Wallenberg Wood Science Center, Department of Fiber and Polymer Technology , KTH Royal Institute of Technology , Teknikringen 56 , Stockholm 100 44 , Sweden.
Department of Applied Physics, School of Engineering Sciences , KTH Royal Institute of Technology , Isafjordsgatan 22 , Kista 164 40 , Sweden.
ACS Appl Mater Interfaces. 2019 Sep 25;11(38):35451-35457. doi: 10.1021/acsami.9b11816. Epub 2019 Sep 13.
Transparent wood (TW) is an emerging optical material combining high optical transmittance and haze for structural applications. Unlike nonscattering absorbing media, the thickness dependence of light transmittance for TW is complicated because optical losses are also related to increased photon path length from multiple scattering. In the present study, starting from photon diffusion equation, it is found that the angle-integrated total light transmittance of TW has an exponentially decaying dependence on sample thickness. The expression reveals an attenuation coefficient which depends not only on the absorption coefficient but also on the diffusion coefficient. The total transmittance and thickness were measured for a range of TW samples, from both acetylated and nonacetylated balsa wood templates, and were fitted according to the derived relationship. The fitting gives a lower attenuation coefficient for the acetylated TW compared to the nonacetylated one. The lower attenuation coefficient for the acetylated TW is attributed to its lower scattering coefficient or correspondingly lower haze. The attenuation constant resulted from our model hence can serve as a singular material parameter that facilitates cross-comparison of different sample types, at even different thicknesses, when total optical transmittance is concerned. The model was verified with two other TWs (ash and birch) and is in general applicable to other scattering media.
透明木材（TW）是一种新兴的光学材料，具有高透光率和高雾度，可用于结构应用。与无散射吸收介质不同，TW 的光透过率随厚度的变化较为复杂，因为光学损耗也与多次散射引起的光子路径长度增加有关。在本研究中，从光子扩散方程出发，发现 TW 的角度积分总光透过率与样品厚度呈指数衰减关系。该表达式揭示了一个衰减系数，它不仅取决于吸收系数，还取决于扩散系数。对一系列 TW 样品（包括乙酰化和非乙酰化巴沙木模板）进行了总透过率和厚度的测量，并根据推导的关系进行了拟合。拟合结果表明，乙酰化 TW 的衰减系数低于非乙酰化 TW。乙酰化 TW 的衰减系数较低归因于其较低的散射系数或相应较低的雾度。因此，当涉及总光透过率时，我们的模型得出的衰减常数可以作为一个奇异的材料参数，便于不同类型的样品（甚至不同厚度）之间的交叉比较。该模型经过另外两种 TW（灰烬和桦木）的验证，通常适用于其他散射介质。
