As fas as you explain your blend, it can be tested by DMA or ARES.

Hi Victor,

Yes, I'm thinking to use rotational rheometer to check the viscoelastic property. However, what is the best way of checking the stability?

Do I do "continuous" measurement of the SAOS test at a constant frequency? Or do frequency sweep every X hours? Or any other measurement mode?

Is it also important to look into the structure as time progress by using some kind of microscopy? What kind of microscopy would be suitable? SEM may be not suitable since the sample is wet.

I don't think, any of the microscopy technique would be possible for estimation of the stability. Actually the question is not clear so much. Are you working with two different composition? If there is a any phase separation that would cause for the generation of the aggregates which could be find out through light scattering. My point of view, DLS could be useful for certain interval of time. In case of rheology, if major phases contains with oil, frequency sweep would be very difficult because oil has very low elastic part and minimal storage modulus. If you suppose to estimate its viscosity, you can only work with flow behavior of  blend. 

For further discussion, you have to define the exact composition of your system(s). Our experience with natural oil or mineral oil in polyurethanes is to investigate it by a rheometer to measure the Newtonian and non-Newtonian viscosity, to investigate DSC curves, DMA, and use AFM. Any of these methods gives a brick of the total picture to be combined to find the answer as to the behaviour of the oil. For publication of the results, please, check for V. Stoycheva.

Hi Jit and Gerhard,

Thanks for the replies. I edited the question, I hope it's clearer now.

Jit: I managed to find the viscosity of the oil by rotational test. However, I'm more interested in the viscoelastic stability of the blend.

Gerhard: Could you give more clues on the publications you are referring to? Thanks.

hi Firdaus

for cheeking rheological parameters use rotational  rheometer.

can u say the composition of blend?

Sorry, but you did not mention the type of oil you use. If it is natural oil, there are numerous types as to plant, region, year of harvest, quality of production, ageing etc. Any of these factors will change the miscibility. If you use mineral oil the degree of branching and mol weight are essential. Next, the hydrophobic character will have an effect, so you have to test e. g. castor oil, rape seed oil, soy bean oil, linseed oil etc for their miscibility. In case of silicone rubber you'll have to test several to find one type of oil being miscible - which depends on the type of the silicone rubber (which side groups to which extent?). You can also try by introducing a solubility enhancer such as 2-ethyl-1,3-hexane diol or higher branched diols...

The work of Dr. Vesela Stoycheva was published in a presentation at TH Wildau in German and in their Wissenschaftliche Beiträge, I think in 2013, but you'll find it in research gate (if not, search fpr Michael Herzog) or in her Ph. D. Thesis which is in Bulgarian.

If further questions in this respect you may diretly contact her at [email protected]

Dear Firdaus: I have a very basic question: What do you mean with blend viscoelastic stability? Given you have explained the question better than before, I realize the problem is at the very compounding, therefore, if you must stay wich such blend then you should establish the goals clearly, as to say: blend viscoelastic stability means there is no blooming at 50°C (as an example).

One publication (in German) you may find at the website of the TH Wildau in Wissenschaftliche Beiträge 2013, pages 77 to 83 - here several results of Dr. Stoycheva are described and discussed

Gerhard:

You are right, the oil may actually be miscible in PDMS. Due to my lack of chemistry background, I don't want to play too much  to change the chemical property. The PDMS is the commercial Sylgard 184 from Dow Corning, and the oil is white oil, coming from petroleum. Basic question: How to check their miscibility?

I found the article you mentioned but unfortunately I don't understand German.

Victor:

My idea is to measure the storage and loss moduli as functuon of time. An example is to do frequency  sweep every 3 hours to the sample and calculate the change of the results. The stability limit can be deduced by considering the experimental error. In other words, if the change of moduli is within experimental error limit then the sample is considered viscoelastically stable.

A check of the composition of the silicone system will give information to your problem with white petrol to mix. This is what I found:

DOW CORNING SYLGARD 184 Divided into two part

Base Part A contains the following:

Dimethyl siloxane, dimethylivinyl terminated – 68083-19-2

Dimethylvinylated and trimethylated silica – 68988-89-6

Tetra (trimethoxysiloxy) silane – 3555-47-3

Ethyl benzene – 100-41-4

VOC Content 8 grams per liter

Curing Agent Part B contains the following:

Dimethyl, methylhydrogensiloxane – 68037-59-2

Dimethyl siloxane, dimethylvinyl terminated – 68083-19-2

Dimethylvinylated and trimethylated silica – 68988-89-6

Tetramethyltetravinylcyclotetrasiloxane – 2554-06-5

Ethyl benzene – 100-41-4

Maximum VOC content including water: 85 grams/liter

This composition is a rather hydrophilic for a silicone containing ethyl benzene as a solvent or mixing aid. If you want to continue with your white petrol you may try to increase the amount of ethyl benzene (best to make a mixture of your oil and ethyl benzene) and add it to the silicone before curing. It may as well turn out that the ethyl benzene is coming to the surface that you simply exceeded the ceiling amount of hydrocarbon load in the silicon.

Gerhard:

I'm puzzled here. The end product of the Sylgard 184, after mixing the 2 parts and crosslinking is hydrophobic. In literature, many researchers treat the PDMS surface with plasma to make it hydrophilic. Usually the hydrophilic property only last for a limited period of time.

See for example: https://www.uic.edu/labs/bml/BML/Publications_files/Eddington_SA_06.pdf

You should look at the composition. The large number of Si-O-bonds cannot make it hydrophobic, this is the result of substituents and the additive ethyl benzene (which may migrate). For such investigation as you proposed with the addition of oil a complex mixture will be difficult to relate for structure property relationships so it would be a better choice to use a simpler material only of two components. With the mixture given any prediction of a homogeneous oil mixture will be rather difficult.

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5147699/

Storage studies and testing.