Doctoral Thesis
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Objectives:
This study investigates the effectiveness of the Cold AP on the alteration of the enamel surface
without using acid etchant by using Conventional photo-activated resin bond to bond the
orthodontic brackets.
Materials and Methods:
One hundred and twenty-five Enamel specimens are prepared from disinfected bovine
mandibular incisors are divided into five groups. Group I: brackets are attached on the enamel
surface with the standard adhesive technique (etch + primer +bond). Group II: the brackets are
attached with the Standard Orthodontic adhesive technique without etching. Group III: the
enamel surface is conditioned with pure Argon Cold atmospheric plasma before the application
of the primer without using an acid etchant. Group IV: the enamel surface is conditioned with
the admixture of Argon Cold atmospheric plasma with 0.5 % Oxygen before the application of
the primer without using acid etchant Group V: after the application of Argon Cold atmospheric
plasma with 0.5 % Oxygen the surface is rewetted by deionized water before the application
of the primer and adhesive. After that, the samples are exposed to thermal cycling. The shear
bond strength of the samples is tested by the universal testing machine which measured the
maximum force at which the brackets are deboned from the tooth surface at a speed of
1mm/minute is measured.
Results:
Significant intergroup differences were found. Group V showed the highest shear bond
strength followed by Group I, VI, III, II respectively. There isn’t a statistical difference in the
values of The Shear bond strength values between Group III and IV.
Conclusions:
this study implies that Cold Atmospheric Plasma is a safe method to change the chemical
surface characteristics of the enamel surface.in addition to the significant importance of plasma
treatment followed by water rewetting, which could enhance adhesion between the orthodontic
attachments and the enamel layer
Recent experimental campaigns in the Wendelstein 7-X stellarator, a
plasma-confining device designed to investigate the Magnetic Confinement Fusion
(MCF) approach to generating electrical power, have shown that the injection of
fuelling pellets had an unexpected and considerable impact on the performance of
the plasma. Rather than simply refuelling the device and `diluting' the plasma
energy, pellet injection is followed by a significant increase in the ratio of
the ion temperature to the electron temperature. It has been suggested that this
is not merely due to the improved confinement following the reduction of
turbulent transport after the pellet material has homogenised with the bulk
plasma, but also due to a direct transfer of energy from electrons to ions. The
proposed mechanism for this energy transfer is the ambipolar expansion of the
pellet plasmoid, the localised plasma structure produced by the
ionisation of ablated pellet material, along magnetic field lines.
Early work on pellet plasmoid expansion predicted that half the heating power
deposited in plasmoid electrons by collisions with hot ambient electrons is
transferred to plasmoid ions in the form of flow velocity as the plasmoid
expands. The complicated nature of the system of the pellet plasmoid embedded in
the ambient plasma, particularly the behaviour of electrons, which experience
many collisional and collisionless phenomena on multiple disparate timescales,
means that early models of the expansion were not wholly self-consistent, but
rather made use of strong approximations that apply in some regions of the
plasmoid but not in others. For example, only electrons and ions associated with
the plasmoid were rigorously treated, meaning that the framework was one of
`expansion into vacuum'. Combined with the assumption of Maxwellian electrons,
this led to an electric potential that was unbounded at infinity. Naturally, the
validity of the conclusions of such a model are called into question because the
approximations lose their validity far from the plasmoid and as time advances,
yet predictions about the final state of the plasma are desired. A deeper
investigation is required: careful consideration of the phenomena in question
and the timescales (and lengthscales) on which they act must be made in order to
rigorously construct a model that is valid throughout the entire expansion.
The first two papers presented in this thesis iterate on the model established
in the paper that first predicted the electron-to-ion energy transfer; their aim
was to find out how the character of the expansion changes with a more
sophisticated and accurate description of various phenomena, while remaining
within the existing framework of expansion into vacuum. Ultimately, we find that
the qualitative character is unchanged, and that approximately half the heating
power deposited in plasmoid electrons is transferred to ions.
Two other papers in this thesis address the limitations of the original model.
This is achieved by properly considering the electron kinetic problem in a
plasmoid. One paper considers the electron kinetic problem when electrons are
highly isotropised. In this case the kinetic equation can be integrated to
remove all but two independent variables, which is the maximum possible
reduction considering it is a time-dependent problem. The full nonlinear
integro-differential Landau self-collision operator is integrated exactly and
few approximations are made, leading to a rather general kinetic equation.
However, for fuelling pellets some anisotropy in the electron distribution is
expected. Another paper considers the electron kinetic problem (and the entire
plasmoid expansion) allowing for electron anisotropy. Careful consideration of
the ordering of timescales of electron phenomena in a pellet plasmoid leads to a
steady-state kinetic problem that we call collisional quasi-equilibrium (QE). QE
appears in many ways similar to the collisional steady-state characterising a
true thermal equilibrium. It was found that the time-dependent kinetic problem
of the earlier paper, with isotropic electrons, produces the QE distribution
function, corroborating the existence of the QE state. We then take moments of
the electron kinetic equation that is valid on the expansion timescale, assuming
that the electron distribution is that given as the solution to the QE kinetic
problem. This is completely analogous to what is done to obtain the Braginskii
equations or any Chapman-Enskog theory. The result is a set of equations for the
long-term evolution of the macroscopic quantities that describe the distribution
function existing in a quasi-steady-state at each point in time. It is from this
point that one may feasibly describe the plasmoid expansion with an accurate
picture of the electron kinetics and finally obtain the electron-to-ion energy
transfer so desired in a rigorous model of the expansion.
From a broader point of view, the two frameworks provided by these rigorous
investigations of the electron kinetic problem serve as a basis for the future
study of plasmoids. Such a `first-principles' approach to plasmoid dynamics is
novel and interesting in its own right, but it will be demonstrated that such an
approach is essential for pellet plasmoids owing to the fact that they are
poorly described by the `standard tools' of plasma physics.
Using the QE framework it was found that, once more, about half the heating
power experienced by plasmoid electrons is transferred to plasmoid ions. The
incredible robustness of the prediction of such an energy transfer is, in the
author's opinion, the result of the self-similar nature of the expansion found
as a solution to the original model. As a rule, the profiles of self-similar
solutions tend to be attractors for the `real', more complicated, system, and
the qualitative predictions involving no parameters, of which the
electron-to-ion energy transfer is one, tend to be very sturdy.
Aside from fuelling pellets, composed of hydrogen or deuterium, one paper in
this thesis investigates the physics of high-Z pellets that are designed to
terminate the plasma safely in the event of a `disruption', where much of the
magnetic field energy is channelled into a runaway electron beam with
potentially disastrous consequences if the beam encounters a plasma-facing
component. The paper draws on the work carried out in the paper concerning the
kinetic problem of isotropised electrons in a plasmoid.
This thesis is `cumulative'; the vast majority of the work carried out is
described within a set of Papers, labelled A-E, placed at the back of the text.
There is a preceding `wrapper text' (given in numbered Sections) tasked with
introducing the reader to the topic, guiding the reader through the papers, and
expounding some of their main results. Some amount of material not present in
the papers is also provided in the wrapper text. Naturally, the wrapper text
mainly focusses on the results of the papers which are under my first
authorship. In the course of publishing papers over an extended period of time
the nomenclature is bound to vary. Although it is mostly consistent between the
papers, a few difference do arise, and the section `Common symbols and
subscripts' is provided in the frontmatter to alleviate confusion. Particular
care should be taken with the symbols x and z; both can refer to the
coordinate parallel to the magnetic field line, but in papers where z is used
for this purpose x tends to have another definition. In the wrapper text the
choice of symbols is generally chosen to reflect those in the corresponding
paper.
There is a growing interest in the application of non-thermal atmospheric pressure plasma for the treatment of wounds. Due to the generation of various ROS and RNS, UV radiation and electric fields plasma is a very promising tool which can stimulate skin and immune cells. However, not much is known about the mammalian cell responses after plasma treatments on a molecular level. The present work focusses on the impact of plasma on cell signaling in the human keratinocyte cell line HaCaT by using the methods DNA microarray, qPCR, ELISA and flow cytometry. Here, cell signaling mediators such as cytokines and growth factors which could promote wound healing by enhancing angiogenesis, reepithelization, migration and proliferation were of major interest. Additionally, the crosstalk between keratinocytes and monocytes was studied using a co-culture. For the first time extensive investigations on the impact of plasma on cell signaling in human keratinocytes were conducted. The most prominent cytokines and growth factors which were regulated by plasma at gene and protein level were VEGF-A, GM-CSF, HB-EGF, IL-8, and IL-6. The latter was not activated due to the JAK/STAT-pathway but probably by a combined activation of MAPK- and PI3K/Akt-pathways. By the use of conditioned medium it was found out that ROS and RNS generated directly after plasma treatment induced larger effects on cell signaling in keratinocytes than the subsequently secreted growth factors and cytokines. Furthermore, monocytes and keratinocytes hardly altered their secretion profiles in co-culture. From these results it is deduced that the plasma generated reactive species are the main actors during cell signaling. In order to differentiate the impact of ROS and RNS on the cellular response the ambience of the plasma effluent was controlled, varying the ambient gas composition from pure nitrogen to pure oxygen. Thereby a first step towards the attribution of the cellular response to specific plasma generated reactive species was achieved. While IL-6 expression correlated with ROS generated by the plasma source, the cell signaling mediators VEGF-A, GM-CSF and HB-EGF were significantly changed by RONS. Above all hydrogen peroxide was found to play a dominant role for observed cell responses. In summary, plasma activates wound healing related cell signaling mediators as cytokines and growth factors in keratinocytes. It was also shown that the generated reactive species mainly induced cell signaling. For the first time cell responses can be correlated to ROS and RONS in plasma treated cells. These results underline the potential of non-thermal atmospheric pressure plasma sources for their applications in wound treatment.
Magnetic reconnection is a fundamental plasma process where a change in field line connectivity occurs in a current sheet at the boundary between regions of opposing magnetic fields. In this process, energy stored in the magnetic field is converted into kinetic and thermal energy, which provides a source of plasma heating and energetic particles. Magnetic reconnection plays a key role in many space and laboratory plasma phenomena, e.g. solar flares, Earth’s magnetopause dynamics and instabilities in tokamaks. A new linear device (VINETAII) has been designed for the study of the fundamental physical processes involved in magnetic reconnection. The plasma parameters are such that magnetic reconnection occurs in a collision-dominated regime. A plasma gun creates a localized current sheet, and magnetic reconnection is driven by modulating the plasma current and the magnetic field structure. The plasma current is shown to flow in response to a combination of an externally induced electric field and electrostatic fields in the plasma, and is highly affected by axial sheath boundary conditions. Further, the current is changed by an additional axial magnetic field (guide field), and the current sheet geometry was demonstrated to be set by a combination of magnetic mapping and cross-field plasma diffusion. With increasing distance from the plasma gun, magnetic mapping results in an increase of the current sheet length and a decrease of the width. The control parameter is the ratio of the guide field to the reconnection magnetic field strength. Cross-field plasma diffusion leads to a radial expansion of the current sheet at low guide fields. Plasma currents are also observed in the azimuthal plane and were found to originate from a combination of the field-aligned current component and the diamagnetic current generated by steep in-plane pressure gradients in combination with the guide field. The reconnection rate, defined via the inductive electric field, is shown to be directly linked to the time-derivative of the plasma current. The reconnection rate decreases with increasing ratio of the guide field to the reconnection magnetic field strength, which is attributed to the plasma current dependency on axial boundary conditions and the plasma gun discharge. The above outlined results offer insights into the complex interaction between magnetic fields, electric fields, and the localized current flows during reconnection.
The aim of this thesis is to concentrate on the investigation of these ROS&RNS composition distribution and their production pathways in the gas phase produced by a plasma jet. By understanding the physical mechanisms behind the generation of the ROS&RNS a precise tuning and design of the composition distribution in the gas phase can be achieved. One crucial physical parameter is the dissipated power inside the plasma. Only if this parameter is known a meaningful comparison of different feed gas settings is possible. Therefore, a concept for measuring the dissipated power inside the plasma for the modified micro-scaled atmospheric pressure plasma jet( µAPPJ) is designed. Additionally, due to achievements within this thesis it is now possible to ignite a homogeneous discharge in argon and helium within the geometry of the µAPPJ. The used feed gas is a determining factor concerning the electron energy distribution function and consequently influencing the production mechanism of the ROS&RNS. First of all, the electrical characterisation of the modified µAPPJ was performed including the alpha-to-gamma transition. It is shown that the alpha-to-gamma transition power is increasing with increasing frequency. For the first time it is now feasible to investigate the influence of the dissipated power on the neutral gas temperature, the metastable atom densities and the ROS&RNS production for the modified µAPPJ with argon and helium as feed gas. Due to the possibility of changing the feed gas and controlling the dissipated power a fundamental insight into the production mechanism of the ROS&RNS generated by the plasma jet is achieved. With rising dissipated power the temperature and the metastable densities as well as the ozone and nitrogen dioxide concentrations are increasing. By adding molecular oxygen and nitrogen to the feed gas of a plasma jet the ROS&RNS composition can be tuned. However, also the dissipated power is changed by the small amount of admixtures. Due to the developed dissipated power measurements within this thesis it was possible to disentangle the influence of the admixture on the power and on the ROS&RNS production. If the dissipated power is fixed for the µAPPJ with argon and helium feed gas, respectively, the highest amount of ozone was measured with oxygen admixture in an argon discharge, the highest amount of dinitrogen pentoxide with nitrogen admixture in an argon discharge and the highest amount of nitrogen dioxide with nitrogen admixture in a helium discharge. Beyond the influence of the dissipated power and the molecular admixture on the ROS&RNS production the feed gas temperature is a crucial parameter for the corresponding chemical reactions. By changing this parameter the distribution of ozone and nitrogen dioxide can be tuned precisely in such a way that with increasing temperature the ozone density goes down and the nitrogen dioxide density rises. Another determinant for the ROS&RNS composition produced by an atmospheric pressure plasma jet is the influence of ambient air. If the ambient air is changing from pure nitrogen to pure oxygen atmosphere the ozone density produced by the plasma jet is increasing. For the same conditions the nitrogen dioxide has a maximum at an oxygen-to-nitrogen ratio of 1:1. To avoid the influence of the ambient air on the reactive species production the afterglow of the µAPPJ was prolonged with a glass tube. By increasing the amount of molecular admixtures to the feed gas with each in equal quantities a totally different ROS&RNS composition can be obtained compared without the glass tube. It figures out that for small molecular admixtures the reactive species composition is nitrogen dominated and for higher admixtures it is oxygen dominated. Consequently, by shielding the ambient air from the active effluent and by admixing molecular oxygen and nitrogen the ROS&RNS composition can be designed.
The thyroid as the largest endocrine gland mainly produces and secretes the thyroid hormones (TH): 3,3’,5-triiodo-L-thyronine (T3) and its pro-hormone L-thyroxine (T4). Besides the impact on growth, normal development, bone marrow structure, the cardiovascular system, body weight and thermogenesis, TH play a vivid role in many metabolic regulatory mechanisms in almost all tissues. Thyroid diseases are relatively prevalent and cause, due to the resulting TH imbalances, a broad spectrum of effects. Many of them manifest in pathologically increased or decreased TH levels defined as hyperthyroidism or hypothyroidism, respectively. Routinely, determination of the thyroid state is based on the assessment of the classical markers TSH and free T4. However, this practice has several drawbacks. Moreover, elucidation of the pleiotropic effects of TH on multiple molecular pathways is mostly based on cell culture, tissue and rodent models. Analysis of animal biofluids like serum and urine using metabolomics approaches demonstrated the extensive impact of TH on other body compartments. In contrast, proteome profiling has not been exploited for the comprehensive characterization of the general metabolic effects of TH. Plasma as a large and diverse compartment of the human proteome provides a great opportunity to identify novel protein markers of thyroid function as well as to characterize metabolic effects of TH in humans.
Therefore, a study of experimental thyrotoxicosis was performed with 16 male volunteers treated with 0.25 mg/d levothyroxine (L-T4) for 8 weeks to induce a hyperthyroid state. Plasma samples were collected before the L-T4 application started, two times during the treatment and additionally two times after withdrawal. Proteome analysis revealed remarkable alterations including increased levels of two known proteins known to correlate with TH levels (sex hormone-binding globulin and cystatin C). The correlation with free T4 levels revealed 76 out of 437 detected proteins with a Pearson correlation coefficient of r ≥ |0.9|. One prominent signature included 10 coagulation cascade proteins exhibiting significantly increased plasma levels during thyrotoxicosis, thereby revealing a trend towards a hypercoagulative state in hyperthyroidism. To overcome the statistical drawbacks of the Pearson correlation analysis, additionally a mixed-effect linear regression model using serum free T4 concentrations as exposure and protein abundances as outcome while controlling for age, BMI, and batch was implemented. Application of this model resulted in the detection of 63 proteins with significant associations to free T4 levels. Besides the already mentioned augmented coagulation, a significant drop in the amounts of three apolipoproteins (ApoD, ApoB-100 and ApoC3) was observed. Furthermore, an increased abundance of proteins assigned to the complement system was detected.
Experimental studies in humans were complemented by corresponding analyses in murine models. In the current work, plasma samples of two murine studies including male C57BL/6 wildtype mice were analyzed to elucidate the impact of thyroid dysfunction on the plasma proteome. The first study was similarly designed as the human model of experimentally induced thyrotoxicosis and assigned the animals to three groups: a control group, a T4 treatment group, and a T4 recovery group, whereupon the latter first received T4 followed by a subsequent TH normalization period. A high proportion of plasma proteins exhibited significantly different protein levels during T4 application (n = 120), where 90 of these also showed a corresponding reverse trend after T4 withdrawal (T4 recovery vs. T4), thereby displaying transient alterations. The molecular pattern of hyperthyroidism in the murine model indicated, as in the human study, a pronounced decrease in apolipoproteins. However, in clear contrast to the human data, the levels of proteins related to the coagulation cascade and complement system were also transiently decreased in mice, while being increased in humans.
The second murine analysis focused on the impact of hyper- and hypothyroidism caused by T3 or T4 treatment and MMI/KClO4 application, respectively. In general, compared to the first murine study less clear alterations of protein levels were detected. Proteins related to the complement system revealed fewer changes in the T3 group and only marginal changes after T4 induction. Unexpectedly, the MMI/KClO4-induced hypothyroidism caused a reduction of the levels of several proteins assigned to the complement system, although different components and factors were affected.
Generally, rodent studies partially provided a divergent picture of TH action as compared to human studies. However, in spite of inconsistent results in studies regarding the effects of TH that are possibly due to species-specific differences, an important role of TH on several metabolic and other pathways, e.g. in the process of blood coagulation and apolipoprotein regulation, is evident. The results from both murine and human studies presented here provide novel insights into changes in the plasma proteome in the context of thyroid diseases which might contribute to a better understanding of TH action on metabolism and other pathways.
The here presented dissertation investigated the molecular mechanisms, by which the food industry model bacteria Pseudomonas fluorescens and Listeria monocytogenes, grown either as planktonic cultures, were inhibited by plasma treated water (PTW) produced by a microwave-induced plasma source (MidiPLexc). As a starting point, optimal operating parameters were determined with 5 standard liters per minutes(slm)compressed air during the treatment of 10 ml deionized water within a treatment time of up to 15 min (pre-treatment time). Treatment times of 1, 3 and 5 min were selected (post-treatment time). In addition to physical parameters, i.e. temperature measurements at different spots at the plasma source during the production of the PTW, the chemical composition of PTW was determined by pH measurements, chronoamperometry (determination of the H2O2 concentration), ion chromatography (determination of the NO2-, NO3- and ONOO- concentrations) and mass spectrometry (qualitative determination of the molecules). In addition, concentration changes of reactive species over a period of 3 h indicated a decrease of the NO2- concentration as well as an increase of the NO3- and ONOO- concentration in the PTW. Microbiological assays, i.e. quantification of colony-forming units (CFU), fluorescence and XTT assays, revealed a significant reduction of the proliferation ability of the cells, membrane damages and metabolic activity have been demonstrated for planktonic cultures as well as mono- and multispecies biofilms. PTW effects on biofilm structures were investigated using microscopic methods such as fluorescence microscopy, confocal laser scanning microscopy (CLSM), atomic force microscopy (AFM), and scanning electron microscopy (SEM), as well as physical methods such as contact angle measurements. Significant changes in the biofilm structure have been shown, which indicate an ablation of the biofilm mass from top to bottom by approximately 2/3 of the biofilm mass and a destruction of the extracellular matrix (ECM) by the reactive species within the PTW. Subsequently, fresh-cut lettuce has been treated with PTW produced by up-scaled plasma sources. Apart from qualitative parameters of the lettuce after PTW treatment such as texture and color, the concentration of PTW reactive species have been determined. These experiments showed that the composition of the reactive species were slightly different from that of the laboratory-scaled plasma source MidiPLexc. Notably, the PTW treatment did not cause significant changes in texture and color of the fresh-cut lettuce. Finally, a synergistic effect of PTW treatment followed by plasma-processed air (PPA) drying was demonstrated application-specific.
The concept of the electron surface layer introduced in this thesis provides a framework for the description of the microphysics of the surplus electrons immediately at the wall and thereby complements the modelling of the plasma sheath. In this work we have considered from a surface physics perspective the distribution and build-up of an electron adsorbate on the wall as well as the effect of the negative charge on the scattering of light by a spherical particle immersed in a plasma. In our electron surface layer model we treat the wall-bound electrons as a wall-thermalised electron distribution minimising the grand canonical potential and satisfying Poissons equation. The boundary between the electron surface layer and the plasma sheath is determined by a force balance between the attractive image potential and the repulsive sheath potential and lies in front of the crystallographic interface. Depending on the electron affinity x, that is the offset of the conduction band minimum to the potential in front of the surface, two scenarios for the wall-bound electrons are realised. For x<0 electrons do not penetrate into the solid but are trapped in the image states in front of the surface where they form a quasi two-dimensional electron gas. For x>0 electrons penetrate into the conduction band where they form an extended space charge. These different scenarios are also reflected in the electron kinetics at the wall which control the sticking coefficient and the desorption time. If x<0 electrons from the plasma cannot penetrate into the solid. They are trapped in the image states in front of the surface. The transitions between unbound and bound states are due to surface vibrations. Trapping of electrons is mediated by one-phonon transitions and takes place in the upper bound states. Owing to the large binding energy of the lowest bound state transitions from the upper bound states to the lowest bound state are due to multi-phonon processes. For low surface temperatures relaxation to the lowest bound state takes place while for higher temperature a relaxation bottleneck emerges. Desorption occurs in cascades for systems without relaxation bottleneck and as a one-way process in systems with a relaxation bottleneck. From the perspective of plasma physics the most important result is that the sticking coefficient for electrons is relatively small, typically on the order of 0.001. For x>0 electron physisorption takes place in the conduction band. For this case sticking coefficients and desorption times have not been calculated yet but in view of the more efficient scattering with bulk phonons, responsible for electron energy relaxation in this case, we expect them to be larger than for the case of x<0. Finally, we have studied the effects of surplus electrons on the scattering of light by a spherical particle. For x<0 the electrons form a spherical electron gas around the particle and their electrical conductivity modifies the boundary condition for the magnetic field. For x>0 the electrons in the bulk of the particle modify the refractive index through their bulk electrical conductivity. In both cases the conductivity is limited by scattering with surface or bulk phonons. Surplus electrons lead to an increase of absorption at low frequencies and, most notably, to a blue-shift of an extinction resonance in the infrared. This shift is proportional to the charge and is strongest for submicron-sized particles. The particle charge is also revealed in a blue-shift of the rapid variation of one of the two polarisation angles of the reflected light. From our work we conclude that the electron affinity is an important parameter of the surface which should affect the charge distribution as well as the charge-up. Therefore, we encourage experimentalists to study the charging of surfaces or dust particles as a function of x. Interesting in this respect is also if or under what conditions the electron affinity of a surface exposed to a plasma remains stable. Moreover, we suggest to use the charge signatures in Mie scattering to measure the particle charge optically. This would allow a charge measurement independent of the plasma parameters and could be applied to nano-dust where conventional methods cannot be applied.
This thesis constitutes a computational study of charge and ion drag force on micron-sized dust particles immersed in rf discharges. Knowledge of dust parameters like dust charge, floating potential, shielding and ion drag force is very crucial for explaining complex laboratory dusty plasma phenomena, such as void formation in microgravity experiments and wakefield formation in the sheaths. Existing theoretical models assume standard distribution functions for plasma species and are applicable over a limited range of flow velocities and collisionality. Kinetic simulations are suitable tools for studying dust charging and drag force computation. The main aim of this thesis is to perform three dimensional simulations using a Particle-Particle-Particle-Mesh ($P^3M$) model to understand how the dust parameters vary for different positions of dust in rf discharges and how these parameters on a dust evolve in the presence of neighboring dust particles. At first, rf discharges in argon have been modelled using a three-dimensional PIC-MCC code for the discharge conditions relevant to the dusty plasma experiments. All necessary elastic and inelastic collisions have been considered. The plasma background is found collisional, charge-exchange collisions between ions and neutrals being dominant. Electron and ion distributions are non-Maxwellian. The dominant heating mechanism is Ohmic. Then, simulations have been done to compute the dust parameters for various sizes of dust located at different positions in the rf discharges. Dust charge and floating potential in the presheath are slightly larger than the values in the bulk due to the higher electron flux to the dust particle in the presheath. From presheath to the sheath the charge and floating potential values decrease due to the decrease of the electron current to the dust. A linear dependence of dust potential on dust size has been found, which results in a nonlinear dependence of the dust charge with the dust size when the particle is assumed to be a spherical capacitor. This has been verified by independently counting the charges collected by the dust. %where indeed it has been noted that the dust charge %scales nonlinearly with the dust size. The computed dust parameters are also compared with theoretical models. Simulated dust floating potentials are comparable to values obtained from Allen-Boyd-Reynolds (ABR) and Khrapak models, but much smaller than the values obtained from Orbit Motion Limited (OML) model. The dust potential distribution behaves Debye-H\"{u}ckel-like. The shielding lengths are in between ion and electron Debye lengths. % indicating shielding by both ions and electrons. Further, the orbital drag force is typically larger than the collection drag force. The total drag force for the collisional case is larger than for the collisionless case and it scales nonlinearly with the dust size. The collection drag values and size-scaling agrees with Zobnin's model. The charging and drag force computation is then extended to two and multiple static dust particles in the rf discharge to study the influence of neighboring dust particles on the dust parameters. Initially, the dust parameters on two dust particles are computed for various interparticle separation distances and for dust particles placed at different locations in the rf discharge. It is observed that for dust separations larger than the shielding length the dust parameters for the two dust particles match with the single dust particle values. As the dust separation is equal to or less than the shielding length the ion drag force increases due to the buildup of a parallel drag force component. However, the main dust properties like charge, potential, vertical component of ion drag are not affected considerably. This is attributed to the smaller collection impact parameter values compared to the dust separation. %This is because the %collection impact parameter values in the sheath and the presheath are smaller %than the smallest dust separation and in case of the dust in the bulk, the %collection impact parameter is comparable with the dust separation. Then the dust charges on multiple dust particles located at different positions in the discharge and arranged along the discharge axis are also computed. It is found that the charges of the multiple dust particles in the bulk or presheath do not differ much from the single particle values at that location. But the dust charges of multiple dust particles located in the sheath drastically differ from the single dust parameter values. Due to ion focusing from dust particles in the upper layers, the ion current increases to dust particles in the lower layers resulting in smaller charge values. This is as well the case where dust particles are vertically aligned as in the standard experiments of dusty plasmas. In conclusion, this work used a fully kinetic (PIC and MD or $P^3M$) model to study the physics of dust charging in rf plasmas. Our simulations revealed that the dust parameters vary considerably from the bulk to the sheath. The CX collisions increase flux to the dust thereby affecting the dust parameters and their scaling with dust size. Also, a dust particle affects the charging dynamics of its neighbor only when their separation is within the shielding length. In the plasma sheath, ion focussing can cause great reduction in dust charges.