Viscoelasticity enhancement

Smith KD, Burt WL. Fluorescent viscoelastic enhancement. J Cataract Refract Surg 1992 18 572-576 Smith SG, Lindstrom RL, Miller RA, Hazel S, Skelnik D, Williams P, Mindrup E. Safety and efficacy of 2% methylcellulose in cat and monkey cataract-implant surgery. J Am Intraocular Implant Soc 1984 10 160-163... 

Fig, 11. Viscoelastic enhancement factor as a function of the normalized crack velocity. Symbols represent the numerical solution of Eqs. 74, 79 and 81 and the solid lines represent the corresponding empirical relationships given by Eq. 82. 

Tackifying resins enhance the adhesion of non-polar elastomers by improving wettability, increasing polarity and altering the viscoelastic properties. Dahlquist [31 ] established the first evidence of the modification of the viscoelastic properties of an elastomer by adding resins, and demonstrated that the performance of pressure-sensitive adhesives was related to the creep compliance. Later, Aubrey and Sherriff [32] demonstrated that a relationship between peel strength and viscoelasticity in natural rubber-low molecular resins blends existed. Class and Chu [33] used the dynamic mechanical measurements to demonstrate that compatible resins with an elastomer produced a decrease in the elastic modulus at room temperature and an increase in the tan <5 peak (which indicated the glass transition temperature of the resin-elastomer blend). Resins which are incompatible with an elastomer caused an increase in the elastic modulus at room temperature and showed two distinct maxima in the tan <5 curve. 

The treatment of blends as a two phase system opened up an interesting field of modifying the composite properties by the use of a (third component within the interface boundaries, which is termed as compatibilizers [1]. Such modifications are still being extended to the formation of microgel out of the interaction between the two blend partners having a reactive for functionalities. This type of interchain crosslinking does not require any compatibilizer to enhance the blend properties and also allows the blends to be reprocessed by further addition of a curative to achieve still further improved properties [3,4]. Such interchain crosslinking is believed to reduce the viscoelastic mismatch between the blend partners and, thus, facilitates smooth extrusion [5,6]. 

Many of the new plastics, blends, and material systems require special, enhanced processing features or techniques to be successfully injection molded. The associated materials evolution has resulted in new plastics or grades, many of which are more viscoelastic. That is, they exhibit greater melt elasticity. The advanced molding technology has started to address the coupling of viscoelastic material responses with the process parameters. This requires an understanding of plastics as viscoelastic fluids, rather than as purely viscous liquids, as is commonly held... 

Al-Assaf, S. Phillips, G.O. Aoki, H. Sasaki, Y. (2007). Characterization and properties of Acacia Senegal (L.) Willd. var. Senegal with enhanced properties (Acacia (sen) SUPER GUM ) Part 1-Controlled maturation of Acacia Senegal var. Senegal to increase viscoelasticity, produce a hydrogel form and convert a poor into a good emulsifier Food Hydrocollotds, Vol.21, No.3, (May 2007), pp. 319-328, ISSN 0268-005X. 

Hyaluronic acid is a linear polysaccharide found in the highest concentrations in soft connective tissues where it fills an important structural role in the organization of the extracellular matrix (23,24). It has been used in ophthalmic preparations to enhance ocular absorption of timolol, a beta blocker used for the treatment of glaucoma (25), and in a viscoelastic tear formulation for conjunctivitis (26). The covalent binding of adriamycin and daunomycin to sodium hy-aluronate to produce water-soluble conjugates was recently reported (27). 

Intcrmolecular Contributions. Increasing concentration reduces the effects of excluded volume and intramolecular, hydrodynamic on viscoelastic properties (Section 5). Internal viscosity and finite extensibilty have already been eliminated as primary causes of shear rate dependence in the viscosity. Thus, none of the intramolecular mechanisms, even abetted by an increased effective viscosity in the molecular environment, can account for the increase in shear rate dependence with concentration, e.g., the dependence of power-law exponent on coil overlap c[r/] (Fig. 8.9). Changes in intermolecular interaction with increased shear rate seems to be the only reasonable source of enhanced shear rate dependence, at least with respect to the early deviations from Newtonian behavior and through a substantial portion of the power law regime. 

As noted in Section HE, both layers decrease the absorption rate, especially of large water-soluble molecules, since the diffusion coefficient is directly proportional to the reciprocal values of both the hydrodynamic radius and the viscosity of the layers. About the influence of absorption enhancers on mucus rheology very little is known. Bib salts and phospholipids are known to reduce the viscoelasticity of bronchial mucus aid probably also of mucus layers in the gastxointestinal tract [40. Hie results should be interpreted with caution since it is not the observed macro )viscosity that determines the diffusion rate in polymer... 

When calculating the Laplace transform, one finds an enhancement of the dynamic modulus due to the macromolecular coils in the viscoelastic liquid... 

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