Viscosity and fragility of confined polymer nanocomposites: a tale of two interfaces

Nimmi Das A; Nafisa Begam; Mohd Ibrahim; Sivasurender Chandran; Venkat Padmanabhan; Michael Sprung; J. K. Basu

doi:10.1039/c8nr10362c

Viscosity and fragility of confined polymer nanocomposites: a tale of two interfaces

Nanoscale ◽

10.1039/c8nr10362c ◽

2019 ◽

Vol 11 (17) ◽

pp. 8546-8553 ◽

Cited By ~ 3

Author(s):

Nimmi Das A ◽

Nafisa Begam ◽

Mohd Ibrahim ◽

Sivasurender Chandran ◽

Venkat Padmanabhan ◽

...

Keyword(s):

Polymer Nanocomposites ◽

Mechanical Stability ◽

Glassy Polymers ◽

Confined Polymer

Viscosity and fragility are key parameters determining the processability and thermo-mechanical stability of glassy polymers and polymer nanocomposites (PNCs).

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Polymer Nanocomposites for Photocatalytic Applications

Catalysts ◽

10.3390/catal9120986 ◽

2019 ◽

Vol 9 (12) ◽

pp. 986 ◽

Cited By ~ 11

Author(s):

Violeta Melinte ◽

Lenuta Stroea ◽

Andreea L. Chibac-Scutaru

Keyword(s):

Visible Light ◽

Polymer Nanocomposites ◽

Mechanical Stability ◽

Catalytic Performance ◽

Inorganic Nanoparticles ◽

Environmental Stability ◽

Separation Processes ◽

Chemical Inertness ◽

Selection Of ◽

Photocatalytic Materials

In the present comprehensive review we have specifically focused on polymer nanocomposites used as photocatalytic materials in fine organic reactions or in organic pollutants degradation. The selection of the polymer substrates for the immobilization of the active catalyst particles is motivated by several advantages displayed by them, such as: Environmental stability, chemical inertness and resistance to ultraviolet radiations, mechanical stability, low prices and ease availability. Additionally, the use of polymer nanocomposites as photocatalysts offers the possibility of a facile separation and reuse of the materials, eliminating thus the post-treatment separation processes and implicitly reducing the costs of the procedure. This review covers the polymer-based photocatalytic materials containing the most popular inorganic nanoparticles with good catalytic performance under UV or visible light, namely TiO2, ZnO, CeO2, or plasmonic (Ag, Au, Pt, Pd) NPs. The study is mainly targeted on the preparation, photocatalytic activity, strategies directed toward the increase of photocatalytic efficiency under visible light and reuse of the hybrid polymer catalysts.

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The synthesis, characterisation and rheological properties of clay-polymer nanocomposites

10.7190/shu-thesis-00316 ◽

2020 ◽

Author(s):

◽

Hassan Judah

Keyword(s):

Thermogravimetric Analysis ◽

Rheological Properties ◽

Polymer Nanocomposites ◽

Mechanical Stability ◽

Crosslinking Agent ◽

Polymer Nanocomposite ◽

Crosslinking Density ◽

Mechanical Analysis ◽

Morphological Examination ◽

X Ray

This study aims to investigate the effect of different crosslinking agent and different crosslinking agent content on the material properties of the clay-polymer nanocomposite. A lot of materials were tried to be mixed to form a fully-reacted clay-polymer nanocomposite for the first time, which is a part of the novelty for this work. The overall properties governed by clay properties and clay/polymer relationship are prime aspects of this study. The Enhancement of significant properties of nanocomposites is a measure of clay platelets dispersion within the polymer matrix. Different approaches were adopted to understand the influence of clay properties on the nanocomposite; (i) by examining and comparing different clays as raw, dry, powder material using spectroscopy and thermogravimetric analysis (ii) mechanical examination of clay/water suspension of different clay types/grads, and different concentrations varying from 0.5 % - 10 % using rheological studies (iii) chemical and mechanical and morphological examination of Clay/Polymer nanocomposite with different clay types/grades, concentration, and polymers. The synthesis of such material addresses issues including heterogeneity, processability, injectability, crosslinking and mechanical stability. The synthesis requires no purification steps no specialist equipment, and basic typical components of crosslinked nanocomposite/hydrogels (water, monomer, clay and initiator). Morphological, pore size and scaffolding general arrangement which shows the effect of different crosslinking agents and crosslinking density were examined by Scanning Electron Microscope (SEM) to acquire information on wide/small pores are, diffusion kinetics in the system if required for further applications. The nature and elemental composition of the clay-polymer nanocomposites were determined by X-ray diffraction (XRD), X-ray fluorescence (XRF), and Fourier Transfer Infrared (FTIR) spectroscopy. The water content in the dry clay-polymer nanocomposite was determined and examined by Thermogravimetric analysis (TGA). Mechanical and rheological properties of the result were examined using a rheometer that operates on different modes (as a Dynamic Mechanical Analysis (DMA) technique) to evaluate the structure, performance, strength, and mechanical modules of these nanocomposites under different rotational and oscillatory loads. This offers the opportunity to relate the differences to the clays and polymers the hydrogels were synthesised from.

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An improved design for an Scanning Tunnelling Microscope (STM) for use in a Transmission Electron Microscope (TEM)

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100086222 ◽

1991 ◽

Vol 49 ◽

pp. 384-385

Author(s):

W.K. Lo ◽

J.C.H. Spence

Keyword(s):

Electron Microscope ◽

Transmission Electron Microscope ◽

Mechanical Stability ◽

Scanning Tunnelling Microscope ◽

Reflection Mode ◽

Specimen Holder ◽

Transmission Electron ◽

Scanning Tunnelling ◽

Improved Design

An improved design for a combination Scanning Tunnelling Microscope/TEM specimen holder is presented. It is based on earlier versions which have been used to test the usefulness of such a device. As with the earlier versions, this holder is meant to replace the standard double-tilt specimen holder of an unmodified Philips 400T TEM. It allows the sample to be imaged simultaneously by both the STM and the TEM when the TEM is operated in the reflection mode (see figure 1).The resolution of a STM is determined by its tip radii as well as its stability. This places strict limitations on the mechanical stability of the tip with respect to the sample. In this STM the piezoelectric tube scanner is rigidly mounted inside the endcap of the STM holder. The tip coarse approach to the sample (z-direction) is provided by an Inchworm which is located outside the TEM vacuum.

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Experiments with a scanning tunneling microscope (STM) mounted in a scanning electron microscope (SEM)

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100144620 ◽

1986 ◽

Vol 44 ◽

pp. 636-639

Author(s):

Oliver C. Wells ◽

Mark E. Welland

Keyword(s):

Electron Microscope ◽

Scanning Electron Microscope ◽

Mechanical Stability ◽

Tunneling Current ◽

Feedback System ◽

Scanning Tunneling ◽

Surface Profiling ◽

Close Proximity ◽

Metal Tip ◽

Scanning Electron

Scanning tunneling microscopes (STM) exist in two versions. In both of these, a pointed metal tip is scanned in close proximity to the specimen surface by means of three piezos. The distance of the tip from the sample is controlled by a feedback system to give a constant tunneling current between the tip and the sample. In the low-end STM, the system has a mechanical stability and a noise level to give a vertical resolution of between 0.1 nm and 1.0 nm. The atomic resolution STM can show individual atoms on the surface of the specimen.A low-end STM has been put into the specimen chamber of a scanning electron microscope (SEM). The first objective was to investigate technological problems such as surface profiling. The second objective was for exploratory studies. This second objective has already been achieved by showing that the STM can be used to study trapping sites in SiO2.

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Electron microscopy of keratinocytes cultured on a collagen substrate used as an allograft for the treatment of chronic wounds

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100130158 ◽

1992 ◽

Vol 50 (2) ◽

pp. 1104-1105

Author(s):

Debby A. Jennings ◽

Michael J. Morykwas ◽

Louis C. Argenta

Keyword(s):

Electron Microscopy ◽

Cell Suspension ◽

Single Cell ◽

Chronic Wounds ◽

Mechanical Stability ◽

Uv Light ◽

Type I ◽

Single Cell Suspension ◽

Collagen Substrate ◽

Dermal Collagen

Grafts of cultured allogenic or autogenic keratlnocytes have proven to be an effective treatment of chronic wounds and burns. This study utilized a collagen substrate for keratinocyte and fibroblast attachment. The substrate provided mechanical stability and augmented graft manipulation onto the wound bed. Graft integrity was confirmed by light and transmission electron microscopy.Bovine Type I dermal collagen sheets (100 μm thick) were crosslinked with 254 nm UV light (13.5 Joules/cm2) to improve mechanical properties and reduce degradation. A single cell suspension of third passage neonatal foreskin fibroblasts were plated onto the collagen. Five days later, a single cell suspension of first passage neonatal foreskin keratinocytes were plated on the opposite side of the collagen. The grafts were cultured for one month.The grafts were fixed in phosphate buffered 4% formaldehyde/1% glutaraldehyde for 24 hours. Graft pieces were then washed in 0.13 M phosphate buffer, post-fixed in 1% osmium tetroxide, dehydrated, and embedded in Polybed 812.

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P20 phosphor on polyimide as a large area high-resolution transmission screen for slow scan CCD systems

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100136477 ◽

1995 ◽

Vol 53 ◽

pp. 20-21

Author(s):

C. C. Ahn ◽

S. Karnes ◽

M. Lvovsky ◽

C. M. Garland ◽

H. A. Atwater ◽

...

Keyword(s):

Mechanical Stability ◽

High Energy ◽

Practical Implementation ◽

Line Pair ◽

Modulation Transfer ◽

Large Area ◽

Ccd Imaging ◽

Transmission Electron ◽

The One ◽

Beam Broadening

The bane of CCD imaging systems for transmission electron microscopy at intermediate and high voltages has been their relatively poor modulation transfer function (MTF), or line pair resolution. The problem originates primarily with the phosphor screen. On the one hand, screens should be thick so that as many incident electrons as possible are converted to photons, yielding a high detective quantum efficiency(DQE). The MTF diminishes as a function of scintillator thickness however, and to some extent as a function of fluorescence within the scintillator substrates. Fan has noted that the use of a thin layer of phosphor beneath a self supporting 2μ, thick Al substrate might provide the most appropriate compromise for high DQE and MTF in transmission electron microcscopes which operate at higher voltages. Monte Carlo simulations of high energy electron trajectories reveal that only little beam broadening occurs within this thickness of Al film. Consequently, the MTF is limited predominantly by broadening within the thin phosphor underlayer. There are difficulties however, in the practical implementation of this design, associated mostly with the mechanical stability of the Al support film.

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A conduction-cooled stage for high-resolution Cryo-SEM

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100131048 ◽

1992 ◽

Vol 50 (2) ◽

pp. 1282-1283

Author(s):

John G. Sheehan

Keyword(s):

High Resolution ◽

Liquid Nitrogen ◽

Mechanical Stability ◽

Cooling System ◽

Cold Trap ◽

Nitrogen Gas ◽

Particulate Suspensions ◽

Advantages And Disadvantages ◽

Convection Cooling ◽

Styrene Butadiene

The goal is to examine with high resolution cryo-SEM aqueous particulate suspensions used in coatings for printable paper. A metal-coating chamber for cryo-preparation of such suspensions was described previously. Here, a new conduction-cooling system for the stage and cold-trap in an SEM specimen chamber is described. Its advantages and disadvantages are compared to a convection-cooling system made by Hexland (model CT1000A) and its mechanical stability is demonstrated by examining a sample of styrene-butadiene latex.In recent high resolution cryo-SEM, some stages are cooled by conduction, others by convection. In the latter, heat is convected from the specimen stage by cold nitrogen gas from a liquid-nitrogen cooled evaporative heat exchanger. The advantage is the fast cooling: the Hexland CT1000A cools the stage from ambient temperature to 88 K in about 20 min. However it consumes huge amounts of liquid-nitrogen and nitrogen gas: about 1 ℓ/h of liquid-nitrogen and 400 gm/h of nitrogen gas. Its liquid-nitrogen vessel must be re-filled at least every 40 min.

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