Interactions Between Polymer Brushes: Varying the Number of End‐Attaching Groups

Abstract

Summary: We use a surface force balance (SFB) to study the normal interactions between polymer brushes, which are self‐assembled from solution. They consist of polystyrene (PS) chains in toluene (neutral chains in a good solvent) anchored on the interacting mica surfaces via sulfozwitterionic end groups. The properties of the brush depend on the length, N, of the chain, and the energy, αkBT, with which the end group adsorbs on the surface. In contrast to earlier studies where N was varied, we attempt to vary the sticking energy by using polymer chains with one, two, and three zwitterions attached to their ends. We use the theory of Alexander and de Gennes to predict how the normal force profile should vary with α and N, finding, for example, that the brush height L0 obeys $L_0 = a \cdot N^{3/5} \cdot \alpha ^{2/5}$. Surprisingly, our measurements show that the grafting density does not vary significantly between polymers with 1, 2, and 3 end groups. This could be attributed to dipole‐dipole interactions between the zwitterions themselves. It is also possible that the effect could be kinetic: that the brush is unable to reach its equilibrium state because successive polymer chains are hindered from attaching to the surface by those already in the brush. Measurements on longer time scales will be necessary to determine whether kinetic effects are important.

Density Effects on Collapse, Compression, and Adhesion of Thermoresponsive Polymer Brushes

“…To this aim, we compare the low temperature compression curves, F (D)/R, with R the radius of curvature of the surfaces [49,50], with the following prediction for the free energy per unit area of two compressed brushes [45,51,52]:…”

Structure and Collapse of a Surface-Grown Strong Polyelectrolyte Brush on Sapphire

“…Notably, acrylate- and methacrylate-based ATRPs have been used to create a wide variety of brushes with different functionalities and architectures, based on a common synthetic approach (for reviews, see, e.g., refs − ). The advantages of grafted-from brushes include the ability to access higher density regimes, due to bypassing the kinetic limitations on grafted-to brush density that arises from the slow diffusion of preexisting polymer chains through a partially formed brush. ,− Also, it is generally straightforward to devise brushes that are strongly surface-anchored, for example through the use of covalently anchored self-assembled monolayers of initiator molecules. Finally, the use of grafting-from can bypass physical limitations that apply to the self-assembly of preexisting polymer, e.g., by permitting unlimited overcompensation of the electrical charge on a substrate surface …”

Interaction Forces between Microsized Silica Particles and Weak Polyelectrolyte Brushes at Varying pH and Salt Concentration

“…These switching effects are regarded as very important for the design of biomaterial interfaces and have found numerous applications in the field of controlled protein adsorption, − the design of microfluidic devices, responsive wetting, , lubrication, , sensors, − immobilization or controlled motion of nanoparticles, − and smart colloids. , On the other hand, the interaction of colloidal particles covered by polyelectrolyte brushes with charged surfaces can be controlled. , Polyelectrolytes as binding media have the great advantage that each molecule contains a large number of charged groups resulting in a high binding strength provided by electrostatic interactions. In the dissociated state, charged groups interact electrostatically with charged surfaces, but they also may form hydrogen bonds with polar species …”

“…Most of them were done in systems where both surfaces are covered with identical brushes. They were performed using the surface force apparatus, − the surface force balance, , and the AFM colloidal probe technique. − Forces between two microsized particles carrying polyelectrolyte brushes were determined very recently by optical tweezers , and by microsurface potential measurements …”