Gel modulus

Figure H3.2.7 Concentration dependence of gel modulus (G). G can be either the storage modulus, G, or the complex modulus, G, as both usually coincide within expermiental error. C, concentration.

Figure 3-46 U-Tube Apparatus for Determination of Gel Modulus Based on (redrawn from Saunders and Ward, 1954).

Hence, the more general Panyukov form [Eq. (7.70)] reduces to the Flory form [Eq. (7.69)] for swelling in -solvents. The gel modulus in a -solvent is then proportional to the 1 /3 power of concentration ... 

Originally derived by James and Guth, this weak concentration depend-ence of the network modulus comes from two competing effects. As concentration is lowered, the number density of strands naturally decreases. However, the strands also stretch as concentration is lowered, and this stretching raises the modulus somewhat through the proportionality to (see Problem 7.29). The net effect is the weak decrease of the gel modulus upon swelling, given by Eq. (7.74). 

The gel modulus in an athermal solvent has a stronger concentration dependence than in a -solvent ... 

Poly(N-(2-hydroxyproyl) methacrylamide (HPMAm)-oligolactate) (MW = 10-20 K Daltons) was linked to PEG (MW = 10 K Daltons) to show thermogelling polymer aqueous solution (Fig. 13.10). The gel modulus eould be controlled by the molecular weight of the poly(HPMAm-oligolactate) (Fig. 

Although this theory of the dependence of gel modulus on structure cannot be exact, because one can imagine structures which will not fit Equation (11.8), the expression is useful in describing the experimental results. More precise theories have been postulated, for example that of Batchelor who... 

The dependence of the gelation process of carrageenans on electrolyte concentration has been the subject of many investigations e.g. [522, 543-546,553-555, 561, 562, 566-568], In general, it was concluded that the alkali metal ions are able to increase the gelation tendencies of both iota and kappa carrageenans. The cation dependence of the gel modulus follows the Hofmeister series Cs" > Rb" > Na > Li , which is in agreement with what has been said... 

Figure 1.8 Bending curvature of hydrogels in an applied field, effect of gel modulus [200] (Reprinted with permission from Li, FI., Ng, T. Y., Yew, Y. K. and Lam, K. Y. Meshless Modeling ofpFI-Sensitive Flydrogels Subjected to Coupled pFI and Electric Field Stimuli Young Modulus Effects and Case Studies, Macromo. Chem. Phys., 208, 1137-46, Copyright (2007) Wiley-VCFI Verlag GmbFI).

The variation of the modulus accompanying the sol-gel transition depends on the model as seen in Table 1, item (9). Because the modulus, in a sense, corresponds to the energy density of the system, it can be calculated by evaluating the stored thermal energy in a polymer chain due to the deformation. Only the gel components contribute to the gel modulus. Thus,... 

Various other techniques are also available for measurement of gel modulus, including the torsion pendulum [42], pulse shearometer [43], and dynamic mechanical... 

The entanglements relax with a characteristic time At short wavevectors the relaxation is possible and the gel modulus does not contribute to the diffusion constant. At larger wavevectors a rubbery behavior could be observed. A detailed comparison of the amplitude of these two modes, taking into account the relaxation phenomena, has been made by Brochard and De Gennes. ... 

The analogy has been tested by an analysis of the temperamre dependent gel modulus using the formalism which describes the mbbery plateau region. For this purpose, superposition of the modulus data was achieved with appropriate shift factors for temperamre, concentration, and molecular weight. Superposition of the data for six molecular weights between 5,000 and 900,000 and five concentrations between 12.5 and 200 g/1 was achieved when the quantity... 

Nanocomposites based on PMMA were also obtained by SiO dispersion and PMMA solubilisation in PC/LiCFsSOs liquid electrolyte. Improved ionic conductivity was obtained with 2 wt% Si02 for temperatures higher than 50 °C, but at room temperature the addition had no effect on ionic conductivity. No change in Tg following incorporation of Si02 was observed. The incorporation of fumed silica resulted in more physical linkages in the gel electrolyte in the form of siloxane linkages, which caused a substantial increase in the gel modulus. 

Sharp increases in both the storage modulus (G ) and loss modulus (G") of PAL-PLX-PAL aqueous solutions were observed as the temperature increased (Fig. 11). G and G" are an elastic component and a viscous component of the complex modulus of a system, respectively. When G is greater than G", the system is considered to be a gel, and the crossover point was defined as the sol-to-gel transition temperature. The sol-to-gel transition temperatures defined by the test tube inverting method coincided with those defined by dynanfic mechanical analysis of G and G" within 2 to 3 °C. By varying the polymer concenlration, not only sol-to-gel transition temperature but also modulus of the gel could be controlled. The control of gel modulus (G ) has a significant effect on 3D cell culture as well as the differentiation of the stem cell. In the case of chondrocytes, the modulus of 300-2,500 Pa showed a cytocompatible microenvironment for proliferation of the cells. The gel prepared from 10.0 wt% aqueous solution of PAL-PLX-PAL formed a gel with a G of 380 Pa at 37 °C, thus being recommendable as a 3D culture matrix for chondrocytes. 

Clark, A.H., Gidley, M.J., Richardson, R.K., Ross-Murphy, S.B. Rheological studies of aqueous amylose gels the effect of chain length and concentration on gel modulus. Macromolecules 22(1), 346-351 (1989)... 

---