Unit 3 Flashcards
What are 2 techniques that measure thermal properties of polymers?
- Differential Scanning Calorimetry (DSC) 2. thermal gravimetric analysis (TGA)
Describe one technique that measures thermal properties of polymers.
DSC: differential scanning calorimetry. 2 Compartments are used, one has a sample, one is a reference. Compartments are heated and sample undergoes transition, enthalpy changes. Varying electrical energy must flow into sample pan in order to keep the 2 pans at the same temperature. On the heat flow v. temperature plot, a peak denotes more heat required in the reference pan and sample undergoes endothermic phase transition (sample absorbing heat). Tc (crystallization temperature) is found by measuring area within inflexion peak. On the plot, a dip denotes less heat requred in reference pan and sample undergoes exothermic transition(releasing heat). The area found under the point is the Tm (melting temperature)
State 3 advantages of SIMS over XPS
SIMS: secondary ion mass spectroscopyXPS: x-ray photoelectron spectroscopy. SIMS has higher sensitivity than XPS, more sensitive to top surface of material than XPS, applicable to any solid.
What principle is thermogravimetry analysis based on?
examines process of weight changes as function of time, temperature, and other environment conditions. can obtain material composition and stability information.
What is gel permeation chromatography?
a technique for structural and organic analysis. It determines molecular weight distrubution of a polymer by comparing speeds of small and large polymer molecules. There is a compartment with columns filled with gel beads and spaces between columns. The polymer sample is diluted then placed in compartment. larger molecules elute more quickly because they travel through spaces while small polymers molecules travel through all gel pores.
What is contact angle measurement?
The angle between the surface and a line that is tangent to a drop of liquid on the surface. 90= hydrophobic, >90=hydropgobic, <90 = hydrophilic
What is atomic force microscopy?
an image analysis technique. a member of scanning probe microscopy “family.”
How does atomic force microscopy work?
shows intermolecular interaction between small atomic probe and molecules on surface. uses probe across surface, deviations characterize material surface. a 3D model can be produces.
What are the modes of probe contact for scanning probe microscopy?
Contact: characterizes by dragging probe continuously across surface
Non-contact: characterizes by forces such as van der walls and runs just above the surface.
Tapping: minimizes contact and damage, intermittant contact,
When the contact angle is below 90 degrees, what is hydrophobicity?
Hydrophilic
What are advantages and disadvantages to an in vivo experiment?
Advantages: Better approximation to human body environment
Disadvantages: demanding protocols by Animal Welfare act, must have an animal that has a comparative model to human body environment
Name 2 techniques for surface analysis.
Contact Angle measurement, X-ray photoelectron spectroscopy
Describe information obtained by contact angle measurement
Qualifies hydrophobicity of surface
Describe information obtained by XPS
X-ray Photoelectron Spectroscopy
Provides information about elemental composition. A series of element specific peaks are created which correspond to binding energies of photoelectrons. Elemental composition of surface can be quantified by measuring area under the peaks.
The X-ray excited the surface electrons, if their binding energy < x-ray energy, the electrons will be emitted from the parent atom as a photoelectron.
This qualifies as only surface analysis bc the x-ray can only excite photoelectrons on the outer surface of the material , these ezcaped electrons can be measured
State 2 techniques for image analysis and describe information obtained by each of these techniques.
- Atomic Force Microscopy: a scanning electron probe test that characterizes surface by use of probe straveling across and can create 3D models based on info obtained.
- Scanning Electron Microscopy: provide image of sample with high resolution and high depth of field. Image is created by scanning a sample with high energy beam of electrons. The electrons and their interaction with the surface produce the image
What is GPC and what information does this technique provide?
Gel Permeation Chromatography
Determines molecular weight distribution of a polymer. (structural and organic analysis)
Quantifies larger v. smaller polymer molecules in a polymer.
A sample is diluted and passed through a compartment with colums containing gel beads. Small molecules pass through pores of columns while large molecules pass through space between columns. Larger chains elute the sample more quickly and these results are quantified by UV or light detectors.
Plot is concentration agaist elution volume.
What is XRD and what information does this technique provide? How is data interpreted?
X-Ray Diffraction
- Uses x-rays to determine crystal structure.
- Planar spacing value of unit cell in crystalline structure is obtained by shooting an x-ray beam into a sample at an angle
- then measuring the intensity of reflected (outgoing) rays and diffraction angle of outgoing rays.
- The distance between planes can be computed with this info
- Distances could also be obtained by calculating area under peaks of the intensity v. diffraction angle graph.
**Crystalline structure spacing values can be matched to atoms since the have already been characterized. **
