Revisiting polymer surface diffusion in the extreme case of strong adsorption.

Revisiting polymer surface adsorption with a level of quantification not possible at the time of earlier seminal contributions to this field, we employ fluorescence microscopy to quantify the in-plane diffusion of end-labeled polystyrene adsorbed onto quartz and mica from cyclohexane solution, mostly at 25 °C. Care is taken to prohibit a surface-hopping mechanism, and the experimental techniques are adapted to measurements that persist for up to a few days. The main conclusion is that we fail to observe a single Fickian diffusion coefficient: instead, diffusion displays a broad multicomponent spectrum, indicating that the heterogeneity of surface diffusion fails to average out even over these long times and over distances (∼600 nm, the diameter of a diffraction-limited spot) greatly exceeding the size of the polymer molecules.

Polymers zippered-up by electric charge reveal themselves.

In the current issue of ACS Nano, Löbling, Haataja et al. craft polymeric nanoparticles with a hierarchy of nontrivial surface structures by combining conventional interpolyelectrolyte complexation with steric control from an uncharged copolymer block. Remarkable cylindrical and lamellar nanodomains are produced on the polyionic coronae of spherical micelles.

Super-resolution study of polymer mobility fluctuations near c*.

Nanoscale dynamic heterogeneities in synthetic polymer solutions are detected using super-resolution optical microscopy. To this end, we map concentration fluctuations in polystyrene-toluene solutions with spatial resolution below the diffraction limit, focusing on critical fluctuations near the polymer overlap concentration, c*. Two-photon super-resolution microscopy was adapted to be applicable in an organic solvent, and a home-built STED-FCS system with stimulated emission depletion (STED) was used to perform fluorescence correlation spectroscopy (FCS).

Selective Janus particle assembly at tipping points of thermally-switched wetting.

Thermal wetting can simply, selectively and reversibly join patchy particles into clusters (2D and 3D) and also colloidal crystals over the narrow temperature range of 1-2 °C. This is demonstrated with Janus particles (gold half-coated silica spheres) immersed in a binary mixture of water/2,6-lutidine, such that the relative strength of gold-gold bonding through hydrophobic interaction and silica-silica bonding through the wetting-induced attraction is reversibly switched according to temperature.

Single-molecule observation of long jumps in polymer adsorption.

Single-molecule fluorescence imaging of adsorption onto initially bare surfaces shows that polymer chains need not localize immediately after arrival. In a system optimized to present limited adsorption sites (quartz surface to which polyethylene glycol (PEG) chains adsorb from aqueous solution at pH 8.2), we find that some chains diffuse back into bulk solution and readsorb at some distance away, sometimes multiple times before they either localize at a stable position or diffuse away into bulk solution.

Effects of anions on the aggregation of charged microgels.

In the present study, we have prepared poly(N-isopropylacrylamide-co-vinylbenzyl trimethylammonium chloride) (NIPAM-co-VT) and poly(N-isopropylacrylamide-co-sodium acrylate) (NIPAM-co-SA) thermally sensitive microgels, which are positively and negatively charged, respectively. By use of laser light scattering (LLS), we have investigated the temperature-induced aggregation of microgels in the presence of salts with the same cation but different anions. The studies demonstrate that neither kosmotropic nor chaotropic anions can lead to the aggregation of NIPAM-co-VT microgels.

Chemical oscillation induced periodic swelling and shrinking of a polymeric multilayer investigated with a quartz crystal microbalance.

Poly(acrylic acid- co-3-azidopropyl acrylate) and poly(acrylic acid- co-propargyl acrylate) have been alternately fabricated into a multilayer via the click reaction. The layer-by-layer deposition was monitored with a quartz crystal microbalance with dissipation (QCM-D) in real time. The response of the multilayer under continuous flow of a bromate-sulfite-ferrocyanide solution with pH oscillation has also been investigated by use of QCM-D.