On The Origins of Silicate Dispersion in Polysiloxane/Layered‐Silicate Nanocomposites

Abstract

We report the first multi‐system study of a layered‐silicate dispersion in polysiloxane/layered‐silicate nanocomposites. A variety of layered silicates (montmorillonite, synthetic fluoromica, laponite, and fluorohectorite) and cationic modifiers (single‐, twin‐, and triple‐tailed surfactants with tails of varying lengths and both primary and quaternary head‐groups) are combined to form organically modified layered silicates, which are then screened for compatibility with low‐molecular‐weight silanol‐terminated poly(dimethylsiloxane) (PDMS). Promising combinations are then selected and studied in greater depth with respect to both molecular weight and polysiloxane end‐group and substituent chemistry. We find that the PDMS backbone is generally incompatible with the layered silicates, regardless of modification type, and that dispersion in PDMS systems results from the presence of polar end‐groups, a result unprecedented in the field of polymer nanocomposites. We go on to quantify the substituent effect, not only with respect to end‐group chemistry, but taking into account changes in the polysiloxane backbone itself. For instance, in the absence of polar end‐groups we observe dispersion in the case of poly(methylphenylsiloxane) but not poly(3,3,3‐trifluoropropylmethylsiloxane). Finally, we apply a new epoxy/amine PDMS curing chemistry to PDMS‐nanocomposite production and show higher levels of layered‐silicate dispersion than observed in comparable silanol‐terminated PDMS‐based systems. Our findings serve as an indication of what is necessary to achieve a layered‐silicate dispersion in polysiloxane/layered‐silicate nanocomposites, and may indicate a more general approach for improving dispersion in systems where the polymer backbone is otherwise incompatible with the layered silicate.

Controlled Release in Transdermal Pressure Sensitive Adhesives using Organosilicate Nanocomposites

“…Therefore, with minimal backbone contribution to the dispersion, end-group polarity plays a key role in the dispersion and exfoliation of the clay platelets. 23 With decreasing molecular weight, the end-group effects will become even more prominent in the case of associating or H-bonding chain ends. Thus, with a judicious choice of end-groups, an appropriately low molecular weight and suitable surfactant chain length, it is possible to develop a thermodynamically stable nanocomposite adhesive dispersion with minimal mixing.…”

“…Due to the softness of the PDMS adhesive, it was not possible to ultra microtome a sample for a TEM image. However, tapping mode AFM has been successfully used to study dispersion of organo-clay in polymers 23 and was applied in this study to determine dispersion of OC in the PDMS adhesives. An AFM image of the PDMS adhesive layer ( Figure 2B) indicates an even dispersion of the OC nanoparticles.…”

Reinforcement of poly(dimethylsiloxane) by sol-gel in situ generated silica and titania particles

“…This may be due to the volatility of TEOS thus reducing the amount of cross-linker required for the alkoxyfunctional condensation reaction. Much greater ratios of cross-linker functions to chain ends than that required by stoichiometry have already been used in the literature [13,14] …”

Preparation, characterization, and property testing of condensation‐type silicone/montmorillonite nanocomposites

“…The increased viscosity did not play a critical role in the dispersion capability of the filler particles, which was mainly affected by the silanol end-group concentration. 11 On the other hand, an increase in the system viscosity was responsible for higher shear stresses during the mixing procedure and might have been beneficial for better filler dispersion. However, the relatively high molecular weight of PDMS used in this study reflected the long polymer chain and, furthermore, a reduced end-group concentration, which confined the dispersion ability.…”

“…However, it was reported that in real NCs, complete exfoliation cannot be achieved, but most materials show a combination of various dispersion states, either as a result of inhomogeneous mixing or, simply, because of the fact that the transition from intercalated structure to an exfoliated cannot be clearly defined and numerous intermediate states may exist. 16 A series of XRD patterns of PDMS composites containing various OMMT loadings are shown in Figure 2. The featureless patterns for loadings of 2-and 3.5-phr OMMT suggest that exfoliation or delamination hybrids were formed.…”