We present an overview of recent investigations of photopolymerizable nanocomposite photonic materials in which, thanks to their high degree of material selectivity, recorded volume gratings possess high refractive index modulation amplitude and high mechanical/thermal stability at the same time, providing versatile applications in light and neutron optics. We discuss the mechanism of grating formation in holographically exposed nanocomposite materials, based on a model of the photopolymerization-driven mutual diffusion of monomer and nanoparticles. Experimental inspection of the recorded grating’s morphology by various physicochemical and optical methods is described. We then outline the holographic recording properties of volume gratings recorded in photopolymerizable nanocomposite materials consisting of inorganic/organic nanoparticles and monomers having various photopolymerization mechanisms. Finally, we show two examples of our holographic applications, holographic digital data storage and slow-neutron beam control.

We report a breakthrough in the search for versatile diffractive elements for cold neutrons. Nanoparticles are spatially arranged by holographical means in a photopolymer. These grating structures show remarkably efficient diffraction of cold neutrons up to about 50% for effective thicknesses of only 200 m. They open up a profound perspective for next generation neutron-optical devices with the capability to tune or modulate the neutron diffraction efficiency.

Polymer-nanoparticle composites (PNCs) play an increasing role in technology. Inorganic or organic nanoparticles are usually incorporated into a polymer matrix to improve material properties. Polyurea is a spontaneously occurring PNC, exhibiting a phase segregated structure with hard nanodomains embedded in a soft (elastically compliant) matrix. This system shows two glass transitions at Tg1 and Tg2. It has been argued that they are related to the freezing of motion of molecular segments in the soft matrix (usual polymer α-glass transition at Tg1) and to regions of restricted mobility near the hard nanodomains (α'-process) at Tg2, respectively. We present detailed dynamic mechanical analysis (DMA) measurements for polyurea networks with different segmental lengths l(c) (2.5, 12.1, 24.5 nm) of the polymer chains, i.e. different volume fractions ϕ(x) (0.39, 0.12, 0.07) of the hard domains. The two glass transitions show up in two distinct peaks in tan δ at Tα and Tα'. Analysing the data using a Havriliak-Negami term for the α- and α'-relaxation, as well as Vogel-Fulcher dependencies for the corresponding relaxation times, it is found that the α-glass transition at Tg1 increases strongly (up to ΔT = 70 K) with increasing ϕ(x), whereas the α'-transition at Tg2 remains unchanged. At ϕ(x)(c) ≈ 0.19 the two curves intersect, i.e. Tg1 = Tg2. This value of ϕ(x)(c) is very close to the percolation threshold of randomly oriented overlapping ellipsoids of revolution with an aspect ratio of about 1 : 4-1 : 5. We therefore conclude that around 19% of the hard nanodomains polyurea changes from a system of hard nanoparticles embedded in a soft matrix (ϕ(x) ≤ ϕ(x)(c)) to a system of soft domains confined in a network of percolated hard domains at ϕ(x) ≥ ϕ(x)(c).

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We introduce a model for the kinetics of grating formation during holographic recording in optically excitable two-state systems. An unexpected characteristic time dependence of the diffraction efficiency is found. We show that it originates from a nonlinear transformation of the light interference pattern into a refractive-index profile. Our findings strongly resemble and explain by nature the experimental data of two-state systems in general, here represented by two examples: sodium nitroprusside and terbium gallium garnet.