生物材料消光特性研究进展

生物材料作为一种有别于传统无机消光材料的新型烟幕介质，悬浮于空气中，以烟幕的形式存在，通过对光的吸收和散射作用改变光波的传输特性。本文根据生物材料的复折射率特点，介绍了生物材料的吸收和散射特性，概括了生物材料单粒子、单分散凝聚粒子和多分散凝聚粒子的消光特性的表征方式，分析了影响生物材料消光特性的因素，总结了生物材料消光性能的测试方法。最后，本文提出了生物材料在复杂空间结构模拟精确化、消光特性影响因素分析多元性、消光特性测试标准化方面的发展趋势，以期为新型消光材料的制备和改进等提供有益参考。

Abstract

Significance

In recent years, laser and infrared detection technology has been rapidly developed. The material preparation, generation method, extinction performance test, and effect evaluation of multi-band smoke screens have garnered widespread attention. Traditional inorganic extinction materials, such as metal powder, red phosphorus, and expanded graphite, often possess drawbacks such as a narrow extinction band, high costs, combustibility, difficulty in degradation, a single release method, and environmental harm. Consequently, environmentally friendly extinction materials characterized by a broad extinction band, long duration, low preparation cost, pollution-free, and non-combustibility emerge as research hotspots both domestically and internationally.

Artificially controlled biomaterials, such as spores or hyphae, represent a new type of smoke screens medium, distinct from traditional inorganic extinction materials. Once released into the air, these biomaterials form smoke screens, altering light transmission properties through absorption and scattering. Hence, biomaterials can diminish the detection capabilities of visible, laser, and infrared detection systems and equipment, making them suitable for the photoelectric protection of critical targets or facilities. Biomaterials aggregated particles systems formed from tiny biological particles due to static electricity, collision, or adhesion, possess complex spatial structures and random orientations.

There is a significant progress in researching the extinction properties of biomaterials. Biomaterials can be prepared with attributes such as controllable morphology, cost-efficiency, ease of batch preparation, high impedance, environmental friendliness, and non-toxicity. Researchers have constructed structure models of spherical particles, typical non-spherical particles, monodisperse aggregated particles, and polydisperse aggregated particles and have analyzed their static extinction properties. Additionally, the dynamic extinction properties of biomaterials have been examined under varying wind speeds, surface roughnesses, and relative humidities. Regarding the differential extinction properties of viable and dead biomaterials, the activity ratio of biomaterials can be qualitatively determined. Although many advances have occurred, challenges persist in the simulation, testing, and enhancement of biomaterials' extinction characteristics. Thus, outlining current research on the extinction characteristics of biomaterials becomes essential, paving the way for future developments in safer and more eco-friendly broadband smoke screen materials.

Progress

First, the extinction characteristics of biomaterials are introduced, with absorption and scattering attributes based on the characteristics of complex refractive index. The calculation flowchart for the extinction characteristics of biomaterials is presented (Fig. 5), and characterization methods for different biomaterial structures are summarized. These structures include spherical single particles, typical non-spherical single particles, monodisperse aggregated particles, and polydisperse aggregated particles. Although the extinction properties are primarily determined by the composition and structural parameters of biomaterials (as shown in Fig. 6 and Fig. 9), other influential factors are examined. These factors are represented by biomaterial activity (Fig. 10), wind speed (Fig. 12), ground roughness (Fig. 13), and relative humidity (Fig. 14). Subsequently, static and dynamic testing methods for biomaterials are listed. In the static methods, the scanning electron microscope (SEM) test (Fig. 15) and infrared spectroscopy test (Fig. 16) are featured, while in the dynamic methods, the smoke box test (Fig. 17) and field test (Fig. 19) are included. In conclusion, emerging trends such as precise simulations of intricate spatial structures, analyses of factors influencing extinction characteristics, and standardization of extinction characteristics testing are emphasized.

Conclusions and Prospects

In recent years, significant advancements have been observed in the study of extinction characteristics and test techniques of biomaterials. However, certain challenges persist that require attention in the forthcoming research, including the simulation of randomly oriented aggregation for biological particles, the multivariate analysis of dynamic extinction properties of biomaterials, and the standardization of extinction performance testing. Initially, given that biological particles generally possess irregular shapes and biological particle aggregations exhibit complex and variable structures, only a model accounting for the randomly oriented aggregation of these irregular particles can accurately represent the spatial structure of aggregated biological particles, ensuring precise calculations of the biomaterials' extinction properties. At this juncture, due to the absence of an established model for randomly oriented aggregation of irregular particles, simulations are restricted to particles with regular shapes. Furthermore, a comprehensive consideration of factors, such as wind speed, temperature, and atmospheric stability, becomes imperative, surpassing the simplicity of previous analyses affecting the extinction properties of biomaterials. Additionally, addressing issues of a low effectiveness-cost ratio and limited repeatability by standardizing the collection and analysis of experimental data emerges as a crucial research direction. Anticipated improvements for the near future include the development of a randomly oriented aggregation model for diverse irregular biological particles, enabling the study of extinction characteristics for non-spherical biological materials. There is also the need for accurate simulations and predictions of sedimentation diffusion of aggregated particles under varied meteorological conditions. This would involve the consideration of multiple influencing factors, the enhancement of specific organic groups performance and the integration of other material components to bolster biomaterial performance. Lastly, the establishment of clear evaluation tests and criteria for the extinction performance of biomaterials is crucial, ensuring experimental data are gathered and analyzed following a relatively consistent standard.

1　引言

近年来，随着激光和红外探测技术的迅速发展，多波段烟幕的材料制备、生成方式、消光性能测试及效果评估等受到了广泛关注^［1］。烟幕通过悬浮分散于空气中的固体、液体或固液混合物微粒对光的吸收和散射来衰减光波信号，达到遮蔽和保护我方目标的目的^［2］。金属粉末、化合物和金属混合物等传统的无机消光材料大部分存在消光波段单一、制备成本高、易燃烧、难降解、对环境不友好、释放方式单一等不足^［3-4］，因而具有强衰减、宽波段、长留空、低成本、无污染、无燃烧等特性的安全环保型宽波段消光材料受到了广泛关注。

人工可控制备的生物孢子或菌丝等生物材料是一些微小的生物粒子在静电、碰撞或黏附作用下形成的具有分形特征和复杂空间结构的随机取向凝聚粒子体系^［3］。生物材料是一种新型的安全环保型宽波段烟幕介质，其释放到空气中形成的烟幕会对光产生吸收和散射，从而能够有效地衰减紫外波段、可见波段和红外波段等宽波段光波^［5］。目前，生物材料消光特性的研究工作已经取得了一定进展。根据生物材料的电镜图，研究人员构建了球形粒子^［6-8］、典型非球形粒子^［9-12］、单分散凝聚粒子和多分散凝聚粒子^［13-15］等粒子结构模型，并开展了相应结构生物材料的消光特性研究。同时，根据不同活性状态的生物材料的消光特性差异，从定性^［16-17］、定量^［18-20］两个角度对材料的活性进行了判定，并研究了不同风速^［21-23］、地面粗糙度^［23］和湿度^［24］等条件下生物材料的消光特性。通过研究人工可控制备的微生物菌丝和孢子等生物材料的消光特性发现，生物材料具有形态多样、消光能力强、波段宽、阻抗高、环保无毒等特点^［25］，是一种潜在的安全环保型宽波段消光材料，对于重要目标或设施的光电防护具有重要意义。

本文首先介绍了生物材料的消光特性，概括了不同结构生物材料消光特性的表征方式；然后从生物材料活性、风速、地面粗糙度和湿度等方面，分析了生物材料消光特性的影响因素，总结了生物材料的静态和动态测试方法；最后展望了生物材料在复杂空间结构模拟精确化、消光特性影响因素多元性、消光特性测试标准化等方面的发展趋势。本文所提及的生物材料均为具有宽波段消光能力的人工可控制备的生物孢子或菌丝等生物材料。

2　生物材料的消光特性

生物材料的消光特性主要包括其对光能量的吸收和散射。复折射率表征材料对光波的色散和吸收能力，是分析生物材料光波散射特性以及识别生物材料粒子种类的重要参数^［6］。生物材料因组成成分和空间结构的差异，具有不同的吸收和散射特性，从而具有不同的复折射率。研究生物材料的复折射率，便于计算消光截面、质量消光系数等参数，有助于分析不同结构生物材料的消光特性。

2.1　生物材料的复折射率

复折射率 $m (λ)$ 是描述生物材料消光性能的重要参数，是先采用傅里叶变换红外光谱仪或显微红外光谱仪测量样品的光谱数据，然后根据样品在全波段的反射率 $R (λ)$ ，利用Kramers-Kronig（K-K）关系^［26-27］计算得到的。单粒子结构生物材料的复折射率为 $m (λ)$ ，可以表示为

m (λ) = n (λ) + i k (λ)

，（1）

式中： $λ$ 是反射波的波长；实部 $n (λ)$ 表征材料对光波的色散；虚部 $k (λ)$ 表征材料对光波的吸收^［17］。实部 $n (λ)$ 和虚部 $k (λ)$ 可以根据反射率 $R (λ)$ 和反射相移 $θ (λ)$ 计算得到，计算公式^［28-29］为

n (λ) = \frac{1 - R (λ)}{1 + R (λ) + 2 \sqrt[]{R (λ)} c o s θ (λ)}

，（2）

k (λ) = \frac{- 2 \sqrt[]{R (λ)} s i n θ (λ)}{1 + R (λ) + 2 \sqrt[]{R (λ)} c o s θ (λ)}

。（3）

测量全波段反射率 $R (λ)$ 时，需要考虑实际测试仪器的测量角度和工作波段。 $R (λ)$ 通常利用经验公式外推或常数外推^［29］得到。反射相移 $θ (λ)$ 的计算公式^［28］为

θ (λ) = \frac{λ}{π} P \int_{0}^{\infty} \frac{l n R (λ^{'})}{({λ^{'}}^{2} - λ^{2})} d λ^{'}

，（4）

其中P是柯西主值函数。生物材料的成分决定了复折射率的性质，当生物材料的成分和结构特征发生变化时，其复折射率也随之发生变化，从而影响消光特性。生物凝聚粒子的等效复折射率m_eff利用孔隙率 $p$ 和单粒子结构生物材料的复折射率 $m (λ)$ 计算得到，计算公式^［14］表示为

m_{e f f}^{2} = 1 + \frac{3 (1 - p) (m^{2} - 1) / (m^{2} + 2)}{1 - (1 - p) (m^{2} - 1) / (m^{2} + 2)}

。（5）

图1给出了某种生物孢子在0.24~14.00 μm波段的复折射率、透过率、消光比、吸收比和散射比等性能参数，其中，图1（a）为复折射率实部，图1（b）为复折射率虚部。