Rapid bulk assembly of nanoparticles into microstructures is challenging, but highly desirable for applications in controlled release, catalysis, and sensing. We report a method to form hollow microstructures via a two-stage nematic nucleation process, generating size-tunable closed-cell foams, spherical shells, and tubular networks composed of closely packed nanoparticles. Mesogen-modified nanoparticles are dispersed in liquid crystal above the nematic-isotropic transition temperature (TNI). On cooling through TNI, nanoparticles first segregate into shrinking isotropic domains where they locally depress the transition temperature. On further cooling, nematic domains nucleate inside the nanoparticle-rich isotropic domains, driving formation of hollow nanoparticle assemblies. Structural differentiation is controlled by nanoparticle density and cooling rate. Cahn-Hilliard simulations of phase separation in liquid crystal demonstrate qualitatively that partitioning of nanoparticles into isolated domains is strongly affected by cooling rate, supporting experimental observations that cooling rate controls aggregate size. Microscopy suggests the number and size of internal voids is controlled by second-stage nucleation.

We present three-dimensional microshells formed by self-assembly of densely-packed 5 nm gold nanoparticles (AuNPs). Surface functionalization of the AuNPs with custom-designed mesogenic molecules drives the formation of a stable and rigid shell wall, and these unique structures allow encapsulation of cargo that can be contained, virtually leakage-free, over several months. Further, by leveraging the plasmonic response of AuNPs, we can rupture the microshells using optical excitation with ultralow power (<2 mW), controllably and rapidly releasing the encapsulated contents in less than 5 s. The optimal AuNP packing in the wall, moderated by the custom ligands and verified using small angle x-ray spectroscopy, allows us to calculate the heat released in this process, and to simulate the temperature increase originating from the photothermal heating, with great accuracy. Atypically, we find the local heating does not cause a rise of more than 50 °C, which addresses a major shortcoming in plasmon actuated cargo delivery systems. This combination of spectral selectivity, low power requirements, low heat production, and fast release times, along with the versatility in terms of identity of the enclosed cargo, makes these hierarchical microshells suitable for wide-ranging applications, including biological ones.

Using triphenylmethylium tetrakis(pentafluorophenyl)borate as a convenient Brønsted acid precatalyst, β-(α,α-dimethylbenzyl)styrenes are shown to cyclize efficiently to afford a variety of new indanes that possess a benzylic quaternary center. The geminal dimethyl-containing quaternary center is proposed to be necessary to arm the substrate for cyclization through steric biasing.

When nanoparticle self-assembly takes place in an anisotropic liquid crystal environment, fascinating new effects can arise. The presence of elastic anisotropy and topological defects can direct spatial organization. An important goal in nanoscience is to direct the assembly of nanoparticles over large length scales to produce macroscopic composite materials; however, limitations on spatial ordering exist due to the inherent disorder of fluid-based methods. In this paper we demonstrate the formation of quantum dot clusters and spherical capsules suspended within spherical liquid crystal droplets as a method to position nanoparticle clusters at defined locations. Our experiments demonstrate that particle sorting at the isotropic–nematic phase front can dominate over topological defect-based assembly. Notably, we find that assembly at the nematic phase front can force nanoparticle clustering at energetically unfavorable locations in the droplets to form stable hollow capsules and fractal clusters at the droplet centers.

Syntheses and enzymological characterization of fluorogenic substrate probes targeting secretory phospholipase A2 (sPLA2) for detection and quantitative assays are presented. Three fluorogenic phosphatidylcholine analogs PC-1, PC-2, and PC-3 each containing the duo of 7-mercapto-4-methyl-coumarin fluorophore and 2,4-dinitroanaline quencher on either tail were synthesized from (R)-3-amino-1,2-propanediol and R-(−)-2,2-dimethyl-1,3-dioxolane-4-methanol. These small reporter groups are advantageous in preserving natural membrane integrity. Phosphocholine was incorporated into the sn-3 position of the glycerol backbone. Acyl amino group at the sn-1 position in PC-1 and PC-2 is meant to block sPLA1. The sn-1 and sn-2 positions of the glycerol backbone in PC-1 have a quencher terminated 12-carbon chain and fluorophore terminated 11-carbon chain respectively. PC-2 has a quencher terminated 3-carbon chain at the sn-2 and chain terminating fluorescent reporter at the sn-1 positions. PC-3 resembles PC-1 except for an ester instead of amide at the sn-1 position, because of which it is more similar to natural phospholipids than PC-1. It was designed to elucidate the effect of replacing the ester group with amide by comparing its hydrolysis rate with that of PC-1. Design principles apply to synthesis of other labeled phospholipids. Enzymological characterization using bee-venom sPLA2 was performed by a fatty-acid-binding-protein fluorescence assay and by pH-Stat method in which the amount of fatty acid released by hydrolysis is given by the amount of base required to maintain a constant pH of 8.0. Hydrolytic activity toward PC-1 and PC-3 were each about 238 ± 25 μmol/mg/min and 537 μmol/mg/min on unmodified phospholipid. Ester to amide change did not affect hydrolysis rates. Activity toward PC-2 was about 45-μmol/mg/min. PC-1 and PC-3 show potential for targeted real-time spectrophotometric assay of sPLA2.

Liquid crystal (LC) phase transition dynamics can be used as a powerful tool to control the assembly of dispersed nanoparticles. Tailored mesogenic ligands can both enhance and tune particle dispersion in the liquid crystal phase to create liquid crystal nano-composites-a novel type of material. Soft nanocomposites have recently risen to prominence for their potential usage in a variety of industrial applications such as photovoltaics, photonic materials, and the liquid crystal laser. Our group has developed a novel phase-transition-templating process for the generation of micron-scale, vesicle-like nanoparticle shells stabilized by mesogenic ligand-ligand interactions. The mesogenic ligand's flexible arm structure enhances ligand alignment with the local LC director, providing control over the dispersion and stabilization of nanoparticles in liquid crystal phases. In this paper we explore the capsule formation process in detail, generating QDbased capsules over a surprisingly wide range of radii. We demonstrate that the initial nanoparticle concentration and cooling rate are important parameters influencing capsule size. By increasing particle concentration of nanoparticles and reducing the cooling rate we developed large shells up to 96±19 μm in diameter whereas decreasing concentration and increasing the cooling rate produces shells as small as 4±1 μm.

Modification of textiles with new applications target such as electroconductive fabrics has recently attracted researchers. In this article, carbon black nanoparticles (CB NPs) were applied to polyester fabric through two separate high temperature (HT) exhaustion processing with NaOH and cetyltrimethylammonium bromide (CTAB) as alkali hydrolysis catalyst and dispersing agents. To improve the stability of CB NPs on the fabric a self‐polymerized compound, dopamine (DA) was used in a simple dipping method at room temperature for 24 h to form a thin layer of PDA on CB NPs‐treated fabric. Field emission scanning electron microscopy (FESEM) was used to study the morphology of the fabrics confirming presence of CB NPs. EDX and mapping patterns showed the percentage and distribution of carbon, nitrogen, and oxygen elements on the fabric surface. The treated fabric indicated an electrical resistance of 14 kΩ turns a LED device on with a 10 V power supply. Self‐polymerized DA on the fabric surface led to more nitrogen and oxygen caused higher CB NPs stability. Furthermore, the tensile strength results revealed a 25.8% lower tenacity on the treated fabric. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019, 136, 48035.

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