Optimization of scanning transmission X-ray microscopy for the identification and quantitation of reinforcing particles in polyurethanes
A.P.Hitchcock(a) *, I.Koprinarov(a), T.Tyliszczak(a) , E.G. Rightor(b) ,G.E. Mitchell(b) , M.T. Dineen(b) ,F.Hayes (b) ,W.Lidy (c), R.D.Priester (c), S.G.Urquhart (d) , A.P.Smith (d) and H.Ade (d)
a Brockhouse Institute for Materials Research,McMaster University,1180 Main Street West,Hamilton,ON,Canada
b Dow Chemical,1897 Building ,Midland,MI 48667,USA
c Dow Chemical,Building B-1608,2301 N.Brazosport Blvd Freeport,TX 77541,USA
d Department of Physics,North Carolina State Univrsity,Raleigh,NC 27695,USA
Received 2 May 2000; received in revised form 13 October 2000
The morphology, size distributions, spatial distributions, and quantitative chemical compositions of co-polymer polyol-reinforcing particles in a polyurethane have been investigatedwith scanning transmission X-ray microscopy (STXM). A detailed discussion of microscope operating procedures is presented and ways to avoid potential artifacts are discussed. Images at selected photon energies in the C1s,N1s and O1s regions allow unambiguous identification of styrene –acrylonitrile-based (SAN) copolymer and polyisocyanate polyaddition product-based (PIPA) reinforcing particles down to particle sizes at the limit of the spatial resolution (50 nm). Quantitative analysis of the chemical composition of individual reinforcing particles is achieved by fitting C1s spectra to linear combinations of reference spectra.Regression analyses of sequences of images recorded through the chemically sensitive ranges of the C1s, N1s and O1s spectra are used to generate quantitative compositional maps, which provide a fast and effective means of investigating compositional distributions over a large number of reinforcing particles.The size distribution of all particles determined by STXM is shown to be similar to that determined by TEM. The size distributions of each type of reinforcing particle,which differ considerably, were obtained by analysis of STXM images at chemically selective energies.
# 2001 Elsevier Science B.V.All rights reserved.
Keywords: X-ray microscopy; Polymers; Quantitative chemical mapping; Particle size distributions