Orientational Behavior of Ellipsoidal Silica- Coated Hematite Nanoparticles Integrated within an Elastomeric Matrix and its Mechanical Reinforcement

Hybrid nanocomposite materials made out of integrated inorganic nanoparticles within an organic polymeric matrix canbe foundasgels, thermoplastics, thermosets or elastomers. This class of materials can exhibit the combined advantages of both the integrated nanoparticles, in terms of optical and electrical properties, and the processability of the polymeric matrix. As a result, bulk modification of the strength, stiffness, and toughness of the resulting materials are generally observed. Different approaches have been reported in the past for the integration of nanoparticles within a polymer network leading to nanocomposites, including particle/polymer hydrogels, particle/elastomer composites, silicathermoset networks via in situ polymerization, or linear polymer networks induced by particles. In most cases, aggregationandmigrationof the integratedfillersunder an external trigger (e.g., electricalfield,magneticfield, orahigh shear rate) appears as a drawback of this specific route. A potential solution is to integrate the nanoparticles in a covalent manner, binding them to the polymer backbone, which leads to a cooperativemotion of both the continuous and dispersed phases. In thisway, potential phase separationof the integratednanoparticles canbeavoidedor reduced. Few examples can be found in the literature of integrating anisometric nanoparticles within a polymer matrix, and most of those are polymer/clay nanocomposites or block copolymer/carbon nanotube nanocomposites, with improvement of mechanical properties, A. Sánchez-Ferrer, R. Mezzenga ETH Zurich, Institute of Food, Nutrition & Health, Food & Soft Materials Science, 8092 Zurich, Switzerland H. Dietsch Adolphe Merkle Institute and Fribourg Center for Nanomaterials, University of Fribourg, PO Box 209, 1723 Marly 1, Switzerland E-mail: [email protected] The mechanical and orientational properties of IOENs consisting of integrated ellipsoidal SCH spindle-type nanoparticles within an elastomeric matrix are reported. The influence of the SCH surface chemistry, leading either to dispersed nanoparticles or crosslinked nanoparticles within the surrounding elastomeric matrix, is studied by mechanical uniaxial deformation (stress-strain) and SAXS measurements under stress. Without surface modifications, the SCH nanoparticles act as defects, and the Young’smodulus of the elastomericmatrix remains unmodified. Surface-modified SCH nanoparticles acting as crosslinkers increase Young’s modulus by a factor 1.2. SAXS measurements demonstrate that the integrated ellipsoidal nanoparticles orient upon a deformation larger than 50% independently of the specific integration strategy.