materials can be referred to as Interface-Dominated Materials (IDMs).Complex interfaces can be formed by a wide range of surface active components, such as proteins, colloidal particles, polymers, lipids, or mixtures of these components. In this proposal we will focus on complex interfaces stabilized by amphiphilic multi-block copolymers. These polymers consist of alternating blocks of a hydrophilic repeating unit A, and a hydrophobic repeating unit B. Amphiphilic copolymers can form interfaces with exceptional mechanical properties. This makes them ideal candidates for application in highly stable emulsions, or encapsulation systems with high mechanical stability, for application in food and pharmaceutical products.
Amphiphilic copolymers may form 2d gels, 2d (soft) glass phases, 2d (liquid) crystalline phases, or even 2d metastable emulsions (phase-separated mixtures of immiscible copolymers) after adsorption. The type of structure formed depends on surface concentration, and length, distribution, rigidity, and hydrophobicity of the sub-blocks of the copolymer. The response of polymer stabilized fluid-fluid interfaces to deformations or gradients in temperature is often highly nonlinear. The nonlinearity in their response to perturbations is a result of changes in this interfacial microstructure, induced by the applied gradients. The effect of deformations on interfacial microstructure, and the effect of these changes on macroscopic dynamics of interface-dominated materials is still poorly understood. A more fundamental understanding of the nonlinear response of polymer interfaces, is essential for a targeted design of high-end polymer stabilized IDMs, such as encapsulation systems with environmental triggers, nanoparticles with structured interfaces, or foam and emulsions with extreme stability. In view of the widespread occurrence of IDMs, the study of dynamic mechanical properties of these interfaces is highly relevant for many disciplines, such as colloid and interface science, physical chemistry, polymer physics, pharmaceutical science, food science, coating technology, or soft matter physics.
The aim of this project is to characterize the microstructure and mechanical properties of interfaces stabilized by multi-block copolymers, using a multiscale multidisciplinary approach, which integrates state of the art computational methods with surface rheological experiments, and experimental interfacial structure evaluation. The computational modeling will be done using Monte Carlo (MC) and Molecular Dynamics (MD) simulations. We will measure both shear and dilatational surface properties, and the microstructure will be evaluated using various forms of microscopy (AFM, TEM, SEM), and neutron and X-ray reflectivity measurements. We will determine the mechanical properties and interfacial structure as a function of surface polymer concentration, chemical structure of the polymers (variation of number, size, and distribution of blocks), and degree of hydrophobicity and rigidity of the sub-blocks. A detailed insight in the dynamic behavior of copolymer interfaces will provide new insight in the macroscopic dynamic behavior of polymer stabilized interface-dominated materials (emulsions, foam, encapsulation systems, nanoparticles), and will allow a more targeted design of these systems with tailor made properties, tuned for specific industrial applications.
29 April 2024 mk