In this work we present a general methodology to enhance the interfacial adhesion in polymeric composites by creating nanoscale morphologies on the surfaces of particles. The surface morphology, which appears as inorganic whiskers, is achieved by treating silicate particles (zeolites 4A) with thionyl chloride, followed by subsequent reaction with methylmagnesium bromide (Grignard reagent). Poly(vinyl acetate) and Ultem composites containing this type of modified particles exhibit defect-free interfaces. Dynamic mechanical analysis testing reveals that such composites have higher moduli as compared to those embedded with nontreated fillers with the same loadings. Furthermore, gas permeation measurements demonstrate that these materials also show impressive enhancements in gas separation efficiency. The dramatic increase in the topological roughness (physical heterogeneity) on the sieve surfaces is proposed to provide improved interaction at the interface via thermodynamically induced adsorption and physical interlocking of polymer chains in the nanoscopic inorganic whisker structure. The presented strategy need not be tailored to a specific polymer/filler pair and therefore has potential to be extended to many other polymeric composites for a variety of applications, where tailoring polymer/solid interface compatibility is important.

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A two-step reaction sequence, dealumination via thionyl chloride followed by reaction with a Grignard reagent, has created a nanoscale morphology that appears as significantly roughened outer surfaces on zeolite 4A particles. X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD) measurements revealed that such surface nanostructures are composed of Mg(OH) 2 crystals. The formation mechanism of this specific surface morphology was explored. It was discovered by solid-state 29 Si and 27 Al NMR and XPS surface analysis that thionyl chloride partially removes aluminum from the zeolite 4A framework and yields NaCl and AlCl 3 . Precipitation of these extracted inorganic salts on the surfaces of zeolite particles occur. Subsequently, methylmagnesium bromide is reacted with 2-propanol in a quenching process and generates Mg(OH) 2 . The previously deposited NaCl and AlCl 3 nanoparticles on zeolite surfaces are believed to function as heterogeneous nuclei for the growth of Mg(OH) 2 crystals and thereby creates the nanostructured surface morphology. The modified particles are shown in previous work to provide enhanced interfacial adhesion in polymeric composites.

Dealumination of as-synthesized zeolites is an important step in adjusting the Si/Al ratio and hence their acidities and catalytic properties. The dealumination of zeolite 4A by thionyl chloride treatment was investigated near room temperature in the liquid phase with and without the assistance of sonication. The structural changes observed by 29Si and 27Al solid-state NMR showed that the experimental condition, that is, in the presence and absence of sonication, significantly affected the efficiency of the dealumination process of zeolite 4A. Successful dealumination was achieved with the assistance of sonication at room temperature, while simple stirring led to negligible changes. It was also found that the degree of dealumination could be tailored by the duration of sonication to generate zeolites with various Si/Al ratios. XPS surface elementary analysis detected chlorine rich sieve surfaces after the sonication treatment, which is attributed to AlCl3 and NaCl, the byproducts of the dealumination reaction. These results confirmed that sonication accelerated dealumination reaction under ambient conditions. XRD tests, unit cell calculation, and nitrogen physisorption analysis revealed partial loss in framework integrity after the treatment. This new procedure allows convenient preparation of alumina-deficient zeolites of a wide range of Si/Al ratios under ambient conditions. The dramatic local heating resulted from ultrasound is proposed to explain the unusual observation of dealumination by thionyl chloride near room temperature.

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