<< Chapter < Page Chapter >> Page >
A schematic representation of the generation of a spin echo. Copyright: Halliburton Energy Services, Duncan, OK (1999).

Nmr relaxation mechanism in solid suspensions


From an atomic stand point, T 1 relaxation occurs when a precessing proton transfers energy with its surroundings as the proton relaxes back from higher energy state to its lower energy state. With T 2 relaxation, apart from this energy transfer there is also dephasing and hence T 2 is less than T 1 in general. For solid suspensions, there are three independent relaxation mechanisms involved:-

  1. Bulk fluid relaxation, which affects both T 1 and T 2 relaxation.
  2. Surface relaxation, which affects both T 1 and T 2 relaxation.
  3. Diffusion in the presence of the magnetic field gradients, which affects only T 2 relaxation.

These mechanisms act in parallel so that the net effects are given by [link] and [link]

1 T 2 = 1 T 2, bulk + 1 T 2, surface + 1 T 2, diffusion size 12{ { {1} over {T rSub { size 8{2} } } } = { {1} over {T rSub { size 8{2, ital "bulk"} } } } + { {1} over {T rSub { size 8{2, ital "surface"} } } } + { {1} over {T rSub { size 8{2, ital "diffusion"} } } } } {}
1 T 1 = 1 T 1, bulk + 1 T 1, surface size 12{ { {1} over {T rSub { size 8{1} } } } = { {1} over {T rSub { size 8{1, ital "bulk"} } } } + { {1} over {T rSub { size 8{1, ital "surface"} } } } } {}

The relative importance of each of these terms depend on the specific scenario. For the case of most solid suspensions in liquid, the diffusion term can be ignored by having a relatively uniform external magnetic field that eliminates magnetic gradients. Theoretical analysis has shown that the surface relaxation terms can be written as [link] and [link] , where ρ = surface relaxivity and s/v = specific surface area.

1 T 1, surface = ρ 1 ( S V ) particle size 12{ { {1} over {T rSub { size 8{1, ital "surface"} } } } =ρ rSub { size 8{1} } \( { {S} over {V} } \) rSub { size 8{ ital "particle"} } } {}
1 T 2, surface = ρ 2 ( S V ) particle size 12{ { {1} over {T rSub { size 8{2, ital "surface"} } } } =ρ rSub { size 8{2} } \( { {S} over {V} } \) rSub { size 8{ ital "particle"} } } {}

Thus one can use T 1 or T 2 relaxation experiment to determine the specific surface area. We shall explain the case of the T 2 technique further as [link] .

1 T 2 = 1 T 2, bulk + ρ 2 ( S V ) particle size 12{ { {1} over {T rSub { size 8{2} } } } = { {1} over {T rSub { size 8{2, ital "bulk"} } } } +ρ rSub { size 8{2} } \( { {S} over {V} } \) rSub { size 8{ ital "particle"} } } {}

One can determine T 2 by spin-echo measurements for a series of samples of known S/V values and prepare a calibration chart as shown in [link] , with the intercept as 1 T 2, bulk size 12{ { {1} over {T rSub { size 8{2, ital "bulk"} } } } } {} and the slope as ρ 2 size 12{ρ rSub { size 8{2} } } {} , one can thus find the specific surface area of an unknown sample of the same material.

Example of a calibration plot of 1/T 2 versus specific surface area (S/V) of a sample.

Sample preparation and experimental setup

The sample must be soluble in the solvent. For proton NMR, about 0.25-1.00 mg/mL are needed depending on the sensitivity of the instrument.

The solvent properties will have an impact of some or all of the spectrum. Solvent viscosity affects obtainable resolution, while other solvents like water or ethanol have exchangeable protons that will prevent the observation of such exchangeable protons present in the solute itself. Solvents must be chosen such that the temperature dependence of solute solubility is low in the operation temperature range. Solvents containing aromatic groups like benzene can cause shifts in the observed spectrum compared to non-aromatic solvents.

NMR tubes are available in a wide range of specifications depending on specific scenarios. The tube specifications need to be extremely narrow while operating with high strength magnetic fields. The tube needs to be kept extremely clean and free from dust and scratches to obtain good results, irrespective of the quality of the tube. Tubes can cleaned without scratching by rinsing out the contents and soaking them in a degreasing solution, and by avoiding regular glassware cleaning brushes. After soaking for a while, rinse with distilled water and acetone and dry the tube by blowing filterened nitrogen gas through a pipette or by using a swob of cotton wool.

Questions & Answers

How we are making nano material?
what is a peer
What is meant by 'nano scale'?
What is STMs full form?
scanning tunneling microscope
what is Nano technology ?
Bob Reply
write examples of Nano molecule?
The nanotechnology is as new science, to scale nanometric
nanotechnology is the study, desing, synthesis, manipulation and application of materials and functional systems through control of matter at nanoscale
Is there any normative that regulates the use of silver nanoparticles?
Damian Reply
what king of growth are you checking .?
What fields keep nano created devices from performing or assimulating ? Magnetic fields ? Are do they assimilate ?
Stoney Reply
why we need to study biomolecules, molecular biology in nanotechnology?
Adin Reply
yes I'm doing my masters in nanotechnology, we are being studying all these domains as well..
what school?
biomolecules are e building blocks of every organics and inorganic materials.
anyone know any internet site where one can find nanotechnology papers?
Damian Reply
sciencedirect big data base
Introduction about quantum dots in nanotechnology
Praveena Reply
what does nano mean?
Anassong Reply
nano basically means 10^(-9). nanometer is a unit to measure length.
do you think it's worthwhile in the long term to study the effects and possibilities of nanotechnology on viral treatment?
Damian Reply
absolutely yes
how to know photocatalytic properties of tio2 nanoparticles...what to do now
Akash Reply
it is a goid question and i want to know the answer as well
characteristics of micro business
for teaching engĺish at school how nano technology help us
How can I make nanorobot?
Do somebody tell me a best nano engineering book for beginners?
s. Reply
there is no specific books for beginners but there is book called principle of nanotechnology
how can I make nanorobot?
what is fullerene does it is used to make bukky balls
Devang Reply
are you nano engineer ?
fullerene is a bucky ball aka Carbon 60 molecule. It was name by the architect Fuller. He design the geodesic dome. it resembles a soccer ball.
what is the actual application of fullerenes nowadays?
That is a great question Damian. best way to answer that question is to Google it. there are hundreds of applications for buck minister fullerenes, from medical to aerospace. you can also find plenty of research papers that will give you great detail on the potential applications of fullerenes.
what is the Synthesis, properties,and applications of carbon nano chemistry
Abhijith Reply
Mostly, they use nano carbon for electronics and for materials to be strengthened.
is Bucky paper clear?
carbon nanotubes has various application in fuel cells membrane, current research on cancer drug,and in electronics MEMS and NEMS etc
advantages of NAA
Sai Reply
how I can reaction of mercury?
Sham Reply

Get the best Physical methods in ch... course in your pocket!

Source:  OpenStax, Physical methods in chemistry and nano science. OpenStax CNX. May 05, 2015 Download for free at http://legacy.cnx.org/content/col10699/1.21
Google Play and the Google Play logo are trademarks of Google Inc.

Notification Switch

Would you like to follow the 'Physical methods in chemistry and nano science' conversation and receive update notifications?