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Defence Prep Flashcards

Background information how how electrospinning works

1
Q

Why does a voltage need to be applied in electrospinning?

A

The polymeric solution will form droplets at the tip of the spinneret owing to surface tension. An applied voltage causes uniform charges, leading to charge repulsion and deformation of the droplet into a Taylor cone instead.

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2
Q

What happens to the jet between the spinneret and collector plate?

A

The jet experiences instability, resulting in a whipping motion

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3
Q

What happens to resulting fibres when the polymer molecular weight is too low?

A

Electrospraying occurs because the solution jet breaks up into small droplets, forming nanoparticles. Beaded fibres can also result.

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4
Q

What happens to the resulting fibres when the polymer solution concentration is too low? Why?

A

The fibres are beaded. There aren’t enough chain entanglements to cause smooth fibre formation

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5
Q

What happens to fibres when the MW is too high?

A

Fibres are typically flat and aggregated.

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6
Q

What would happen to the fibres if the concentration was too high?

A

It would be difficult to form a jet as the droplets would be too heavy to be deformed

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7
Q

What role does solution viscosity play in the formation of fibres?

A

Optimal solution viscosity produces continuous fibre formation during the jet creation; however, if the viscosity is too high, the fibre jet may not be pulled effectively

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8
Q

What happens if the tip-to-collector distance is too short?

A

The solvent wouldn’t have enough time to evaporate, resulting in wet fibres

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9
Q

What conditions result in a stable jet formation?

A

When the jet flow rate is lower than the feed rate

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10
Q

What results in a fluctuating jet?

A

When the jet flow rate is higher than the feed rate

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11
Q

Stable fibre formation occurs at x entanglements per chain

A

2.5 which can be achieved by increasing concentration or MW

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12
Q

what happens when viscosity is too low?

A

Beaded fibres are formed

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13
Q

What unit is viscosity measured in?

A

centipoise

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14
Q

How is viscosity measured?

A

Different types of viscometers can be used, such as:

  1. Capillary viscometer: Measuring how long it takes for a solution to flow through capillary tubes
  2. Rotational viscometer: How much torque needs to be applied for a spindle to be rotated at constant speed in the solution
  3. Falling ball viscometer: Measuring how long it takes for a ball to drop in a solution under gravity
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15
Q

What effect does solution surface tension have on spinabillity?

A

Solutions with high surface tension are more difficult to spin and can lead to beads on a string (e.g., water is more likely to lead to this)

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16
Q

What happens when additives that increase solution conductivity are added to the polymer solution?

A

In general this improves solution spinnability. Sometimes this leads to thicker nanofibre diameters (non-covalent interactions) and sometimes thinner

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17
Q

What role does tip-to-collector distance play?

A

If the distance is too large then the fibres cannot reach the collector plate. If the distance is too short then the solvent will not evaporate and the resulting fibres will be wet/not elongated.

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18
Q

If a solution is prone to beading, a larger tip-to-collector distance results in

A

larger beads

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19
Q

What effect does applied voltage have on fibres?

A

Can increase the coarseness, typically will decrease diameter but studies have shown this increase diameters as well (Alongside a broader distribution of sizes)

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20
Q

What is a stable jet

A

When the jet flow rate is lower than the feed rate

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21
Q

What is a fluctuating jet

A

When the jet flow rate is higher than the feed rate. This results in beads

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22
Q

What is fluorescence

A

Fluorescence is a radiative decay process whereby after a molecule absorbs energy, it releases that energy as a photon with a longer wavelength than what was absorbed

23
Q

What is Kasha’s rule

A

An excited electron will relax back down to the lowest excited state before a photon is emitted

24
Q

What is a photon

A

A particle that carries electromagnetic radiation

25
Q

How can quantum yield be measured

A

quantum yield = photons emitted/photons absorbed

26
Q

What is a more complicated way of describing quantum yield

A

By comparing the competing rates.
qauntum yield = kf/kf+knr+kET

27
Q

A largely conjugated D-A system can result in what type of a shift in fluorescence?

A

batochromic shift

28
Q

What are the rates of absorption and emission in order from fastest to slowest?

A

Absorption (10^-15)
Internal conversion
Vibrational relaxation
Intersystem crossing
Fluorescence
Phosphorescence
Non radiative decay

29
Q

What is the Pauli exclusion princple?

A

No 2 electrons can have the same 4 quantum numbers (n, l, ml, ms)

30
Q

what is the equation for multiplicity?

A

2s+1

31
Q

What role does oxygen play in fluorescence?

A

Dynamic quenching can quench fluorescence due to molecular collisions

32
Q

How can a fluorophore interact with triplet state oxygen to form singlet oxyen?

A

?

32
Q

How does the chosen solvent affect fluorescence?

A

Polar solvents can reorient themselves around the excited-state fluorophore to lower the energy of the excited state. This red-shifts fluorescence.

33
Q

What is pi stacking

A

A non-covalent interaction between aromatic groups

34
Q

What are the two pi stacking arrangements?

A

Eclipsed and displaced. Eclipsed is when they are one on top of another. Displaced is when they are offset. Eclipsed is less favoured because of electrostatics.

35
Q

Describe staggered pi stacking

A

In staggered pi stacking, the partial negative carbon and partial positive hydrogen are on top of one another

36
Q

Why were most of the nanofibres on the um scale?

A

could be because of the needle (16G), could be because our distance was too short, could be because our voltage was too low

37
Q

Why would solid state emission differ from solution?

A

Less movement, could aggregate, no solvent effects,

38
Q

Why is BODIPY not affected much by different states when it comes to fluorescence

A

It is symmetrical

39
Q

Would DAPI be affected by the solvent polarity?

A

This derivative maybe not so much, but others could be. This generally wasn’t affected

40
Q

Why did BODIPY fluoresce more strongly than DAPI?

A

Has a higher quantum yield (.9 vs .58)

41
Q

What are the rules for aromaticity?

A
  1. The molecule is planar
  2. The molecule is fully conjugated
  3. The molecule follows Huckel’s rule. 4n + 2 pi electrons = (if n is 0 or a positive integer, this rule is met)
  4. The molecule is cyclic
42
Q

What is an excimer?

A

An excited state complex, which typically has shifted fluorescence emission. Around 100 nm

43
Q

How many atoms comprise quantum dots?

A

100 - 100,000 atoms, making a size of 2-10 nm

44
Q

Give examples of atoms that are typically in quantum dots

A

Cd, Se, Hg, Pb, Zn

45
Q

What are the advantages of using quantum dots over molecules in FRET?

A

Greater FRET distance and have higher extinction coefficients. Narrow absorbance and emission bands

46
Q

Why is the emission of quantum dots size dependent?

A

Because the band gap changes as the size of the dot changes

47
Q

Benefits of ratiometric sensing

A
  1. Accuracy & Reliability: Internal calibration corrects for experimental variations.
  2. Environmental Interference: Less sensitive to changes in pH, temperature, and other factors.
  3. Enhanced Sensitivity: Detects small changes more effectively.
48
Q

How does LCMS work

A
  1. Sample Introduction
    Liquid Chromatography (LC): The sample is injected into the LC system, where it is dissolved in a solvent and passed through a column filled with a stationary phase (a solid or liquid material that interacts with the sample molecules). Different molecules in the sample interact with the stationary phase to varying degrees, causing them to elute (exit the column) at different times.
  2. Separation of Molecules
    As the sample passes through the column, molecules are separated based on their chemical properties, such as polarity, size, and affinity to the stationary phase. The separation results in different molecules eluting from the column at different times (retention times).
  3. Detection by Mass Spectrometry
    Ionization: The separated molecules are then directed into the mass spectrometer, where they undergo ionization. The ionization process converts the molecules into charged ions, typically by removing or adding an electron.
    Common Ionization Techniques:
    Electrospray Ionization (ESI): A technique where the liquid containing the molecules is sprayed into a fine mist, and the solvent is evaporated, leaving behind charged ions.
    Atmospheric Pressure Chemical Ionization (APCI): A technique where the solvent is evaporated, and the molecules are ionized using a corona discharge.
    Mass Analyzer: The ions are then directed into a mass analyzer, which separates them based on their mass-to-charge ratio (m/z). The mass analyzer generates a mass spectrum, a plot that shows the relative abundance of ions as a function of their m/z ratio.
  4. Detection and Data Analysis
    The mass spectrometer detects the ions and records the mass spectrum. The resulting data can be used to determine the molecular weight of the molecules and, with further analysis, their structure.
    Quantification: By comparing the intensity of the detected ions to those of known standards, the amount of each molecule in the original sample can be quantified.
  5. Output and Interpretation
    The final output is a chromatogram (from the LC) that shows the retention time of each compound and a corresponding mass spectrum (from the MS) that provides detailed information about the mass and structure of the molecules.
49
Q

What does Mw and Mn mean when it comes to polymers

A

The difference between Mw (Weight-Average Molecular Weight) and Mn (Number-Average Molecular Weight) lies in how they account for the distribution of molecular weights in a polymer sample.

Mn (Number-Average Molecular Weight):
It’s the simple average of the molecular weights of all the polymer molecules in a sample.

MW (weight-average molecular weight) = Instead of just averaging the molecular weights (like Mn), Mw considers both the molecular weight and the amount (or mass) of each molecule.

50
Q

What is polydispersity index (PDI)

A

The Polydispersity Index (PDI) is a measure of the distribution of molecular weight in a polymer sample. It indicates how uniform or varied the molecular weights of the polymer chains are.

51
Q

What are the different types of polymers

A

Homopolymers: Polymers made from a single type of monomer.

Copolymers: Polymers made from two or more different types of monomers.
1. Random: The monomers are arranged in a random sequence along the polymer chain.
2. Alternating: The two monomers alternate in a regular pattern.
3. Block Copolymers: The monomers are grouped into blocks, where each block is a long sequence of one type of monomer.
4. Graft Copolymers: One type of monomer forms the main chain, while branches of another type of monomer are grafted onto it.

Cross-linked polymers: Create 3-dimensional networks

52
Q
A

Defence Prep (3 decks)

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