In‐situ cure monitoring of diamine cured epoxy by fiberoptic fluorimetry using extrinsic reactive fluorophore

Abstract

This paper describes the application of a molecular sensor for in‐situ monitoring of epoxy‐diamine cure via remote sensing fiberoptic probes. A custom‐built, fiberoptic fluorimeter allows on‐line recording of fluorescence spectra directly from the cure environment. Cure reactions in epoxy‐diamine network, such as diglycidyl ether of bisphenol A‐diaminodiphenyl sulfone (DGEBA‐DDS) or diglycidyl ether of butanediol‐diaminodiphenyl sulfone (DGEB‐DDS), have been monitored by a reactive molecular sensor, diamino azobenzene (DAA). DAA exhibits sensitive changes in UV‐visible and fluorescence spectra due to the conversion of its primary amine groups to secondary and tertiary amine groups. Fluorescence intensities are correlated with extent of reaction in epoxy network and processing parameters, such as cure temperatures and time. The use of an internal reference dye for normalization of fluorescence intensities is necessary for the quantitative correlation of spectral signals with the network structure. Variables affecting the fluorescence intensity such as excitation volume, probe location, excitation intensity fluctuation, temperature, and background intensities from optical fiber can be calibrated by normalizing the signal intensities against the internal reference. Sulforhodamine 101 was found to be a satisfactory reference dye which provides stable, readable signals over temperatures up to 200°C.

<title>Cure monitoring of epoxy resin with silica optical fiber and OTDR</title>

“…In multimode case, the number of modes that the sensing region guides M is approximately given by": M= (2) Where V ,the normalized frequency, is given by: A short length of the fiber was etched to remove the cladding and expose the core.…”

Luminescence spectroscopy applied to a study of the curing process of diglycidyl-ether of bisphenol-A (DGEBA)

“…This band was also observed by Sung and Paik 19 . After the DGEBA/DDS mixture was cured, a red shift occurred in the excitation band (Figure 6.2) and the relative intensity of the band at 365 nm increased due to a conversion of primary amines into secondary and tertiary amines 1,12,19,20 . Figure 6 shows the fluorescence spectra of the DGEBA and DDS mixture before (Figure 6.3) and after the heat treatment ( Figure 6.4).…”

Combinatorial Approach to Characterizing Epoxy Curing

“…The restricted fluorophore mobility increases the emission intensity because the fluorophore can dissipate the excitation through non-radiative processes less effectively. While fluorescence has been used to study the curing characteristics of bulk epoxy resin and silanized glass/epoxy interfaces, [3,[16][17][18][19] confocal microscopy has not been used to map a temperature gradient cured epoxy library at or near the surface of the film.…”