PS_(3000)-b-PAA_(5000)球形胶束温度效应的原位小角X射线散射技术研究

应用小角X射线散射技术(SAXS)对两亲嵌段共聚物聚苯乙烯聚丙烯酸(PS-b-PAA)胶束形貌的温度影响进行了原位表征.SAXS结果表明:随着水含量的增加,粒子尺寸相应增加;对于水含量10%的PS_(3000)-b-PAA_(5000)胶束溶液,发现了明显的SAXS双峰现象;双峰的位置不随着温度的变化而改变,但是peak 1和peak 2的相对强度随着温度发生了减弱和增强的交错变化;相邻的SAXS双峰说明在PS_(3000)-b-PAA_(5000)胶束溶液中最初形成的粒子尺寸并不是均匀的,主要分为尺寸极其相近的两种球形粒子;随着温度的升高,粒径大小不同的两种粒子存在着一种消融和生长的过程,并且保持着一个相同的归一化动态平衡速率.

Temperature dependence of spherical micelles of PS3000-b-PAA5000 studied by in-situ small angle X-ray scattering

Amphiphilic block copolymer has a character that it spontaneously self-assembles into various micellar morphologies when dissolved in selective solvents with different proportions. Amphiphilic block copolymer has wide potential applications in drug delivery such as the targeting delivery, controlled release, molecular recognition, etc. Poly (styrene)-block-poly (acrylic acid) (PS-b-PAA) is a representative amphiphilic block copolymer whose self-assembly in the selective solvents has been widely studied during the past years. Micellar morphology of PS-b-PAA sensitive to temperature, and temperature effect of PS-b-PAA are of great importance for the drug delivery. However, the micellar morphologies of PS-b-PAA have been investigated mainly at the room temperature so far. The understanding is still limited to micellar morphology of PS-b-PAA in the varying temperature processes. In the present work, an investigation of the relationship between micellar morphology of PS-b-PAA and the temperature is conducted by using in-situ small-angle X-ray scattering (in-situ SAXS). The SAXS experiments are performed on the BL19U2 beamline of Shanghai Synchrotron Radiation Facility. The energy is selected to be 10 keV and the wave length is 0.1033 nm. The two-dimensional (2D) SAXS patterns are recorded by Pilatus 1 M with a pixel size of 172 μm×172 μm. A sample-to-detector distance of 5340 mm is chosen, giving access to a range of scattering vectors q of 0.11-0.89 nm^-1. The temperatures of the specimens are monitored by using a Linkam thermal stage THMS600 (Linkam Scientific Instruments). One-dimensional (1D) integrated intensity curves are obtained from the 2D SAXS patterns by employing the Fit2D software. The PS-b-PAAs (PS:PAA=3000:5000) is purchased from Sigma-Aldrich Inc and used directly (without any treatment prior to experiment). The PS-b-PAA is dissolved in solvents of N, N-Dimethylformamide and H₂O with various proportions. The concentration of solution of PS-b-PAA is 10 mg/mL. The experiments show that the sizes of micelle particles in PS₃₀₀₀-b-PAA₅₀₀₀ solution are grown with water content increasing, and double scattering peaks (q_peak1=0.418 nm^-1, q_peak1=0.456 nm^-1) appear for the solution with 10% water. A temperature-dependent change of SAXS intensity is demonstrated by in-situ SAXS. The intensities of peak 1 and peak 2 vary in a contrary waywith the sample's warming up, but the positions of the peaks are independent of temperature. The double peaks in SAXS profiles suggest that the size of micelle particles in the solution is not homogeneous but the micelles with two close sizes coexist. It is interesting that the number of two-sized particles changes at the same rate in the heating process although there is a significant difference between the initial number and the final number of micelles.