In this thesis we have studied systems that driven by mechanisms broadly known as phoresis. More specifically, in the second chapter we calculate the excess noise in electrophoresis of a colloid due to microion fluctuations. In the next three chapters we study in detail a system of self-phoretic colloids, propelled by the energy released when an ambient fuel molecule makes contact with a catalytic region on the particle’s surface. We start with the behaviour of a single particle in a linear substrate gradient, then go on to study interactions between two particles due to their diffusion clouds, and finally obtain the collective equations of motion by a systematic coarse-graining of the microscopic Langevin dynamics. To understand the role of nonequilibrium fluctuations in an electrophoretic system we have theoretically analyzed the dynamics of a single colloidal particle in an externally applied electric field. We have studied the colloidal dynamics in two scenarios: a particle free to move in an unbounded fluid and a colloid near a wall which is stationary due to a balance between gravity and the electric field. The thermal motions of microions lead to an anisotropic, nonequilibrium noise, proportional to the field, in the effective Langevin equation for the colloid. The fluctuation-dissipation ratio depends strongly on frequency, in contrast to an equilibrium system, and the colloid if displaced from its steady-state position relaxes with a velocity not proportional to the gradient of the logarithm of the steady-state probability. Other measurable effects of this noise are a superdiffusive peak at short times and an enhanced diffusity at long times. We have then studied the effective potential and obtained a non-dimensional measure of the size of the excess noise. Possible extensions of this study to include the behaviour of the mean and fluctuation properties in the case of an applied alternating potential, and the effect of the excess noise on electrohydrodynamic aggregation of colloids. We next turn to a phoretic system that has been much studied in the recent years – active Janus colloids . On one hand these colloids are an important contribution to the general class of problems on self-propulsion at low Reynolds number. On the other hand since their behaviour can be tuned at the level of single particle we can ask how their collective behaviour depends on the swimmer design. This makes it a very rich field with lots of challenging questions. We first study the single particle behaviour of an active Janus colloid in an imposed substrate gradient, then build the two-particle interactions and ultimately the collective equations of motion by a generalisation of these results. Our work presents a new approach to active matter. We show theoretically how to design particles that are not only motile but can reorient in response to gradients, thus mimicking chemotaxis. We outline the collective behaviour emerging from these single-particle properties, including colloidal realisations of gravitational collapse, plasma oscillations and spontaneously ringing states, and present a phase diagram, in terms of single particle parameters, that can be tested in experiments. This provides a template to design collective behaviours of interest by tuning the surface properties of the colloids. We can also control the range of the interaction by varying the concentration of reactant. Our coarse-grained equations of motion for the polar orientation and number density fields for a collection of colloids propelled by and interacting through long-ranged dif-fusion fields are novel in a number of ways. This is the first example in active matter literature of a microscopic derivation of collective dynamics for particles interacting via long-ranged diffusion fields. The instabilities and possible phases that we predict are different from those in traditional flocking models, which consider only short-ranged aligning interactions. The long-ranged interactions of interest here cannot produce a globally polar ordered state, and we work in a concentration regime where steric and collisional interactions are not important. Instabilities towards flocking, and the advective nonlinearities of the Toner-Tu model, although not ruled out by the symmetries of our model, do not play a significant role in our system. The collective behaviour we predict will not be seen in purely locally interacting active-particle systems. The mechanisms at work in the “saturated” case where reactant is abundant cannot be viewed as totally generic features of collections of self-driven particles; they require interactions mediated by the production or consumption of long-ranged diffusing solute fields. Earlier work on saturated systems resolved neither interactions mediated by the polarity of the objects nor chemotactic effects. Their treatment truncated the equations at the level of the concentration [1]. In the “unsaturated” case more than one mechanism operates. One is related to the motility-induced phase separation discussed phenomenologically in refs. [2,3] (for which our system provides an important microscopic realisation). The other is due to chemo-taxis and phoresis which we report for the first time. Our expression of the various coefficients in the equaions of motion in terms of the single particle properties can also be used to design systems in which one or the other of these mechanisms dominate. We are now planning to study a collection of these particles in a fluid and examine the diffusion of a tracer particle as was done by Yeomans et al. [4] for hydrodynamic interactions. The Levy flights obtained in [4] is due to the long-ranged nature of the hydrodynamic fields, which cause effects like entrainment leading to interesting tracer dynamics. In this thesis we have considered colloids in which the symmetry axis of the colloid and the catalytic coat coincide. It might be of interest to consider cases when the axes are at an angle making the swimmer biaxial, or more complicated arrangements leading to chirality and thus rotation. Collective dynamics and two particle interaction between such swimmers can also be interesting. The formalism developed for the study of interaction between two active colloids through their diffusion fields and hydrodynamics can be extended to study their interaction with extended passive surfaces like walls or spheres. The collective dynamics of this class of active systems when it is confined between parallel walls is also of interest. Work in progress includes studies of the motion of the swimmer in a periodic array of passive colloids. In this study of collective dynamics, we have ignored the role of hydrodynamics, as the slowest decay of the field is 1/r3, which is subdominant to the decay of the chemical fields and in the dilute limit is expected to change things only qualitatively. However their role would be more important when we consider the stability of ordered structures like an aster in the saturated case. Another effect of hydrodynamics is to stir the fluid. It might be interesting to study the finite-P´eclet number regime [5, 6] of our system particularly in the unscreened region when advection of the scalar fields s and p by the velocity can affect clustering. We have derived the form of the nonlinear equations of motion in both the saturated and the unsaturated regimes. It will be interesting to investigate their relevance in the dynamics and phases that this extremely rich system can form. Even in the overdamped limit where we obtain an effective density equation it is not clear that the dynamics will resemble that of the Keller-Segel model due to the presence of the interesting nonlinear terms. Also, in this thesis, we have only looked at the fluid-like state of the system. We have just started exploring the high concentration regime where we can check the propensity of the system to develop crystalline order. In the screened limit where we obtain a condensation due a negative squared sound speed, it is posssible to study the condensation phenomenon in greater detail. In future we also plan to examine whether the tendency to condense at nonzero wavenumber (See Fig 5.1), i.e., microphase separation, can lead to liquid-crystalline phases like smectics. The systems described in this thesis are extremely rich and the few ideas mentioned above form just a small subset of the plethora of exciting theoretical and experimental explorations that can be performed with them. Since they can be “designed”, unlike biological substances, they can also become a test-bed for testing theoretical predictions of the nonequilibrium statistical mechanics of self-propelled systems.

Electron microscopy was first conducted in the 1930s with the advent of theTEM and later the STEM. In 1969, the first commercial SEM was released,with the possibility of retrofitting it to behave like a STEM following soonafterwards. In 1979, Danilatos and Robinson advanced electron microscopyby creating a new type of SEM which allowed a controlled quantity of gasinto the sample chamber, termed ESEM. The most recent evolution in thisline was the combination of ESEM and STEM in 2005, a procedure termedWet STEM.The focus of this work is on investigating applications of this new technique,along with the contrast mechanisms involved in forming an image. Tothat end, a wide variety of samples will be imaged. Clay and paint suspensions(colloids) are used to test Wet STEM’s capacity to image submergedobjects, as well as thin objects which are stacked together. Diblock copolymerfilms are used to test Wet STEM’s ability to distinguish chemically similarmaterials without staining, the physical effects of heavy metal staining andto demonstrate the necessity of gas for the purpose of charge neutralisation. Single cell biological samples are also investigated. Internal contrast inmammalian cells is visible without recourse to staining, but chemical fixationis required despite maintaining a high relative humidity. Bacteria are moreresilient and as such are easier to image than animal cells, requiring no priortreatment. When exposed to low relative humidity, bacteria are found tocollapse. The collapse pattern is observed to differ between wild-type andcytoskeletal-deficient bacteria of the same species and strain, so it is likelythat dehydration-induced collapse offers information about the position andshape of the bacterial cytoskeleton.

The dispersion of graphene in 1,2-dichloroethane (DCE), its subsequent attachment at the water-DCE interface and the reduction of oxygen at the water-DCE interface proceeding via interfacial graphene have been investigated. Using addition of an electrolyte which screens surface charge, it was found that electrostatic repulsions play a significant role in determining the kinetic stability of lyophobic non-aqueous graphene dispersions. The onset of aggregation was determined and it was found that dispersions prepared from higher-oxygen content graphite were more stable than those prepared from lower-oxygen content graphite, indicating that oxygen content is important in determining the surface charge on graphene in non-aqueous dispersion. The presence of organic electrolyte was also found to promote assembly of graphene into a coherent film at the liquid-liquid interface. Measurement of the liquid-liquid interfacial tension and three-phase contact angle revealed that the energetics of particle attachment did not change in the presence of organic electrolyte, thus indicating a mechanism of inter-particle electrostatic repulsion minimisation through surface charge screening. Interfacial graphene was found to display a catalytic effect toward the oxygen reduction reaction at the water-DCE interface. A bipolar cell was developed which showed that this reaction occurs heterogeneously, with graphene acting as a conduit for electrons across the water-DCE interface.

The emergence of optical applications, such as lasers, fiber optics, and semiconductor based sources and detectors, has created a drive for smaller and more specialized devices. Nanophotonics is an emerging field of study that encompasses the disciplines of physics, engineering, chemistry, biology, applied sciences and biomedical technology. In particular, nanophotonics explores optical processes on a nanoscale. This dissertation presents nanophotonic applications that incorporate various forms of the organic polymer N-isopropylacrylamide (NIPA) with inorganic semiconductors. This includes the material characterization of NIPA, with such techniques as ellipsometry and dynamic light scattering. Two devices were constructed incorporating the NIPA hydrogel with semiconductors. The first device comprises a PNIPAM-CdTe hybrid material. The PNIPAM is a means for the control of distances between CdTe quantum dots encapsulated within the hydrogel. Controlling the distance between the quantum dots allows for the control of resonant energy transfer between neighboring quantum dots. Whereby, providing a means for controlling the temperature dependent red-shifts in photoluminescent peaks and FWHM. Further, enhancement of photoluminescent due to increased scattering in the medium is shown as a function of temperature. The second device incorporates NIPA into a 2D photonic crystal patterned on GaAs. The refractive index change of the NIPA hydrogel as it undergoes its phase change creates a controllable mechanism for adjusting the transmittance of light frequencies through a linear defect in a photonic crystal. The NIPA infiltrated photonic crystal shows greater shifts in the bandwidth per ºC than any liquid crystal methods. This dissertation demonstrates the versatile uses of hydrogel, as a means of control in nanophotonic devices, and will likely lead to development of other hybrid applications. The development of smaller light based applications will facilitate the need to augment the devices with control mechanism and will play an increasing important role in the future.

Fluid resuscitation with crystalloid and colloid solutions is a common treatment in perioperative medicine. However, a variety of unbalanced or balanced solutions is used in clinical practice and there is still a vivid debate going on regarding the selection of optimal fluid with minimal negative effect on coagulation. The goal of the dissertation was to investigate the adverse effect of balanced crystalloids and colloids on whole blood coagulation measured by method of rotational thromboelastometry. In the first phase of the work we had assessed the adverse effect of balanced crystalloid, hydroxyethyl starch and gelatin after dilution of blood with the solution in vitro. Parametrs of EXTEM and FIBTEM tests were evaluated by using rotational thromboelastometry. In the second phase of the work we evaluated the negative effect of infusion solution after dilution in vivo. We had obtained blood samples from 30 patients during knee arthroscopy before and after administration of 500 ml of crystalloid or hydroxyethyl starch or gelatin. Parametrs of EXTEM and FIBTEM tests were evaluated by using rotational thromboelastometry.In compliance with the results of the dissertation, hydroxyethyl starch has the most obvious negative effect on clot formation followed by gelatin and finally by crystalloids. Based on...

Polymer gels undergo the volume phase transition in response to an infinitesimal environmental change. This remarkable phenomenon results in many potential applications of polymer gels. This dissertation systematically investigates the chemical and physical properties of polymer gels. It is found that infrared radiation laser not only induces a volume phase transition in N-isopropylacrylamide (NIPA) gel, but also causes the gel to bend toward the laser beam. The transmission of visible laser light through a NIPA gel can also be controlled by adjusting the infrared laser power. A new class of environmentally responsive materials based on spatial modulation of the chemical nature of gels has been proposed and demonstrated. Three simple applications based on the modulated gels are presented: a bi-gel strip, a shape memory gel, and a gel hand. The bending of bi-gels has been studied as a function of temperature, acetone aqueous solution, and salt solution. As the polymer network concentration increases, the behavior of shear modulus of acrylamide (PAAM) gels deviates significantlyfromthe classical theory. The ionic NIPA gels undergo two sequential volume phase transitions: one occurs in dilute NaCl solution, the other occurs in concentrated NaCl solution. An interpenetrating polymer network (IPN) of PAAM--NIPA has also been synthesized using free radical polymerization. It is found that the IPN gels preserve the essential properties of individual components. The volume phase transition of the IPN gels can be triggered by multiple external stimuli including temperature, acetone concentration, and salt concentration.

Polymer gels undergo a volume phase transition in solvent in response to an infinitesimal environmental change. This remarkable phenomenon has resulted in many potential applications of polymer gels. The understanding of its mechanical properties has both scientific and technological importance. For this purpose, we have developed a novel method for measuring Poisson's ratio, which is one of the most important parameters determining the mechanical property of gels. Using this method, Poisson's ratio in N-isopropyacrylamide (NIPA) and polyacrylamide (PAAM) gels has been studied.

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M. S.