MOLECULAR DYNAMICS SIMULATION OF POLYBENZOXAZINE RESIN FOR PROCESS MODELING

In this work, Molecular Dynamics (MD) simulations are performed to predict the physical properties (gelation point, mass density, volumetric shrinkage) and mechanical properties (Bulk modulus, Shear modulus, Young’s Modulus, Poisson’s ratio) of a PolyBenzoxazine (PBZ) resin system as a function of crosslinking density. The molecular models are developed using the Reactive Interface Force Field (IFF-R). The results obtained from MD are in good agreement with the experimental data.

Vibrational Spectroscopic Monitoring of the Gelation Transition in Nafion Ionomer Dispersions

Infrared and Raman spectroscopy techniques were applied to investigate the drying and aggregation behavior of Nafion ionomer particles dispersed in aqueous solution. Gravimetric measurements aided the identification of gel-phase development within a series of time-resolved spectra that tracked transformations of a dispersion sample during solvent evaporation. A spectral band characteristic of ionomer sidechain end group vibration provided a quantitative probe of the dispersion-to-gel change. For sets of attenuated total reflection Fourier transform infrared (ATR FT-IR) spectra, adherence to Beer's law was attributed to the relatively constant refractive index in the frequency region of hydrated –[Formula: see text] group vibrations as fluorocarbon-rich ionomer regions aggregate in forming the structural framework of membranes and thin films. Although vibrational bands associated with ionomer backbone CF2 stretching vibrations were affected by distortion characteristic of wavelength-dependent refractive index change within a sample, the onset of band distortion signaled gel formation and coincided with ionomer mass % values just below the critical gelation point for Nafion aqueous dispersions. Similar temporal behavior was observed in confocal Raman microscopy experiments that monitored the formation of a thin ionomer film from an individual dispersion droplet. For the ATR FT-IR spectroscopy and confocal Raman microscopy techniques, intensity in the water H–O–H bending vibrational band dropped sharply at the ionomer critical gelation point and displayed a time dependence consistent with changes in water content derived from gravimetric measurements. The reported studies lay groundwork for examining the impact of dispersing solvents and above-ambient temperatures on fluorinated ionomer transformations that influence structural properties of dispersion-cast membranes and thin films.

Anisotropic and heterogeneous dynamics in an aging colloidal gel

We investigate the out-of-equilibrium dynamics of a colloidal gel obtained by quenching a suspension of soft polymer-coated gold nanoparticles close to and below its gelation point using X-ray Photon Correlation Spectroscopy (XPCS).

Synthesis and rheology of thermoreversible polyurethane hydrogels

Polyurethanes based on poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) triblock copolymer, succinic or citric acid, and ethyl ester L-lysine diisocyanate were synthesized and characterized by FT-IR and GPC. Wetting properties were evaluated by contact angle determinations. The critical micelle concentration was determined from surface tension measurements. Their abillity to undergo self-aggregation and temperature induced gelation was investigated through dynamic oscillatory measurements. The gelation point, sol-gel transitions, and gel structure are influenced by polymer structure, composition, molecular weight, concentration, and heating rate.

Synthesis and Characterization of Polysilane-Organometallic Complexes

A new polysilane with pendant metal complex segments was synthesized and characterized. For this purpose a macroligand has been prepared starting from a iodopropyl-functionalized polysilane and a bis(salicylideneimine) derivative. Under mild reaction temperature this polymeric ligand was able to form crosslinked structures. The material was then doped with metal cations and was investigated to observe the system behavior near the gelation point. The UV-vis spectrum of the new material indicated that the electronic structures of the conjugate polysilane chain and metal complex remained unaffected by the condensation reaction process. Similar polymeric structures could be useful to build new organic electroconductive devices.