Turn‐Number‐Dependent Motion Behavior of Catalytic Helical Carbon Micro/Nanomotors

Helical micro/nanomotors (MNMs) can be propelled by external fields to swim through highly viscous fluids like complex biological environments, which promises miniaturized robotic tools to perform assigned tasks at small scales. However, the catalytic propulsion method, most widely adopted to drive MNMs, is seldom studied to actuate helical MNMs. Herein, we report catalytic helical carbon MNMs (CHCM) by sputtering Pt onto helical carbon nano‐coils (HCNC) that are in bulk prepared by a thermal chemical vapor deposition method. The Pt‐triggered H₂O₂ decomposition can drive the MNMs by an electrokinetic mechanism. The MNMs demonstrate versatile motion behaviors including both directional propulsion and rotation depending on the turn number of the carbon helix. Besides, due to the ease of surface functionalization on carbon and other properties such as biocompatibility and photothermal effect, the helical carbon MNMs promise multifunctional applications for biomedical or environmental applications.     

Recent advances in the use of the quartz crystal microbalance with dissipation for the study of the collapse of polyelectrolyte brushes

The combination of Quartz Crystal Microbalance and ellipsometry to quantify polyelectrolyte brush hydration and how this impacts on the study of brush collapse is discussed here. Recent articles study collapse after quantifying hydration of poly (2-methacryloyloxy ethyl trimethyl ammonium chloride) (PMETAC) and poly(potassium sulfo propyl methacrylate). Water lost increases with ionic strength but only a 50% of their water content is lost at 1 M NaCl. For PMETAC brushes the exchange of Cl⁻ by ClO₄⁻ is more effective, causing 50% lost at 0.05 M. The hydration and water lost for PMETAC brushes synthesized from thiol monolayers with variable density of initiators from 1 to 100% show that the freely entrapped water of the brushes is around a 10%. Irrespectively of initiator percentage the brush does not lose at 1 M NaCl more than 50% of the original water content. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2013, 51, 1068–1072     

Water Content of Hydrated Polymer Brushes Measured by an In Situ Combination of a Quartz Crystal Microbalance with Dissipation Monitoring and Spectroscopic Ellipsometry

Poly(methacryloyloxy ethyltrimethylammonium chloride) (PMETAC), poly(sulfopropylmethacrylate potassium salt), or poly(N‐isopropyl acrylamide) (PNIPAM) brushes are synthesized by means of the atom transfer radical polymerization technique from gold surfaces coated with a monolayer of the initiator ω‐mercaptoundecyl bromo isobutyrate. The brush growth is followed in situ and in real time by the combination of quartz crystal microbalance with dissipation technique (QCM‐D) and spectroscopic ellipsometry in a single device. The combination of QCM‐D and ellipsometry allows for the simultaneous determination of both the acoustic mass, m_acous, comprising the mass of the polymer and the solvent, and the optical mass, m_opt, which corresponds to the polymer mass alone. Brush hydration is calculated from the difference between the values obtained for m_acous and m_opt for each polymer synthesized. Brush hydration is then used to quantify the percentage of water released in the brush during collapse; a 30–40% release of water for PMETAC and PSPM brushes in 1 M NaCl and 80% for PNIPAM brushes when the temperature is increased to values above the lower critical solution temperature is observed.     

Self‐Propelled Janus Mesoporous Silica Nanomotors with Sub‐100 nm Diameters for Drug Encapsulation and Delivery

The synthesis of an innovative self‐propelled Janus nanomotor with a diameter of about 75 nm that can be used as a drug carrier is described. The Janus nanomotor is based on mesoporous silica nanoparticles (MSNs) with chromium/platinum metallic caps and propelled by decomposing hydrogen peroxide to generate oxygen as a driving force with speeds up to 20.2 μm s^?1 (about 267 body lengths per second). The diffusion coefficient (D) of nanomotors with different H₂O₂ concentrations is calculated by tracking the movement of individual particles recorded by means of a self‐assembled fluorescence microscope and is significantly larger than free Brownian motion. The traction of a single Janus MSN nanomotor is estimated to be about 13.47×10^?15 N. Finally, intracellular localization and drug release in vitro shows that the amount of Janus MSN nanomotors entering the cells is more than MSNs with same culture time and particle concentrations, meanwhile anticancer drug doxorubicin hydrochloride loaded in Janus MSNs can be slowly released by biodegradation of lipid bilayers in cells.     

Poly‐p‐phenylenevinylene‐g‐poly(2‐(methacryloyloxy)Ethyl)trimethylammonium chloride (PPV‐g‐PMETAC): A fluorescent,water‐soluble,selective anion sensor

The photophysical and ion‐sensing properties of densely grafted conjugated polymer poly‐p‐phenylenevinylene‐g‐poly(2‐(methacryloyloxy)ethyl)trimethylammonium chloride (PPV‐g‐PMETAC) are presented herein. The grafted polymer exhibits excellent iodide‐sensing which is easily observed using fluorescence spectroscopy. The iodide detection limit for PPV‐g‐PMETAC was found to be 10 nM and was independent of temperature and pH <12. The change in fluorescence of PPV‐g‐PMETAC, upon exposure to iodide, was attributed to polymer aggregation due to changes in the morphology of the grafted PMETAC side chains, which was observed using atomic force microscopic and dynamic light scattering studies. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2018 , 56, 1997–2003     

Responsive Copolymer Brushes of Poly[(2‐(Methacryloyloxy)Ethyl) Trimethylammonium Chloride] (PMETAC) and Poly(1H,1H,2H,2H‐Perfluorodecyl acrylate) (PPFDA) to Modulate Surface Wetting Properties

Polymer brushes have a large potential for controlling properties such as surface lubrication or wetting through facile functionalization. Polymer chemistry, chain density, and length impact on the wetting properties of brushes. This study explores the use of diblock copolymer brushes with different block length and spatial arrangement of the blocks to tune surface wettability. Block copolymer brushes of the polyelectrolyte [2‐(methacryloyloxy)ethyl] trimethylammonium chloride (PMETAC) with a contact angle of 17° and a hydrophobic block of ¹H, ¹H, ²H, ²H‐perfluorodecyl Acrylate (PPFDA) with a contact angle of 130° are synthesized by RAFT polymerization. By changing the sequence of polymerization either block is synthesized as top or bottom block. By varying the concentration of initiator the length of the blocks is varied. Contact angle values with intermediate values between 17° and 130° are measured. In addition, by changing solvent pH and in presence of a different salt the contact angle of the copolymer brushes can be fine tuned. Brushes are characterized by atomic force microscopy, Raman confocal microscopy, and X‐ray photoelectron spectroscopy.

     

β‐Cyclodextrin polymer brushes based on hyperbranched polycarbosilane: Synthesis and characterization

In this article, our main goal is to combine hyperbranched polymer with β‐cyclodextrin (β‐CD) to establish a novel functional polymer species with core‐shell structure and supramolecular system for further application in inclusion technologies and the complex drugs delivery system. Therefore, two β‐CD polymer brushes based on hyperbranched polycarbosilane (HBP) as a hydrophobic core and poly(N,N‐dimethylaminoethyl methacrylate) (PDMA) carrying β‐CD units as a hydrophilic shell were synthesized. Hyperbranched polycarbosilane macroinitiator carrying ? Cl groups (HBP‐Cl) was also prepared by using 1,1,3,3‐tetrmethyldisiloxane, allyl alcohol, and chloroacetyl chloride as reagents. The molecular structures of HBP‐Cl macroinitiator and β‐CD polymer brushes were characterized by Fourier transform infrared spectroscopy (FTIR), ¹H nuclear magnetic resonance (¹H NMR), ¹³C nuclear magnetic resonance (¹³C NMR) spectroscopies, size exclusion chromatography/multi‐angle laser light scattering (SEC/MALLS) and laser particle size analyzer. The results indicate that the grafted chain length of two β‐CD polymer brushes can be controlled by changing the feed ratio. Differential scanning calorimetry (DSC) results show that two β‐CD polymer brushes have two glass transition temperatures (T_gs) from a hydrophobic core part and a hydrophilic shell part, respectively, and the T_g from PDMA is higher than that of HBP‐g‐PDMA. Thermalgravimetric analyzer (TGA) analysis indicates that the thermostability of two β‐CD polymer brushes is higher than that of HBP, but is lower than that of HBP‐g‐PDMA. Using phenolphthalein (PP) as a guest molecule, molecular inclusion behaviors for two β‐CD polymer brushes were studied. It reveals that two β‐CD polymer brushes possess molecular inclusion capability in PP buffer solution with a fixed concentration. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 5036–5052, 2008     

Aligning poly[1,6‐di‐(N‐carbazolyl)‐2,4‐hexadiyne] crystalline fibers as conducting channels for transistor applications

Aligned crystallites of 1,6‐di‐(N‐carbazolyl)‐2,4‐hexadiyne (DCHD) were prepared on the phenyltrichlorosilane‐modified SiO₂/Si surface using the brush‐coating method. The length and width as well as the orientation of the crystallites depend on the coating speed. At a lower coating speed of 0.2 ~ 0.3 mm/s, well‐separated fibers with a width of 1–2 μm and a length of hundreds of μm were grown along the coating direction. Higher speeds resulted in shorter fibers together with randomly oriented tiny crystallites appearing in between. The diacetylene crystallites upon UV irradiation gave polydiacetylene fibers with deformations along the fiber axis. The poly(ene‐yne) backbones were shown to align along the fiber axes. With these poly‐DCHD fibers as a conducting channel for transistor fabrication, a highest field‐effect mobility of 0.039 cm²/Vs was obtained.     

An Adjustable‐Porosity Plastic Crystal Electrolyte Enables High‐Performance All‐Solid‐State Lithium‐Oxygen Batteries

The limited triple‐phase boundaries (TPBs) in solid‐state cathodes (SSCs) and high resistance imposed by solid electrolytes (SEs) make the achievement of high‐performance all‐solid‐state lithium‐oxygen (ASS Li‐O₂) batteries a challenge. Herein, an adjustable‐porosity plastic crystal electrolyte (PCE) has been fabricated by employing a thermally induced phase separation (TIPS) technique to overcome the above tricky issues. The SSC produced through the in‐situ introduction of the porous PCE on the surface of the active material, facilitates the simultaneous transfer of Li⁺/e^?, as well as ensures fast flow of O₂, forming continuous and abundant TPBs. The high Li⁺ conductivity, softness, and adhesion of the dense PCE significantly reduce the battery resistance to 115 Ω. As a result, the ASS Li‐O₂ battery based on this adjustable‐porosity PCE exhibits superior performances with high specific capacity (5963 mAh g^?1), good rate capability, and stable cycling life up to 130 cycles at 32 °C. This novel design and exciting results could open a new avenue for ASS Li‐O₂ batteries.     

Microphase‐Separated Brushes on Square Platelets in PS‐b‐PEO Thin Films

In polystyrene‐block‐poly(ethylene oxide) thin films, microphase‐separated brushes on the square platelets can be obtained via fast solvent evaporation by controlling the tethering density (0.08 < σ < 0.11). The tethering density of the brushes is proportional to the thickness of the PEO crystal and increases with increasing initial solution heating temperature (T_i). When T_i < T_m, where T_m is the melting point of PEO, brushes with microphase‐separated structures are observed. The formation of microphase‐separated brushes depends on two factors: the strong incompatibility between PS and noncrystalline PEO chains (attached to the crystalline PEO) and the weak interaction between PS‐PS brushes.

     

RAFT‐mediated synthesis and temperature‐induced responsive properties of poly(2‐(2‐methoxyethoxy)ethyl methacrylate) brushes

Well‐defined, high‐density poly(2‐(2‐methoxyethoxy)ethyl methacrylate) [poly(MEO₂MA)] brushes were fabricated through a reliable strategy by the combination of self‐assembly of a monolayer of 3‐aminopropyltrimethoxy silane on silicon surface to immobilize 4‐cyano‐4‐(dodecylsulfanylthiocarbonyl)sulfanyl pentanoic acid chain transfer agent and reversible addition‐fragmentation chain transfer‐mediated polymerization of MEO₂MA. The whole fabrication process of the poly(MEO₂MA) brushes was followed by water contact angle, grazing angle‐Fourier transform infrared spectroscopy, X‐ray photoelectron spectroscopy, and atomic force microscopy. Characterization of the poly(MEO₂MA) brushes, such as molecular weight and thickness determination, were measured by gel permeation chromatography and ellipsometry, and the grafting density was estimated. The temperature‐responsive property of the poly(MEO₂MA) brushes was further investigated and the result verified the brush‐to‐mushroom phase transition of the poly(MEO₂MA) chains from low to high temperature. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013     

Synthesis of amphiphilic copolymer brushes: Poly(ethylene oxide)‐graft‐polystyrene

A well‐defined amphiphilic copolymer brush with poly(ethylene oxide) as the main chain and polystyrene as the side chain was successfully prepared by a combination of anionic polymerization and atom transfer radical polymerization (ATRP). The glycidol was first protected by ethyl vinyl ether to form 2,3‐epoxypropyl‐1‐ethoxyethyl ether and then copolymerized with ethylene oxide by the initiation of a mixture of diphenylmethylpotassium and triethylene glycol to give the well‐defined polymer poly(ethylene oxide‐co‐2,3‐epoxypropyl‐1‐ethoxyethyl ether); the latter was hydrolyzed under acidic conditions, and then the recovered copolymer of ethylene oxide and glycidol {poly(ethylene oxide‐co‐glycidol) [poly(EO‐co‐Gly)]} with multiple pending hydroxymethyl groups was esterified with 2‐bromoisobutyryl bromide to produce the macro‐ATRP initiator [poly(EO‐co‐Gly)_(ATRP). The latter was used to initiate the polymerization of styrene to form the amphiphilic copolymer brushes. The object products and intermediates were characterized with ¹H NMR, matrix‐assisted laser desorption/ionization time‐of‐flight mass spectrometry, Fourier transform infrared, and size exclusion chromatography in detail. In all cases, the molecular weight distribution of the copolymer brushes was rather narrow (weight‐average molecular weight/number‐average molecular weight < 1.2), and the linear dependence of ln[M₀]/[M] (where [M₀] is the initial monomer concentration and [M] is the monomer concentration at a certain time) on time demonstrated that the styrene polymerization was well controlled. This method has universal significance for the preparation of copolymer brushes with hydrophilic poly(ethylene oxide) as the main chain. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 4361–4371, 2006     

Molecular Dynamics,Phase Transition and Frequency‐Tuned Dielectric Switch of an Ionic Co‐Crystal

Dielectric switches that can be converted between high and low dielectric states by thermal stimuli have attracted much interest owing to their many potential applications. Currently one main drawback for practical application lies in the non‐tunability of their switch temperatures (T_S). We report here an ionic co‐crystal (Me₃NH)₄[Ni(NCS)₆] that contains a multiply rotatable Me₃NH⁺ ion and a solely rotatable one due to a more spacious supramolecular cage for the former one. This compound undergoes an isostructural order–disorder phase transition and it can function as a frequency‐tuned dielectric switch with highly adjustable T_S, which is further revealed by the variable‐temperature structure analyses and molecular dynamics simulations. In addition, the distinct arrangements and molecular dynamics of two coexisting Me₃NH⁺ ions confined in different lattice spaces as well as the notable offset effect on the promoting/hindering of dipolar reorientation after dielectric transition provide a rarely observed but fairly good model for understanding and modulating the dipole motion in crystalline environment.     

Molecular Dynamics,Phase Transition and Frequency‐Tuned Dielectric Switch of an Ionic Co‐Crystal

Dielectric switches that can be converted between high and low dielectric states by thermal stimuli have attracted much interest owing to their many potential applications. Currently one main drawback for practical application lies in the non‐tunability of their switch temperatures (T_S). We report here an ionic co‐crystal (Me₃NH)₄[Ni(NCS)₆] that contains a multiply rotatable Me₃NH⁺ ion and a solely rotatable one due to a more spacious supramolecular cage for the former one. This compound undergoes an isostructural order–disorder phase transition and it can function as a frequency‐tuned dielectric switch with highly adjustable T_S, which is further revealed by the variable‐temperature structure analyses and molecular dynamics simulations. In addition, the distinct arrangements and molecular dynamics of two coexisting Me₃NH⁺ ions confined in different lattice spaces as well as the notable offset effect on the promoting/hindering of dipolar reorientation after dielectric transition provide a rarely observed but fairly good model for understanding and modulating the dipole motion in crystalline environment.     

Hairy polymeric nanocapsules with ph‐responsive shell and thermoresponsive brushes: Tunable permeability for controlled release of water‐soluble drugs

The hairy poly(methacrylic acid‐co‐divinylbenzene)‐g‐poly(N‐isopropylacrylamide) (P(MAA‐co‐DVB)‐g‐PNIPAm) nanocapsules with pH‐responsive P(MAA‐co‐DVB) inner shell and temperature‐responsive PNIPAm brushes were prepared by combined distillation–precipitation copolymerization and surface thiol‐ene click grafting reaction using 3‐(trimethoxysilyl)propyl methacrylate‐modified silica (SiO₂‐MPS) nanospheres as a sacrificial core material. The well‐defined PNIPAm was synthesized by a reversible addition fragmentation chain transfer (RAFT) polymerization. The chain end was converted to a thiol by chemical reduction. The PNIPAm was integrated into the nanocapsules via thiol‐ene click reaction. The surface thiol‐ene click reaction conduced to tunable grafting density of PNIPAm brushes. The grafting densities decreased from 0.70 chains nm^?2 to 0.15 chains nm^?2 with increasing the molecular weight of grafted PNIPAm chains. Using water soluble doxorubicin hydrochloride (DOX·HCl) as a model molecular, the tunable shell permeability of the nanocapsule was investigated in detail. The permeability constant can be tuned by controlling the thickness of the P(MAA‐co‐DVB) inner shell, the grafting density of PNIPAm brushes, and the environmental pH and temperature. The tunable shell permeability of these nanocapsules results in the release of the loaded guest molecules with manipulable releasing kinetics. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 2202–2216     

Influence of nitroxide structure on polystyrene brushes “grafted‐from” silicon wafers

Alkoxyamine derivatives based on 2,2,6,6‐tetramethyl‐1‐piperidinyloxy (TEMPO), N‐tert‐butyl‐N‐(1‐diethylphosphono‐(2,2‐dimethylpropyl)) nitroxide (SG1) and N‐tert‐butyl‐N‐(2‐methyl‐1‐phenylpropyl) nitroxide (TIPNO) containing a C₁₁ hydrophobic spacer and a reactive triethoxysilyl polar head, were synthesized and anchored to silicon wafers by the Langmuir–Blodgett reactive deposition technique at surface pressures ranging from 15 to 32 mN/m. Polystyrene brushes (M_n ～ 8500–66,400 g/mol) were grown from the alkoxyamine functionalized silicon wafers by nitroxide mediated radical polymerization and characterized by ellipsometry and water contact angle measurements. The main parameters influencing the grafting density and the degree of stretching of the brushes are the nitroxide polarity and, therefore, the behavior of the corresponding alkoxyamines at the air/water interface of the Langmuir–Blodgett trough. Depending on the alkoxyamine chemical structure and the surface pressure during Langmuir–Blodgett deposition, polystyrene brushes with grafting densities of 0.3–1.0 chains/nm² and stretching values of 40–70% were obtained. Regarding alkoxyamines deposited at high surface pressures, size exclusion chromatography experiments performed on both cleaved polystyrene brushes and chains simultaneously grown in the bulk revealed that the polymerization degree of the bulk and surface chains are significantly different, suggesting that steric constrains affect the polymerization kinetics occurring at the silicon surface. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 3367–3374, 2008     

PVDF/PMMA brushes membrane for lithium‐ion rechargeable batteries prepared via preirradiation grafting technique

Poly(methyl methacrylate) (PMMA) was anchored to multiporous poly(vinylidine fluoride) (PVDF) surface via electron beam preirradiation grafting technique to prepare PVDF/PMMA brushes. The conformation of the PVDF/PMMA brushes was verified through Attenuated total reflection‐Fourier transform infra red spectroscopy (ATR‐FTIR), energy dispersive X‐ray spectroscopy (EDX), and scanning electron microscopy (SEM). Thermal stability of PVDF/PMMA brushes was characterized by thermo gravimetric analysis (TGA). The degradation of PVDF/PMMA brushes showed a two‐step pattern. PVDF/PMMA brushes membrane could be used as polymer electrolyte in lithium‐ion rechargeable batteries after it was activated by uptaking 1 M LiPF₆/EC‐DMC (ethylene carbonate/dimethyl carbonate; EC:DMC = 1:1 by volume) electrolyte solution. The activated membrane showed high ionic conductivity, 6.1 × 10^?3 S cm^?1 at room temperature, and a good electrochemical stability up to 5.0 V. The excellent performances of multiporous PVDF‐g‐PMMA membranes suggest that they are suitable for application in high‐performance lithium‐ion batteries. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 751–758, 2008     

Collapse and swelling of poly(N‐isopropylacrylamide‐co‐sodium acrylate) copolymer brushes grafted on a flat SiO2 surface

Poly(N‐isopropylacrylamide‐co‐sodium acrylate) copolymer brushes grafted on SiO₂‐coated quartz crystal surface were prepared with a surface‐immobilized initiator. The collapse and swelling of the thermally sensitive copolymer brushes in water were studied with quartz crystal microbalance in situ. The frequency and dissipation changes with the temperature increasing in the range 20–38 °C indicate that the brushes undergo a continuous collapse transition. Our results show that the copolymer brushes collapse to a state where the brushes were prepared. A hysteresis was observed in the cooling process. Fourier transform infrared (FTIR) results revealed that the formation of some additional hydrogen bonds within the copolymer chains at their collapsed state is responsible for the hysteresis. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 770–778, 2006     

Motion‐Based,High‐Yielding,and Fast Separation of Different Charged Organics in Water

We report a self‐propelled Janus silica micromotor as a motion‐based analytical method for achieving fast target separation of polyelectrolyte microcapsules, enriching different charged organics with low molecular weights in water. The self‐propelled Janus silica micromotor catalytically decomposes a hydrogen peroxide fuel and moves along the direction of the catalyst face at a speed of 126.3 μm s^?1. Biotin‐functionalized Janus micromotors can specifically capture and rapidly transport streptavidin‐modified polyelectrolyte multilayer capsules, which could effectively enrich and separate different charged organics in water. The interior of the polyelectrolyte multilayer microcapsules were filled with a strong charged polyelectrolyte, and thus a Donnan equilibrium is favorable between the inner solution within the capsules and the bulk solution to entrap oppositely charged organics in water. The integration of these self‐propelled Janus silica micromotors and polyelectrolyte multilayer capsules into a lab‐on‐chip device that enables the separation and analysis of charged organics could be attractive for a diverse range of applications.     

Biomimetic Artificial Inorganic Enzyme‐Free Self‐Propelled Microfish Robot for Selective Detection of Pb2+ in Water

The availability of drinking water is of utmost importance for the world population. Anthropogenic pollutants of water, such as heavy‐metal ions, are major problems in water contamination. The toxicity assays used range from cell assays to animal tests. Herein, we replace biological toxicity assays, which use higher organisms, with artificial inorganic self‐propelled microtubular robots. The viability and activity of these robots are negatively influenced by heavy metals, such as Pb²⁺, in a similar manner to that of live fish models. This allows the establishment of a lethal dose (LD₅₀) of heavy metal for artificial inorganic microfish robots. The self‐propelled microfish robots show specific response to Pb²⁺ compared to other heavy metals, such as Cd²⁺, and can be used for selective determination of Pb²⁺ in water. It is a first step towards replacing the biological toxicity assays with biomimetic inorganic autonomous robotic systems.