Abstract:

For studying the nanoparticle size distribution, under the condition of “long wave-length”, the technical approaches of increasing frequency, increasing frequency band width, and improving ultrasonic stability were used to obtain the exact ultrasonic attenuation spectrum (UAS).A 50MHz broad-band high-frequency ultrasonic transducer was used for measuring the testing sample suspensions of nanoAg with volume fraction of 0.5% by the method of variable acoustic-path and the comparison of the first reverberation which was reflected by the interface between buffer block and suspensions. The broad-band UAS of 25—62 MHz was obtained in the experiment. The particle size distribution of nanoAg was inversed by combining the McClements & BLBL theoretical model and the optimum regularization technique (ORT).The average particle size d₃₂ was 13.69 nm, the size distribution was from 3.414 nm to 24.34 nm, and the lower theoretical measurement limit was 5 nm at the frequency of 50 MHz. The UAS method showed good agreement with TEM (transmission electron microscope) pictures and centrifugal sedimentation particle size analyzer’s measurement, which indicated that measuring nanometer particle size distribution by UAS was feasible and reliable.

摘要：

为研究纳米颗粒粒度的表征，在“长波长”条件下，通过提高超声波频率、增加频带宽度以及提高纳米颗粒悬浊液中超声波检测的稳定性等技术手段，实现了纳米级颗粒粒度分布的准确测量。实验中，采用中心频率50MHz宽频超声换能器，通过缓冲块内一次回波校验和变声程方法，以体积分数0.5%的纳米银-水悬浊液为验证性测量对象，获得了频率为25～62MHz的宽带声衰减谱。粒度反演过程中，采用McClements&BLBL理论模型结合最优正则化算法，将实测声衰减谱进行反演计算获得了纳米银颗粒的粒度分布，并证实了在50MHz频率下的理论测量下限可以达到5nm。与CPS离心沉降纳米颗粒测量仪、TEM图像等结果相比较，表明超声衰减谱法测量纳米颗粒的结果是可信的。