In recent years

core-shell micro-particles and hollow capsules have aroused great research interests as new useful microstructures for many potential applications.In this work

core-shell spheres and hollow capsules containing azo polyelectrolytes were prepared by electrostatic layer-by-layer self-assembly and core-dissolution after the multiplayer deposition.In the electrostatic layer-by-layer self-assembling process

a side-chain azo polyelectrolytes (PEAPE) as polyanion was alternately adsorbed onto surfaces of polystyrene (PS) colloidal spheres together with a polycation of poly(diallyldimethylammonium chloride) (PDAC).PEAPE is a random copolymer composed of acrylic and azobenzene-containing acrylate units.PEAPE samples with degree of functionalization (DF) of 9.3% and 41.4% were used.Solutions of the polyelectrolytes (PEAPE and PDAC) in water and an aqueous medium of 0.1 mol/L NaCl were alternately added into the diluted suspension of PS latex for electrostatic layer-by-layer adsorption.After 15 min

PS spheres were separated and washed by high-speed centrifuge (ultracentrifuge

Hitachi CR 22G).Then the sediment was dispersed in Milli-Q water again for further experiment.The experiment steps were repeated several times until the required layer number was reached.The resulted core-shell particles were characterized by transmission electron microscopy (TEM

JEM-1200EX) and dynamic light scattering (DLS

Malvern Zetasizer 3000 HS).The layer-by-layer adsorption of PEAPE and PDAC was evidenced by the diameter increase from the TEM images and DLS measurements.The oscillation of Zete-potenctial after each adsorption step

which indicates the over charge compensation

also confirmed the successive self-assembly of azo polyelectrolytes.Changing the ionic strength of PDAC solution (in water or in aqueous medium of 0.1 mol/L NaCl) could obviously shift the Zete-potenctial of the colloids

but had little influence on the diameter increasing of the colloidal spheres.The photoisomerization of the azobenzenes was studied by UVVis spectroscopy.These azobenzene-containing core-shell particles show typical photochromic effect upon UV light irradiation.After adsorbed to colloidal surfaces

the H-aggregation of azobenzene groups decreased in certain degree and resulted in red shifts in UV-Vis spectrum.As a consequence

the azobenzene chromophores exhibited quickly photo-response behavior upon UV irradiation.To obtain hollow capsules with stable shells

a photosensitive cinnamate-containing polyelectrolyte (PAAEH

DF = 27%)

synthesized in authors’ lab

was applied to induce covalent crosslinking in the shells of colloidal spheres.In the process

PAAEH was adsorbed onto the core-shell particles of PS/(PDAC/PEAPE)3 through electrostatic self-assembly together with PDAC.In the process

PAAEH was dissolved in Milli-Q water with a concentration of 1 mg/mL and used as polyanions.After two or three layers of PDAC/PAAEH adsorbed

the core-shell colloidal spheres were exposed to UV light (18 mW/cm2) for 30 min.The photosensitive shells were cross-linked upon UV-light radiation.Then PS core of colloidal spheres was removed by dissolving with tetrahydrofuran/H2O (Ｖ:V=1:1).Finally

hollow capsules containing azo chromophores were obtained.Due to their photoresponsive composition

the core-shell particles and hollow capsules may have potential applications in areas such as bio-medicine and photoelectronics.