Thermosensitive poly­(N-isopropylacrylamide) (PNIPAAm) microgel colloids were prepared by using water and high-boiling alcohol as binary solvent. Their thermosensitive behavior and solar modulation ability were studied by differential scanning calorimetery, ultraviolet–visible–near-infrared spectrophotometery, dynamic light scattering, and rheology. Effects of alcohol content and cross-linker dose on their microstructures and optical properties were investigated. A model house was constructed to test their energy-saving performance in smart windows. It was found that the solar modulation ability of PNIPAAm microgel colloids decreased with increasing N,N′-methylenebis­(acrylamide) (BIS) dose or alcohol content. Compared to glycol, glycerol showed better compatibility with PNIPAAm hydrogels, inducing less deterioration of the solar modulation ability. With 0.1 wt % (of NIPA) BIS, when glycerol was added as a cosolvent, the prepared PNIPAAm microgel colloids exhibited spherical morphology, controllable LCST, short response time, suitable viscosity, low freezing point, restrained evaporation rate, and excellent energy-saving performance, which makes them much better candidates for application in smart windows than those using a single solvent.

This work investigated how particle softness can influence the initial adhesive capture of submicrometer colloidal particles from flow onto collecting surfaces. The study focused on the case dominated by potential attractions at the particle periphery (rather than, for instance, steric stabilization, requiring entropically costly deformations to access shorter-range van der Waals attractions.) The particles, "spherical polyelectrolyte brushes" with diameters in the range of 150-200 nm depending on the ionic strength, consisted of a polystyrene core and a corona of grafted poly(acrylic acid) chains, producing a relatively thick (20-40 nm) negative brushy layer. The adhesion of these particles was studied on electrostatically heterogeneous collecting surfaces: negatively charged substrates carrying flat polycationic patches made by irreversibly adsorbing the poly-l-lysine (PLL) polyelectrolyte. Variation in the amount of adsorbed PLL changed the net collector charge from completely negatively charged (repulsive) to positively charged (attractive). Adjustments in ionic strength varied the range of the electrostatic interactions. Comparing capture kinetics of soft brushy particles to those of similarly sized and similarly charged silica particles revealed nearly identical particle capture kinetics over the full range of collecting surface compositions at high ionic strengths. Even though the brushy particles contained an average of 5 vol % PAA in the brushy shell, with the rest being water under these conditions, their capture was indistinguishable from that of similarly charged rigid spheres. The brushy particles were, however, considerably less adherent at low ionic strengths where the brush was more extended, suggesting an influence of particle deformability or reduced interfacial charge. These findings, that the short time adhesion of brushy particles can resemble that of rigid particles, suggest that for bacteria and cell capture, modeling the cells as rigid particles can, in some instances, be a good approximation.

Our present work investigated the phase behaviour of polybutadiene–poly acrylic acid (PB–PAA) brushes–solvent–CO2 ternary system in detail. The phase separation pressures increased with increasing temperatures and solid contents of PB–PAA solution, and decreased with increasing sizes of the brushes. Considering that the expansion of water was much smaller than that of ethanol by compressed CO2, a higher cloud point pressure of CO2 could be employed to reach the phase separation when water was added as the co-solvent. Owing to the penetration of CO2 into the periphery of the shell, the chains of the polymer brushes initially shrank and then turned to aggregations before finally precipitating upon CO2 addition. Our results provide a simple and effective way for separation and recovery of polymer brushes that could promote a wider range of their applications.