Bending modes and transition criteria for a flexible fiber in viscous flows

The present paper follows our previous work in which a coupling approach of smoothed particle hydrodynamics （SPH） and element bending group （EBG） was developed for modeling the interaction of viscous incompressible flows with flexible fibers. It was also shown that a flexible object may experience drag reduction because of its reconfiguration due to fluid force on it. However, the reconfiguration of deformable bodies does not always result in drag reduction as different deformation patterns can result in different drag scales. In the present work, we studied the bending modes of a flexible fiber in viscous flows using the presented SPH and EBG coupling approach. The flexible fiber is immersed in a fluid and is tethered at its center point, while the two ends of the fiber are free to move. We showed that the fiber undergoes four different bending modes： stable U-shape, slight swing, violent flapping, and stable closure modes. We found there is a transition criterion for the flexible fiber from slight swing, suddenly to violent flapping. We defined a bending number to characterize the bending dynamics of the interaction of flexible fiber with viscous fluid and revealed that this bending number is relevant to the non-dimensional fiber length. We also identified the critical bending number from slight swing mode to violent flapping mode.

Deciphering the lithium storage chemistry in flexible carbon fiber-based self-supportive electrodes

Flexible carbon fiber cloth(CFC)is an important scaffold and/or current collector for active materials in the development of flexible self-supportive electrode materials(SSEMs),especially in lithium-ion batteries.However,during the intercalation of Li ions into the matrix of CFC(below 0.5 V vs.Li/Li+),the incompatibility in the capacity of the CFC,when used directly as an anode material or as a current collector for active materials,leads to difficulty in the estimation of its actual contribution.To address this issue,we prepared Ni_(5)P_(4)nanosheets on CFC(denoted CFC@Ni_(5)P_(4))and investigated the contribution of CFC in the CFC@Ni_(5)P_(4)by comparing to the powder Ni_(5)P_(4)nanosheets traditionally coated on a copper foil(CuF)(denoted P-Ni_(5)P_(4)).At a current density of 0.4 mA cm^(−2),the as-prepared CFC@Ni_(5)P_(4)showed an areal capacity of 7.38 mAh cm^(−2),which is significantly higher than that of the PNi_(5)P_(4)electrode.More importantly,theoretical studies revealed that the CFC has a high Li adsorption energy that contributes to the low Li-ion diffusion energy barrier of the Ni_(5)P_(4)due to the strong interaction between the CFC and Ni_(5)P_(4),leading to the superior Li-ion storage performance of the CFC@Ni_(5)P_(4)over the pristine Ni_(5)P_(4)sample.This present work unveils the underlying mechanism leading to the achievement of high performance in SSEMs.

Structural design of light-emitting fibers and fabrics for wearable and smart devices

Flexible light-emitting fibers and fabrics serve to bridge human–machine interactions. The desire for practical applications and the commercialization of flexible light-emitting fibers has accelerated structural progress and improvements. This review focuses on the structural design of light-emitting fibers and fabrics, starting with a summary of design principles, emission mechanisms, and structural evolution of coaxial structured light-emitting fibers. Subsequently, we explore recent advances in the helical structure design strategies that boost the mechanical sensitivity of light-emitting fibers. Following that, we analyze continuous preparation processes and the development of large-area intelligent light-emitting fabrics based on interwoven structures. Examples based on stiff and rigid inorganic-based lightemitting diodes integrated into flexible systems are also presented. Finally, we discuss the current challenges and future opportunities for light-emitting applications in the field of wearable and smart devices.

Fiber Bending Flexibility Evaluation by Worm-like Chain Model

A new method for characterizing fiber bending flexibility was developed by worm-like chain model proposed by Kratky-Porod,[1]which was first introduced to the pulp and paper field in this study.For the three types of pulps,the experimental results were compared with the KP chain model,and the resulting determination coefficients were all above 0.95,which proved that the model was feasible to be applied to these three fibers.The relation between fiber bending rigidity and that of cellulosic chains inside was discussed to deduce the fiber bending flexibility.The flexibility of an individual fiber can be approximated as the contribution of that of all the cellulose chains inside.By this method,the fiber flexibility values were determined to be in the range of 0.6×10^(11)-3.5×10^(11)N^(-1)·m^(-2),which was comparable to that of the conventional methods recorded in the literature.

基于调控Cr^(3+)锐线发射带宽的柔性光纤温度传感器

我们设计并制备了一种基于LiGa_(4)(MgGe)_(0.5)O_(8):Cr荧光粉变温发光特性的柔性温度传感光纤.通常来说,随着温度的升高,发光材料基质的电子-声子作用将加剧,这会导致其发射峰的半高宽(FWHM)在升温时不断加宽.在本工作中,随着LiGa_(5-x)(MgGe)_(x)O_(8):Cr中[Mg^(2+)-Ge^(4+)]化学单元成分比例的增加,荧光粉近红外发光的FWHM出现明显展宽,其外量子效率也从24.8%增加到50.0%.进一步研究发现,LiGa_(4)-(MgGe)_(0.5)O_(8):Cr纳米荧光粉的发光具有优异的热稳定性和温度传感特性,在443 K时绝对灵敏度可达7.51 cm^(-1)K^(-1),303 K下相对灵敏度为0.64%K^(-1).基于此,我们搭建了具有可重复性、高精度和优异稳定性的柔性全光纤系统,并将其用于实时监测物体的温度.本研究不仅探索了具有锐线发射的Cr^(3+)掺杂发光材料的应用,而且丰富了基于荧光材料带宽特性的光学测温新思路.