光纤后向动态光散射测量纳米颗粒的浓度适用范围研究

Measurable range of nanoparticle concentration using optical fiber backward dynamic light scattering

常用的动态光散射法在测量高浓度纳米颗粒时需要充分稀释样品,避免多次散射效应,以得到准确的测量结果。基于单模光纤后向动态光散射原理发展了一套光纤后向动态光散射测量装置,利用单根单模光纤同时发射激光与接收散射光来抑制多次散射,无须稀释样品,实现了高浓度纳米颗粒粒度的直接测量。为确定该测量方法的浓度适用范围,开展了理论与实验研究。首先,理论分析了不同粒径的颗粒散射平均自由程与体积浓度的关系,并根据该装置的散射区域特性计算了理论测量浓度上限。其次,利用该装置对不同粒径纳米颗粒多种体积浓度的样品进行了颗粒粒度测量。理论与实验结果表明,随着粒径的增加,测量浓度的上限降低,二者趋势一致,但在颗粒大于300 nm后实验结果与理论分析结果的偏差逐渐增大,实验浓度略低于理论浓度1%~2%(体积)。

The commonly used dynamic light scattering(DLS)method requires sufficient sample dilution when measuring high-concentration nanoparticles to avoid multiple scattering effects to obtain accurate results.In this paper,a set of optical fiber backward DLS measurement device based on the principle of single-mode optical fiber backward dynamic light scattering was developed.By simultaneously emitting laser and receiving scattered light through a single-mode optical fiber,multiple scattering can be suppressed without diluting the sample,achieving direct measurement of the particle size of high-concentration nanoparticles.The device uses the heterodyne mode,with the back-reflected light on the fiber end face serving as the reference light signal,and the volume concentration of particles below 14%can meet the requirements of this mode.To determine the applicable concentration range of the device,theoretical and experimental research was carried out.First,the relationship between the scattering mean free path of particles of different sizes and the volume concentration was theoretically analyzed,and the upper limit of the theoretical measurement concentration was calculated based on the scattering area characteristics of the device.Secondly,the device was used to measure the particle size of nanoparticles with different particle sizes and various volume concentrations.Theoretical and experimental results show that with the increase of particle size,the upper limit of measured concentration decreases,and the trend of both is consistent.However,when the particle size is larger than 300 nm,the deviation between experimental results and theoretical analysis results gradually increases,and the experimental concentration is slightly lower than the theoretical concentration by 1%—2%(volume).