Self-assembly Behavior Research Of Hydrophobic Modified Dextran/PLA System

A series of amphiphiles were synthesized by hydrophobically modified aldehyde dextran with three different hydrophobic functional groups—cholesterol (CH), lauric acid (Lau), and poly(ethyl glycol) (PEG) ,which all have been analysized by 1H-NMR. The critical aggregate concentrations of their micellizations formed in aqueous medium were measured by means of fluorescent spectroscopy with pyrene as the hydrophobic probe. The CAC values for CH-DEX-CHO, DEX-Lau, and DEX-PEG were 0.22mg/ml, 0.14mg/ml, and 0.014mg/ml respectively.In this article, the microemulsions of dextran derivates / poly(lactic acid) (PLA) were prepared by the co-dialyzing method. Transmission electron microscopy (TEM) combined with dynamic light scattering (DLS) technique was used to characterize the morphologies of the self-aggregates and their size. It is demonstrated that the two ways, increasing the concentrations of the amphiphiles and raising the weight ratio of the PLA in the system, have the same effects on the self-assembly behaviors, i.e. the sizes of the nanoparticles falls first and then arise;Furthermore, by changing the cholesterol's hydrophobic substitution degree, we find out that with the hydrophobic substitution degree increases, the size of the nanoparticle increases.Setting the DEX-Lau as the research model, a series of DEX-Lau/PLA microemulsions with the different weight content of PLA and different hydrophobic substitution degrees were prepared by co-dialyzing method. Indicated by the results of TEM, whatever the hydrophobic substitution degrees are, by increasing the PLA content, the corona thickness increases, core size decreases, there is a trend of the shapes of the aggregates changing from vesicles to spheres. Through the discussion of the way of PLA worked with amphiphile and the conformation of PLA existed in the inner of aggregate, it explains that why the aggregate shape changed in the DEX-Lau/PLA system. Furthermore, DEX-Lau with a low hydrophobic substitution degree is apt to form vesicles and owns better vesicle shapes than those with a high hydrophobic substitution degrees, owing to the hydrophobic interaction weak in the inner micelles. And the former is a better"container"for PLA than the latter. Additionally, a simple explaination is did on some special morphologies observed in the DEX-Lau/PLA.