Abstract
Using liquid crystalline self-assembly of cellulose nanocrystals, we achieve long-range alignment of anisotropic metal nanoparticles in colloidal nanocrystal dispersions that are then used to deposit thin structured films with ordering features highly dependent on the deposition method. These hybrid films are comprised of gold nanorods unidirectionally aligned in a matrix that can be made of ordered cellulose nanocrystals or silica nanostructures obtained by using cellulose-based nanostructures as a replica. The ensuing long-range alignment of gold nanorods in both cellulose-based and nanoporous silica films results in a polarization-sensitive surface plasmon resonance. The demonstrated device-scale bulk nanoparticle alignment may enable engineering of new material properties arising from combining the orientational ordering of host nanostructures and properties of the anisotropic plasmonic metal nanoparticles. Our approach may also allow for scalable fabrication of plasmonic polarizers and nanoporous silica structures with orientationally ordered anisotropic plasmonic nanoinclusions.
Highlights
Nanostructured materials are poised to revolutionize scientific instruments, technologies, and consumer devices
Cellulose nanocrystals (CNCs) and mesoporous silica have been utilized as templates to assemble and synthesize nanoparticles [14,15,16], but the alignment of rod-like nanoparticles in these hosts has not been achieved. We first use these colloidal dispersions of CNCs to align co-dispersed Gold nanorods (GNRs) of much shorter aspect ratio, with a longitudinal surface plasmon resonance (SPR) peak within the visible optical spectrum, and use the ensuing cellulose-gold colloidal nano-dispersion to obtain thin solid films with orientationally ordered organization of both cellulose and gold nano-colloids. We demonstrate that these structured films can be converted into mesoporous silica films decorated with aligned GNRs
We found that the simple by-hand shearing of CNC-GNR co-dispersions produced films of variable quality with some relatively large areas of uniform alignment (Figure 1a,b) with the GNRs having scalar order parameter
Summary
Nanostructured materials are poised to revolutionize scientific instruments, technologies, and consumer devices. Liquid crystalline intermediate phases confer long-range orientational order that has been previously used to improve the properties of fibers and deposited films for biomedical [1], optical [2], and electronic [3,4] applications. Liquid crystals (LCs) can act as smart hosts that align anisotropic nanoparticle inclusions and leverage nanoscale anisotropy into device scale polarization sensitivity [5]. Self-assembly of plasmonic nanoparticles in LCs has been extensively studied recently [6,7,8]. Gold nanorods (GNRs) have two surface plasmon resonance (SPR) modes, the transverse mode at 525 nm and red-shifted longitudinal mode dependent on the aspect ratio, associated with short and long axes of the rod, respectively [9]. Aligning GNRs allows one to produce so-called “plasmonic polarizers”, which have been previously realized in stretched polyvinyl alcohol films [10]
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