RESUMEN
There is a cosine function between the reflected light intensity of a solid surface and its refractive index. And the mean squared fluctuation of refractive index is related to fluctuation of density and concentration. So some internal structures changes of materials can be reflected by changes in reflected light. Based on this theory, the synchronous scanning spectrum (SSS) technique was successfully applied to monitor melting and nonisothermal melt-crystallization of poly(ε-caprolactone) (PCL) film on a copper substrate. SSS can be implemented on a spectrofluorimeter by simultaneously scanning the excitation and emission monochromators (i. e, Δλ = λex-λem = 0 nm). In SSS of PCL films, two dominant peaks correlated to the light source spectrum of the spectrofluorimeter (at 467 and 473 nm) were used to characterize the macromolecular structure evolution during the melting and nonisothermal melt-crystallization processes. Detailed thermodynamic and crystallization kinetics parameters obtained by SSS method. The Avrami exponent n obtained by SSS method is in the range of 2.8-3.2 with an average of 3.13, illustrating a heterogeneous nucleation process followed by a three-dimensional spherulitic crystal growth mechanism. The crystallization activation energy is -158.2 kJ · mol(-1). These results are in agreement with values determined from differential scanning calorimetry (DSC) method. It indicates that SSS technique is a simple, effective in situ method for measuring the dynamic melting and crystallization process of polymers. Moreover, the SSS method is a universal spectroscopic technique based on a spectrofluorimeter for monitoring both luminescent and non-luminous solid polymers.
RESUMEN
Chitosan (CS)-modified poly(D,L-lactide-co-glycolide) (PLGA/CS) nanoparticles with cationic surface were prepared by means of emulsion-solvent evaporation technique using polyviny alcohol and chitosan as costabilizers. The preparation conditions of the cationic nanoparticles were optimized by orthogonal factorial design, and the influences of the experiment variables such as polymer concentration, the molecular weight of chitosan, etc., on the size and zeta potential of the nanoparticles were evaluated. It was shown that the diameter of the PLGA/CS nanoparticles can be controlled in the range of 150-200 nm as determined by dynamic light scattering with the optimized conditions. The zeta potential of PLGA/CS nanoparticles increased with increasing the concentration of CS (C(CS)) or decreasing the pH, it was up to 55 mV when C(CS) was 3 mg/mL at pH 4 and inversed around pH 8. The optimization conditions for fabricating the relatively small diameter and high zeta potential cationic nanoparticles were C(CS) 3 mg/mL, C(PLGA) 10 mg/mL, and the volume ratio of organic solution to aqueous medium 1/4. X-ray photo electron spectroscopy and fluorescence inverted microscope observations approved that CS molecules were adsorbed on the surface of PLGA nanoparticles, DNA-condensing ability of the PLGA/CS nanoparticles and cell transfection efficiency of the nanoparticle-DNA complexes were estimated by gel electrophoresis and transfection experiment to 293FT cell, respectively.