Phase behavior of flowerlike micelles in a SCF cell model

We study the interactions between flowerlike micelles, self-assembled from telechelic associative polymers, using a molecular self-consistent field (SCF) theory and discuss the corresponding phase behavior. In these calculations we do not impose properties such as aggregation number, micellar structure and number of bridging chains. Adopting a SCF cell model, we calculate the free energy of interaction between a central micelle surrounded by others. Based on these results, we predict the binodal for coexistence of dilute and dense liquid phases, as a function of the length of the hydrophobic and hydrophilic blocks. In the same cell model we compute the number of bridges between micelles, allowing us to predict the network transition. Several quantitative trends obtained from the numerical results can be rationalized in terms of transparent scaling argument

Brownian particles in transient polymer networks

We discuss the thermal motion of colloidal particles in transient polymer networks. For particles that are physically bound to the surrounding chains, light-scattering experiments reveal that the submillisecond dynamics changes from diffusive to Rouse-like upon crossing the network formation threshold. Particles that are not bound do not show such a transition. At longer time scales the mean-square displacement (MSD) exhibits a caging plateau and, ultimately, a slow diffusive motion. The slow diffusion at longer time scales can be related to the macroscopic viscosity of the polymer solutions. Expressions that relate the caging plateau to the macroscopic network elasticity are found to fail for the cases presented here. The typical Rouse scaling of the MSD with the square root of time, as found in experiments at short time scales, is explained by developing a bead-spring model of a large colloidal particle connected to several polymer chains. The resulting analytical expressions for the MSD of the colloidal particle are shown to be consistent with experimental findings

Relaxation dynamics at different time scales in electrostatic complexes: Time-salt superposition

In this Letter we show that in the rheology of electrostatically assembled soft materials, salt concentration plays a similar role as temperature for polymer melts, and as strain rate for soft solids. We rescale linear and nonlinear rheological data of a set of model electrostatic complexes at different salt concentrations to access a range of time scales that is otherwise inaccessible. This provides new insights into the relaxation mechanisms of electrostatic complexes, which we rationalize in terms of a microscopic mechanism underlying salt-enhanced activated processe

Elastic networks of protein particles

This paper describes the formation and properties of protein particle suspensions. The protein particles were prepared by a versatile method based on quenching a phase-separating protein–polysaccharide mixture. Two proteins were selected, gelatin and whey protein. Gelatin forms aggregates by means of reversible physical bonds, and whey protein forms aggregates that can be stabilized by chemical bonds. Rheology and microscopy show that protein particles aggregate into an elastic particle gel for both proteins. Properties similar to model systems of synthetic colloidal particles were obtained using protein particle suspensions. This suggests that the behaviour of the particle suspensions is mainly governed by the mesoscopic properties of the particle networks and to a lesser extent on the molecular properties of the particle

Dynamics of polymer bridge formation and disruption

In this Letter we show, with colloidal probe AFM measurements, that the formation and subsequent disruption of polymer bridges between two solid surfaces is characterized by slow relaxation times. This is due to the retardation of polymer dynamics near a surface. For colloidal particles, that are in constant (Brownian) motion, kinetic aspects are key. To understand these effects, we develop a model of polymer bridging and bridge disruption that agrees quantitatively with our experiment

Hierarchical Adsorption of Network-Forming Associative Polymers

In this paper, we discuss the hierarchical adsorption of micelles formed from network-forming, telechelic, associative polymers at an air-water interface. We propose an interfacial mechanism that involves three distinct steps: (i) adsorption of the micellar coronas at the interface, (ii) unfolding of the micelles to anchor the hydrophobic tails at the interface, and (iii) formation of a secondary adsorption layer by bridging between the primary layer and micelles in the bulk. While the first, transport-limited process is relatively fast, the latter processes are surprisingly slow; it may take up to 10(6) s for the adsorption to complete

Physics of associative polymers : bridging time and length scales

cum laude graduation (with distinction

Crystallization and intermittent dynamics in constricted microfluidic flows of dense suspensions

A strong coupling between shear, confinement and microstructure governs the flow of dense colloidal suspensions through narrow channels. In this paper we explore the additional complexity that arises when the channel is partially blocked by a constriction in the centre of the channel. The reduction of the particle flux due to the constriction induces a densification upstream from the constriction, resulting in the formation of extended crystalline domains. A dynamic equilibrium establishes, which is characterized by large fluctuations in the instantaneous flow velocity and the local density. In some cases, the individual events leading to this intermittent behaviour are clearly visible as transient and localized jamming and unjamming events

Physical chemistry of supramolecular polymer networks

Supramolecular polymer networks are three-dimensional structures of crosslinked macromolecules connected by transient, non-covalent bonds; they are a fascinating class of soft materials, exhibiting properties such as stimuli-responsiveness, self-healing, and shape-memory. This critical review summarizes the current state of the art in the physical–chemical characterization of supramolecular networks and relates this knowledge to that about classical, covalently jointed and crosslinked networks. We present a separate focus on the formation, the structure, the dynamics, and the mechanics of both permanent chemical and transient supramolecular networks. Particular emphasis is placed on features such as the formation and the effect of network inhomogeneities, the manifestation of the crosslink relaxation dynamics in the macroscopic sample behavior, and the applicability of concepts developed for classical polymer melts, solutions, and networks such as the reptation model and the principle of time–temperature superposition (263 references)

Geometry- and rate-dependent adhesive failure of micropatterned surfaces

The dynamic nature of adhesive interface failure remains poorly understood, especially when the contact between the two surfaces is localized in microscopic points of adhesion. Here, we explore the dynamic failure of adhesive interfaces composed of a large number of micron-sized pillars against glass. Surprisingly, we find a large influence of the microcontact geometry; ordered arrays of these pillars exhibit significantly stronger adhesive properties than equivalent surfaces in which the pillars are disordered. This can be understood with a simple geometric argument that accounts for the number of adhesive bonds that needs to be broken simultaneously to propagate the crack front. Moreover, the adhesive strength in both cases depends largely on the velocity with which the surfaces are separated. This rate dependence is explained on the basis of a semi-phenomenological model that describes macroscopic failure as a consequence of microscopic bond-rupture events. Our results suggest that the dynamics of adhesive failure, in the limit explored here, is predominantly stress-driven and highly sensitive to local geometry effects