Amphiphilic azo polymers with different azo chromophores and degree of functionalization (DF) were synthesized

and colloidal spheres of the polymers were prepared by gradual hydrophobic aggregation in selective solvents.To obtain suspensions of colloidal spheres

the required amounts of water were added into the THF solutions at a certain stirring rate.As the water content reached ca.70 vol%

an excess of water was added into the suspensions to “quench” the formed structures.The obtained suspensions of colloidal spheres were sealed after THF was completely volatilized and were characterized by DLS and UV-Vis spectroscopy.The size and size-distribution of colloidal spheres were measured by using a DLS/SLS-5022F laser light scattering apparatus.Before the measurement

the sample was clarified by a 0.45 μm Millipore filter to remove dust

and all the DLS measurements were carried out with 90° scattering angle.UV-Vis spectroscopy was used to study the azo chromophore structure variation in the colloid formation process by measuring the parameters such as the trans-to-cis photoisomerization rate and the isomerization degree at the photostationary state.In the photoresponse experiments

the sample was irradiated by a 365 nm UV light source

and the light intensity was 7000 mV/cm2 at a distance of 38 cm and 21000 mV/cm2 at a distance of 5 cm

respectively.In our experiment

the sample was 15 cm away from the UV light

and the temperature of the environment was 30℃.The influences of molecular structure and preparation conditions on the size and photoresponsive properties of the colloidal spheres were studied in some detail. The result shows that the functional group type and DF as well as the preparation conditions (initial polymer concentration

the rate of water addition

etc.) have significant effects on the size and photoresponsive properties of the colloidal spheres. The size of colloidal spheres increases with the increase of DF and initial concentration

but decreases with the increase of the rate of water addition.The photoinduced isomerization rate of poly{2-4-(4-ethoxyphenylazo)phenoxy］ethyl acrylate-co-acrylic acid} (PEAPE) colloids is higher than that of poly{2-[-4-(4-cyanophenylazo)phenoxy］ethyl acrylate-co-acrylic acid} (PCNPE) colloids.The PEAPE colloids with higher DF show a slower photoisomerization rate. The photoinduced isomerization rate of the colloids decreases with the increase of initial concentration and the decrease of the rate of water addition.The possible mechanism for the influence is also discussed based on thermodynamics and kinetics consideration.It is believed that the colloidal spheres form through a self-assembling process controlled by the dynamic conditions.For high initial concentration and slow water dropping rate

more polymer chains tend to aggregate on the compact cores formed from the most hydrophobic chains as the water content is above the critical water content (CWC).Moreover

the polymeric chains had chance to rearrange themselves to form stable and compact structures due to the slow rate of water addition.On the other hand

as the rate of water addition increased

the polymeric chains attached to the cores were quickly “frozen" before they could completely adjust their conformations.Also

they could form new less compact cores so as to weaken the continuous aggregation probability.As a result

the formed aggregates had loose structures

and the photoinduced isomerization rate was relatively fast.