Interaction forces and molecular adhesion between pre-adsorbed poly(ethylene imine) layers

Abstract

Interaction forces between pre-adsorbed layers of branched poly(ethylene imine) (PEI) of different molecular mass were studied with the colloidal probe technique, which is based on atomic force microscopy (AFM). During approach, the long-ranged forces between the surfaces are repulsive due to overlap of diffuse layers down to distances of a few nanometers, whereby regulation of the surface charge is observed. The ionic strength dependence of the observed diffuse layer potentials can be rationalized with a surface charge of 2.3 mC/m 2 . The forces remain repulsive down to contact, likely due to electro-steric interactions between the PEI layers. These electro-steric forces have a range of a few nanometers and appear to be superposed to the force originating from the overlap of diffuse layers. During retraction of the surfaces, erratic attractive forces are observed due to molecular adhesion events (i.e., bridging adhesion). The frequency of the molecular adhesion events increases with increasing the ionic strength. The force response of the PEI segments is dominated by rubber-like extension profiles. Strong adhesion forces are observed for low molecular mass PEI at short distances directly after separation, while for high molecular mass weaker adhesion forces at larger distances are more common. The work of adhesion was estimated by integrating the retraction force profiles, and it was found to increase with the ionic strength.

Chain Length and Grafting Density Dependent Enhancement in the Hydrolysis of Ester-Linked Polymer Brushes

“…The sensitivity of the cantilevers was determined from the constant compliance regime of the force−distance curves recorded on a cleaned glass slide; the spring constant was evaluated by thermal noise analysis before each experiment. The polymer chain length was determined from the tip−sample separation at the point of the last detachment 16 , and HMTETA (60 μL) were added successively into a glass tube followed by adding 12 mL of Milli-Q water. The solution was degassed with three freeze−pump−thaw cycles.…”

Charging and stability of anionic latex particles in the presence of linear poly(ethylene imine)

“…BPEI is known to reverse the charge of negatively charged particles, and one knows that in the presence of BPEI, colloidal suspensions become unstable and have high-yield stress close to the IEP [19,20]. Repulsive forces due to diffuse layer overlap set in above the IEP as has been shown with the AFMbased colloidal probe technique [31].…”

“…Forces between surfaces with adsorbed polyelectrolytes were measured directly with the surface forces apparatus and with the colloidal probe technique based on the atomic force microscope (AFM) [28][29][30][31][32][33][34]. These studies have demonstrated that interaction forces are repulsive at high polyelectrolyte dose and that they are controlled by the surface charge induced by the adsorbed polyelectrolyte and the resulting overlap between the diffuse parts of the electrical double-layer.…”

“…Poly(ethylene imine) is an important polyelectrolyte within this class, and is known in two different forms [38,39]. Highly branched poly(ethylene imine) (BPEI) is obtained by ring-opening polymerization of ethylenimine and linear poly(ethylene imine) (LPEI) is synthesized by the hydrolysis of poly(2-oxazoline)s. These polyelectrolytes were investigated in substantial detail [31,38,[40][41][42][43][44]. Being a weak polybase, the charging characteristics are determined by the ionization constants of the different amine groups present and the interactions between these groups.…”

Conformation of Poly(styrene sulfonate) Layers Physisorbed from High Salt Solution Studied by Force Measurements on Two Different Length Scales

“…This is a behavior very different from polyelectrolytes adsorbed from salt-free solution, which show an electrostatic repulsion. [16][17][18] While for linear polyelectrolytes adsorbed from high salt concentration no electrostatic force was directly observed, the thickness of the physisorbed layer scales like a salted brush (this is one of the phases occurring in polyelectrolyte brushes and is characterized by incorporation of counterions into the brush leading to charge neutralization within the brush). Therefore, we concluded that in the presence of 1 M NaCl linear polyelectrolytes adsorb in a coiled conformation onto the surface.…”