Polymer Rheology - Science topic

Ravi Purbey please write message my email kuzmin.a.m@yandex.ru

Antonio Alves

Dependence of the maximum dynamic reduced viscosity η_red of polyacrylic acid solutions on the concentration (c) in H2O c=8x 10-9 mol/l and in D2O c=100 x 10 -9 mol/l at 25 0C. Firstly, this shows that the dependence is complex. Secondly, the difference in behavior in the two solvents shows the participation of the nuclear quantum effect, i.e. quantum fluctuations, in the viscosity.

Oops, my mistake. I answered too quickly. So, let's see if I got this right:

You did a flow curve test with preshear at 20s-1 and then an increasing shear rate ramp from 0s-1 to 200s-1 (in how long?).

Unfortunately, this test protocol is hard to interpret, because you are seeing the balance between two phenomena: i) Structural breakdown/buildup and ii) thixotropy (reversible structural breakdown/buildup). Depend how fast/slow each of these occur, you can see a wide range of results. The rate of ramping will also have an effect. See more details in my open access paper "Texture profiling with the vane", available on Researchgate.

Dear Siavash Sarrafan, swelling test is the most used technique. Most techniques are reviewed in the following paper. My Regards

1. Use a high-shear mixing element in the extruder to ensure that the particles are evenly dispersed.

2. Use a low screw speed to reduce the risk of particle breakage.

3. Use a low temperature setting to prevent thermal degradation of the particles.

4. Use a low back pressure setting to reduce the risk of particle agglomeration.

5. Use a vacuum system to remove air from the extruder barrel and reduce the risk of particle oxidation.

6. Use a cooling system to reduce the risk of thermal degradation of the particles.

7. Use a filter system to remove any particles that may have been damaged during the extrusion process.

8. Use a pelletizing system to ensure that the particles are evenly distributed in the masterbatch.

Treatment of Lignocellulosic stock for bioethanol production requires removal of lignin barrier from Cellulose. Lignin has glassy transition temperature about 170 degrees centigrade.(Please get it reconfirmed as I have been out of touch with the subject for very long time). Heating biomass to the desired temperature and heating time are important parameters for pre-treatment of biomass.

Thanks a lot!

By using the samples of lower molecular weight which is below Me it is not possible to estimate Me experimentally. However Mc values for different linear polymers can be obtained from literature and then using (Me ~ Mc/2) will give Me. However please note that Mc / Me may be higher than 2 depending on polymer.

Pl. refer to [https://polymerdatabase.com/polymer%20physics/Crossover%20Length.html]

Dr.B R Gupta

When two adhesive substrates are brought in contact the molecules on the surfaces start entangling. The process of entangling is a rate process i.e. it will try to adhere slowly and the its strength will increase. The increase of shear strength of the joint will increase slowly first and then it will increase quite fast. The entanglement of surface molecules increases the interphase viscosity finally resulting in strong joint after maturity time

b r gupta

Dear Ahmed Amer Flayeh,

I have atached one article which the pelofsky equation was used for polyethylene solution. In general, it is possible to use some equation of solution for polymer solution at low concentration.

It work as labricant so that reduces the viscosity.

Those are material properties and thus, in theory, they are the same value regardless of the volume of the samples measured. However, in practice, some internal defects may exists and these defect will, to some extent, influence the measured value by the difference in cross-sectional areas. For example, if you measure the storage modulus of exactly the same dimension samples, the values of two different specimens may still be different due to the shape factor difference. If one sample is near perfect and the other one might contain internal, undetected cracks or voids, the apparent cross-sectional area used to calculate the modulus may be the same but the true cross-sectional areas are different. Thus, the measured storage moduli of those samples are slightly different. The same is true for loss moduli. This is the reason why tan delta value is sometimes used to study Tg since tan delta is the ratio of the loss modulus against the storage modulus and thus eliminates the shape factor contribution, leading to a better baseline and sharper peak to determine the temperature.

Great videos.

There are many texts available via simple search. Thé following RG document deals with the answer. It is in accordance with my first contribution. My Regards

First what polysaccharides (there are many of them with extremely different properties, e.g. towards the formation of gels), and then at what concentration. In addition, for rheology studies, it may be necessary to use LAOS instead of SAOS. From the rheological point of view, they are soft matter systems.

You should try transient tests such creep behaviour or stress relaxation in order to get accurate values of relaxation time or its spectrum.

If a defect occurs in an injection molded product, it is most likely to come from either the improper properties of the selected raw material or the incorrect flow properties during the processing of the raw material. If it is a processing issue, then studying the flow properties through a capillary rheometer or using a rotational rheometer under high shear rates under identical conditions to those used for the injection molding will help in developing a correlation between the rheological properties and the defects. On the other hand, if the issue is with the properties of the selected raw material then gathering rheological data in the low shear rate range with a rotational rheometer will aid in seeing the correlation between the raw material properties and the molded product defect. A better understanding can be got through the following books:

In case, fillers or reinforcing fibers have been added to the raw material then the following book may help in showing how the rheology is affected by their presence.

3. Aroon V. Shenoy, Rheology of Filled Polymer Systems, Kluwer Academic Publishers, Netherlands (1999).

So it is a polypeptide. Here is a good reference to read. Good Luck

Like others mentioned, you want a high degree of Long Chain Branching, which will increase extensional stress growth and also will favor shear thinning.

Hi Fanny, Polyamides such as nylon can be dried between 80 - 120C, depending on their MW, but recommended to use vacuum drying at 104C for a couple of hours at least. Other places recommend 8 or 12 hours at lower temperatures. The drying condition could also be considered to relate to the dampening conditions the sample may have experience, for instance if exposed to atmospheric humidity for two hours, then only superficial absorption will have occurred and drying can be for just an hour or two. If the sample could be thoroughly wetted, then a longer slower drying would be necessary. The viscosity will be lower when the polymer is damp but will plateau when dry, so you could study this yourself as well if needed. Please also see:

ABS is recommended 70-80C for 3-4 hours.

Hope this helps!

Hi Bhaskar,

Sorry my mistake, I thought you had matrix with fillers and reinforced with fibers.

Nevertheless, the basic underlying principle stays the same. In order to achieve good adhesion of PEEK with nanofiller particles, you should apply coupling agent on surface of nanofillers. The coupling agent chemically or chemophysically bonds the nanofiller with the polymer matrix. In order to choose this coupling agent you should consider chemistry of both nanoparticles and PEEK.

To suggest a correct coupling agent I must know which nanofiller. Generally, I may suggest to try using y-APS (gamma-APS) silane coupling agent. This one and other silane coupling agents are very popular. Hope this helps

Best Regards,

Andrey

Hi

Build master curve based on time-temperature superposition (TTS) concept, find plateau modulous and the cross-over between G' and G" as the reptation relaxation time (Td= 1/lowest value of angular frequency (rad/s) before the material starts to flow).

Thank you, Mr Abdelkader.

My argument is that a Bengham fluid (such as Mountain bee Honey) is temperature dependent and act linearly after exceeding the critical shear stress. If the critical shear stress is for example 1MPa which is very near to the origin, then we can consider this fluid as a Newtonian one, given the fact that viscosity will be constant.

To clarify my argument:

Equation of a Newtonian fluid would be in the form of y = mx

Equation of a Bengham fluid would be in the form of y = mx + c , where c is the critical shear stress. Therefore, for small c, y will depend mainly on mx.

https://dasher.wustl.edu/chem478/reading/md-intro-2.pdf (see chapter 4)

All these links are about MD calculation of polymer systems. The autocorrelation function can be fitted by a realxation time distribution (Laplace transform) - but in my opinion this is somewhat arbitrary. It is much better to simulate the correlation function itself - if possible. It telles more about the physics behind the process.

A purely Newtonian liquid has a delta of 90°, i.e. tandelta is inifinity (theoretically). In my practical experience, obtaining tandelta above 100 is difficult especially for low moduli.

concerning your polyLMA : I am not exactly sure about this, but it sounds as if you might have a problem with delta due to various rheometer artefacts. I would suggest you do a strain sweep and check how delta changes as a function of deformation. if you see large scatter, it is most likely and arefact you are chasing.

@Oleg: I disagree with your statement "Materials have their maximal tan(delta) exactly at the glass transition temperature." One of the common definitions is that glass transition is exactly at the maximum of tan(delta), but that usually is around delta ca. 45°. Above and below the glass transition tan(delta) is lower.

Hello Mohammad,

There is nothing typical about these block copolymers

There are many unkowns in the formulation of your question some belong to the definition of your fluid (1) some belong to the measuring procedure(2).

(1) -Do you know the size of the various blocks?

     - what is the overall molecular weight or molecular weight distribution?

     - What did you utilize to dilute your hydrogel and what dilution did you use?

     - what is the temperature of the LCST and UCST of your block copolymer?

(2) - For the dynamic measurements for which you give the moduli you would need also to specify the frequency and the strain of the measurement.

      - It seems that in the experimental conditions you've chosen you hydrogel is in a gelled or partially gelled formed. Thus it is difficult to talk about viscosity therefore I have strong doubt that for that specific point you will find a relationship between the complex viscosity and the steady shear viscosity.

      - Hydrogels are tricky materials to deal with, whet procedure did you utilize to check and make sure that there is no slip.

    - what fixtures did you utilize?

    - how did you check that you where in the linear viscoelastic range?

    - what was the frequency range?

Indeed, polymers are complex materials and hydrogels even more so and rheology is a field of science that requires quite a bit of expertise to make proper experiments and interpretations.

Regards

Hello Ceren,

When you are dealing with polymers unlike with other organic molecules there is no such a thing as "the molecular weight" even for nature made polymers such as chitosan but rather a molecular weight distribution.

To characterize such a distribution you will have first either to separate the various molecular weights for example by centrifugation or column chromatography then measure the viscosity of each extracts as suggested above or utilize SEC/GPC techniques.  In any case you will have to dilute your sample down to maybe 50mg/L the solvent and molecular weight.

You could also utilize a rheometer with the solution as it is, but then you will need some extensive work of calibration and  deconvolution to figure out the molecular weight distribution and its various averages. Today this is more of a research work and that is not a popular technique.

Regards

Thank you very much for your time and help. So what I understood from your effort is: since G* is the sum of G' +iG'', G* is independent of both of them in behaviour. Now,  "i" is also a depending factor (may be). Moreover, do u suggest me to follow G* trend to conclude on the viscoelastic properties?

Hi Ernest,

Yes certainly, it is pretty simple if your sample is Newtonian (ie viscosity doesn't change with shear rates) and you just need to know the dimensions of the Ubbelohde capillary and density of the sample if it's non-Newtonian to approximate the same shear conditions.

If you think the sample is either Newtonian or nearly so, use the rheometer in the normal way and use a table of shear rates from the toolkit (Toolkit_V001 Shear Rate Table).  Using a range of 10 - 500 1/s with a cone or parallel plates should give good data for almost any low viscosity liquid.  The kinematic viscosity (as would be derived from an Ubbelohde tube) can then be calculated from measured shear viscosity using the density of the sample (Kinematic Viscosity = Shear viscosity / density in g/ml).

If you have a non-Newtonian sample, please let me know and I'll address that more complicated situation.

Regards,

Phil

Hello Pierluigi, based solely on the information that you provided, I tend to believe that this is not an intrinsic property of the material (since abrupt changes are not as common in a rheological experiment), but your measurement might be approaching certain physical limits of the configuration of the experiment (geometry size, frequency used) including reaching limits of the instrument (minimum torque, motor inertia).  These might ultimately lead to your experimental conditions to be less optimized when your material gets very low in viscosity due to increases in Temperature, where it was optimized when the test was at lower temperatures.  With that said, this could result in the rheometer/geometry configuration possibly having inertia affects when measuring bitumen-like material at 90°C where the material is very low in viscosity (" G" quite linear") and you get an abrupt change in G'.  IF your phase angle is close to 90° before the abrupt change, then it could mean that your measurements are instrument inertia dominated.  One of the best ways to determine if this is the case, is to plot "raw phase angle" (might be a different variable name based on the rheometer manufacturer), however if this value nearing 180° or above 170°, then the inertia correction being applied by your rheometer is significant (even if you have calibrated the inertia of the geometry and instrument), and your sample response is therefore being masked by the significant inertia correction, which might result in "abrupt" changes in the calculated G' and G" that relies on the "corrected phase angle".  I would suggest that you contact your rheometer manufacturer's helpdesk and provide them the data file for them to investigate your experimental conditions under the higher temperatures, to suggest improving the experimental setup.  This might result in a different geometry, a different frequency, a smaller gap, etc.  If the experimental conditions are determined to be fine in that temperature range, then further investigation of what could cause an abrupt change and back to the same value will need to be conducted.  However, as you are doing, rule out the instrument configuration and experimental conditions first.

Regards,

Fred 

Thank you very much

What you are observing seems plausible and here is why? To start off, crystalline in a typical TPU is relatively low say coampred to PE or PP resin.  In general, it is believed that crystallinity in TPU depends on arrangement/stacking of hard segments (HS). So, I can see how its counterintuitive to you. But keep in mind that here you are comparing two different types of prepolymer (PP), isocyanate end-capped ester with ether.  Ester PP being softer will also have longer ester backbone , which being ester is capable of crystallizing by itself. So,  in your case you are seeing the effect of ester backbone crystallization + HS stacking. The same is not true for the ether based TPU. Now, your thought about Durometer tracking with % crystallinity is not entirely correct either. There are many amorphous TPUs that have higher hardness than crystalline one. One example would be Isoplast 80D TPU. This TPU is almost amorphous and yet is one of the highest durometer TPU available in the market place. Hope this helps.

I think it is possible but you have to play with the concentration. I do have viscoamylograph and if you can send sample we can try.

Answer is yes, definitely yes. There is a process called vis-breaking. The whole PP industry uses vis-breaking to make injection molded PP from low MFR (extrusion grade). Basically vis-breaking means process of breaking down larhe MW to smaller MW. Various types of Peroxides are used to break down high Mw PP in controlled fashion to get desired lower Mw and MWD suited for injection molding. There are hundreds of literature out there on this subject. Check out an old Patent 4287076 that will describe the entire process. Or check out book "Processing and Finishing of Polymeric materials-vol 2", published by Wiley 2011.You may also want to talk to some one who works at PP manufacture and can tell you the correct type of peroxide to control Mw and MWD (Lyondelbasell, Exxon, Sabic etc.). 

Hi Tim, do you have a source you recommend?

Equilibrium swelling or/and Young Modulus could be useful to compare crosslinking density, but also DSC determination, could be an answer of crystalinity change due to crosslinking, crosslinking decrease crystallinity and increase Tg.

There is another issue pertaining the adhesive formation, I will be grateful if you share your view on it.

We know phenolic resins are used for adhesive preparation. But we have observed that strength of adhesive increases with increase in the amount of resin, but after a certain limit the strength starts declining as more amount of resin is added. Now as resins is used as tackifier, what could be the possible mechanism affecting the strength increasing the amount of resin to a certain limit.

Hi Ariel,

The properties you are looking for in support gels are high yield stress with shear thinning behaviours. With high yield stress, the support gels will stop flowing very fast once the needle passed by, in that way your printed shape will be retained very well. And the shear thinning property, as for most of gels are shear thinning, here you should be looking at the ones that particularly with a fast drop in viscosity, combining with a high yield stress. 

I haven't done it myself, but I think, to test the support gels, you might want to do the rheology tests with a stress-relaxation setting. The stress should be calculated to correlate to your printing speed and needle size etc. 

Hope this helps. Good luck with your project!

Cheers,

Binbin

Thank you for your help

A general procedure would be drying over CaH₂ and vacuum distillation. Main impurity would be water.

Negative loss would mean the specimen was putting power into the oscillation.  If I really exercise my imagination, I can come up with ways this could happen, but not without going to a lot of trouble to create an external drive mechanism...which is clearly not your case. 

The fact that the negative loss appeared at 500 Hz may be significant to an explanation. In Rheometrics (TM) equipment this used to be the maximum frequency, though I'm not necessarily up to date now.  If odd behavior caused by instrument error is going to show up, I would expect it most likely at one extreme or the other of the instrument's range.

Can you get at the same region but at a lower frequency by temperature shift? 

Hi Panarin,

The above answers are broadly correct.  The MW is proportional to the zero shear viscosity by the Kuhn-Mark-Houwink-Sakurada relationship for a melt or concentrated solution where the exponent ~3.4 for concentrated samples.  The same relationship can be used for dilute polymer solutions (below a critical concentration) where the intrinsic viscosity is proportional to the MW raised to the power alpha (where alpha is ~0.5-0.8). In the semi concentrated range, other factors such as shear rate and MWD also play a role, and the analysis becomes more difficult.   

Normally one would measure 3 or more samples by GPC to obtain their MW and then a rheometer or viscometer to get their intrinsic or zero shear viscosity.  The data (log viscosity vs log MW) is then plotted in a spreadsheet and a correlation created using the power law relationship which relates to the Mark Houwink relationship.

Hope this helps,

Best

Phil

Stringiness is due to the gel's elasticity. You can quantify this with creep tests. In particular, elasticity causes oscillations in the creep curve at short times. Type "Baravian creep" into Google Scholar. You will find pdfs of several papers on Researchgate that show how to analyze the results.

Christophe Baravian was my scientfic buddy. He died far too young, RIP.

Do we usually consider a specific value for the standard deviation (SD) for G' and G" in the amplitude sweep test when we take 3 or more measurements.  Acually I couldn't find any reference on that.

If you are looking for the gelation with DMA.  It is at the crossover of G' and G".

I would choose h = D/3 or D/4 at most. For example, in hydrogel systems I work with I often use D=25mm and h~1mm. Be careful of going too low as well though - pieces of dust can get trapped and ruin your measurement if your gels have a very low modulus. I agree with Paul - you could try a few to make sure your measurements are consistent.

There are other, more complicated reasons for choosing a particular gap size in certain measurement regimes, e.g. high-velocity flows or very low torque signal. I recommend Prof. Randy Ewoldt's book chapter on avoiding bad data for more information on those cases: http://ewoldt.mechanical.illinois.edu/pubs/Ewoldt_2015_SpringerChapter_Author-generatedPREPRINT.pdf

You need to give geometry and solve for the Reynolds equation. Parametrically investigate your simulation.

You need add wax and increase the extrusion tempearture for better mixing and hig MFI.

Thanks for the reply Philip Rolfe sir. Both the moduli is changing during the scan but there isn't any crossover point so as to determine the exact time at which gelation occurs. So I was a little skeptcial about the same. Thnaks for the suggetsion. 

Thanks Abaneshwar for your interest

Dear Mr. Price and Mr. Koehler,

Thank you for your support. Honestly I didn't look the product in the microscope but only make some thermal analysis and IR (and no diffrences can be found in the clear and opaque areas). It is a good idea to look it in the microscope. Maybe it is only the air bubbles as Mr. Koehler said.

Again, thank you :-)

I tried very hard to find specific references for you that described your solvent choices, but the following two attached references were the best that I could do.  I hope that the acrylates and general theoretical principles they describe are sufficient for explaining the polymerization phenomena that you are seeking to elucidate.  If you have any other specific questions, please don't hesitate to contact me.

when crosslinking is inceasing, the bond number is increasing. when you make macrmolecules move or fluctuate, it will need more energy.so the Tm is inceasing.but when the crosslinking is inceasing, the orientation force is decreasing, and total material is one macromolecule which becomes stiff and brittle like the rubber aging.

Dear Waldemar Koczkodaj;

would you please let me know the link on that software. Regards

You might want to look at "The Handbook of Vinyl Formulating" Chapter 13, Plastisol Technology.

As crosslinker increase, the G'' dependent of frequency decrease. And G' become less dependent on frequency, suggesting stronger gel structures formed.

If your PUR contains crosslinks (which is frequently the case even in polyurethanes which should be linear, because of secondary reactions) it may not dissolve at all.

No. Just need to use a grade with tg above 100C and a solvent with low vapor pressure. 

There is a classic book: “Physical Chemistry of Macromolecules” 1961 by Charles Tanford, John Wiley & Sons Inc. The book has a particular section that discuss the relationship between the diffusion coefficient and the molecular weight of the polymer. If you know the molecular weight of the monomer, you could estimate the molecular weight of your polymer from values of the diffusion coefficient. The author gives some interesting examples of D vs M dependence and useful references.    

In my experience, the only thing that will a priori occur with the matching of refractive indices is that you will have a clear solution, dispersion, or composite.  There is no necessary reason for mechanical interactions to behave in any particular fashion.

However, if you match 3D solubility parameters, then you will be directly and strongly influencing interactions. 

But perhaps I'm missing something.  Please elaborate.

Dear Paula Veske,

the answer of A. Bouaziz is in accord with my opinion - you have calculated the MW value correctly. Only you have to round the obtained values - both to 65 600 since exactness of your measurements as well as values of the Kuhn-Mark-Houwink-Sakurada constants is limited. Three valid numbers are usually valid, no more.

With best regards, J.V. 

Quite a different approach to blending immissible polumers is solid-state co-extrusion (pulverization). Of course in this case crosslinking may proceed not exactly uniformely. But sometimes this approach gives very good results

Chai:

Alan is absolutely correct. Bingham model initiates flow after overcoming its yield. SInce, your product does not have yield so you can plot shear stress vs shear rate and try to fit Power law model. 

Seems good enough to me.

Your estimate of about 2 J/g.C is OK.

I estimated cp from cp = HF/HR.m where HF is heat flow rate in mW, HR heating rate in C/s (not C/min) and m is sample mass in mg.

Did you subtract an empty pan measurement from your sample measurement?

You find the procedure described in most thermal analysis books (Wunderlich or Hoehne or Mathot ...).

I discussed this in

Article: Differential scanning calorimetry (DSC) of semicrystalline polymers.

Anal Bioanal Chem

C Schick ·

[Show abstract]

Analytical and Bioanalytical Chemistry 11/2009; 395(6):1589-611. DOI:10.1007/s00216-009-3169-y · 3.44 Impact Factor

The paper is available for download from ResearchGate.

Hi Helen. Seems the manufacturers may have given the original MM of the second polymer, i.e. of the polyvinyl acetate used to make the PVA in which case  the DP is correct as this remains more or less unchanged dureing hydrolysis (although this is not always true). I would suggest checking the details with the suppliers, but if this is the case, it is possible that the second, more polydisperse one, with lower average DP may be more readily soluble, but in this range I have read that the solubility is not much affected by DP. Other factors such as stereoregularity, "blockiness" and 1,2-glycol content that depend on how the PVA was made may also play a role. Best regards. Deon

Because of neither filler no modifier aren't identified (at least its nature) it is difficult to make any recommendation. But anyway I could propose you to observe crosslinking behavior in follow model composite systems: (i) matrix/crosslink agent/unmodified filler/catalyst(and/or solvent); (ii) matrix/crosslink agent/modifier/catalyst(and/or solvent); (iii) matrix/crosslink agent/unmodified filler/modifier/catalyst(and/or solvent); (iiii) matrix/crosslink agent/model/catalyst(and/or solvent) (model is a compound, which functionality (functional groups) is similar with modifier ones, but could not interact (in the same way as modifier and filler) with filler). If you compare the results of the experiments you can have defined decision. And, finally, if you not sure in mutual effect of any couple of the component, there are no other way to treat the couples under experimental (processing of composite) conditions. 

This is a generic response for transient tests, and not something particular to your material. The answer, from a polymeric perspective, is that the normal stress differences are proportional to the square of the applied shear rate. As the squaring procedure removes all sign information, the period of oscillation will be twice that of the shear stress response, from which the effective viscosity is obtained. See, for example, the text by J.D. Ferry (1980).

MEK (methyl ethyl ketone) may be a good candidate. MEK is generally an excellent solvent for the urethane part and is likely to dissolve most acrylates and epoxy derivates.

Thank you, Prof. D'Amore, I really appreciate your kindly explanations.

As you descried, the linear strain threshold is crucial in this kind of test. Dynamic strain sweep, of course, has been done before my measurement. Initially, the step strain was prescribed with rise time of 100ms by the stress-controlled rheometer with parallel-plate geometry. 

Since I just aim to detect the stress relaxation in the melt state, so melt rheology rather than DMA was employed. The results with parallel-plate geometry are far from satisfactory since no obvious damping with increasing strain amplitude was observed, regardless of the extremely high strain amplitude beyond linear regimes. That might be due to the stiff nature of  test melt and the possible wall slip. Parallel-plate geometry is insensitive therein. Instead, now I turn to cone-plate geometry, it is better than before.

Solution based SBR may contain water or other solvent depending on process. Other impurities may be thiol or organometallic compound. I suggest you carry out curing in stages so that any entrapped molecule or catalyst or ther agent will be destroyed. Then the final curing at high temperature can be carried out. Alternatively, as suggested by other you carry out curing in vacuum. In this case raise the temperature slowly.

In amorphous polymers the alpha transition belongs to the glass transition, while the beta transition to some local motion (it can be side group motion as in polyacrylates and methacrylates, or short segment motion in polymers not having rotating side groups, e.g. polyolefins). Amorphous polymers exhibiting significant   beta relaxation usually have good impact strength (e.g PMMA or polycarbonate). Below the beta transition these motions are frozen, therefore they cannot absorb impact energy, the material becomes brittle. In semicrystalline polymers the "safe" range (leathery behavior) is between the crystalline melting point and the glass transition of the amorphous phase. There are several excellent books on the relaxation transitions of various polymers. Here I mention only two old ones: Mc Crum, Read, Williams: Dielectric and Anelastic Effects in Polymers and Hedvig. Dielectric Spectroscopy of Polymers.

Hydrogels would behave as viscoelastic non-Newtonian materials; so they are prone to odd behavior during creep recovery experiments.  On the other hand, dynamic oscillatory tests are more robust in their response and hence samples in such deformation modes will give better experimental results. 

Through creep recovery tests, often one is looking for getting a measure of the non-recovered compliance J_NR.  The following papers show that J_NR can be got through dynamic oscillatory measurements.  The results measured through dynamic oscillatory tests should be more repeatable.   You may want to consider trying this.

An expression for J_NR during a dynamic oscillatory test has been derived and shown to be J_NR = (1 – (1/tandsind)) / |G*|.  Though this expression has been derived in a different context, it should be applicable to the system conditions that you are dealing.  You may read one or more of the following papers to get a better idea of this term.

1.       Aroon Shenoy, Refinement of the Superpave specification parameter for performance grading of asphalt, J. Transportation Engineering., Vol. 127, pp. 357-362 (Sept/Oct 2001).

2.       Aroon Shenoy, High temperature performance grading of asphalts through a specification criterion that could capture field performance, Journal of Transportation Engineering., Vol. 130, No. 1, 132-137 (Jan/Feb 2004).

3.       Aroon Shenoy, A comprehensive treatise of the high temperature specification parameter |G*|/(1-(1/tandsind)) for performance grading of asphalts, Applied Rheology, Vol. 14(6), pp. 303-314 (2004).

4.       Aroon Shenoy, Non-recovered compliance from dynamic oscillatory test vis-à-vis non-recovered compliance from multiple stress creep recovery test in the dynamic shear rheometer, The International J. of Pavement Engg., Vol. 9, No.5, pp. 329-341 (2008).

I'm supposing you are dealing with a polycondensation syhthesis. There is a lot of information regarding REX, please look for it carefully.

Hello dear, I agree with Mr Risch. Additionally, I think that if you need to employ PP you have to use functionalized PP, for example PP-g-MA

It dépends  on the concentration range where micellizatin is expected. Below 0.01 moles per li, surface tensionb and conductivity works well, for ionic sytems of course in the case of conductivity. At higher concentration, any thermodynamic property woks well.

Hello

1) You can not use a solvent, in which the polymer dissolves. You would lose a part of your material and this would render your swelling data incorrect. So the NaOH/urea is not suitable for you.

2) The Flory-Rehner equation enables you to estimate the extent of cross-linking based on the measured swelling behavior and some additional parameters. It is not a way of evaluating the degree of swelling. Weighing the sample is ok, but you have to be careful about the procedure. If the sample will be fragile, you can have problems with manipulation. You must also dry the sample prior to weighing so that you do not measure liquid on the surface. It is therefore highly preferable to have the polymer in a compact form (e.g., film). This method is sometimes used for studying the sorption of liquids in polymer membranes, so you can try to find a paper on this topic as inspiration for your experiment. My former colleagues tested the same method for PE films, but it is sadly not yet published.

Regards, Josef

Certain levels of irradiation degrades polymers.

When measuring the rheology of a reactive system, it would be best to hold the shear rate and temperature of measurement constant and observe the build-up of the viscosity in order to determine the kinetics of the reaction.  Nevertheless, if for some reasons, the interest is to observe the evolution of viscosity changes as a function of shear rate then the interpretation of the resulting curve becomes a little complex due to the confounding effects of competing phenomena. 

The time for recording the data point at the low shear rates is long as compared to the time for recording the data point at the higher shear rates.  On account of this, the reactive thermosetting system has more time to build-up the cross-linked structure at lower shear rates before the data point is recorded.   This will manifest as an increase in viscosity. 

At some critical shear rate, the time given to the material for structure build-up will not be long enough, and at the same time, the increased shear rate will aid in breaking down the built-up structure to demonstrate shear thinning behavior.  Also there is a possibility that if the built-up structure is very strong and does not break-up due to increasing shear, then its affinity to the measuring plate will decrease, thereby resulting in slippage and an apparent decrease in the viscosity curve.  The jaggedness in the decreasing part of the viscosity curve could be because there is non-uniform structural destruction or uneven slippage at the higher shear rates.

Dr. M. Johlitz investigated the mechanical characterisation of the interphase between a metallic substrate and an adhesive elastomer. His works can help you, perhaps.

Here are some examples for articles

You can measure the osmotic pressure of the suspension, to get the compressability. Simplest way is to dialyse the suspension against a high molecular weight polymer solution such as polyvinyl pyrolidone, and then either calculate the osmotic pressure from the polymer concentration and virial coefficients or measure the osmotic pressure using a vapour pressure osmometer. Then measure the particle concentration simply by drying the gel particles.

see paper SIMPLE DETERMINATION OF THE OSMOTIC-PRESSURE OF STERICALLY STABILIZED COLLOIDS

By: COSTELLO, BA; KIM, IT; LUCKHAM, PF

JOURNAL OF THE CHEMICAL SOCIETY-FARADAY TRANSACTIONS Volume: 86 Issue: 21 Pages: 3693-3694 Published: NOV 7 1990

You could also get an idea of this by measuring the viscoelastic properties of the suspension by measuring the elastic modulus as a function of particle concentration. 

See paper CONCENTRATION-DEPENDENCE OF THE LINEAR ELASTIC BEHAVIOR OF MODEL MICROGEL DISPERSIONS

By: EVANS, ID; LIPS, A

JOURNAL OF THE CHEMICAL SOCIETY-FARADAY TRANSACTIONS Volume: 86 Issue: 20 Pages: 3413-3417 Published: OCT 21 1990

Agreed. The G' and G'' values are in fact results of Fourier transform of the raw signal (stress or displacement). When one of the values dominate, the accuracy of determination of another one gets poorer. As a rule of thumb, when the lower modulus is below1% of the higher one (this gives two order of magnitude difference), the lower modulus cannot be measured accurately.