Laser imaging polarimetry of nacre

Abstract

Nacre is a complex biomaterial made of aragonite-tablet bricks and organic mortar that is considerably resilient against breakage. Nacre has been studied with a wide range of laboratory techniques, leading to understanding key fundamentals and informing the creation of bio-inspired materials. In this article, we present an optical polarimetric technique to investigate nacre, taking advantage of the translucence and birefringence of its microcomponents. We focus our study on 3 classes of mollusks that have nacreous shells: bivalve (Pinctada fucata), gastropod (Haliotis asinina and Haliotis rufescens) and cephalopod (Nautilus pompilius). We sent polarized light from a laser through thin samples of nacre and did imaging polarimetry of the transmitted light. We observed clear distinctions between the structures of bivalve and gastropod, due to the spatial variation of their birefringence. The patterns for cephalopod were more similar to bivalve than gastropod. Bleaching of the samples disrupted the transmitted light. Subsequent refilling of the bivalve and gastropod nacre samples with oil produced optical patterns similar to those of unbleached samples. In cephalopod samples, we found that bleaching produced irreversible changes in the optical pattern.

Heart cockle shells transmit sunlight to photosymbiotic algae using bundled fiber optic cables and condensing lenses

“…We report the results for index 0.001 in the main text and the other in Supplemental Figure S4. Generally, molluscan shells are about 0.1-5% organic matrix by weight and the rest calcium carbonate (68); we varied the width of the organic matrix between pillars over three values: 100 nm, 50 nm, 25 (69). We report the results for organic matrix width 100 nm in the main text and the others in Supplemental Figure S4.…”

Polarimetry of Pinctada fucata nacre indicates myostracal layer interrupts nacre structure

“…Figure 1 presents a diagram of the experimental set-up used in the polarimetry experiments [28,29]. A helium–neon (HeNe) laser beam of wavelength 632.8 nm was passed through a neutral density filter ( F ) to adjust the intensity to a level that was appropriate for the camera.…”

“…Here we use a new technique, imaging polarimetry [25–29], to probe the myostracal layer of the bivalve Pinctada fucata and its interaction with nacre growth. Our technique [28,29] uses single-wavelength light of selectable polarization to probe the sample, examining the light transmitted through the sample as a function of polarization and position.…”

“…Our technique [28,29] uses single-wavelength light of selectable polarization to probe the sample, examining the light transmitted through the sample as a function of polarization and position. Our polarimetry analysis, in conjunction with scanning electron microscopy (SEM), finds an increase in tablet thickness and a decrease in the variation in orientation of the nacre tablets from before the myostracal layer to after the myostracal layer.…”