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1. Effect of processing conditions on the mechanical properties of bio-inspired mechanical gradient nanocmposites

   Zhang, Y. ; Edelbrook, A.N. ; Rowan, S. J. ( March 2019 , European Polymer Journal)

   Photo-induced thiol-ene crosslinking of allyl-functionalized cellulose nanocrystal (CNC)/polymer nanocomposites allows access to films that mimic the water-enhanced mechanical gradient characteristics of the squid beak. These films are prepared by mixing the functionalized CNCs and polymer in a solvent before solution casting and drying. The photocrosslinking agents are then imbibed into the film before UV exposure. Reported herein are studies aimed at better understanding the effect of the film preparation procedure, film thickness and the conditions under which the UV treatment is carried out. It was found that when the film is heated at a temperature higher than its glass transition temperature (Tg) during the UV irradiation step there is a greater enhancement in the mechanical properties of the films, presumably on account of more efficient crosslinking between the CNC fillers. Moreover, composite films that were compression molded (at 90°C) before the imbibing step displayed lower mechanical properties compared to the as-cast films, which is attributed to phase separation of the CNC fillers and polymer matrix during this additional processing step. Finally, the film thickness was also found to be a critical factor that affects the degree of crosslinking. For example, thinner films (50 µm) displayed a higher wet modulus ca. 130 MPa compared to ca. 80 MPa for the thicker films (150 µm). Understanding the processing conditions allows access to a larger range of mechanical properties which is important for the design of new bio-inspired mechanical gradient nanocomposites. 

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2. A single-parameter hygroscopicity model for functionalized insoluble aerosol surfaces

   https://doi.org/10.5194/acp-22-13219-2022  

   Mao, Chun-Ning ; Gohil, Kanishk ; Asa-Awuku, Akua A. ( January 2022 , Atmospheric Chemistry and Physics)

   Abstract. The impact of molecular level surface chemistry for aerosol water-uptake and droplet growth is not well understood. In this work, spherical, nonporous, monodisperse polystyrene latex (PSL) particles treated with different surface functional groups are exploited to isolate the effects of aerosol surface chemistry for droplet activation. PSL is effectively water insoluble and changes in the particle surface may be considered acritical factor in the initial water uptake of water-insoluble material. The droplet growth of two surface modified types of PSL (PSL-NH2 andPSL-COOH) along with plain PSL was measured in a supersaturated environmentwith a Cloud Condensation Nuclei Counter (CCNC). Three droplet growth models – traditional Köhler (TK), Flory–Huggins Köhler (FHK) and the Frenkel–Halsey–Hill adsorption theory (FHH-AT) were compared with experimental data. The experimentally determined single hygroscopicity parameter, κ, was found within the range from 0.002 to 0.04. The traditional Köhler prediction assumes Raoult's law solute dissolution and underestimates the water-uptake ability of the PSL particles. FHK can be applied to polymeric aerosol; however, FHK assumes that the polymer is soluble and hydrophilic. Thus, the FHK model generates a negative result for hydrophobic PSL and predicts non-activation behavior that disagrees with the experimental observation. The FHH-AT model assumes that a particle is water insoluble and can be fit with two empirical parameters (AFHH and BFHH). The FHH-AT prediction agrees with the experimental data and can differentiate the water uptake behavior of the particles owing to surface modification of PSL surface. PSL-NH2 exhibits slightly higher hygroscopicity than the PSL-COOH, whereas plain PSL is the least hygroscopic among the three. This result is consistent with the polarity of surface functional groups and their affinity to water molecules. Thus, changes in AFHH and BFHH can be quantified when surface modification is isolated for the study of water-uptake. The fitted AFHH for PSL-NH2, PSL-COOH, and plain PSL is 0.23, 0.21, and 0.18 when BFHH is unity. To simplify the use of FHH-AT for use in cloud activation models, we also present and test a new single parameter framework for insoluble compounds, κFHH. κFHH is within 5 % agreement ofthe experimental data and can be applied to describe a single-parameterhygroscopicity for water-insoluble aerosol with surface modified properties. 

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3. Employing Heterocyclic Hypervalent Iodine Compounds with ICl Bonds as Initiators and Chain Transfer Agents in the Synthesis of Branched Polymers

   https://doi.org/10.1002/macp.201800471  

   Cao, Yakun ; Kumar, Rajesh ; Tsarevsky, Nicolay V. ( January 2019 , Macromolecular Chemistry and Physics)

   Heterocyclic hypervalent (HV) iodine(III) compounds with ICl bonds and various substituents at the N atom are synthesized and found to be very efficient chain transfer agents in the polymerization of styrene with transfer coefficients exceeding that of CCl₄by 2–3 orders of magnitude, depending on the structure. The chain transfer rate coefficients are also determined. Due to the presence of thermally labile HV bonds, the compounds degrade homolytically upon heating and can initiate radical polymerization. For instance, 1‐chloro‐2‐hexyl‐1,2‐benziodazol‐3(2H)‐one, is used in the polymerization of styrene, which yields low molecular weight polymers with alkyl chloride groups at the α‐ (initiation) and the ω‐chain ends (transfer). Chain‐end functionalization reactions with azide and chain extension under low‐catalyst‐concentration atom transfer radical polymerization (ATRP) conditions of the prepared telechelic polymers are carried out. The same initiator/chain transfer agent is successfully employed in the synthesis of highly branched polymers with multiple alkyl chloride‐type chain ends when added to mixtures of styrene and 1,4‐divinylbenzene containing 10–80 mol% of the divinyl crosslinker, or even pure crosslinker. In all cases, soluble hyperbranched polymers are obtained up to moderate monomer conversions. The effects of crosslinker and HV iodine(III) compound concentrations on the polymerization outcome are studied systematically.

    

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4. Ionically crosslinked cellulose nanocrystals by metal nitrates for the preparation of stable emulsions with tunable interface properties

   https://doi.org/10.1038/s41598-023-48703-3  

   Batta-Mpouma, Joseph ; Kandhola, Gurshagan ; Kim, Jin-Woo ( December 2023 , Scientific Reports)

   Biologically extracted cellulose nanocrystals (CNCs) are rod-like and amphiphilic materials with surface-exposed (hydrophilic sites) and hidden (hydrophobic sites) hydroxyl groups. These physicochemical characteristics make CNCs suitable for use as emulsifying agents to stabilize emulsions. Stable oil-in-water emulsions, using sulfated (i.e., –$${{\text{SO}}}_{3}^{-}$$${\text{SO}}_3^{-}$) CNCs that were ionically crosslinked with alkaline-earth (i.e.,$${{\text{Mg}}}^{2+}$$${\text{Mg}}^{2+}$) or transition-d-block (i.e.,$${{\text{Zn}}}^{2+}$$${\text{Zn}}^{2+}$) metal cations, were developed without the use of any synthetic surfactants or prior functionalization of pure CNCs with hydrophobic molecules. Various emulsion surface properties such as interfacial tension, surface charge, surface chemistry, as well as rheology were characterized. Ionically crosslinked CNCs (iCNCs) adsorbed at the interface of an oil and water and fortified the emulsion droplets (5–30 µm) against coalescence by lowering the interfacial tension from 65 mN/m (i.e., pure CNC mixture with oil) to 25 mN/m (i.e., iCNC mixture with oil) and reducing zeta potential with surface charge values (–30 mV to –10 mV), ideal to maintain droplet layer assembly at the water–oil interface. This study provided an alternative approach to achieve particle-stabilized and surfactant-free emulsions by using divalent metal nitrates to develop “clean” emulsion-based technologies for applications in many industries from agriculture to food to pharmaceuticals.

    

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5. Plasmonic‐Enhanced Cholesteric Films: Coassembling Anisotropic Gold Nanorods with Cellulose Nanocrystals

   https://doi.org/10.1002/adom.201801816  

   Cheng, Zheng ; Ma, Yi ; Yang, Lin ; Cheng, Feng ; Huang, Zhongjie ; Natan, Avi ; Li, Hongyan ; Chen, Yong ; Cao, Daxian ; Huang, Zhifeng ; et al ( February 2019 , Advanced Optical Materials)

   Incorporating photonic crystals with nanoplasmonic building blocks gives rise to novel optoelectronic properties that promise designing advanced multifunctional materials and electronics. Herein, the free‐standing chiral plasmonic composite films are designed by coassembling anisotropic plasmonic gold nanorods (GNRs) and rod‐like cellulose nanocrystals (CNCs). The effects of surface charge and concentration of the GNRs on the structure and optical properties of the CNC/GNR films are examined within this study. The CNC/GNR hybrid films retain the photonic characteristic of the CNCs host while concomitantly possessing the plasmonic resonance of GNRs. The negatively charged GNRs distribute uniformly in the layered CNCs host, inducing strong electrostatic repulsion among the CNCs and thus promoting the formation of a larger helical pitch than the case without GNRs. The positively charged GNRs decrease the chiroptical activity in the composite films with increasing the concentration of GNR, which is confirmed by the circular dichroism spectra. Notably, the surface plasmon resonances of GNRs enhance the fluorescence emission, which has been demonstrated by surface‐enhanced fluorescence signals in this work. This study sheds light on fabricating functional chiral plasmonic composite films with enhanced chiral plasmonics by utilizing CNCs as a dynamic chiral nematic template and adjusting surface charges.

    

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