DLS Reporte

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    To Study the Colloidal Properties of

    Semiconductor Nanoparticles using DynaLight Scattering

    Research Report (Chem 751)

    Pushpa Chhetri

    May 9, 2014

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    Importance of DLS in the scientific world

    DLS

    Study the properties of colloids

    Particle size distribution of particles

    Observing aggregation effects in colloids

    Application in observe the stability with time eg. Emulsi

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    Why and when DLS is used

    Polymer and particle science: routine characterization

    Experimental physicist and physical chemist: study gels, netwliquid crystals, hydrodynamic interactions

    Obtaining precise particle size

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    Video Display

    Autocorrelacin

    digital ymicrocomputadora

    PMT

    Abertura

    Lente

    LASER

    Schematic of DLS Instrument

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    Particles move or diffuse in random walk

    fashion Collision of neighboring solvent molecules

    It Probes density or conc. fluctuations

    The fluctuation in scattering intensity oflaser due to the Brownian motion ofparticles in liquid can be recorded andparticle size can be calculated usingStokes-Einstein relation.

    +

    +

    + +

    +

    +-

    -

    --

    -

    -

    +

    Brownianmotion

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    Ia(t)

    Tiempo, t

    Pequeo

    Mediano

    Largo

    Effect of Diffusion

    Intensity Vs time plotPhase

    scatte

    PMT

    Fluctu

    the fl

    partic

    that s

    Becau

    interf

    the n

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    How well a particle can scatter depends on

    MW or V

    Polarizability of the particle which is related to refraction of particle relative to the solvent.

    Is= f(np,ns).(MW)2.I0

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    Obtaining particle size

    Step 1. Obtaining raw data as intensity of scattered signal

    Step 2. diffusion coefficient from fluctuating light scattering signal

    T = Temperature

    = viscosity of solvent

    R = particle radius

    Step 3. obtaining autocorrelation function0

    0.2

    0.4

    0.6

    0.8

    1

    1.2

    1

    1.

    33

    1.76

    2.

    33

    3.

    1

    4.

    11

    5.

    45

    7.

    22

    9.58

    12.7

    1

    16.8

    6

    22.3

    6

    29.6

    6

    39.3

    4

    Relativein

    tensity

    ofscattered

    signal

    Diameter (nm)

    25 nM DSNPs in Me

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    Autocorrelation function: definition

    C(t) =

    C(t) = averaged over many wigglesof the fluctuating intensity Is

    Is(t) = Intensity at given time t

    Is(t-t) = Intensity at earlier time t-t

    Study of similarity between the values

    of Is(t) and Is(t-t)

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    5 min duration on 200 nm particles DLS module performs approximately 15 million

    multiplications

    And obtains C(t) for one value of t (eg. t=20microsecond for channel #1)

    The instrument makes 64 such sets of calculationssimultaneously for 64 different values of t.

    0

    100000

    200000

    300000

    400000

    500000

    600000

    700000

    800000

    -6 4 14 24

    C(t')

    # of ch

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    Obtaining particle size

    Step 1. Obtaining raw data as intensity of scattered signal

    Step 2. diffusion coefficient from fluctuating light scattering signal

    T = Temperature

    = viscosity of solvent

    R = particle radius

    Step 3. obtaining autocorrelation function

    1/= 2DK2

    Or D = (1/2K2)*(1/ )

    decay

    Cha

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    Challenges

    Challenges in collecting data

    - Sample preparation: sonication- Sample purification: dust is big enemy

    - Right use of cuvette

    Challenges in interpreting data

    Intensity weight

    Volume weight

    Number weight

    Distribution of particle size manipulations depends on: x axis sc

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    Advantages

    Simple experimental set up

    Less expensive

    Hydrodynamic size range 1nm to 1m

    Eg

    micro-emulsion

    Peptides

    Micelles

    Macromolecules

    Polymer

    Paint pigments

    disadvantages

    Clean samples required

    Only transparent samp

    Does not work for Settlsamples

    Gives data for everythin

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    Experimental datainterpretations

    0

    100000

    200000

    300000

    400000

    500000

    600000

    700000

    800000

    -6 4 14 24 34 44

    C(t')

    # of channel

    Autocorrelation function

    0

    0.2

    0.4

    0.6

    0.8

    1

    1.2

    1

    1.

    33

    1.76

    2.

    33

    3.

    1

    4.

    11

    5.

    45

    7.

    22

    9.58

    12.71

    16.

    86

    22.

    36

    29.

    66

    39.

    34

    52.

    18

    69.

    22

    91.

    81

    121.78

    161.53

    214.

    25

    284.

    19

    376.

    95

    500

    Relativ

    e

    intensity

    ofscattered

    signal

    Diameter (nm)

    25 nM DSNPs in MeOH

    No TBAP run 102 before EC

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    My observations as a DLS data us

    The main goal is to determine diffusion coefficient D of partraw data of scattered light intensity signal using decay const

    DLS is highly sensitive to aggregation.

    Effect of Migration is none.

    Brownian motion induced diffusion as well as the natural cois prevalent which constantly fluctuates the net intensity.

    Mathematic behind calculations is quite complicated.

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    References:

    PSS Nicomp ZLS 380 manual Experimental Data obtained using PSS Nicomp ZLS 380 in Dr

    lab, UNR.

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    Thank You

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    C(0) =

    C() = 2

    > 2

    Now the function C(t) for diffusing particles must fall from the value

    at t=0 to the baseline value 2 atvery large t

    Ideal case of uniform particle size: exponential