英語翻譯
3.Results and discussion
3.1.Water uptake and diffusion coefficients
Gravimetric results are presented in Fig.1 were the frac-tional amount of water is plotted against t1/2.In Fig.2,the water content measured by FT-NIR for the different samples is also presented.
From the initial linear portion of the curves,water diffu-sion coefficients can be calculated according to the follow-ing equation:
where wt,w0 and w∞ are the weights of the samples at immersion time t,t=0 and at the saturation equilibrium,e is the thickness of the sample,and D the water diffusion coefficient.In Table 1,D and the equilibrium water content are presented.No great differences are observed in function of curing degree.
3.2.Volume change during water uptake
From FT-NIR spectra at different immersion times it is possible to obtain information on the volume change following water uptake.According to the Lambert–Beer law,absorbance at a certain wavenumber,A,were absorption takes place is proportional to the number of absorbing species perunit section.Therefore,A−3/2 should be proportional to the volume in which the absorbing species are distributed.If we select some wavenumber specific of the IR spectrum of the neat resin,sufficiently far away from absorption of water molecules,we can measure the fractional volume change using the following expression:
were A0 and At are the integrated absorbances of the reference band at 4623 cm−1 at immersion times t=0 and t,ΔV/V0the fractional volume change following water uptake.In Fig.3,the fractional volume change is plotted against immersion time.
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