Classes of Materials

In general, research on classes of materials is connected with that on materials with specific properties but includes somewhat more general research on composites, polyurethanes, epoxies, fluoropolymers, ferroelectric liquid crystals (especially those with fast switching times), polymer-polymer miscibility, double network elastomers, crystallization in polymers, polymeric Langmuir-Blodgett and other multilayer films, and polymer-stabilized synthetic membranes.

The application of composites to naval needs is the motif for research on joining techniques, hydrothermal effects and other damage and failure mechanisms, response to transient shock loading, and impact and underwater shock response. The research on ferroelectric liquid crystals includes their behavior as Langmuir-Blodgett multilayers.

Because of a general interest in polymer blends for various applications, some fundamental studies of such blends have been undertaken. For example, small-angle neutron scattering (SANS) and CP-MAS NMR studies showed that polyisoprene-polyvinylethylene (PIP-PVE) blends were miscible at molecular weights exceeding 106 and had a negative Flory interaction parameter. Also, segmental dynamics have been studied in various polymer-polymer mixtures to gain a general understanding of the effects of different diluents. The morphology of a freeze-dried dilute polymer solution was also studied.

There are some ongoing general studies of surface modification of elastomers and studies on the synthesis and characterization of double-network elastomers. Research was done on the suppression of crystallization in blended natural rubber and neoprene. Other studies of crystallization, for example, on positron emission tomography (PET), have also been done.

A number of rather complex fluorinated monomers and the resulting polymers have been synthesized and studied because of the Navy's interest in low-permittivity materials.

The Navy's interest in coatings has led to the synthesis and study of various classes of polymers. For example, the curing reaction of epoxies with amidoamines has been studied, as has the polymerization of spirobislactones with epoxy resins.

CHARACTERIZATION

Materials mentioned above are characterized and their properties measured by standard approaches for which NRL is well equipped, and these are discussed in this report. However, some novel characterization methods have been developed or extended at NRL.

The use of 129Xe NMR to probe phase separation in polymer blends has been particularly useful for probing miscibility in those polymer blends in which the components have comparable glass transition temperatures, making it difficult, if not impossible, to study miscibility by using methods such as differential scanning calorimetry. There are plans to use this NMR method to measure domain size in phase-separated polymer blends.

Nondestructive characterization techniques such as NMR imaging of solid polymers are being studied. It has been possible to exploit methods that provide contrast discrimination based on molecular mobility. In addition, a method was recently demonstrated that provides an NMR image with contrast based on local polymer alignment in response to a strain field.

Research is in progress to use electron spin resonance (ESR) to characterize the interior surfaces in composites. Spin probes are to be deposited near the interface of a fiber/polymer matrix composite, and ESR is to be used to monitor the local orientation of the spin probes. The goal is to assess the spatial range of the “interphase” and to understand how the mechanical load is transferred from the fiber to the matrix.

Several groups at NRL have been working to better understand polymeric structure-property relationships with respect to particular uses of polymers. In addition, the composite



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