Marc Lemmers | Wageningen University (original) (raw)

Papers by Marc Lemmers

Soft Matter, 2012

ABSTRACT We study the influence of charge ratio on the transient network formation of bridged pol... more ABSTRACT We study the influence of charge ratio on the transient network formation of bridged polyelectrolyte complex micelles. The polyelectrolyte complex micelles are based on mixing an ABA triblock copolymer in which the A-blocks are positively charged and the B-block is neutral and hydrophilic, and a negatively charged homopolymer. We investigate the microstructure of our samples with (dynamic) light scattering and small-angle X-ray scattering, and the mechanical properties by rheometry. At charge stoichiometric conditions, we obtain flowerlike polyelectrolyte complex micelles. These micelles become interconnected at high concentrations, leading to a sample-spanning transient network. For excess negative charge conditions, we obtain so-called ‘soluble complexes’ which are small aggregates carrying the excess negative charge on the polyelectrolyte complex parts. For excess positive charge conditions, micelles stay intact, because the triblock copolymers can localize the excess positive charge at the periphery of the micellar corona. This structural asymmetry is not reflected in the mechanical properties, which show a strong decrease in viscosity on either side of the charge stoichiometric point.

Soft Matter, 2011

In this paper we study transient networks formed by co-assembly of an ABA triblock copolymer with... more In this paper we study transient networks formed by co-assembly of an ABA triblock copolymer with charged A blocks and neutral water-soluble B blocks, and an oppositely charged homopolymer. Above the CMC, the polymers associate into flowerlike micelles consisting of a polyelectrolyte complex core and a neutral corona of loops formed by the middle blocks. At higher concentrations, the micelles

Physical Review Letters, 2010

In this Letter we show that in the rheology of electrostatically assembled soft materials, salt c... more 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 processes.

Journal of Colloid and Interface Science, 2011

When aqueous solutions of polycations and polyanions are mixed, polyelectrolyte complexes form. T... more When aqueous solutions of polycations and polyanions are mixed, polyelectrolyte complexes form. These are usually insoluble in water, so that they separate out as a new concentrated polymer phase, called a complex coacervate. The behavior of these complexes is reviewed, with emphasis on new measurements that shed light on their structural and mechanical properties, such as cohesive energy, interfacial tension, and viscoelasticity. It turns out that stoichiometric complexes can be considered in many respects as pseudoneutral, weakly hydrophobic polymers, which are insoluble in water, but become progressively more soluble as salt is added. In fact, the solubility-enhancing effect of salt is quite analogous to that of temperature for polymers in apolar solvents.

Angewandte Chemie International Edition, 2010

Langmuir, 2012

We have prepared an aqueous physical gel consisting of negatively charged silica nanoparticles br... more We have prepared an aqueous physical gel consisting of negatively charged silica nanoparticles bridged by ABA triblock copolymers, in which the A blocks are positively charged and the B block is neutral and water-soluble. Irreversible aggregation of the silica nanoparticles was prevented by precoating them with a neutral hydrophilic polymer. Both the elastic plateau modulus and the relaxation time increase slowly as the gel ages, indicating an increase both in the number of active bridges and in the strength with which the end blocks are adsorbed. The rate of this aging process can be increased significantly by applying a small shear stress to the sample. Our results indicate that charge-driven bridging of nanoparticles by triblock copolymers is a promising strategy for thickening of aqueous particle containing materials, such as water-based coatings.

Soft Matter, 2012

ABSTRACT We study the influence of charge ratio on the transient network formation of bridged pol... more ABSTRACT We study the influence of charge ratio on the transient network formation of bridged polyelectrolyte complex micelles. The polyelectrolyte complex micelles are based on mixing an ABA triblock copolymer in which the A-blocks are positively charged and the B-block is neutral and hydrophilic, and a negatively charged homopolymer. We investigate the microstructure of our samples with (dynamic) light scattering and small-angle X-ray scattering, and the mechanical properties by rheometry. At charge stoichiometric conditions, we obtain flowerlike polyelectrolyte complex micelles. These micelles become interconnected at high concentrations, leading to a sample-spanning transient network. For excess negative charge conditions, we obtain so-called ‘soluble complexes’ which are small aggregates carrying the excess negative charge on the polyelectrolyte complex parts. For excess positive charge conditions, micelles stay intact, because the triblock copolymers can localize the excess positive charge at the periphery of the micellar corona. This structural asymmetry is not reflected in the mechanical properties, which show a strong decrease in viscosity on either side of the charge stoichiometric point.

Soft Matter, 2011

In this paper we study transient networks formed by co-assembly of an ABA triblock copolymer with... more In this paper we study transient networks formed by co-assembly of an ABA triblock copolymer with charged A blocks and neutral water-soluble B blocks, and an oppositely charged homopolymer. Above the CMC, the polymers associate into flowerlike micelles consisting of a polyelectrolyte complex core and a neutral corona of loops formed by the middle blocks. At higher concentrations, the micelles

Physical Review Letters, 2010

In this Letter we show that in the rheology of electrostatically assembled soft materials, salt c... more 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 processes.

Journal of Colloid and Interface Science, 2011

When aqueous solutions of polycations and polyanions are mixed, polyelectrolyte complexes form. T... more When aqueous solutions of polycations and polyanions are mixed, polyelectrolyte complexes form. These are usually insoluble in water, so that they separate out as a new concentrated polymer phase, called a complex coacervate. The behavior of these complexes is reviewed, with emphasis on new measurements that shed light on their structural and mechanical properties, such as cohesive energy, interfacial tension, and viscoelasticity. It turns out that stoichiometric complexes can be considered in many respects as pseudoneutral, weakly hydrophobic polymers, which are insoluble in water, but become progressively more soluble as salt is added. In fact, the solubility-enhancing effect of salt is quite analogous to that of temperature for polymers in apolar solvents.

Angewandte Chemie International Edition, 2010

Langmuir, 2012

We have prepared an aqueous physical gel consisting of negatively charged silica nanoparticles br... more We have prepared an aqueous physical gel consisting of negatively charged silica nanoparticles bridged by ABA triblock copolymers, in which the A blocks are positively charged and the B block is neutral and water-soluble. Irreversible aggregation of the silica nanoparticles was prevented by precoating them with a neutral hydrophilic polymer. Both the elastic plateau modulus and the relaxation time increase slowly as the gel ages, indicating an increase both in the number of active bridges and in the strength with which the end blocks are adsorbed. The rate of this aging process can be increased significantly by applying a small shear stress to the sample. Our results indicate that charge-driven bridging of nanoparticles by triblock copolymers is a promising strategy for thickening of aqueous particle containing materials, such as water-based coatings.