Carbon dots (CDs) are a new class of materials which have been extensively studied due to their unique optical properties, low toxicity, and abundance of raw materials to synthesize them. In this minireview, it is highlighted that the stability of the optical properties of CDs is an important aspect that has received very little attention. While CDs are usually considered to be photostable, several recent reports show they are prone to photobleaching. Studies of blinking, photobleaching, and photoswitching of CDs are reviewed here. It is noted that there is a lack of systematic studies about the photostability of CDs, and efforts are needed to further study this aspect. Furthermore, it is observed that the stability of CDs is somewhat related to their photoluminescence quantum yield, excitation dependence of PL emission, precursor, and synthesis method used to produce CDs. 相似文献
Hyaluronic acid is a polysaccharide with viscoelastic and mechanical properties that are crucial for the normal functioning of osteoarticular junctions. It is demonstrated that introduction of a hexadecyl side chain into HA yields an injectable polysaccharide capable of forming physical hydrogels, which are stable at very low polymer concentrations, whereas native hyaluronic acid forms viscous solutions at concentrations that are ten times higher. Characterization of this system showed that the driving force for its gel‐like behavior is the occurrence of hydrophobic interactions involving aliphatic side chains, despite the low degree of substitution, as confirmed by molecular dynamics simulations of HYADD4 and HA hydrogels.
A detailed study of color change in poly(vinyl chloride) (PVC) sheets due to high intensity ultraviolet (UV) irradiation was undertaken, focusing on the first 50 h of change. Color changes were monitored with a Datacolor check spectrophotometer and compared with a set of controls. Measurements were taken after 1, 3, 5, 10, 15, and 20 h of irradiation, then at 10 h intervals for the next 40 h. Further measurements were conducted at 100, 240, and 480 h. Data were analyzed using the reflectance spectra (350–800 nm) as well as the CIE (International Commission on Illumination) L* a* b* color values (L*, a*, and b* are lightness value, redness-greenness value, and yellowness-blueness value, respectively) and the total color change (ΔE). The majority of color changes were found to occur within the first 50 h. After 50 h, the color change slowed and began to reverse toward 480 h. Surface microstructure properties, such as morphology, surface tension and oxidized products, were characterized to allow a comparison of sensitivity between the color monitoring methods and a comprehensive understanding of the color change. The results show that color evolution was attributable to the competition between the formations of polyene sequences (dehydrochlorination reaction) and their subsequent oxidation (photobleaching), which was slightly different from the behavior under a xenon arc lamp. According to the color behavior and the microstructure analysis a general scheme accounting for the mechanism of ageing behavior of PVC under high intensity UV irradiation is proposed. 相似文献
药物分子从药物载体中的释放行为与载体的结构有密切关系.本实验中采用丙烯酰胺和丙烯酸等材料,运用水相沉淀的方法,制备了4种不同单体配比的聚丙烯酰胺-丙烯酸(P(Am-co-Ac))共聚物水凝胶.运用红外分析方法对P(Am-co-Ac)组成进行表征.使用荧光漂白恢复法(FRAP,fluorescence recovery after photobleaching)观察荧光素FITC标记的牛血清白蛋白(BSA)在聚丙烯酰胺-丙烯酸中的扩散行为,并以激光共聚焦显微镜进行实时成像.实验表明,FITC-BSA在不同单体配比的共聚物中的扩散系数是不同的.通过调节聚合物中单体的配比能够达到控制蛋白释放速率的作用,从而为调控蛋白和多肽类药物的缓控释放提供了可能性. 相似文献