Chemical imaging of phase-separated polymer blends by fluorescence microscopy

Blends of poly(vinylacetate) (PVAc) and poly(cyclohexylmethacrylate) (PCHMA ) labeled by copolymerization with 4-methacryloylamine-4'-nitrostilbene (Sb ), with (1-pyrenylmethyl)methacrylate (Py), or with 3-(methacryloylamine)pr opyl-N-carbazole (Cbz) were prepared by casting dilute solutions in tetrahy drofurane (THF) or chloroform. Films about 10 mu m thick were formed. Phase separation in two types of domains is observed by transmission optical mic roscopy (TOM) and epifluorescence microscopy (EFM): small craters of 1 to 1 0 mu m placed at the polymer-air interface and larger domains, on the scale of 100 mu m. The morphology of samples depends on the composition of the p olymer blend and on solvent. The green fluorescence of Sb, the violet of Py , or the blue of Cbz provides imaging of the distribution of PCHMA in the d ifferent domains and in the matrix. It is thus observed that (i) superficia l craters and large domains are formed mainly by PCHMA and (ii) the matrix is composed of PVAc in films cast from THF and it is a blend of the two pol ymers, homogeneous at the submicrometric scale, for chloroform. The emissio n intensity of Py, recorded by microfluorescence spectroscopy (MFS), yields a mapping similar to imaging detection. It is remarkable that in films cas t from chloroform, the smaller domains are distributed with a 2D hexatic or der disrupted by dislocations and disclinations, whereas in films cast from THF, a larger heterogeneity is found, denoting different mechanisms of sol vent evaporation.