My sample include small liquid crystal, monomer and photoinitiator. the mixture is a little viscous at room temperature. The sample was tested by rheometer. The resulr was G' was higher than G'' at the beginning, which is contrary to theory. When the Uv light was turned on, G' dropped signnificantly and was lower than G'' and then rose again over G'', which means I got two intersection points in this test. Theoretically it shoud be that G'' is greater than G' and lower G' after passing the gelation point. I'm very confused and fail to figure it out. thank you if you can help me fix this.
Hi,
what is the physical appearance of the sample? Does it flow? Keep in mind that the G' and G'' moduli scale with testing frequency, so you may run a frequency sweep and establish the crossover frequency, above which the material behaves as a gel. You may then repeat the test at the conditions below the crossover. If you cannot see the crossover, raise the temperature.
At the specific testing conditions, your sample already starts in the gel state, so the first modulus crossover is not a gel point. Some fillers, especially the nano-sized ones, increase the viscosity due to the interaction with the monomer/oligomer/polymer.
Article Bulk Polymer Nanocomposites with Preparation Protocol Govern...
See the fig. 4.
This interaction depends on multiple factors such as affinity, molecular weight, particle size, etc. You may refer to our study for more details:
Article Phase diagram of bare particles in polymer nanocomposites: U...
Apparently, the physical crosslinks are disrupted by UV light, which is probably caused by the specific properties of liquid crystals. The gel is recovered as the photopolymerization proceeds, but it is a chemically cross-linked gel this time. You could see the difference in the strain sweep behavior, or access the crosslink density from oscillatory data. The procedure is explained in detail here:
Article 3D printing and post-curing optimization of photopolymerized...
because free radical changes,have occurred when activating,or exposted to uv radiation
Make a try to analyze elasticity/viscosity component ratio change due to UV radiation.
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