Interfacial Phenomena in Macromolecular Systems. II. Relaxation Modulus of Uncrosslinked Silica-Polydimethylsilosane Composites

Abstract

Relaxation modulus measurements on uncured silica-filled polydimethylsiloxane composites were correlated in terms of the polymer /filler interfacial energy. The heat of adsorption of a model compound (octamethylcyclotetrasiloxane) on the filler surface was taken as a measure of the interaction energy. The results on uncured composites containing these silicas revealed a strong correlation between the relaxation modulus and the net heat of adsorption. Roughly, 1.5 kcal/mol difference in the net heat of adsorption per siloxane bond caused a change in the relaxation modulus of two orders of magnitude. Dispersion of the fillers was examined with the electron microscope and revealed no significant difference in the dispersion of different silicas. The effect of interfacial energetics on the relaxation modulus can be entirely lost when cross-links are introduced into the system.

Retardation of spherulitic growth rate in the crystallization of isotactic polystyrene due to the presence of nucleant

“…The addition of silica is seen to cause a decrease in the spherulite growth rate at higher temperatures, so that the maximum in the growth rate is depressed by approximately 8 K. These results are consistent with the view that the silica particles interact with the polymer to create entanglements which restrict the diffusion of polymer segments through the melt. 4 The greatest effect of the entanglement is observed at higher temperatures, where the viscous melt flow is normally most facile. A qualitative argument for this behavior is that at low temperatures the viscosity of the melts of i-PS and of nucleated i-PS are very similar.…”

Rheological Characterization of Next-Generation Ballistic Witness Materials for Body Armor Testing

“…The characteristics of each constituent are important factors that influence the overall composite properties and material behavior. The structure–property relationship within fumed-silica-filled PDMS systems have been extensively explored by rheological studies [16,17,38,39,41,44,48,49]. Untreated fumed silica possesses a large volume of silanol groups on the silica surface as a result of the flame hydrolysis of silicon tetrachloride and the irreversible silica aggregates, with open fractal structures, that are generated from this fabrication process.…”

“…The PDMS has a molecular weight that is slightly more than the entanglement molecular weight, such that elastic recovery is minimized. The fumed silica is added to the non-crosslinked PDMS liquid as a thickener to provide dimensional stability [16,17], and the corn starch serves as a detackifier. This three-component system is anticipated to meet most criteria for BWM, including the minimal number of components and readily tunable formulation, controllable mechanical properties, nontoxicity, low adhesion to the armor, minimal odor, low cost, minimal temperature sensitivity, and reusability at room temperature [14].…”

Mechanical, electrical, and dielectric properties of polyvinylidene fluoride/short carbon fiber composites with low‐electrical percolation threshold

“…The mechanical, electrical, and dielectric properties of any filler–polymer composite can be controlled by varying filler to polymer proportion, state of filler distribution and dispersion in the matrix polymer, and filler geometry . To achieve properties like mechanical reinforcement, electrical sensing, electromagnetic interference shielding effectiveness (EMI SE), good electric and dielectric properties, thermal properties in the polymer composite, it is necessary to mix and disperse the filler uniformly in the polymer matrix, which provides wetting of filler particles by polymer chains leading to a good bonding in between filler and polymer . It is well documented that electrical, dielectric, mechanical or any other physical property of the polymer composites depend on the nature of polymer and filler individually .…”

“…[1][2][3][4][5][6][7][8] To achieve properties like mechanical reinforcement, electrical sensing, electromagnetic interference shielding effectiveness (EMI SE), good electric and dielectric properties, thermal properties in the polymer composite, it is necessary to mix and disperse the filler uniformly in the polymer matrix, which provides wetting of filler particles by polymer chains leading to a good bonding in between filler and polymer. [9][10][11] It is well documented that electrical, dielectric, mechanical or any other physical property of the polymer composites depend on the nature of polymer and filler individually. [12][13][14][15][16][17][18][19][20] There are several other factors like filler dispersion in polymer matrix, [21][22][23] physicochemical bonding in between polymer and filler, 24,25 polymer-polymer compatibility in case polymer blend is used as matrix, [26][27][28][29] electronic charactrestis of polymer and filler for example presence of lone pair or pi bond or both in conjugation in polymer, 30 duration of mixing time, [31][32][33][34] method of mixing, 35 aspect ratio of filler, tem-perature of mixing.…”