TEM requires sample in the solid  state  while  DLS requires  sample in the solvated state. A big size difference between TEM and DLS is expected, since DLS measures the hydrodynamic size where there solvent molecules  which may be associate with particles ..i.e. particles are  surrounded by solvent molecules . There may be a weak tendency to aggregate  in samples for DLS. Size  of particles with DLS always will be bigger compared to TEM .

https://www.researchgate.net/post/What_is_the_reason_for_a_very_large_size_in_DLS_as_compared_to_TEM_My_particle_is_25nm_in_TEM_whereas_in_DLS_it_shows_a_size_of_more_than_800_nm

 https://www.researchgate.net/post/Why_does_the_particle_size_differ_in_TEM_and_DLS_measurements

 https://www.researchgate.net/post/Why_was_there_size_difference_measured_by_TEM_and_DLS

For eg.

TEM/SEM and DLS these  techniques are all together different.

Mostly TEM/SEM analysis is performed in dry state and DLS is performed in liquid state with specific solvent. These solvents will interact with particles. So the particle size in SEM/TEM will never match with DLS/SLS.

Here, this article is explaining exactly this:

http://iopscience.iop.org/article/10.1088/1742-6596/733/1/012039

TEM requires sample in the solid  state  while  DLS requires  sample in the solvated state. A big size difference between TEM and DLS is expected, since DLS measures the hydrodynamic size where there solvent molecules  which may be associate with particles ..i.e. particles are  surrounded by solvent molecules . There may be a weak tendency to aggregate  in samples for DLS. Size  of particles with DLS always will be bigger compared to TEM .

https://www.researchgate.net/post/What_is_the_reason_for_a_very_large_size_in_DLS_as_compared_to_TEM_My_particle_is_25nm_in_TEM_whereas_in_DLS_it_shows_a_size_of_more_than_800_nm

 https://www.researchgate.net/post/Why_does_the_particle_size_differ_in_TEM_and_DLS_measurements

 https://www.researchgate.net/post/Why_was_there_size_difference_measured_by_TEM_and_DLS

Thank you all.

TEM/SEM need solid sample while for DLS the particle should be well dispersed in a solvent. DLS gives hydrodynamic size which is always greater than actual size of nanoparticle (obtained from TEM/SEM) that takes into account the solvent molecules surrounding the particle in addition to the nanoparticle itself. One more thing DLS result is good technique for spherical nanoparticles whereas for nano rods/tubes its not reliable.

Thanks :) 

First a measurement by any technique is a random number generator without an assigned objective.  See:

http://www.materials-talks.com/blog/2014/02/06/characterization-is-a-number-42-not-a-goal/

An indicated above, all the above-mentioned techniques measure something abstract called ‘particle size’ usually dependent on measuring another property that can be measured and referring to a particle of known shape with the same property (usually the sphere) to map it or them (for a distribution) against.  This is the equivalent sphere concept.  We have the concept of equivalent settling in sedimentation, equivalent scattering in light scattering etc.  It applies to all sizing techniques including imaging (which is essential – we have to have some qualitative idea of degree of agglomeration, aggregation, crystallinity etc) where we have the concept of projected circular equivalent (projected area with the same number of pixels as our imaged target particle).  We note that imaging provides some shape information – usually in 2-D, but shape is a 3-D issue.  There are image analyzers now that will measure statistically valid numbers of particles for quantitative size and shape (and chemical ID in certain cases) distributions. These are philosophical issues described in the attached Basic Principles and in:

Mar 20th, 2008 Complementary information from analytical imaging and light scattering techniques

http://www.brainshark.com/brainshark/vu/view.asp?pi=133863612&text=M021507

Different techniques measure a different property of the particulate system and calculate different types of statistic accordingly (usually we see discussions that intensity, volume, and number distributions are different.  Yes.  They're only the same for a monodisperse system).

Now, all the mentioned techniques can be verified against known traceable (usually NIST) standards which are usually spherical to avoid ambiguity as to which dimension or property is referenced.  Therefore ISO uses x for particle size and other conventions use d or D referring to diameter (and thus implying a sphere).  Note that, for example, for the NIST Au colloidal standards (RM8011, 8012, and 8013), different values are assigned to the standards based on the technique used. This is important to realize.  This comparison against an accepted standard defines the accuracy of all the mentioned techniques – we verify the x or the horizontal size axis.  We can see more about this in a book chapter:

Chapter 12: “Instrument qualification and performance verification for particle size instruments” in “Practical Approaches to Method Validation and Essential Instrument Qualification” Eds: Chung Chow Chan, Herman Lam, Xue-Ming Zhang (Wiley) 2010 http://tinyurl.com/cko9ea7

That deals with the first M of the 3 M’s (machine, method, material).  The rest of the statistical nightmare deals with precision – the technique we use to prepare the sample (all TEM pictures with thin sections are artifacts), dispersion, and representative sampling.  Take a look at these webinars for more explanation of the 3M’s:

January 19th 2011 PST and BDAS - an acronym approach to laser diffraction method development

https://www.brainshark.com/malvern/vu?pi=478888057&text=M021507&r3f1= 

October 28th, 2014 Instrument performance verification in laser diffraction

https://www.brainshark.com/malvern/vu?pi=652296847

I can also recommend the Chapter entitled Characterization of Nanomaterials in Metrology and Standardization of Nanotechnology: Protocols and Industrial Innovations edited by Dr. Elisabeth Mansfield, Dr. Debra L. Kaiser, Professor Daisuke Fujita, and Professor Marcel Van de Voorde.  The first 2 named editors are with NIST:

http://onlinelibrary.wiley.com/doi/10.1002/9783527800308.ch7/summary

This 'discussion' could go on a long time.

@ Nityanshu Kumar  You ask: 'Are the SEM and TEM results consistent with those of DLS and SLS? If yes then up to what extant?',

They can only be the same for a monodisperse spherical system within the limits of each technique.  For example, you'll not see a 100 nm latex on a visible light manual microscope but these will be easily measured by a number of techniques.  Here a comparison between manual microscopy and DLS would be futile.

The killer word in particle size distribution is the last one - distribution.  This implies a lot of things which could be the subject of another long answer, book chapter, or book....

Happy Friday!

Everyone,Thanks for the help.!