Comb copolymers with an adsorbing backbone and nonadsorbing side chains can be very effective dispersants, particularly when a high ionic strength strongly penalizes electrostatic stabilization. For this reason, they have become essential components of concrete over the past decade. This article examines the steric hindrance characteristics of such polymers through the use of atomic force microscopy (AFM) on calcium silicate hydrate, the main hydration product of Portland cement. It is found that solution and surface properties (hydrodynamic radius, radius of gyration, surface coverage, steric layer thickness) and force-distance curves obtained during AFM measurements can be well described by a scaling approach derived in this paper. This represents the first real quantitative step in relating these properties directly to the molecular structure of such comb copolymer dispersants.

Atomic force microscopy has been used to investigate the force at the origin of the cohesion of cement. The cohesion of cement grains is caused by surface forces acting between calcium silicate hydrate nanoparticles in interstitial electrolytic solution. Direct measurement of the interaction between two calcium silicate hydrate surfaces is performed in air and different aqueous solutions. In dry air, starting with the van der Waals forces, the interaction area between calcium silicate hydrate nanoparticles can be estimated. In electrolytic solution, the evolution of these forces is extensively dependent on both surface and solution chemistry. The roles of the calcium hydroxide concentration, pH, and ionic strength are investigated. The force measurements allow us to confirm the pre-eminence of ionic correlation forces in the cohesion of cement.

The time-dependent topology of domains in supported phospholipid bilayers of a binary mixture of dioleoylphosphatidylcholine and dipalmitoylphosphatidylcholine under a buffer solution has been studied by atomic force microscopy. We observe a transient regime of the phase separation until 45 min after a temperature quench from a miscible state of the system into the gel−liquid crystal coexistence region with the earliest observation after 20 min showing large gel-phase domains (containing ∼104−106 molecules) of irregular shapes. The transient regime is characterized by a power law for the growth rate of the domain size (A) with n = 3.0 ± 0.4 in A ∝ t 2/ n . After 45 min, an asymptotic power law with n = 20 ± 10 is observed and is linked to an inhibited domain growth. The evolution of individual domains suggests that domain growth in the transient regime is governed by a ripening mechanism. The growth inhibition is linked to the observation that the gel domains in each leaflet of the bilayer must grow simultaneously at the same sites as they remain superimposed on each other throughout the phase separation process.