If this is a mixture it may simply imply that there is more of the functional group which gives that Raman band present in the sample. It may also result from orientational differences or differences in the chromophore associated with the Raman signal.

Raman intensities increase significantly when there are resonances in the process. The resonance can be related to reaching specific optical transitions, for example. Other possibility is having a kind of SERS (surface enhanced Raman scattering) process going on. In this case, you would need metal particules generating the SERS effect.

Good day!

Which polymer you studies?

This can mean the increase in content of structural units, which give contribution in the Raman lines.

Besides chemical composition, Raman spectra depend strong on polymer supamolecular structure.

The filler can change this structural dramatically

Elena Sagitova

For the same conditions of measurement the intensity is proportionate to the amount of your material (more scatters in your sample). Frequency shift usally can give you information about strain or stress and in polymers it's related to conjugation.

An intensity increment in a particular peak of a Raman spectrum generally indicates that the fraction of substance (maybe polymerized material in this case) in the sample contributing to that vibrational mode increased. This is commonly valid provided the subsequent obtained spectra are taken with the same integration time. There is an important point to take into consideration: you have to be completely sure that the polymerization is not being induced by the laser itself during the spectrum acquisition. This would cause a particular peak to get more and more intense without an apparent reason.

Regards!

As others have said, intensity depends on how much of the polymer is contained within the interrogation volume. If density of the polymer increases, then this should cause an intensity increase. Also, if there is something like cross-linking going on, then the Raman cross-section may change. Finally, absolute intensity of Raman bands is usually not very useful because instrumental effects can change, as well as laser power, sample presentation, etc. More useful is the ratio of the band to other bands in the spectrum.

The easiest answer is that there is a local concentration of the component responsible for that Raman mode.

As we don't know what is the polymer it's not easy to answer. For example in long hydrocarbonated chains, some bands are very sensitive (CH2 stretching for examples) to all-trans or gauche conformations. This depends on temperature but also on chain length and thus on the transition temperature between the different conformations of your mixture.

It might be and indication of :

a) polymorphic form changed

b) changes of the geometrical conformation of the molecule in question, for instance change in the symmetry of the substitutions of the aromatic ring.

c) presence of the residual solvent incorporated in the polymer (could be checked with other method)

d) Presence of small amount of other impurity

There may increase of the concentration of the polymer through cross linking in the polymer composite

There should be no covalent bonding between that polymer and natural polymers. Concentration may not be an issue. As Anna said "changes of the geometrical conformation of the molecule in question, for instance change in the symmetry of the substitutions of the aromatic ring" may be the case. Because heavy atom stretching(C-C and C-O) band of the natural polymer also increased in intensity. I am in doubt about a molecular interaction between the polymer of interest and natural polymer?

This could be due to the crystallinity of the polymer and an orientation effect. Try rotating the sample and making measurements in different orientations and seing if the Raman intensity of the bands in question change their intensity. Also look up dichroic ratios in polymers.

Hi, if the intensity is really increased a lot this might indicate resonance raman scattering.

i.e. the excitation wavelenght corresponds to electronic transition of the material .

change teh wave length and you will know (if it is resoancne it will drop)

Otherwise, there could be some preferential orientation that causes increase of certain bands corresponding to a given symetry...

Here polarized e'xperiments (V-V, V-H) would be helpful....

A Raman band from a compound can become stronger because of several reasons. In your case, you say that you have a mixture of natural polymers, then I think that could be becaouse of:

1.- the band is characteristic of more than one compound, then the intensity is the contribution of two or more compounds, which means that it is stronger than should be for your polymer alone.

2.- there is a cristal orientation and then the relative intensity of the characteristic Raman bands for a compound can change.

3.- You are using a different laser wavelength than in your previous studies (or the references you have from the literature); in that case the relative intensity of some bands can change, even some the most intense using a laser excitation can become medium or even weaker using a different one.

4.- Could also happens that you are using a laser power too strong for your compound and you are inducing molecular changes, then what you are analysing is not the initial molecule but the secondary polymer created by heating the sample. This problem can happen to your polimer or to any other molecule from your sample, since you say that is a mixture.

5.- This problem of heating and molecular changes can also happens when you use a more or less correct laser power but the irradiation over the sample is long (high number of acumulations or large exposition time), the result is similar: the sample is "cold" at the beginning but it gets more and more warm until inducing molecular changes.

6.- Of course, it could be because of more than one of those posibilities!!!

Some metal incursion

Susana E Jorge-Villar .....same thing happened in my sample the intensity of specific peak increase and my sample is MgO.