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Three dissymmetric gemini surfactants (abbreviated as 12-s-14) in which n-dodecyldimethylammonium bromide and n-tetradecyldimethylammonium bromide are connected at the polar headgroups by a flexible -(CH2)s-spacer (s ) 2, 6, or 10) have been synthesized. The influence of the spacer length on the structural and thermal properties of 12-s-14 surfactants was investigated by means of IR and NMR spectral analysis, X-ray diffraction, thermogravimetry, differential scanning calorimetry, and polarizing optical microscopy. Geminis with s ) 2 or 10 form monolayers in which two alkyl chains are in the trans configuration, while the gemini with s ) 6 forms interdigitated bilayers with two alkyl chains in the cis configuration with respect to the spacer. All compounds exhibited a complex polymorphism and thermotropic mesomorphism from the stable crystalline form to the liquid crystalline phases of smectic type. The number of thermal phase transitions and the sequence of phases are markedly affected by the spacer length; that is, they depend on the configuration of the two alkyl chains with respect to the spacer.

The aim of this study was to compare the effects of different silica grades on the structure and morphology of isotactic polypropylene (iPP)/silica composites to better understand their structure-property relationships. Isotactic polypropylene composites with 2, 4, 6, 8 vol % of added silica fillers differing in particle size (micro-vs. nanosilica) and surface modification (untreated vs. treated surface) were prepared by nonisothermal compression molding and characterized by different methods. The addition of all silica fillers grades to the iPP matrix significantly influenced the spherulitic morphology, while phase characteristics of the iPP matrix seemed to be unaffected. Surface modification of silica fillers exhibited stronger effects on spherulite size than size of silica particles. Nonpolar silica particles, more miscible or compatible with iPP chains than polar silica particles, enabled better spherulitic growth. The spherulite sizes tended to reach equal values at 8 vol % of added silicas showing that spherulite size became independent of filler concentration and surface modification above optimum filler concentration.