Solventless Polymerization: Spatial Migration of a Catalyst To Form Polymeric Thin Films in Microchannels

This paper reports a simple, additive process to generate patterned polymer films without using any solvent. This process involves a highly efficient catalyst, a Grubbs's catalyst, and a volatile monomer, norbornene. The catalyst and monomers have higher local concentrations inside the microchannels, formed by contacting poly(dimethylsiloxane) stamps to a solid surface, and allow the polymeric thin films to be defined by the microchannels. The patterned thin film serves as an excellent resistant to reactive ion etching, which promises that this process is a complementary, useful alternative to spin-coating and plasma polymerization in microfabrication

Hollow Interior Structure of Spin-Coated Polymer Thin Films Revealed by ToF-SIMS Three-Dimensional Imaging

Surface patterns were observed on spin-coated poly­(bisphenol A decane ether) (BA-C10) films prepared with chloroform and tetrahydrofuran as the solvents. The interior structure of these surface patterns were analyzed using a time-of-flight secondary ion mass spectrometry (ToF-SIMS) equipped with a bismuth cluster source for ion imaging and a C₆₀⁺ cluster source for depth profiling. For the first time, the surface patterns have been shown to be hollow rather than solid using ToF-SIMS three-dimensional (3D) analysis and optical techniques. Moreover, the microarea depth profiling analysis indicated that the hollow structure was sandwiched between two polymer layers rather than sitting on the substrate. The height of the hollow structure and the thicknesses of the polymer layers above and below the hollow structure were also estimated from the depth profiling results

Time-of-Flight-Secondary Ion Mass Spectrometry and Principal Component Analysis: Determination of Structures of Lamellar Surfaces

In this article, we addressed the applicability of time-of-flight secondary ion mass spectrometry (TOF-SIMS) to examine the effects of molecular weight and of flexible-segment length on the polymer chain arrangement at the folding surfaces of the lamellae. Poly(bisphenol A−etheralkane) (Cn) contains both rigid aromatic and flexible aliphatic CH2 segments. The number of CH2 units per flexible segment, n, varies from 8 to 12. Principal component analysis (PCA) of TOF-SIMS data revealed the chemical and structural variations of the folding surfaces of these polymers and identified the ion peaks contributing to these variations. We highlighted the discriminating power of PCA to distinguish the structural conformations of the amorphous and flat-on lamellar surfaces of these polymers. PCA loadings analyses showed that relatively more flexible structures were deposited on the folding surfaces when the flexible-segment length increased from 8 to 10 CH2 units. The concentration of short loops at folding surfaces and the disorder of folding surfaces increased when the molecular weight increased. All these results led us to conclude that TOF-SIMS has great potential for probing the chemical composition of the folding surfaces of polymers

Hollow Interior Structure of Spin-Coated Polymer Thin Films Revealed by ToF-SIMS Three-Dimensional Imaging

Surface patterns were observed on spin-coated poly­(bisphenol A decane ether) (BA-C10) films prepared with chloroform and tetrahydrofuran as the solvents. The interior structure of these surface patterns were analyzed using a time-of-flight secondary ion mass spectrometry (ToF-SIMS) equipped with a bismuth cluster source for ion imaging and a C₆₀⁺ cluster source for depth profiling. For the first time, the surface patterns have been shown to be hollow rather than solid using ToF-SIMS three-dimensional (3D) analysis and optical techniques. Moreover, the microarea depth profiling analysis indicated that the hollow structure was sandwiched between two polymer layers rather than sitting on the substrate. The height of the hollow structure and the thicknesses of the polymer layers above and below the hollow structure were also estimated from the depth profiling results

Crystallization-Induced Redox-Active Nanoribbons of Organometallic Polymers

Polymer/inorganic functional nanostructures are essential for the fabrication of high-performance nanodevices in the future. The synthesis of hybrid nanostructures is hindered by complicated synthetic protocols or harsh conditions. Herein, we report a facile and scalable method for the synthesis of organometallic polymer nanoribbons through crystallization of polymers capped with a ferrate complex. Nanoribbons consisted of a single crystalline polymer lamella coated with a redox-active ferrate complex on both sides. The nanoribbons had a width of approximately 70 nm and a thickness of 10 nm. With the merit of highly ordered crystalline structures of polymers and functional coating layers, as well as a highly anisotropic nature, the nanoribbons are useful in nanodevices and biosensors

Effective Viscosity of Lightly UVO-Treated Polystyrene Films on Silicon with Different Molecular Weights

Recently, we found that a brief, 1 s exposure to ultraviolet ozone (UVO) can cause the effective viscosity, ηeff, of polystyrene films supported by oxide-coated silicon (PS-SiOx) to increase by more than 100 times. In this experiment, we study the phenomenon with different PS molecular weights, Mw, from 2.4 to 451 kg/mol. We found that ηeff was increased for all Mw’s when the film thickness, h0, was decreased below an onset thickness comparable to the radius of gyration, Rg, of the polymer. For h0 greater than the onset thickness, the ηeff versus h0 dependence varies with Mw. Specifically, for Mw ≥ 60K g/mol ηeff was constant, equal to the bulk viscosity. For Mw eff decreased with decreasing h0 in the same way as that of the pristine counterparts. X-ray photoelectron spectroscopy (XPS) shows that oxygenated groups are formed in the films after the UVO treatment. We propose that the oxygenated groups can interact with the OH groups on the SiOx surface to produce increases in ηeff. Correspondingly, we found that the ηeff data could fit well to a three-layer model containing a dynamically dead layer on the substrate. Results of the fit are consistent with a surface layer with a thickness of ∼Rg and the following attributes. Below entanglement, the mobility of this layer is enhanced relative to the bulk polymer. Above entanglement, couplings between the surface chains and the chains in the inner, bulklike region force the surface chains to flow as the inner chains. As a result, enhanced mobility can only be found in short-range, local motions over depths of the order of the average distance between entanglements. This picture explains a variety of surface relaxation phenomena reported in the literature

Morphology-Driven Surface Segregation in a Blend of Poly(ε-caprolactone) and Poly(vinyl chloride)

A blend of poly(ε-caprolactone) (PCL) and poly(vinyl chloride) (PVC) with 90 wt % PCL was prepared. Two films of this blend, which were grown at 35 and 45 °C, showed the absence and presence of banded spherulites, respectively. A detailed examination conducted with time-of-flight secondary ion mass spectrometry (ToF−SIMS) found that the surface composition of the film grown at 45 °C was related to its structure, which was shown to contain ridges and valleys. Phase images obtained using atomic force microscopy (AFM) indicated that the ridges and valleys consisted of edge-on and flat-on lamellae, respectively. ToF−SIMS imaging revealed that PVC and PCL were located mainly on the surface of the valleys and ridges, respectively. This morphology-driven surface segregation was caused by the difference in the surface energy between the flat-on and edge-on lamellae

Fast Single-Cell Patterning for Study of Drug-Induced Phenotypic Alterations of HeLa Cells Using Time-of-Flight Secondary Ion Mass Spectrometry

A facile single-cell patterning (ScP) method was developed and integrated with time-of-flight secondary ion mass spectrometry (TOF-SIMS) for the study of drug-induced cellular phenotypic alterations. Micropatterned poly­(dimethylsiloxane) (PDMS) stencil film and centrifugation-assisted cell trapping were combined for the preparation of on-surface single-cell microarrays, which exhibited both high site occupancy (>90%) and single-cell resolution (>97%). TOF-SIMS is a surface-sensitive mass spectrometry and is increasingly utilized in biological studies. Here we demonstrated, for the first time, its successful application in high-throughput single-cell analysis. Drug-induced phenotypic alterations of HeLa cells in the early stage of apoptosis were investigated using TOF-SIMS. The major molecular sources of variations were analyzed by principle component analysis (PCA)

Crystallization-Induced Hybrid Nano-Sheets of Fluorescent Polymers with Aggregation-Induced Emission Characteristics for Sensitive Explosive Detection

Fluorescent organic hybrid nanosheets were generated by crystallization of polymers capped with luminogenic molecules exhibiting aggregation-induced emission characteristics (AIE). During crystallization of polymers, AIE molecules were expelled out of lamellar crystals of polymers, and finally resided on the surface. The fluorescent nanosheets with dangling AIE molecules showed sensitive and specific response to explosives. Such polymer crystallization-induced fluorescent nanomaterials offers a unique avenue to fabricate functional nanomaterials with AIE molecule-enriched domains for potential applications in nanodevices, biological engineering, and so on