Fabrication And Functionalization Of Multilayer Films Assembled Through Layer-By-Layer Technique

Layer-by-layer(Lb L) self-assembly has emerged as a versatile and convenient method for the construction of thin films with precise control of film thickness and compositions. In last two decades, the rapid development of Lb L technology has a inseparable relationship with the fabrication of films with functional diversification. In this work, several Lb L films were assembled for drug delivery, optical and electrical applications respectively. The main contents of research in the paper were listed below:(1) In our previous studies, it was found the the drug loading capacity of Polyurethane(PU) based Lb L films were variable in large scale. Here, it was investigated in detail to find the regultriay between molecular structure of the film components and the drug loading capacity of the assembled films. Three polysaccharides, sodium hyaluronate(NaHA), sodium carboxymethyl cellulose(CMC) and sodium alginate(ALG) were used to fabricate Lb L films with PU, respectively. The adsorption behaviors of PU/Na HA, PU/CMC, PU/ALG multilayer films were investigated using methylene blue(MB) as model drug under different pH and ionic strength conditions. Results showed that the adsorption behavior of the three films well fit the Langmuir adsorption and pseudo second-order model. The amount and type of functional groups of polysaccharides played a crucial role in the adsorption behavior of Lb L films.(2) Novel photochromic polyethyleneimine/phosphotungstic acid(PEI/PTA) multilayer film were assebmled. Under the irradiation of UV-light, PEI/PTA multilayer film turned from colorless to blue gradually. The absorption maxima(λmax) of the colored LbL film(formed after UV-irradiation) was 710 nm. The strong colorability of the Lb L film may be attributed to the transformation of W6+â†'W5+corresponding to the reduction of heteropoly acid to heteropoly blue. And the Lb L film would be bleached from blue to colouless when exposed to air or O2 environment. After 10 circles of colouring and bleaching, it seemed that the absorbance value of Lb L films almost keep a constant. It suggested that the stability and reversibility of photochromism of the PEI/PTA multilayer films were very well.(3) A novel electrochemical sensor was prepared by alternatively deposition of anionic phosphotungstic acid and polyelectrolyte poly(ethyleneimine) on ITO glass through Lb L assembly technique. The as-prepared sensor was characterized Cyclic voltammetry. The sensor was used to determine H2O2 and ascorbic acid in solution, it was found that linear range was from 3.5×10-3-3.5×10-2 and 1.0×10-3-1.2×10-2 mg/mL with a detection limit of 8.4×10-4 and 6.4×10-4 mg/mL and recoveries of 99.64% and 100.15% to H2O2 and ascorbic acid, respectively. And the sensor was further used to determine ascorbic acid in three real juice beverage samples. Validated by high performance liquid chromatogrphy method, the results were satisfied. Compared with previous reports, the PEI/PTA multilayer film modified electrode exhibited high sensitivity, good stability and reusability to both of the electrocatalytic reduction of H2O2 and oxidation of ascorbic acid. It indicated that PEI/PTA multilayer films modified electrode was a promising alternative to detect compounds with oxidability or reducibility.