63 research outputs found
Polymers at surfaces: nanostructures and adhesion studied by atomic force microscopy
No full textUnderstanding and characterising the behaviour of polymers at surfaces is of great
fundamental interest, in addition to being vitally important for many applications.
Composite materials, films and coatings, functional membranes, and nanoelectronics are
only a few examples of applications which rely on polymers functioning at surfaces. The
interactions between polymers and surfaces are extremely influential in governing the
overall bulk properties of materials and products. Despite this, the behaviour of
polymers at surfaces is not fully understood and there are many unexplored areas in this
field of research.
Atomic force microscopy (AFM) is a technique which can image features with a high
spatial resolution down to a sub-nanometre scale. It can accurately image a variety of
polymer nanostructures on surfaces such as droplets, networks, thin films, and even
single chains. AFM can also be used in a mode of operation called force spectroscopy
which generates information regarding the strength of adhesion between different
materials with a piconewton force resolution. It can be used to measure the magnitude
of interaction forces between single polymer chains and surfaces.
The primary aim of this study was to characterise the behaviour of poly(styrene-cobutadiene)
random copolymers on various surfaces at the nanoscale using AFM
techniques. Poly(styrene-co-butadiene) is heavily utilised within industry, particularly
in the manufacturing of automotive tyres where it is mixed with carbon black to form a
robust composite material. This study is the first work to provide a comprehensive
report on the morphology of poly(styrene-co-butadiene) nanostructures on various
surfaces, under different experimental parameters. Furthermore, it is the first time
where the specific interactions and adhesion between poly(styrene-co-butadiene) and
various surfaces have been examined using AFM force spectroscopy.
A systematic study was carried out which investigated the structural behaviour of
adsorbed poly(styrene-co-butadiene) random copolymers on mica and graphite surfaces
using AFM imaging. A large range of concentrations and molecular weights allowed
investigations and discussions of many phenomena such as thin film formation (and
dewetting), networks, spherical cap nanodroplets, and single chain conformations.
Polymer morphology was generally more consistent on the mica, and varied significantly
on graphite. The contact angles of the nanodroplets on the mica surface were shown to
be size dependent by a specific trend irrespective of molecular weight. A minimum
contact angle was observed for droplets with radii ranging from 100 - 250 nm across
each molecular weight. This was due to influences from line tension, changes in elastic
modulus, and surface heterogeneities. On the graphite, the nanostructures exhibited
distinct ordering at the nanoscale. The features reflected the crystalline symmetry of the
graphite by orientating themselves at intervals of 60° due to π-π stacking interactions.
The ordering was extremely precise at the lowest concentration and became less defined
at higher concentrations, but remained statistically significant.
An AFM force spectroscopy study was implemented in order to investigate the adhesion
and specific interactions between poly(styrene-co-butadiene) and mica, silicon, and
graphite substrates. AFM tips were dip coated into polymer solutions to physically
adhere polymer chains to the surface of the tips at varying molecular weights and surface
coverages. Polymer chains were also adhered to AFM tips using force spectroscopy
techniques. The results showed that capillary forces were increasing polymer/substrate
adhesion on the more hydrophilic substrates. Single chain desorption events did occur,
but had a very low probability. The experimental system was redesigned to reduce
capillary effects and increase desorption events. Thin polymer films were deposited onto
each substrate using dip coating and the AFM tips were left blank. The results revealed
that capillary forces were eliminated using this system and the probability of single chain
desorption events occurring was extremely high. It was demonstrated that the specific
interactions between poly(styrene-co-butadiene) and graphite were the strongest of the
three substrates due to π-π stacking interactions and van der Waals forces
Thin Polymer Film Force Spectroscopy: Single Chain Pull-out and Desorption
No full textAtomic force microscopy
(AFM) was utilized to investigate the force associated with chain
pull-out and single chain desorption of poly(styrene-co-butadiene) random copolymer thin films on mica, silicon, and graphite
substrates. Chain pull-out events were common and produced a force
of 20–25 pN. The polymer desorption force was strongest on
the graphite substrate and weakest on the mica, which agreed with
the calculated work of adhesion for each system and the substrate
hydrophobicity. Furthermore, it was demonstrated that there was a
systematic order to when each of these phenomena occurred during the
tip retraction from the surface, which provided information about
the structure of the thin films
Thin Polymer Film Force Spectroscopy: Single Chain Pull-out and Desorption
No full textAtomic force microscopy (AFM) was utilized to investigate the force associated with chain pull-out and single chain desorption of poly(styrene-co-butadiene) random copolymer thin films on mica, silicon, and graphite substrates. Chain pull-out events were common and produced a force of 20–25 pN. The polymer desorption force was strongest on the graphite substrate and weakest on the mica, which agreed with the calculated work of adhesion for each system and the substrate hydrophobicity. Furthermore, it was demonstrated that there was a systematic order to when each of these phenomena occurred during the tip retraction from the surface, which provided information about the structure of the thin films
Design and testing of a thick-film dual-modality sensor for composition measurements in heterogeneous mixtures
No full textThe current paper focuses on design and laboratory evaluation of a dual-modality sensor, developed for the needs of oil and gas extraction industry to measure the composition of heterogeneous mixtures in harsh conditions. The sensor combines ultrasonic and electrical measurement techniques, which are non-destructive, rapid and can potentially provide an on-line industrial measurement. Such a ‘dual-modality’ measurement could potentially be reliable in a wider range of process conditions. A distinct feature of the sensors presented here is their construction, which makes use of the thick-film technology, enabling the construction of multi-layered structures of both conductive and non-conductive layers, some of which may exhibit piezoelectric properties for ultrasonic measurement purposes. These are later fired on a ceramic substrate to provide rugged sensors, capable of working in aggressive industrial environments. Laboratory experiments to investigate the feasibility of the dual-modality sensors were conducted and some comparisons with the theoretical predictions are presented
Emotional arousal rather than memory mediates punishment preferences for murder
No full textThis thesis was scanned from the print manuscript for digital preservation and is copyright the author.
Researchers can access this thesis by asking their local university, institution or public library to
make a request on their behalf. Monash staff and postgraduate students can use the link in the References field
Emotional arousal rather than memory mediates punishment preferences for murder
No full textThis thesis was scanned from the print manuscript for digital preservation and is copyright the author.
Researchers can access this thesis by asking their local university, institution or public library to
make a request on their behalf. Monash staff and postgraduate students can use the link in the References field
Food Nanotechnology De Gruyter STEM Ser.
No full textDescription based upon print version of record.Nanotechnology is increasingly being utilized within the food industry to create innovative products with new or improved properties. This book introduces the history of nanotechnology applications in the food industry. It then discusses the key physicochemical and structural characteristics of the different kinds of nanoparticles found in foods, as well as showing how these characteristics lead to their unique functional attributes. Applications of nanotechnology in the food and agricultural industries are then covered, including the creation of nanopesticides, nanofertilizers, nutrient delivery systems, functional ingredients, smart packaging materials, nanofilters, and sensors, as well as for the conversion of waste materials into value-added products. Finally, the potential toxicity of both organic and inorganic nanoparticles found in foods is critically assessed. The author is a Distinguished Professor of food science who uses physics, chemistry, and biology to improve the quality, safety, and healthiness of foods. He has published over a thousand scientific articles and numerous books in this area and is currently the most highly cited food scientist in the world. He has won numerous awards for his scientific achievements. The aim of this book is to provide scientists and technologists with an understanding of the basic principles of nanotechnology and how they can be used in the food and agricultural industry to improve the quality, sustainability, safety, and healthiness of our foods.Intro -- Acknowledgments -- Contents -- About the author -- Chapter 1 Introduction -- Chapter 2 Nanomaterial properties and their characterization -- Chapter 3 Applications of nanotechnology in agriculture -- Chapter 4 Applications in food and nutrition -- Chapter 5 Advanced nanomaterials for food and agriculture applications -- Chapter 6 Nanotoxicology: The potential risks of food nanotechnology -- Index1 online resource (194 p.)
Measuring the Interactions between Carbon Black Nanoparticles and Latex Thin Films in Aqueous Media using AFM Force Spectroscopy
No full textAFM force spectroscopy was utilised to measure the interactions between latex and carbon black nanoparticles in neutral ultrapure water and basic ultrapure water with 0.7% ammonia (pH of 11.6 ± 0.05) by weight added. For the first time, carbon black nanoparticles were adhered to AFM tips with epoxy using force spectroscopy techniques and characterised using SEM and AFM. The carbon-functionalised tips were then utilised to interact with thin films (prepared from concentrated and field latex suspensions) in the two liquid media. The results demonstrated that both attractive (during tip approach) and adhesive (during tip retraction) forces were considerably greater between the latex and carbon nanoparticles when the experiments were carried out in ultrapure water compared to ultrapure water with 0.7% ammonia. This was because the basic ammonia solution increased the negative surface charges of the latex and carbon particles which was confirmed by zeta potential measurements. Therefore, in the ammonia solution, only repulsion was observed on the tip approach and only small amounts of adhesion were observed on the tip retraction. Furthermore, the results demonstrated that despite the different processing and treatment of the concentrated and field latex samples, their interactions with the carbon black nanoparticles were similar in each medium. This study directly measures the interactions between carbon black nanoparticles and natural rubber latex, which has a significance for the manufacturing of automotive tyres and other polymer/carbon composites
High-Density Polyethylene–Polypropylene Blends: Examining the Relationship Between Nano/Microscale Phase Separation and Thermomechanical Properties
No full textThe phase separation of high-density polyethylene (HDPE)–polypropylene (PP) blends was studied using atomic force microscopy in tapping mode to obtain height and phase images. The results are compared with those from scanning electron microscopy imaging and are connected to the thermomechanical properties of the blends, characterised through differential scanning calorimetry, dynamic mechanical analysis (DMA), and tensile testing. Pure PP, as well as 10:90 and 20:80 weight ratio HDPE–PP blends, showed a homogeneous morphology, but the 25:75 HDPE–PP blends exhibited a sub-micrometre droplet-matrix structure, and the 50:50 HDPE–PP blends displayed a more complex co-continuous nano/microphase-separated structure. These complex phase separation morphologies correlate with the increased loss modulus (viscous properties) of the corresponding blends as measured by DMA, demonstrating the potential for the creation of strong and simultaneously tough, energy-absorbing materials for numerous applications
Morphology of Poly(styrene-<i>co</i>-butadiene) Random Copolymer Thin Films and Nanostructures on a Graphite Surface
No full textWe
studied the morphology of poly(styrene-co-butadiene)
random copolymers on a graphite surface. Polymer solutions were spin
coated onto graphite, at various concentrations and molecular weights.
The polymer films and nanostructures were imaged using atomic force
microscopy. Above the overlap concentration, thin films formed. However,
total wetting did not occur, despite the polymers being well above
their Tg. Instead, dewetting was observed,
suggesting the films were in a state of metastable equilibrium. At
lower concentrations, the polymers formed networks, nanoislands, and
nanoribbons. Ordered nanopatterns were observed on the surface; the
polymers orientated themselves due to π–π stacking
interactions reflecting the crystalline structure of the graphite.
At the lowest concentration, this ordering was very pronounced. At
higher concentrations, it was less defined but still statistically
significant. Higher degrees of ordering were observed with poly(styrene-co-butadiene) than polystyrene and polybutadiene homopolymers
as the copolymer’s aromatic rings are distributed along a flexible
chain, which maximizes π–π stacking. At the two
lowest concentrations, the size of the nanoislands and nanoribbons
remained similar with varying molecular weight. However, at higher
concentrations, the polymer network features were largest at the lowest
molecular weight, indicating that in this case, a large proportion
of shorter chains stay on top of the adsorbed ones. The contact angles
of the polymer nanostructures remained mostly constant with size,
which is due to the strong polymer/graphite adhesion dominating over
line tension and entropic effects
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