Characterizing the Effects of Washing by Different Detergents on the Wavelength-Scale Microstructures of Silk Samples Using Mueller Matrix Polarimetry

Abstract

Silk fibers suffer from microstructural changes due to various external environmental conditions including daily washings. In this paper, we take the backscattering Mueller matrix images of silk samples for non-destructive and real-time quantitative characterization of the wavelength-scale microstructure and examination of the effects of washing by different detergents. The 2D images of the 16 Mueller matrix elements are reduced to the frequency distribution histograms (FDHs) whose central moments reveal the dominant structural features of the silk fibers. A group of new parameters are also proposed to characterize the wavelength-scale microstructural changes of the silk samples during the washing processes. Monte Carlo (MC) simulations are carried out to better understand how the Mueller matrix parameters are related to the wavelength-scale microstructure of silk fibers. The good agreement between experiments and simulations indicates that the Mueller matrix polarimetry and FDH based parameters can be used to quantitatively detect the wavelength-scale microstructural features of silk fibers. Mueller matrix polarimetry may be used as a powerful tool for non-destructive and in situ characterization of the wavelength-scale microstructures of silk based materials.

Keywords: Mueller matrix; microstructure; polarization; silk.

Figure 1

2D images of Mueller matrices of silk sample washed by fabric softener: (a) before washing; (b) after the third washing; (c) after the sixth washing. The color bar is from −1 to 1 for the m11, m22, m33, and m44, and from −0.1 to 0.1 for other elements.

Figure 2

2D images of Mueller matrices of silk sample washed by color stain net: (a) before washing; (b) after the third washing; (c) after the sixth washing. The color bar is from −1 to 1 for the m11, m22, m33, and m44, and from −0.1 to 0.1 for other elements.

Figure 3

Frequency distribution histograms (FDHs) of Mueller matrix elements of silk sample washed by the fabric softener: before washing (black lines), after the third washing time (red lines) and the sixth washing time (blue lines). The areas under the FDH curves are normalized to 1, and the horizontal axis is divided into 400 parts.

Figure 4

Frequency distribution histograms (FDHs) of Mueller matrix elements of silk sample washed by the color stain net: before washing (black lines), after the third wash (red lines) and the sixth wash (blue lines). The areas under the FDH curves are normalized to 1, and the horizontal axis is divided into 400 parts.

Figure 5

FDH parameters c1_p1 (left), d22_p1 (middle) and d23_p2 (right) of silk samples washed by different detergents. (a–c) are the values of three parameters for the silk samples washed by the group A detergents: fabric softener in black square lines and laundry powder in red dot lines; (d–f) are the values of three parameters for the silk samples washed by the group B detergents: toilet soap in green diamond lines and color stain net in blue triangle lines. The horizontal axis represents the washing times.

Figure 6

Optical microscopic images of silk samples in group A: (a) before washing; (b) after the sixth washing by fabric softener; (c) after the sixth washing by laundry powder. Scanning electron microscopic images (10,000×) of silk samples in group A: (d) before washing; (e) after the sixth washing by fabric softener; (f) after the sixth washing by laundry powder.

Figure 7

Optical microscopic images of silk samples in group B: (a) before washing; (b) after the sixth washing by toilet soap; (c) after the sixth washing by color stain net. Scanning electron microscopic images (10,000×) of silk samples in group B: (d) before washing; (e) after the sixth washing by toilet soap; (f) after the sixth washing by color stain net.

Figure 8

Monte Carlo simulation results of the parameters c1_p1 and d22_p1 using the SCSM. (a) The x-axis represents different values of sphere/cylinder ratio from (1) 10:70 to (2) 13:67; (3) 15:65; (4) 21:59; (5) 22:58; (6) 27:53 and (7) 28:52; (b) The x-axis represents different values of the diameter and standard deviation of angular distribution of the cylinders from (1) 1.5 µm 15 degree to (2) 1 µm 15 degree; (3) 0.9 µm 19 degree; (4) 0.86 µm 19 degree; (5) 0.76 µm 20 degree; (6) 0.68 µm 21 degree; and (7) 0.68 µm, 22 degree.

Figure 9

X-ray diffraction curves of silk samples. (a) 1. The silk before washing; 2. The silk after the sixth washing by fabric softener; 3. The silk after the sixth washing by laundry powder; (b) 1. The silk before washing; 2. The silk after the sixth washing by toilet soap; 3. The silk after the sixth washing by color stain net.

Figure 10

(a) Schematic of experimental setup for the backscattering Mueller matrix measurement. P1, P2: polarizer; R1, R2: quarter-wave plate; L1, L2: lens. The oblique incident angle θ is about 15 degree to avoid the surface reflection from the sample. The diameter of the illumination area is about 1.8 cm; (b) Silk sample used in this study.