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We have demonstrated the utility of hollow silica nanoparticles in fabricating conformal thin film nanoporous antireflection (AR) coatings on both poly(methyl methacrylate) (PMMA) and glass substrates. Layer-by-layer (LbL) assembly was successfully used to produce ultrathin AR coatings on planar and textured surfaces. Hollow silica nanoparticles were synthesized to extend the range of apparent refractive indices possible in an AR coating, enabling the design of both single index and graded index AR coatings on PMMA substrates. The diameter and shell thickness of the silica nanoparticles are the two independent, controllable parameters that we manipulated to tune the refractive index of the coating. The AR coatings reduced the minimum reflection of PMMA from 7% to 0.5%, while the maximum transmission increased from 92% to 98% at the optimized wavelength region that could be adjusted from the near UV into the visible. Cross sectional SEM showed that conformal coatings can be achieved on grooved PMMA Fresnel lenses. AFM was used to study surface topography on flat substrates.

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In this article, we seek to enable large-scale, fully reversible, thermally induced volumetric changes in layer-by-layer (LbL) electrostatically self-assembled thin films through the incorporation of A-B-A triblock copolymers. Poly(N,N-dimethylaminoethyl methacrylate)-b-poly(propylene oxide)-b-poly(N,N-dimethylaminoethyl methacrylate) (abbreviated “PD-PPO-PD”) was used as a dual pH and temperature-responsive component in the electrostatic self-assembly of multilayer thin films. In solutions of this triblock copolymer with poly(N,N-dimethylaminoethyl methacrylate) (PD) weak polyelectrolyte end blocks, the dehydration temperature of the central poly(propylene oxide) (PPO) block was strongly dependent on solution pH, as shown by microdifferential scanning calorimetry (micro-DSC) and dye solubilization techniques. Multilayer films were then assembled with poly(acrylic acid) (PAA) or poly(4-styrene sulfonate) (PSS) as anionic binding partners at various pH values, where the triblock copolymer was incorporated within the film either as unimers or micelles. Using in situ ellipsometry, we showed that the polyanion type and the self-assembly pH were both critical parameters for constructing functional films, which change their swelling degree in response to temperature. In particular, strongly associated PD-PPO-PD/PSS multilayers lacked temperature sensitivity and maintained a constant swelling degree in a wide range of pH and temperature. In contrast, the temperature response of PD-PPO-PD/PAA films was strongly dependent on the self-assembly pH. Whereas swelling of PD-PPO-PD/PAA films constructed at pH ≤ 5 was independent of temperature, multilayers assembled at pH ≥ 6 showed fully reversible, three- to five-fold changes in film thickness in response to temperature cycling between 6 and 20 °C, enabled by the ability of PPO domains to transit reversibly between the swollen hydrated and collapsed dehydrated states. These nanocomposite coatings show highly responsive, reversible swelling transitions that can be useful for future biomedical and device applications.