title: Diffuse reflectance of short-fiber-reinforced composites aligned by an electric field.
abstract: OBJECTIVE
  This study aims to characterize the translucency of aligned, short-fiber composites by determining the effects of filler particle orientation on the Kubelka-Munk absorption and scattering coefficients.
  
  
  METHODS
  Rectangular composite specimens (n = 3) were filled with very short E-glass fibers. The fibers were oriented random, perpendicular, and parallel to the surface normal using an alternating electric field of 0.75 kV/mm. Diffuse reflectances of the composites on white and black backings were acquired with a spectrophotometer. The Kubelka-Munk model was then employed to calculate absorption and scattering coefficients.
  
  
  RESULTS
  The ordering of the reflectances on a white backing is neither the same nor the reverse of the reflectances on the black backing. The effects of orientation were different for the absorption and scattering coefficients. Orientation parallel to the average light flux notably decreases the amount of absorption, while perpendicular orientation appreciably increases the amount of scattering.
  
  
  CONCLUSIONS
  Since orientation affects the absorption and scattering coefficients differently, the ordering of the reflectances may be different when the backing is varied. This is because the translucency is composed of two parameters (absorption and scattering) and cannot be adequately summarized with one parameter such as transmittance or reflectance. Therefore, the use of a diffuse reflectance model, such as Kubelka-Munk, is essential to a quantitative understanding of the translucency effects of filler orientation. Understanding how the filler orientation affects diffuse reflectance of composites will yield insight as to how the orientation of enamel rods affects the diffuse reflectance in teeth by analogy.
authors.affiliation: Macromolecular Science and Engineering, Department of Biologic and Materials Science, University of Michigan, Ann Arbor, MI, USA.
authors.forename: William M
authors.initials: WM
authors.lastname: Chirdon
authors.forename: William J
authors.initials: WJ
authors.lastname: O'Brien
authors.forename: Richard E
authors.initials: RE
authors.lastname: Robertson
mesh_terms: D000042:Absorption; D003188:Composite Resins / Q000737:chemistry* / Q000528:radiation effects; D004563:Electrochemistry; D005898:Glass / Q000737:chemistry* / Q000528:radiation effects; D006801:Humans; D008027:Light; D008422:Materials Testing; D008689:Methacrylates / Q000737:chemistry / Q000528:radiation effects; D008956:Models, Chemical; D055095:Optics and Photonics; D010316:Particle Size; D011140:Polyurethanes / Q000737:chemistry / Q000528:radiation effects; D012542:Scattering, Radiation; D013053:Spectrophotometry; D013499:Surface Properties
chemical_list: D003188:Composite Resins; D008689:Methacrylates; D011140:Polyurethanes; C009753:fiberglass; C029824:urethane dimethacrylate luting resin; C090921:1,6-hexanediol dimethacrylate