Imaging surfaces of nano‐scale roughness by atomic force microscopy with carbon nanotubes as tips: a comparative study

Accurate knowledge of the nanoroughness of surfaces is crucial for many applications related to optics, electronics or tribology. Although atomic force microscopy (AFM) can image surfaces with a nanometre spatial resolution, the finite size of standard tips means that pores, pits or grooves with dimensions similar to or smaller than the tip apex will not be accurately imaged. Furthermore, standard tips are made of silicon or silicon nitride and are prone to wear. Mitigation may arise from the availability of AFM tips with a carbon nanotube (CNT) at their foremost end. This study compares the imaging performance of ultrasharp Si tips, CNT AFM tips prepared by a Langmuir‐Blodgett (LB) technique, and of CNT AFM tips prepared by a chemical vapour deposition (CVD) technique. The free length of the CNT AFM tips is in the range 80–200 and 600–750 nm, respectively. A polycrystalline niobium film surface is imaged that shows nanoroughness. The measurements demonstrate that CNT AFM tips allow excellent imaging if the scan parameters are adjusted very carefully. Nevertheless, in some cases distortions are found. The measured average grain diameter is 19.9 ± 3.6 nm in the case of a CNT AFM tip made by the LB technique, and 18.0 ± 3.3 nm in the case of a CNT AFM tip made by CVD. In addition to cross‐sections of topography images, also the power spectral density (PSD) is analyzed. An empirical approach for the readout of the characteristic length is suggested that involves the first derivative of the decadic logarithm of the PSD. Copyright © 2011 John Wiley & Sons, Ltd.     

Recent developments in entropy‐driven ring‐opening metathesis polymerization: Mechanistic considerations,unique functionality,and sequence control

Entropy‐driven ROMP (ED‐ROMP) involves polymerization of olefin‐containing macrocyclic monomers under entropically favorable conditions. Macrocycles can be prepared from a variety of interesting molecules which, when polymerized, impart unique functionality to the resulting polymer backbone such as degradable linkages, biological moieties, crystallizable groups, or supramolecular hosts. In addition, the sequence of atoms in the cyclic monomer is preserved within the polymer repeating units, allowing for facile preparation of sequence‐defined polymers. In this review article, we consider how the mechanism of ROMP applies to ED polymerizations, how olefinic macrocycles are synthesized, and how polymerization conditions can be tuned to maximize conversion. Recent works in the past 10 years are highlighted, with emphasis on methods which can be employed to achieve fast polymerization kinetics and/or selective head‐to‐tail regiochemistry, thus improving polymerization control. ED‐ROMP, with its unique capability to produce polymers with well‐defined polymer backbone microstructure, represents an essential complement to other, well‐established, metathesis methodologies such as ROMP. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019, 57, 1621–1634     

Role of self‐assembly conditions and amphiphilic balance on nanoparticle formation of PEG‐PDLLA copolymers in aqueous environments

The production of well‐defined and reproducible polymeric nanoparticles (NPs), in terms of size and stability in biological environments, is undoubtedly a fundamental challenge in the formulation of novel and more effective nanomedicines. The adoption of PEGylated lactide (LA) block copolymers as biodegradable and biocompatible nanocarriers at different clinical stages has rendered these materials an attractive polymeric platform to be exploited and their formulation is further understood. In the present work, we synthesized a library of linear polyethylene glycol‐poly(D,L‐lactide) block copolymers with different lengths of LA (15, 25, 50, and 100 LA units) via simple and metal‐free ring‐opening polymerization, in order to alter the amphiphilic balance of the different macromolecules. The produced polymers were formulated into NPs while varying a series of key parameters in the solvent displacement process, including solvent:nonsolvent ratios and the nature of the two media, and the effect on size and stability was assessed. In addition, stability to protein–NPs interaction and aggregation was studied, highlighting the different NP final properties according to the nature of the amphiphilic balance and nanoformulation conditions. Therefore, we have illustrated a systematic and methodological process to optimize a series of NPs parameters balancing particle size, size distribution, surface charge, and stability to guide future works in the nanoformulation field. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019 , 57, 1801–1810