Objective Compared to traditional inorganic extinction materials, biomaterials have advantages relative to environmental protection, non-toxicity, low cost, and controllable form. Thus, biomaterials have become a new type of extinction material. Research into the extinction properties of biomaterials has received increasing attention. And research into the extinction properties of biological aggregate particles is key to studying the extinction properties of biomaterials. The current research results primarily focus on monodisperse biological agglomerate particles; however, in the real-world, there are almost no agglomerate particles with the same radius. Therefore, polydisperse biological agglomerate particles are closer to the actual situation and have greater research value. This paper simulates the polydisperse biological aggregation particles model and calculates the influence of the number of original particles, porosity, and particle size distribution on the extinction performance of polydisperse biological aggregate particles. The purpose of the paper is to calculate factors affecting the extinction performance of biological aggregate particles and provide a reference for future in-depth studies of the extinction properties of biomaterials.

Methods The polydisperse biological aggregation particles model is simulated based on the ballistic particle-cluster aggregation model. The influence of the gyration radius on the porosity and equivalent complex refractive index of aggregate particles is studied. Using the discrete dipole approximation method, we analyze the influence of porosity accuracy on extinction coefficient. In addition, we calculate the extinction coefficient of the polydisperse biological aggregation particles model with different porosity, different numbers of original particles, and different particle size distributions, and we analyze the influence of porosity, particle number, and size distribution on the extinction characteristics of aggregate particles.

Results and Discussions The results demonstrate that the porosity of polydisperse biological aggregate particles increases with increasing gyration radius, and the real and imaginary parts of the equivalent refractive index decrease with increasing gyration radius (Table 1). To study the effect of porosity accuracy on the extinction coefficient, we analyze the influence of porosity accuracy of 0.01, 0.001, and 0.0001 on extinction coefficient. The results demonstrate that, when the porosity error range is within 0.001, the influence can be negligible (Fig. 4). For aggregate particles with the same size distribution and the same number of original particles, the extinction coefficient at the wavelength of 10.6 μm decreases with increasing porosity (Fig. 3). For polydisperse biological aggregate particles with the same particle size distribution and porosity error range within 0.001 at a wavelength of 10.6 μm, the extinction coefficient of aggregate particles increases with an increasing number of original particles (Fig. 5). For polydisperse biological aggregate particles with the same number of original particles, the same mean of the particle size distribution, and error range in porosity within 0.001 at a wavelength of 10.6 μm, the variance of the particle size distribution has nearly no effect on the extinction characteristics (Fig. 6). For polydisperse biological aggregate particles with the same number of original particles, the same variance in particle size distribution, and an error range in porosity within 0.001 at a wavelength of 10.6 μm, the extinction coefficient increases with the increasing mean of the particle size distribution (Fig. 7).

Conclusions Based on the ballistic particle-cluster model, which is used to simulate polydisperse aggregate particles, this paper discusses the pore characteristics of the aggregation particles model comprising the same number of original particles and analyzes the influence of the radius of aggregate particles on porosity and equivalent complex refractive index. The discrete dipole approximation method is employed to calculate the extinction coefficient of different aggregate particles, and the influence of porosity, the number of original particles, and the particle size distribution on the extinction performance at the 10.6-μm laser wavelength is analyzed. The study finds that the porosity of polydisperse biological aggregate particles increases with increasing radius of gyration, and the real and imaginary parts of the equivalent refractive index decrease with increasing radius of gyration. The extinction performance of aggregate particles decreases with the increasing porosity and increases with an increasing number of original particles and increasing mean of the particle size distribution. The results provide a reference for comprehensive understanding of the extinction properties of biological aggregate particles and for the preparation of biological extinction materials. The extinction performance of biomaterials can be improved by changing the porosity of biological aggregate particles, the number of original particles, and the distribution of particle size.