Adhesive and Magnetic Properties of Polyvinyl Butyral Composites with Embedded Metallic Nanoparticles

Magnetic metallic nanoparticles (MNPs) of Ni, Ni82Fe18, Ni50Fe50, Ni64Fe36, and Fe were prepared by the technique of the electrical explosion of metal wire. The average size of the MNPs of all types was in the interval of 50 to 100 nm. Magnetic polymeric composites based on polyvinyl butyral with embedded metal MNPs were synthesized and their structural, adhesive, and magnetic properties were comparatively analyzed. The interaction of polyvinyl butyral (supplied as commercial GE cryogenic varnish) with metal MNPs was studied by microcalorimetry. The enthalpy of adhesion was also evaluated. The positive values of the enthalpy of interaction with GE increase in the series Ni82Fe18, Ni64Fe36, Ni50Fe50, and Fe. Interaction of Ni MNPs with GE polymer showed the negative change in the enthalpy. No interfacial adhesion of GE polymer to the surface of Fe and permalloy MNPs in composites was observed. The enthalpy of interaction with GE polymer was close to zero for Ni95Fe5 composite. Structural characterization of the GE/Ni composites with the MNPs with the lowest saturation magnetization confirmed that they tended to be aggregated even for the materials with lowest MNPs concentrations due to magnetic interaction between permalloy MNPs. In the case of GE composites with Ni MNPs, a favorable adhesion of GE polymer to the surface of MNPs was observed.

Agglomerates of nanoparticles

Nanoparticles tend to agglomerate. The process of agglomeration is ruled by thermodynamics. Depending on the sign of the enthalpy of interaction, ensembles consist of (repelling) poorly agglomerated or (attracting) highly agglomerated particles. For these two cases different distribution functions for the agglomerates were found. The size distribution of the agglomerates is ruled by the maximum of the entropy of the ensemble of agglomerates, which is calculated using Gibbs formula of entropy. The exact determination of the size distribution of the agglomerates also gives the maximum size of the agglomerates. These considerations lead to an improved understanding of ensembles of agglomerated nanoparticles.

In situ studies of gas sorption in porous networks

Selective gas separation is one of the key properties exploited in industrial processes utilizing porous materials. The crystal structure of the native and activated frameworks, along with those of ion exchanged and otherwise modified variants, provide the basis for rational development of gas-selective nanoporous solids. In situ scattering studies of gas-loaded materials provide an understanding of the nature of interactions between sorbed gas and pore surface, which can be vital to development of reliable interatomic potentials, used simulating adsorption behavior. We find that simultaneous observation of the Differential Scanning Calorimetry coupled with x-ray diffraction (DSC-XRD) measurements is a particularly powerful tool 1, 2. The powder diffraction pattern can be monitored for changes, such as framework collapse, as porous materials are heated and activated. Apart from monitoring structural changes, thermal responses accompanying dynamic exposure to gases at variable humidity, and as the temperature is varied, provides a reliable tool in order to screen for new and potentially selective porous materials. The DSC signal provides a reliable means to determine the enthalpy of interaction between framework and gas, and there is experimental evidence this signal may distinguish between gas interactions with bare metal sites in the activated framework and other gas-framework interactions. Studies where the enthalpy of interaction and X-ray scattering from low angle peaks, which are most sensitive to the filling and evacuation of pores of the porous materials are monitored, can be coupled with varying the nature of the gas and the relative humidity. These studies are conveniently carried out with a modified gas manifold interfaced to a slightly modified Rigaku corporation DSC-XRD, which allows studies from about 150 – 600 K. Illustrative examples of the use of this laboratory based equipment, which provide the underpinnings of detailed single crystal studies of gas-loaded materials, include studies of porous calcium based coordination network (CaSDB, SDB: 4,4' - sulfonyldibenzoate), which is selective for CO2, even in the presence of high relative humidity (RH). Recent results from a series of materials studied in the home laboratory and at synchrotron sources will be presented.