Numerical Simulations of Polymers at the Nanoscale

In this thesis we study a variety of nanoscale phenomena in certain polymer systems using a combination of numerical simulation methods and mathematical modelling. The problems considered are: (a) the mixing behaviour of polymeric fluids in micro- and nanofluidic devices, (b) capillary absorption of polymer droplets into narrow capillaries, and (c) modelling the phase separation and self-assembly behaviour in polymer systems with freely deforming boundaries. These problems are significant in nanotechnological applications of polymer-based systems. First, the mixing behaviour of a polymeric melt over two parallely patternedslip surfaces is considered. Using molecular dynamics (MD) simulations, it is shown that mixing is enhanced when the polymer chain size is smaller than the wavelength of the chemical pattern of the surfaces. An off-set in the upper and lowerwall patterns improved themixing in the centre of the channel. Application of a sinusoidally varying body force in addition to the patterned-slip conditions is shown to enhance mixing further, compared to a constant body force case, with some limitations. Simulation findings for the constant body force cases are in qualitative agreement with the continuum theory of Pereira [1]. However, in the case of a sinusoidally varying body force our simulations do not agree with the continuum theory. We explain the reasons for the discrepancy between the two and point out the deficiencies in the continuum theory in predicting the correct behaviour. Second, the capillary phenomena of polymer droplets in narrow capillaries is studied using MD simulations. It is demonstrated that droplets composed of longer chains require wider tubes for absorption and this result is in agreement with our continuum modelling. The observed capillary dynamics deviate significantly from the standard Lucas-Washburn description thus questioning its validity at the nanoscale. The metastable states during the capillary absorption in some cases cannot be explained using the existing models of capillary dynamics. Lastly, the phase separation process in polymer blends between both confined and unconfined boundaries is studied using Smoothed Particle Hydrodynamics (SPH). The SPH technique has the advantage of not using a grid to discretize the spatial domain, which makes it appealing when dealing with problems where the spatial domain can change with time. The applicability of the SPH method in describing phase separation in these systems is demonstrated. In particular, its ability to model freely deforming polymer blends is shown

Ligand Rearrangement and Hemilability in R hodium(I) and Iridium(I) Complexes Bearing Terphenyl Phosphines

We describe the synthesis of a series of cationic rhodium(I) and iridium(I) compounds stabilized by sterically demanding phosphines that contain a terphenyl substituent, PMe 2 Ar’ (Ar’ = 2,6-diarylphenyl radical). Salt metathesis of metal precursors [MCl(COD)(PMe 2 Ar’)] (M = Rh, Ir; COD = cyclooctadiene) with NaBAr F (BAr F = B(3,5-C 6 H 3 (CF 3 ) 2 ) 4 ) results in a series of cationic complexes in which the loss of the chloride ligand is compensated by the appearance of relatively weak π-interactions with one of the flanking aryl rings of the terphenyl substituent. The same experiments carried out with carbonyl compounds [MCl(CO) 2 (PMe 2 Ar’)] led to the corresponding cationic carbonyl complexes, whose CO-induced rearrangement reactivity has been investigated, both experimentally and computationally. The differences in reactivity between rhodium and iridium complexes, and as a result of varying the sterics of terphenyl phosphines are discusse

Light-stable silver N-Heterocyclic carbene catalysts for the alkynylation of ketones in air

The authors gratefully acknowledge the Royal Society (University Research Fellowship to C.S.J.C) for funding.N-Heterocyclic carbene (NHC) silver(I) complexes were efficiently employed in the alkynylation of ketones. These cationic complexes were found highly active and efficient under mild conditions without the need of additive, and in air. The mechanism of this transformation was investigated. Experiments suggest the formation of a silver-acetylide key intermediate and the release of one ligand from the silver centre enabling the transformation.PostprintPeer reviewe

Numerical Simulations of Polymers at the Nanoscale

In this thesis we study a variety of nanoscale phenomena in certain polymer systems using a combination of numerical simulation methods and mathematical modelling. The problems considered are: (a) the mixing behaviour of polymeric fluids in micro- and nanofluidic devices, (b) capillary absorption of polymer droplets into narrow capillaries, and (c) modelling the phase separation and self-assembly behaviour in polymer systems with freely deforming boundaries. These problems are significant in nanotechnological applications of polymer-based systems. First, the mixing behaviour of a polymeric melt over two parallely patternedslip surfaces is considered. Using molecular dynamics (MD) simulations, it is shown that mixing is enhanced when the polymer chain size is smaller than the wavelength of the chemical pattern of the surfaces. An off-set in the upper and lowerwall patterns improved themixing in the centre of the channel. Application of a sinusoidally varying body force in addition to the patterned-slip conditions is shown to enhance mixing further, compared to a constant body force case, with some limitations. Simulation findings for the constant body force cases are in qualitative agreement with the continuum theory of Pereira [1]. However, in the case of a sinusoidally varying body force our simulations do not agree with the continuum theory. We explain the reasons for the discrepancy between the two and point out the deficiencies in the continuum theory in predicting the correct behaviour. Second, the capillary phenomena of polymer droplets in narrow capillaries is studied using MD simulations. It is demonstrated that droplets composed of longer chains require wider tubes for absorption and this result is in agreement with our continuum modelling. The observed capillary dynamics deviate significantly from the standard Lucas-Washburn description thus questioning its validity at the nanoscale. The metastable states during the capillary absorption in some cases cannot be explained using the existing models of capillary dynamics. Lastly, the phase separation process in polymer blends between both confined and unconfined boundaries is studied using Smoothed Particle Hydrodynamics (SPH). The SPH technique has the advantage of not using a grid to discretize the spatial domain, which makes it appealing when dealing with problems where the spatial domain can change with time. The applicability of the SPH method in describing phase separation in these systems is demonstrated. In particular, its ability to model freely deforming polymer blends is shown

Numerical Simulations of Polymers at the Nanoscale

In this thesis we study a variety of nanoscale phenomena in certain polymer systems using a combination of numerical simulation methods and mathematical modelling. The problems considered are: (a) the mixing behaviour of polymeric fluids in micro- and nanofluidic devices, (b) capillary absorption of polymer droplets into narrow capillaries, and (c) modelling the phase separation and self-assembly behaviour in polymer systems with freely deforming boundaries. These problems are significant in nanotechnological applications of polymer-based systems. First, the mixing behaviour of a polymeric melt over two parallely patternedslip surfaces is considered. Using molecular dynamics (MD) simulations, it is shown that mixing is enhanced when the polymer chain size is smaller than the wavelength of the chemical pattern of the surfaces. An off-set in the upper and lowerwall patterns improved themixing in the centre of the channel. Application of a sinusoidally varying body force in addition to the patterned-slip conditions is shown to enhance mixing further, compared to a constant body force case, with some limitations. Simulation findings for the constant body force cases are in qualitative agreement with the continuum theory of Pereira [1]. However, in the case of a sinusoidally varying body force our simulations do not agree with the continuum theory. We explain the reasons for the discrepancy between the two and point out the deficiencies in the continuum theory in predicting the correct behaviour. Second, the capillary phenomena of polymer droplets in narrow capillaries is studied using MD simulations. It is demonstrated that droplets composed of longer chains require wider tubes for absorption and this result is in agreement with our continuum modelling. The observed capillary dynamics deviate significantly from the standard Lucas-Washburn description thus questioning its validity at the nanoscale. The metastable states during the capillary absorption in some cases cannot be explained using the existing models of capillary dynamics. Lastly, the phase separation process in polymer blends between both confined and unconfined boundaries is studied using Smoothed Particle Hydrodynamics (SPH). The SPH technique has the advantage of not using a grid to discretize the spatial domain, which makes it appealing when dealing with problems where the spatial domain can change with time. The applicability of the SPH method in describing phase separation in these systems is demonstrated. In particular, its ability to model freely deforming polymer blends is shown.</p

BEHAVIORAL STUDY OF ROGAR AND ACUTE STRESS ON MALE CRAB BRYTELPHUSA GUERINI

ABSTRACT When an organism is exposed to any toxic agent, some changes occur in the behaviour which can be observed externally. These behavioural changes may be co-related to they changes occurring in the nervous system, as different behavioural responses are sub-served wholly or partly be the different neural circuits which are distributed in the nervous system. Behaviour includes all those process by which an animal senses the external world and internal state of its body, and responds to changes which it perceives. Earlier reports revealed that there is a strong correlation between physiological activities, metabolic changes and behaviour of animals. The paper deals with toxic effect of rogar on fresh water male crab Barytelphusa guerini and its behavioural study. The experimental animal shows various activities which is recorded and discussed