Presentation on theme: "Lecture 4: Characterizing Hybrids. First step in characterizing a hybrid: Use your senses (take pictures to document) – What color? Does it fluoresce."— Presentation transcript:
First step in characterizing a hybrid: Use your senses (take pictures to document) – What color? Does it fluoresce – Transparent or opaque? – Homogeneous in appearance? – Solid or liquid – Tacky or sticky or brittle or tough Mass – compare with theoretical yield
Second, try and dissolve the hybrid in different solvents Water, ethanol, benzene, methylene chloride, tetrahydrofuran, acetonitrile, hexane, acetone, diethyl ether, dimethyl sulfoxide, N- methyl pyrrolidone (NMP) Leave it at room temp overnight. Look for swelling if not dissolved. Boil solvent for 4 hours. If it doesn’t dissolve its probably cross-linked or really crystalline
Types of Polymers & solubility Won’t dissolve Will dissolve
Third, Structural Characterization of soluble polymers 1 H & 13 C & 29 Si Nuclear Magnetic Resonance and infrared spectroscopy Molecular weight by gel permeation chromatography Composition by combustion analyses X-ray diffraction on film or powder Viscosity of dilute solutions- shape of polymer
Or third, Structural Characterization of insoluble polymers Harder to characterize Does it burn (many inorganics do not) Solid state 1 H & 13 C & 29 Si Nuclear Magnetic Resonance and infrared spectroscopy Composition by combustion analyses X-ray diffraction on film or powder X-ray fluorescence if inorganic
Literature procedure: See how experimentals are written in good papers. Use them as model
Morphological Characterization of polymers If opaque or transluscent, SEM and optical microscopy (bifringence)-crystalline or amorphous & more. Fracture polymer and look at fracture surfaces Look for phase separation (like immiscible block copolymers) Look for long range order Look for pores
Thermal characterization of polymers Thermal gravimetric analyses (TGA) – determines decomposition temperature Differential scanning calorimetry (DSC)– detects phase changes (melting or glass transition temperatures) or chemical reactions
Mechanical characterization of polymers Stress-strain curves: – Young’s modulus (brittleness) – Tensile strength-pull sample appart – Flexural strength- bend until it breaks – Compressive strength-crush sample Dynamic mechanical analyses (same info as above but with cyclic application of stress or strain. – Generate modulus temperature curves – Fatigue studies to predict failure under cyclic stress
Not every polymer needs all of these analyses, but structure is the most basic and important Known (described in literature) polymers need less structural characterization. Often just IR and Mw from GPC. New polymers need complete structural characterization: NMR, IR, Combustion analysis, GPC, solubility, glass transition temp and/or melting point.
Morphological and Mechanical studies are dependent on research interests. If you are interested in strong polymers, then morphological, mechanical & thermal studies are important Other applications requiring morphological, mechanical & thermal studies would include preparation and testing of 1) membranes, 2) coatings, 3) paint, 4) polymer foams, 5) organic photovoltaics, 6) OLED’s, 7) adhesives and 8) low friction coatings
Other polymer properties that are important for specialty polymers Coatings, packaging, membranes, Photovoltaics & OLED’s; gas and water permeability should be measured. Battery and fuel cell membranes: gas & water permeability and ion conductivity Dielectrics, wiring insulation: dielectric and electrical conductivity Fabrics & building materials: fire resistance Any polymer used in sunlight or radiation or in the presence of chemicals: resistance to oxidative degradation.