Lec. 5 …………………………………………..……………………………………….Methods of Polymer Morphology Methods of Polymer Morphology Lec. 5 …………………………………………..……………………………………….Methods of Polymer Morphology Microscopic Methods There is a broad spectrum of microscopic techniques available to observe polymer blend morphologies over several orders of magnitudes of length scale. It starts in the 10 μm range using optical microscopy (OM) and it goes down to the nm range using the high resolution transmission electron microscopy. 1. Optical Microscopy (OM) or Light Microscopy (LM) First information on the morphology of polymer blends is simply obtained by visual inspection. Blending two transparent, colorless amorphous polymers that have different refractive indexes usually leads to an opaque material, in which the size of phases exceeds the wavelength of visible light (>500 nm). It is usually assumed that to have opacity the difference of the refractive indexes should be larger than 0.003. In the case when crystalline polymers are involved, the situation becomes more complicated. These polymers are frequently opaque because there are refractive index differences between the amorphous and crystalline regions and the super molecular structures (spherulites) are also large (>500 nm), Thus in the case of blends with semicrystalline polymers, the distinction between homogeneous and heterogeneous structures of the amorphous phase by visual inspection is limited to studies above the melting point of the crystalline component. A more detailed insight into the phase morphology of polymer blends can be obtained by using optical microscopy (OM). The classical light microscopy is limited by diffraction to domains not smaller than 500 nm. In OM, the necessary contrast for detecting different phases might arise from a number of different sources such as color, opacity, refractive index, orientation, absorption or dichroic differences. Lec. 5 …………………………………………..……………………………………….Methods of Polymer Morphology There are numerous imaging methods of OM, e.g., transmission-reflection, bright field-dark field, phase contrast, interference microscopy, polarized light, etc. Lec. 5 …………………………………………..……………………………………….Methods of Polymer Morphology Lec. 5 …………………………………………..……………………………………….Methods of Polymer Morphology 2. Scanning Electron Microscopy (SEM) Scanning electron microscopy (SEM) is normally used to observe surfaces. The resolution is not so good as TEM. Usually, SEM micrographs are obtained by collecting secondary electrons emitted upon bombarding the samples with high energy electrons. This secondary electron image (SEI) gives information about the topography of the sample surface. To obtain an information of morphology in the bulk of the material, it is necessary to remove the surface layer. Only when adhesion between the phases is poor, "new surface", that reflects the bulk morphology can be created by fracturing the sample. Usually, to prevent plastic deformation, the sample is first annealed in liquid nitrogen, then fractured. Another method of removing the surface layer is by etching. This process may be carried out by: 1- Chemical etching, where one polymer is degraded using a chemical reaction and the reaction products can be removed from surface. 2- Solvent etching, to selectively dissolve one of the polymers. 3- Ion beam etching, to preferentially degrade one of the polymers. The low molecular weight by products evaporate under high vacuum. Samples were coated with gold prior to examination under the electron beam. Lec. 5 …………………………………………..……………………………………….Methods of Polymer Morphology Lec. 5 …………………………………………..……………………………………….Methods of Polymer Morphology 3. Transmission Electron Microscopy (TEM) There has been a tremendous development in transmission electron microscopy (TEM) since its discovery by Ruska. To study the polymer morphology by TEM, a sample must be thin, usually thinner than about 200 nm. However, using field emission guns (FEG), thicker specimen (≤ 2μm) can be used. Since polymers are mainly composed of C, H,N and O atoms, the electron density difference between polymers is not large enough to achieve sufficient contrast in heterogeneous materials. Thus staining techniques are usually necessary. Table below gives an overview of the most common staining methods for polymers. Lec. 5 …………………………………………..……………………………………….Methods of Polymer Morphology For most cases staining with osmium or rhutenium tetroxide (OsO4 or RuO4, respectively) yields sufficient results. OsO4 reacts with isolated double bonds (C=O, C=C) such as the double bonds in polyisoprene and poly butadiene, but it does not react with conjugated double bonds. The mechanism of RuO4 staining seems to be different from OsO4. It does not react directly with chemical species, but rather it forms clusters. It stains most polymer but to a different degree dependent mostly on the diffusion rate. The diffusion of RuO4 into the polymer is most important. For crystalline polymers, RuO4 diffuses preferably into the amorphous regions and stains them, whereas the lamellar crystals remain unstained. The double staining technique facilitates a clear contrast for more complicated systems Lec. 5 …………………………………………..……………………………………….Methods of Polymer Morphology Figure : TEM micrograph of HIPS/ABS blend, double-stained with RuO4 and OsO4 Lec. 5 …………………………………………..……………………………………….Methods of Polymer Morphology Lec. 5 …………………………………………..……………………………………….Methods of Polymer Morphology - X-Ray Diffraction Technique (XRD) Lec. 5 …………………………………………..……………………………………….Methods of Polymer Morphology Lec. 5 …………………………………………..……………………………………….Methods of Polymer Morphology Lec. 5 …………………………………………..……………………………………….Methods of Polymer Morphology The interplanar spacing: The magnitude of the distance between two adjacent and parallel planes of atoms (i.e., the interplanar spacing dhkl) is a function of the Miller indices (h, k, and l) as well as the lattice parameter(s). For example, for crystal structures having cubic symmetry, d hkl a2 h2 k 2 l 2 Lec. 5 …………………………………………..……………………………………….Methods of Polymer Morphology Lec. 5 …………………………………………..……………………………………….Methods of Polymer Morphology Lec. 5 …………………………………………..……………………………………….Methods of Polymer Morphology Lec. 5 …………………………………………..……………………………………….Methods of Polymer Morphology Lec. 5 …………………………………………..……………………………………….Methods of Polymer Morphology Lec. 5 …………………………………………..……………………………………….Methods of Polymer Morphology Lec. 5 …………………………………………..……………………………………….Methods of Polymer Morphology Lec. 5 …………………………………………..……………………………………….Methods of Polymer Morphology Lec. 5 …………………………………………..……………………………………….Methods of Polymer Morphology s Lec. 5 …………………………………………..……………………………………….Methods of Polymer Morphology Lec. 5 …………………………………………..……………………………………….Methods of Polymer Morphology